civil eng april 2005 web

April 2005 Vol 13 No 4


CIV IL ENGINEERING • APRIL 2005

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ON THE COVER Franki Africa devised a pilings and lateralsupport solution for Torres Atlantico, a twin-tower office and residential complex beingbuilt by Angola’s three largest oil producers,Sonangol, BP and Exxon. The twin towerswill soon soar over Luanda’s beachfront andstand as testimony to a burgeoning industry in a country emerging from yearsof civil war (see article on page 8)

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The South African Institution of Civil Engineeringaccepts no responsibility for any statements made oropinions expressed in this publication. Consequentlynobody connected with the publication of the maga-zine, in particular the proprietors, the publishers andthe editors, will be liable for any loss or damage sus-tained by any reader as a result of his or her actionupon any statement or opinion published in this maga-zine.

ISSN 1021-2000

COVER FEATURECOVER FEATURE

Torres Atlantico: a challenging geotechnical engineering project 8

FORUM

Wanted – at least 100 retired or available civil

professionals! 2

VIEWPOINT

The state of the South African piling nation 3

PROFILE

Giant in geotechnical field retires 5

PRODUCTS AND PROJECTS

Trenching and embankment support made

easier and safer 29

Maintenance contract for Africa’s giant eye

awarded 31

Exploring new avenues 30

Rockfall protection 31

SAICE AND PROFESSIONAL NEWS

Recipients of honorary fellowships 34

CSIR researcher wins best paper award at

WEDC Conference 36

Diarise this! 36

GEOTECHNICALInteresting geotechnics at Impala Platinum 10Horizontal directional drilling and its application 12Innovative solution for fracturing rockmass 18Geotechnical aspects of the development ofthe Sigma Mooikraal underground colliery20

Prefabricated shoring systems 23GPR technology in concrete and road structureinspection and utility location 24Female engineer heads up geoscience consultancy 26Young Geotechnical Engineers Conference28Local and International Conferences and Symposiums 2005 28

WantedSAICE, FUNDED BY CETA, has been carryingout a major research campaign to determinethe number of engineers, technologists andtechnicians who are operating in the civilengineering field.

In the past, the SAACE and SAFCECheadcounts were normally regarded as beingrepresentative of the industry, but civil staffare to be found in all levels of government,parastatals, the supply chain, mining andindustrial, academia, home building, etc.

Few sectors or companies do not com-plain of being short of experienced technicalstaff. Equally, there are few companies thatescape the pleading letters from young stu-dents begging for vac work or experientialtraining.

It is now time to investigate whetherthere is additional capacity among the ranksof the recently retired and in small compa-nies. If you would like to offer your servicesto mentor or, more correctly, 'knowledge

coach’ young people, or assist with initiat-ing and managing projects, please submitan abridged CV (not more than two pages)to Allyson Lawless at [email protected].

The findings and recommendations ofthe research campaign will be made avail-able in the near future. Watch this space!

Allyson Lawless

Wanted – at least 100 retired or available civil professionals!

F O R U M

OVER THE LAST DECADE the changes inthe South African construction marketplacehave been dramatic. The impact on thecivils industry has been equally affected.Within the civils industry sits the ‘pilingcontractors market’. This market sector, andits competing contractors, has seen a hugechange over the last five years.

The number of market players, the geo-graphic location of contracts, project sizeand type of piling required have beenextremely varied and constantly changing.

The dynamics of this growth has seen thelarger contractors moving into Africa andchasing dollar-based contracts; the smallerestablished contractors have grown in theabsence of the larger players; likewise newplayers have entered the market.

The absence of large civil infrastructure-type projects and the boom in residential

projects have given smaller contractors anideal constant turnover market which hasenabled them to expand and equip them-selves for bigger projects.

The downside to this change and emer-gence has been that smaller contractors withless management and lower overhead struc-tures have created a price war among them-selves.

Price cutting and counter offers are lead-ing to substandard work and designs arebeing pushed to the limits. This situation isbeing exploited by the developers and someprofessionals with a view to driving downthe costs on the project. In this cost-savingdrive, quality testing and pile performancetesting are being overlooked.

Since piling is still a specialist market, itis clear that this unchecked spiral of pricingcutting and lack of concern for design and

pile testing practices must lead to more pro-ject delays, deformations/failures and exces-sive building settlements. The long-termremedial and costly problems for builder anddeveloper will catch up with all parties atsome stage, if this practice of poor work-manship and poor pile construction isallowed to continue unchecked by the pilingcontractors.

It is my strong belief that SAICE or a sim-ilar professional body should consider pro-posals for the formation of a regulating bodythat can oversee and create a more accept-able work climate within which piling con-tractors can operate. Disregard of the currentsituation is definitely leading towards somepotentially major structural failures withinour domestic market.

The state of the South African piling nation

Text Boyd CousinsPilequip SA

V I E W P O I N T

GIAN

TTHE BOY FROM FICKSBURG‘I’ve always wanted to go and farm when Iretire, but now that it’s finally come about, Iworry because it’s a tremendous change inone’s life, especially for my wife, Engela,who’s essentially a city girl. It’s going to bevery challenging indeed.’

The farm in question lies in the easternFree State, in the Ficksburg district. It hasbeen in the Wagener family for nearly 70years and Fritz was born there. While hedecided to follow a career in engineering, hisbrother returned to the farm after universityto cultivate the land full time, with Fritzbecoming the ‘Johannesburg partner’. ‘Ithink, however, that I’ll remain in Johannes-

burg for the time being and do consultingwork until circumstances for grain producersimprove.’

Fritz matriculated from Ficksburg HighSchool, having had very little career advice asa youngster in the mid-1950s. ‘A teacher sug-gested that I should become a scientist, but Idon’t think I would have been good at thatbecause I like to have answers, and engineer-ing, to me, really is a field which rendersanswers. In my matric year I read an articleon engineering in a career guidance brochure.I remember the picture on the front coverwas of an arch dam, and the salary of thedirector of irrigation was quoted as, I think,500 pounds a year. So I said, that’s me – I’m

going to become a civil engineer! Smallthings like that motivate you as a child, butwhen I made that decision I knew very littleabout the profession.’

When Fritz enrolled at Wits for a BScEngdegree he knew nothing about geotechnics.Like so many other students who were fol-lowing the course, he was guided and men-tored by the renowned Prof Jerry Jennings.‘We had a very good relationship and later,when I did my master’s degree under him, webecame close friends.’

Fritz graduated with distinction, the onlyone in the class of ’59. ‘I enjoyed my studiestremendously, but I think one excels evenmore when a person like Jennings is your rolemodel. My parents too were a major influ-ence. We were a close-knit family and theywere very proud of their children, giving usall the encouragement we could want.’

The eldest of four children, Fritz retainsthe close relationship he had with his broth-ers and sister as well as with his mother’s rela-tives, who still live in the Ficksburg area.

SPREADING HIS WINGSAfter obtaining his master’s degree in 1961Fritz spent a year at C A Rigby ConsultingEngineers in Johannesburg. ‘Rigby did a lot ofwork on the gold mines in those days and Ihad a sound introduction to the infrastruc-tural side of gold mining. But then I wasinvited by my uncle to join his firm of con-tractors, Dykerhoff and Widmann, in Ger-many. I spent two years there, at first workingin their design office in Munich and then inBremen and Koblenz. My interest in thosedays lay in bridges and pre-stressed concretestructures and I had ample opportunity towork on such projects. Even though Ichanged to geotechnics later on in my career,the time spent in Germany helped me to gainconfidence in my field.’

Within three months Fritz could speakGerman fluently – although he is of Germanlineage, he grew up in an Afrikaans-speakinghome – and he has retained the skill to thisday. He also speaks seSotho effortlessly.

When Fritz returned to South Africa, hejoined the local branch of Dykerhoff andWidmann (now called DWT because they hadgone into partnership with a local civil engi-neering construction company, JamesThompson). ‘I was appointed contracts man-ager with them and that is where I met myfuture partner, Winston Jones, also a designerand contracts manager.’ It was not longbefore the two started talking about formingtheir own company, either in contracting orconsulting.

Winston was the first to venture out, in

CIV IL ENGINEERING • APRIL 2005 5

Text Lorraine [email protected]

Giant in geotechnical field retires

After almost forty years of co-piloting the firm of Jones and Wagener,Dr Fritz Wagener has decided to bid farewell to the world of consulting engineers and is thinking about taking up a field that hefinds equally absorbing, farming. He says frankly that he finds thethought of retiring from the company that he helped to establish in1966 and embarking on a somewhat uncertain future path dauntingand unnerving. But Fritz von Maltitz Wagener is of Teutonic stock, ayouthful 67, and according to his partners and colleagues, an astutebusinessman with a keen eye for practical solutions – a recipe thatspells success. He spoke to Lorraine Fourie on the eve of retirement,reflecting about his contribution to the field of geotechnical engineering and raising some concerns that reach to the core of theengineering profession

March 1965. ‘The idea was that I would joinhim as soon as enough work had been gener-ated.’ Jones and Wagener Consulting Engi-neers finally opened their offices in PleinStreet, Johannesburg, on 1 November 1966,with a staff complement of one draughtsman.Today Fritz leaves behind six partners and astaff of about 70. Winston also retired about ayear ago.

Contemplating his 38 years in the busi-ness, Fritz regards the extensive work thatwas done for Iscor at Newcastle in Natal asone of the most interesting and challengingprojects he has undertaken. ‘Iscor opened anew integrated steelworks there in 1970 and Ihad the opportunity to handle the geotechni-cal work for the entire project. Our office alsodid quite a lot of structural design for them,but I was in charge of all geotechnics.

‘I think it is only in a country like SouthAfrica where a young engineer is given thekind of responsibilities I had as a young pro-fessional – a situation which continues to thisday. Having been part of the engineeringarena in Germany I knew for how long Iwould have had to work there before I wasallowed to take on that level of responsibility.

‘We worked on the Iscor project forapproximately five years and it just aboutswallowed our entire capacity. But when aproposed steelworks project for them at Ross-lyn, Pretoria, was shelved, we had to pursueother avenues.’

DOLOMITE IGNITES A PASSIONConfidence in the work of Jones and Wagen-er, as witnessed on the Newcastle site, led thechief engineer on that project to introduceFritz and his company to Anglo American. ‘Inthe second half of the seventies we did sever-al geotechnical engineering projects on AngloGold’s Vaal Reefs, Elandsrand and WesternDeep Levels mines, which was our first expo-sure to the mining industry. Here we encoun-tered a totally different set of circumstances,centring mainly on dolomite, particularlyconstruction on various types of dolomite.That’s where my love for dolomite started.’

Not much was known about constructionon dolomite at the time. Building on it wasregarded as extremely risky and the precau-tions which developers adopted were oftenconservative and costly. Over a period ofsome ten years (1975–1985) Fritz immersedhimself in the field, pioneering investigationand founding methods for dolomitic sites.Much of his experience was gained on theOrkney/Stilfontein gold mines where he led ateam which developed appropriate and cost-effective methods for founding all types ofstructures – from reservoirs to mine head-gears, and townships to water-care works – ona wide variety of dolomitic profiles.

His research formed the basis of his doc-toral thesis, titled ‘Engineering constructionon dolomite’, for which he was awarded aPhD degree by the University of Natal in

1983. He has published about 50 papers intotal, not only on dolomite but also on damsand general problem soils, and feels stronglythat one should publish first and foremost inone’s own country. ‘If you publish a paper atan international conference, it might be oneof 1 000 published in five volumes. Very fewrefer to it again. But if you publish in localpublications such as SAICE’s Journal, youreach the people that matter. If I can givesome advice to young engineers it will be toshare their knowledge as widely as possible intheir own country before going international.Don’t do it the other way round.’

Sharing his knowledge and mentoringyoung people flow naturally from Fritz’s‘amazing ability to get on with people’, ascolleague and partner Peter Day describeshim. ‘Fritz has taught me everything I knowabout fieldwork,’ says Peter. ‘When I startedworking with him he spent hours on sitewith me, teaching me how to profile andintroducing me to his clients.’

After years of sanctions against SouthAfrica, which kept Fritz largely homebound,his clients took him as far afield as Malaysiaand the Middle East and he became a respect-ed figure on the conference/lecture circuit. In1984 his contributions were acknowledged byhis peers when SAICE’s Geotechnical Divisionpresented him with the J E Jennings Awardfor his work on dolomite. Twelve years later,in 1996, he received the Division’s GoldMedal for meritorious contribution togeotechnical engineering in South Africa.And the very next year he joined a selectgroup of engineers on whom the JenningsAward was bestowed twice – this time for thepaper that he co-authored on the Merrie-spruit tailings dam disaster and which he subsequently presented at a conference inDenver, Colorado. Not only was he the lead-ing voice on dolomite, he had also becomean expert on tailings dam construction.

SUSTAINABLE DEVELOPMENTFritz retained his active interest in dolomitethrough the years, but the focus of his workshifted in about 1985. ‘You really are guidedby your clients. At that stage gold was declin-ing and coal mining was up and coming. SoJones and Wagener moved into collieries, atfirst underground, where we did a number ofshafts – incline and vertical – for Trans Natal,

Rand Mines and Anglo Coal. Over the next15 years we were involved largely in watercontrol on opencast mines. We did geotech-nical and hydrological investigations as wellas the design of slimes dams, slurry ponds,pollution control dams and stream diversionsat a number of coal mines – at Rietspruit,Vandyksdrift, Syferfontein, Middelburg, Kriel,Klipfontein and Douglas, as well as at Sasol’sSecunda works, to name just a few.’

Because of the nature of their work, at thisearly stage – before legal controls were intro-duced – Fritz and his company were alreadyadvising their clients to sustain the environ-ment where mining activities were undertak-en. ‘We always took our responsibilities veryseriously and voiced our concern that ourmining clients should follow through ontheir environmental policy and exerciseongoing tight control in their maintenanceand rehabilitation programmes.

‘Today, of course, many people think weshould move away from thermal power andembrace nuclear power on a wider scale. I amone hundred per cent behind this ideabecause I believe there will be a lot less pollu-tion all round. Apart from noxious gasesbeing emitted into the atmosphere at powerstations, you have disturbed terrain at open-cast collieries, resulting in water and otherpollution. An open-cast colliery, despitesometimes serious efforts, can never berestored to its original pristine state.’

Fritz displays a special enthusiasm for pro-jects where infrastructure had to be created toaccommodate the moving of massivemachinery. He recalls the challenges that thegigantic draglines (used to excavate the over-burden on a mining site) offered. ‘Thesemachines have booms the length of a rugbyfield and weigh between 3 500 and 4 500tons. To date at Jones and Wagener we havehad to design over 200 km of walkway – thatis often used only once – to move thesemachines. So, obviously, the road should notbe overdesigned and should be constructed ascheaply as possible, but on the other handthe dragline may not get stuck. Once thedragline has made its way across what used tobe, for instance, a maize field, you’ve got torehabilitate the land and restore to the farmera field that will produce the same crop asbefore the interference.’

The subject of the appointment of consul-

SIV IELE INGENIEURSWESE • APRIL 20056

tants in a tendering process stirs up anotherconcern. ‘The work is often awarded to theconsultant who is the cheapest but not nec-essarily the best in that field,’ he says.‘Clients appointing such a firm could end upwith a far costlier project, and that after sav-ing a few rand in design fees. When you goto a medical doctor for an operation, you donot call for tenders and select the cheapest.You rather go to the doctor with the exper-tise in the field.

‘A trend in the past few years has beenthat many clients do not manage their ownprojects any more but appoint project man-agers. All that project managers are interestedin is time. The sooner a project is completedthe more points they score, but the riskier itbecomes for the consulting engineer, who is

rushed into decisions without studying allalternatives. This is the main reason for therecent spate of collapses of bridges and shop-ping centres.

‘Then there are clients who appoint youto do the design on a project but not thesupervision. A design, especially in geotech-nical engineering, doesn’t stop in an office. Itstops on the day you have completed yourconstruction. It is essential that the clientshould not exclude the supervisory role fromyour brief.’

Fritz will not be severing ties completelywith the profession. He will continue to con-sult and lecture part time at JohannesburgUniversity and Wits. He loves working withyoung people. ‘I like to teach young gradu-ates the finer points of geotechnical engineer-

ing – not so much the scientific facts, whichis the lecturer’s task, but the field work, theapplication and problems arising in the field.’

He is concerned because fewer youngstersare entering the engineering profession andmany are leaving South Africa. ‘My advice toyoung engineers is to grab the opportunitiesthat this wonderful country offers them. Youare entrusted here with responsibilities at amuch younger age than would be the caseoverseas. Don’t run away.’

Fritz is facing his new future with thesame indomitable spirit. We wish him and hisfamily, ‘without whose support,’ he says, ‘Iwould not have been able to attain the fewaccomplishments that have been ascribed tome,’ all the best.


Left: Fritz Wagener (right) and ProfTony BrinkMiddle: Fritz in their Ficksburg wheat fieldFar left: Fritz Wagener talking to PeterDay in 1981

EARLY IN 2007, Torres Atlantico, a twin-tower multi-storey office and residentialcomplex, will rise over Luanda’s beachfrontfrom driven cast-in-situ piles and lateral sup-port installed by Franki Africa SucursalAngola, the Angola arm of Franki Africa(Pty) Ltd.

The towers, being built for Angola’s threelargest oil companies – the Angolan Govern-ment Oil Company, (or Sonangol), BP andExxon – will each soar 16 storeys high,include two basements and five storeys ofparking garages, and stand as testimony tothe burgeoning oil and gas industry in thatcountry.

In addition to its prominent position andprofile, the Torres Atlantico project standsout as one of the most challenging anddeepest piling contracts on which FrankiAfrica has ever installed the Franki-DrivenCast-in-Situ piles.

The soil profile of the low-lying narrowcoastal plain that fringes the Bay of Luandaposed a challenge to the project architects,US-based firm EDI, and in June 2000 theycalled upon Franki Africa to review their

professional team’s foundation and lateralsupport proposals.

Having successfully developed techniquesto install Franki DCIS piles to depths up to26 m on the Mozal and Hillside smelter pro-jects, the Johannesburg-based company pro-posed that large groups of 610 mm diameterFranki DCIS piles be installed as support forthe heavily loaded concrete framed structure.

A solution comprising Franki-Titananchorages installed through a diaphragmwall built several years earlier in the Por-tuguese colonial era was put forward as a lat-eral support tie-back solution for the 9 mdeep basement excavation envisaged for theproject.

GOING TO GREAT LENGTHS …In November 2000, the Franki team flew toHouston, Texas, to present their proposedsolution to EDI’s professional team, the Tor-res Atlantico project managers and clientbody.

Soares Da Costa Ltda, a large Portugueseconstruction company with an operation inAngola, were appointed as the main contrac-

tors in September and subsequently appoint-ed Franki Angola to install the piled founda-tions.

Not only were the site conditions at Tor-res Atlantico difficult, but working in acountry that is recovering from 30 years ofcivil war also presented its challenges. Inaddition to the difficulty of clearing customsat Luanda’s harbour, spare parts for Franki’sspecialised equipment are unavailable inAngola and had to be sent from SouthAfrica. In spite of these challenges and thetechnical complexity of the project, Frankicompleted the piling operations in Decem-ber 2004 with only slight delays. Based onthe success of this contract, Franki wasapproached to undertake the design andconstruction of the lateral support for thisproject with an estimated completion dateof mid-March 2005.

SOIL CONDITIONSThe Bay of Luanda comprises deep marineand alluvial sediments underlain by bedrockdeeper than 40 m. Though the soil profileunderlying the Torres Atlantico site is


C O V E R F E AT U R E

Torres Atlantico A challenging geotechnical engineering

Geofranki installing the Franki-Titan anchors through the diaphragm wall

remarkably uniform, the challenge for Franki lay in penetrating the 16 m thick stiffclay horizon and the dense boulder horizonwith a driven piled solution and a boredpiled solution, respectively. Moreover, theshallow phreatic surface and fragile oldbuildings surrounding the construction siteimposed vibration and movement restraintson both the piled foundation and lateralsupport contracts.

To support the twin tower block struc-ture, approximately 850 Super Heavy FrankiPiles in groups of up to 20 were predrilledthrough the stiff clay layer and driven ontothe very dense boulder horizon at depths of24 m to 26 m below existing ground level.An enlarged base was installed for therequired working load capacity of 2 000 kNwith permissible total pile head settlementof 8 mm. Franki DCIS piles were selected fortheir performance as well as their ability toensure the load capacity by measuring thebasing energy in each pile.

Before the project could begin, a trial pro-gramme to demonstrate the load settlementperformance of the 610 mm diameter Super

Heavy pile had to be completed. To mitigateperceived environmental problems, such asthe impact of vibrations, installation tech-niques and pile load capacity on Luanda’smain police station, a building over 200years old situated on the site’s northernboundary, pre-drilling was used optimally.

Measured peak particle velocities of lessthan 5 mm per second resulted in an unin-terrupted contract and the education andawareness programmes developed for the sur-rounding occupants proved that driven pilesremain a viable proposition in city centres.

After Soares Da Costa Ltda’s in-housegeotechnical contractor experienced difficul-ties installing and achieving load capacitywith post-grouted strand anchorages, theconstruction company called upon Geofranki to install the Franki-Titan systemon the Torres Atlantico site.

The problems that resulted from theunsuccessful installation of the anchors ini-tially installed resulted in construction pro-gramme delays and, to make up the losttime, Franki is installing more than fouranchors a day, using one machine.

Once again, Franki had to consider theenvironment while devising the lateral sup-port solution. In very weak ground condi-tions under old structures that are in a poorstate of repair, Franki opted to installapproximately 200 No 40/16 Franki-Titananchors with a 10 m fixed length generatinga working load capacity of 450 kN. Thisfacet of the Torres Atlantico project – theanchor installation – is on programme andthe scheduled completion date should beachieved.

The success of Franki on the TorresAtlantico project thus far is founded notonly on its proven technical proficiency, butalso on the support rendered by the maincontractors Soares Da Costa Ltda and theprofessional team on the project.

Contact Gavin Byrne and Daan Coetzee

Franki Africa (SA) (Pty) LtdTel 011-887-2700Fax 011-887-0958

E-mail [email protected]


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GEOLOGYThe geology of the area belongs to the Rustenburg Layered Suite ofthe Bushveld Complex. According to the 1:250 000 geological map(2526 Rustenburg) the unit present on site is the Pyramid gabbro-norite. This unit comprises gabbro, norite and anorthosite layers thatgently dip to the east. To the west and north-west of the site outcrophills of gabbro-norite are present (2).

TYPICAL PROFILEAt the site a typical profile comprised the following (3):

00,0 to 01,3 m Clay vertisol01,3 to 04,1 m Completely weathered, very closely jointed very

soft rock resembling gravel; norite04,1 to 09,5 m Medium weathered, closely jointed, medium hard

rock; norite09,5 to 18,2 m Slightly weathered, widely jointed, very hard rock;

anorthosite18,2 m + Slightly weathered to fresh rock, very widely joint-

ed very hard rock; norite

SLOPE DESIGNThe above profile meant that the upper weathered materials toapproximately 10 m depth had to be battered back to generate safeslope angles, whilst the lower, less weathered, very hard rock couldstand practically vertically. The general layout of the box cut is

detailed in three-dimensional format in figure (4).However, this simplified design profile was complicated because

seismic forces induced by blasting generate localised instability offaces. Thus sloping to slightly lower face angles and meshing thefaces proved particularly successful, particularly when combinedwith shotcreting selected noses (5).

3,5 mm ϕ, 100 mm diagonal mesh was used in conjunction with1,8 m long split sets to ensure that localised instability would not beproblematic as excavation proceeded (6).

WEDGE FAILUREPossible wedge failure was investigated and mitigating remedial mea-sures were designed (7).

EXCAVATIONRemoval of the approximately 30 000 m3 of blast material wasaccomplished using steeply sloped access ramps and six-wheel-drivearticulated dump trucks (8).

DEWATERINGAlthough significant quantities of water were predicted to occurfrom pump tests conducted during the investigation, initially twopumps (and later a single pump) were capable of controlling waterduring excavation (9).


Text Alan Parrock Geotechnical principalARQ Consulting Engineers (Pty) Ltd

Interesting geotechnics atImpala Platinum

G E O T E C H N I C A L

Impala Platinum has its primary operations concentrated on the western limb of the Bushveld Complex near the towns of Phokeng and Rustenburg in North-West. Expansion of the facilities made it necessary for a headgear with a foundation situated 26 m below surface to be constructed at the proposed site of the new Number 16 Shaft. This article details some interesting aspects of the geotechnics associated with the excavation

1 2


Client alliance partnerRead Swatman and Voigt (Pty) Ltd

Subcontract for box cut designARQ (Pty) Ltd

ClientImpala Platinum Ltd

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HORIZONTAL DIRECTIONAL DRILLING (HDD) is a construction pro-cedure that has been employed internationally for some 25 years. Itdescribes a specific form of trenchless technology that, by definition,enables a variety of underground ducts and pipes to be installed withminimum disruption to the ground surface. The technique combinesthe steering technology developed in the oil industry with boringmethods employed for conventional horizontal trenchless crossings. Itrequires little, if any, excavation to install pipes and conduits in arange of lengths, sizes and depths along pre-assigned vertical and hori-zontal alignments.

The technique has gained worldwide acceptance and is consideredan established method for installing pipes and ducts ranging in sizesfrom 50 mm to 1 500 mm beneath large obstructions such as rivers,wetlands, highways, airfields and buildings.

In 2001 it was estimated that there were over 10 000 HDD rigs ofvarious sizes worldwide, yet in South Africa there are probably fewerthan ten, suggesting that local application of the system has been lim-ited. No doubt there are many reasons for this, not least of whichbeing the high cost of importing the machinery, tooling and consum-ables, compounded by the reluctance of clients and consulting engi-neers to accept an apparently new and untested technology as a viablealternative to conventional construction methods.

APPLICATIONSAs with all trenchless methods, HDD has the advantage of minimisingthe disruption caused by conventional open cut and cover excavationsfor service installations, and it improves safety as it eliminates theneed to support the sidewalls of deep trenches. HDD has the addedadvantage of enabling crossings to be constructed beneath large sur-face obstructions along preset horizontal and vertical alignmentswhere direct, indirect and social costs would otherwise make such analignment unfeasible if conventional construction techniques were tobe employed.

Environmental applications are wide and varied, including limitingsurface disruption in sensitive areas such as wetlands. Others includethe installation of well screens along horizontal curves within or neara contaminated zone, thereby optimising the efficacy of contaminatedwater recovery by enabling substantial lengths of screen to be placedin the areas most needed. In addition, HDD offers the ability to

enhance bio-remediation of pollutants by the injection of appropriateliquids or gasses. Post-installation of leachate drains in tailings andlandfill sites is another application of the technique in the environ-mental field, as is the sealing off of contaminated areas by horizontalinjection of polymers or grouts beneath polluted underground plumes.

HDD can be employed to provide horizontal water extraction wellsbeneath or within rivers or lakes where, owing to set-up costs overwater, conventional vertical boreholes may prove to be too costly.

Another possible application, which requires further study andresearch, is the use of horizontal guided drilling for site investigations.

THE TECHNIQUEHDD essentially involves three processes:

The first stage entails installing a pilot hole drilled from the surfaceat a pre-determined angle and along a prescribed path. The drill pathcomprises straight inclined and straight horizontal sections connect-ed to large radii curves. The latter are dictated by the size of the drillstring, pipe material and pipe diameter and are formed by a smallkink, or bend, in the drill string just behind the drill head, termed a‘bent sub’. Steering is controlled by rotating the drill head to thedesired direction and then pushing the drill string forward until therequired direction is obtained, after which drilling is continuedalong the realigned path. The size of the pilot hole is dictated by,among others, soil conditions, the size of the drilling machine andthe drilling method. The pilot hole is supported by slurry, consistingof a mixture of water and bentonite, and sometimes polymers.The second stage enlarges the pilot hole by reaming to achieve therequired size within which the product pipe or duct is to beinstalled. Typically, the final hole should be between 1,3 and 1,5times the outside diameter of the product pipe, and for large diame-ter holes a number of reaming operations may be required. The pro-cess is normally carried out by attaching the reamer to the drillstring on the side opposite to that of the drill rig, from where it isrotated and pulled back into the pilot hole, which is enlarged bycutters attached to the reamer. Lengths of drill pipe are added to thereamer as it is pulled back to the rig. Slurry is again used to supportthe hole. Depending on ground conditions, forward reaming canalso be carried out. In this process the reamer is thrust forward bythe drill rig and guided by the pre-drilled pilot hole. The final process entails pulling the product pipe into the pre-drilledhole. The pipe, usually steel or HDPE, is prefabricated to the required

length on the side opposite to the drill rig, from where it is connect-ed to the drill string via a pulling head onto which a swivel isattached. The swivel prevents rotation of the pipe as it is pulled bythe drilling rig into the hole until the full length of pipe is in place.

EQUIPMENTThe equipment required to carry out HDD work includes the drillingrig, tracking system, mixing and recycling equipment, tooling,including rods, bits and reamers, and consumables such as bentonite


Text Brian HarrisonPrincipal, Inroads Consulting ccAndré Wood Managing director, TRG International (Pty) Ltd

Horizontal directional drilling and its

Description Pipe diameter Depth range Bore length Torque Thrust/pullback Machine weight(mm) (m) (m) (Nm) (ton force) (tonne)

Mini 50–250 5 to 10 180 Up to 1 300 Up to 90 8Midi 250–600 Up to 20 270 1 300 to 9 500 90 to 450 16Maxi 600 – 1 200 Up to 60 1 500 Up to 108 000 Plus 450 25

Table 1 Industry classification of HDD rigs

Description ApplicationsMini Telecommunications, power cables, water, sewerage and gas

linesMidi Crossings beneath streams, roadways, environmentally sensi-

tive areas such as wetlandsMaxi Substantial crossings beneath rivers, highways and airfields

Table 2 Typical applications for rig classes

and polymers. Drilling rigs are classified into three groups termed mini, midi and

maxi rigs. The type of rig selected depends on the length of pipe to beinstalled, the hole size, thrust and pullback capacity, torque and depthto be drilled. Table 1 illustrates the industry classification of HDD sys-tems developed in 1994. Since then substantially more powerful rigshave been manufactured, enabling larger, deeper and longer crossingsto be achieved, and the classification presented here is probably duefor updating.

Mini rigs are typically used for short distances and small-diameterpipes and conduits associated with municipal service reticulation lines.Maxi rigs, on the other hand, are used for longer distances and largediameter pipes, such as for bulk water and sewer, and beneath sizeablecrossings. Intermediate distances and pipe diameters require a midi rig,the capabilities of which fall between those of the mini and maxi.Table 2 outlines typical applications for the various rigs classes.

In South Africa there are estimated to be seven mini and three midirigs, most of which are located in Gauteng. No maxi rigs are availablelocally, although they can be purchased from overseas suppliers andmanufactures.

Tracking systems are required to ensure that the position of the drillhead is correctly aligned vertically and horizontally. These include thewalkover and wireline steering systems, which provide information onthe magnetic azimuth for horizontal control and inclination for verti-cal control.

The walkover system employs a transmitter, or ‘sonde’, located nearthe drill head. When positioned directly above it, a receiver at groundsurface locates the position and depth of the drill head. The wirelinesystem consists of a magnetic sensor placed in a non-magnetic bottomhole assembly, which is connected to a computer at the surface bywires which pass through the inside of the drill pipe. Magnetic read-outs are interpreted by the computer, providing information on thealignment and depth of the bore.

In South Africa the walkover system is the cheaper and more popu-lar, but it does have its limitations, some of which are discussed below.

Tooling includes drill bits, rods and reamers, the correct choice ofwhich is vital to the successful completion of an HDD project.

Drill bit selection depends on the subsoil conditions and geologyand range from duck bill and jetting or shovel bits for soft soils,through to tricone roller bits for stiff and dense clays and sands, anddownhole hammer and Tricone bits with mud motor for very densesoil and rock conditions.

Drill rods are typically 127 mm (D150) to 171 mm (D300) OD hol-low steel pipes in lengths of 9,1 m. Rod selection is related to the rigspecifications, crossing length and product pipe diameter.

Reamers come in a range of sizes and shapes, each selected to suitthe soil conditions encountered. They include spiral or fluted reamers,which are the most versatile since they can be used in sands, clays,gravels, cobbles and soft rock. Others include wing or open reamers forstiff clays, barrel reamers for loose sands and mixed soils, blade ream-ers for soft and firm clays, and rock reamers for rock formations.

Slurry mixing and recycling consists of a chamber for mixing the ben-tonite, water and additives and a collection pit where the returnedmixture with cuttings from the hole are passed through a system ofsieves and hydro-cyclones to separate the cuttings, which are disposedof, from the bentonite mixture, which is re-used.

Drilling fluid is one of the most important components of the entireHDD operation since it fulfils a variety of functions, including holding

application

the cuttings in suspension and transporting them to surface, stabilisingthe hole, lubricating the drill bit and rods, cooling the tooling and pre-venting loss of slurry through micro-fissures and voids. Polymers andadditives are sometimes mixed with the bentonite slurry. These areexpensive but they do aid in improving lubrication, controlling fluidloss, enhancing suspension of the cuttings, and controlling viscosity.

SOME HDD PROBLEMS Proper investigation, planning and the correct selection of equipmentand tooling, and the use of experienced operators can overcome manyof the problems associated with HDD projects.

Geotechnical conditions underlying the route are probably the mostimportant factors to be considered in any HDD project, as they governthe selection of suitable tooling and provide information for the cor-rect slurry design. Variations in subsoil conditions, both laterally andwith depth, the presence of obstructions, the depth to a perched orregional water table and the presence of shallow rock are just a few ofthe many potential difficulties that may be identified by undertaking ageotechnical investigation before embarking on any HDD project.Potential problems can then be anticipated and addressed at the plan-ning stage before undertaking the work.

Steering problems normally arise when soft clay or loose sand over-lies very dense soil, such as pedocretes, or rock, more so at shallowentry angles. Under these conditions the drill head may deflect off theharder underlying material, leading to deviations from the desiredroute. Pushing the drill rod without rotation may assist in this regard.A similar steering difficulty may be encountered when the drilldeflects off boulders occurring within the formation. Very soft lowstrength clays may also present steering difficulties, as they are unableto offer any significant shear resistance to the steering tool when achange in trajectory is required.

Tracking or locating systems, particularly the walkover system, pre-sent problems where metallic objects or magnetic and electrical inter-ferences are present. Such sources include microwave towers, trafficsignal loops, power lines and electrified security fences. The walkoversystem requires the receiver to be located above the transmitter at thedrill head, and access to certain areas such as over rivers and wetlandsor beneath buildings becomes problematic. The walkover system alsohas depth limitations. Although more expensive, the wireline trackingsystem is one method of overcoming some of these difficulties.

Borehole stability is governed by the material through which thehole is advanced and collapse of the hole may lead to numerous diffi-culties. These include high pullback forces, high torque and surfacesettlement, which occurs if the hole is large or near to the ground sur-face. While slurry often addresses potential borehole collapse, exces-sive use may cause swelling of some active des-iccated clays owing to water absorption by theclay. This causes the borehole to slowly closewith time, resulting in a hole size smaller thanthe product pipe. While potentially preventinghole collapse, thicker, and hence more viscous,slurry requires that more torque be applied bythe rig.

Slurry loss is not uncommon, particularly insands and at shallow depths where seepageoccurs through permeable material. Hydraulicfracture in fissured clays and jointed weatheredrock is another source of fluid loss. Increasingthe fluid density and control of drilling pres-sure can partially assist in reducing these losses.

Drill rod failure occurs when excessive torqueand pullback forces are applied to the string bythe rig, mainly during reaming. Tensile andbending failure may occur during pullbackalong sharp curves which induce high stressesin the rods at the bends. Steep entry anglesrequire high pullback forces. The grinding

action of abrasive silica rich materials such as quartzite may wear therod where it rests on the rock, reducing its diameter and hencestrength.

LIMITATIONSHDD is not the panacea for all installation projects and it does haveits limitations.

For example, machine size limits the length and alignment for agiven pipe diameter. Although sizeable projects can be undertakenwith smaller rigs, the risks are increased, particularly during reamingand pipe installation. Careful planning, detailed investigation andconsiderable operator skill are required to undertake an HDD projectemploying a machine with lower thrust, pullback and torque thanthat ideally required.

Space limitations may in certain situations obviate the use of HDD,especially in developed urban areas. For a given depth, entry angle,pipe size and material type, the drilling rig must be set back to a pre-determined entry point. If obstructions such as buildings and roadsprevent this, then HDD is not feasible at the location intended. Simi-lar requirements are necessary at the exit point. Space is also requiredfor the rig, slurry mixing and recycling plant, disposal and for storageof the tooling and consumables.

Pipe type and diameter place limitations on the radii within whichthe pipe can be installed. Sharp curves with small radii place unduestresses on the drill rod during pullback, and both tensile and bendingstresses on the pipe itself. Large pipes require large bend radii withconcomitant large set-back distances requiring additional space,which, if at a premium, makes the technique unviable.

Buried obstructions such as boulders can seriously effect steering, asdiscussed above. Fill areas containing large blocks of reinforced con-crete rubble are even more problematic. Not only does this affect steer-ing, but the steel interferes with the tracking system and severelywears the drill bit.

PROJECTSA few projects that were undertaken recently are described below,together with the problems encountered and the methods employedto overcome them.

A 200 m long crossing beneath a river underlain by alluvial depositscomprising cobbles and sand was undertaken in the Eastern Cape. A315 mm HDPE pipe was installed after pilot boring with a Trihawkand roller-cone drill bit and staged reaming with hole openers. Prob-lems were encountered in penetrating the dense tightly packed cob-bles, which may have been overcome had a deeper bore beendesigned and a mudmotor employed, as originally proposed. Owing


to limited funds, a shallower depth was selected and an alternativedrilling technique to that ideally required was used. A 284 m long crossing beneath a river underlain by silt and siltysand was undertaken in Mozambique. A 200 mm steel pipelineplaced within a 315 mm HDPE sleeve was installed after the pilotbore had been enlarged to accommodate the sleeve.Two 200 mm diameter HDPE pipe ducts for electric cables wereinstalled beneath a railway line, a road and a stormwater channel,over a distance of some 150 m and within residual granite compris-ing uniform clayey sand of stiff consistency. The crossings werelocated near to a substation and beneath a railway line where highelectromagnetic fields were generated, leading to problems with thewalkover tracking system. This was overcome by utilising a dual fre-quency sonde. Numerous HDPE sewer pipes, ranging in size from 200 to 315 mm,were installed over a total distance of some 1 200 m to depths of theorder of 4 to 5,5 m in a busy urban area. Variable ground conditionswere encountered, ranging from transported silty sands through toclayey silt, residual andesite, residual shale gravel and dense sand,and residual sandstone. Tracking was carried out with Digitrak locat-ing systems and a Magenta 0,1 % drilling sonde, which enableddrilling to the tight tolerances required for the sewer lines.A number of crossings for a gas line were installed in soils rangingfrom fill, alluvial gravels and cobbles, expansive clay and residualsandstone, to quartzite and dolerite. Pipes consisted of bitumen-coat-ed steel of 204 mm OD. Tooling included a standard jetted system,mud motor, directional air hammer and hole openers. All bores weredesigned and logged and the final ‘as-built’ bore installation withdetails and drawings provided.

The main problem was the variable geotechnical conditions ateach of the crossings. No information was provided prior to estab-lishing on site and ground penetrating radar was used in an attempt

to estimate the in-situ density of the soils, and by inference consis-tency, and to locate services.

The bitumen-coated cover to the pipe also created some difficulties,particularly in areas underlain by weathered rock, as the gravel-sizedparticles tended to adhere to the coating, necessitating large pullbackforces to overcome the increased frictional resistance. Care had to betaken to ensure that all gravel and sand suspended in the bentonitewas removed before installation of the pipe was attempted.

In some locations the underlying active clays were dry and stiff.When slurry was introduced, they expanded, resulting in some diffi-culties in installation. Slightly larger holes were reamed where theseconditions occurred. Loss of slurry through fissures, which are com-mon in these clays, particularly in the upper horizon, also occurredwhen crossings were too close to the ground surface.A 450 mm diameter 74 m long HDPE sewer pipe was installed indense ferricrete in a township. Very few problems were encounteredon this contract. Laying out the product pipe before installation didinterfere with access to driveways and some roads, but the local res-idents were informed of this beforehand and were very accommo-dating.A 137 m long crossing beneath a road and located in rock was

undertaken employing a 25 ton midi rig and a directional air percus-sion hammer. Because of space constraints and other restrictions therig was set up on a platform some 4 m above the road level. Com-plex curves were required and continual directional changes had tobe made throughout the bore, together with allowances for bendradii of the drill rod, sleeve pipe and the product line. Rock holeopeners were used to enlarge the bore diameter to the required sizebefore it was finally cleaned and the sleeve pipe installed.In Saudi Arabia, a maxi rig was used to install two crossings, one a406 mm diameter 1 000 m long steel pipeline located beneath a 167 m high sand dune. No problems of any significance wereencountered except that of designing a facility capable of pumpingand recycling 2 000 l /min of slurry down the hole during the ream-ing stages. The second installation consisted of a 610 m long 762 mm diameter steel pipeline placed beneath a highway inter-change. Sandy clay and sandstone were encountered in the bore.The only available water in the area was saline, which required aspecial blend of drilling fluids. Of the few problems encountered,one was that the viscosity of the drilling fluids increased from 40 to120 seconds owing to the sandy nature of the material. An additiveand water were used to constantly adjust the fluid mixtures. Buoyan-cy of the pipe was calculated and adjusted throughout the pullingprocess. The entire installation was completed in 17 days.

CONCLUSIONSHDD is a useful and internationally accepted technique for the instal-lation of pipes and ducts covering a range of sizes and lengths in areasof surface and buried obstructions. It has applications in many fields,including civil infrastructure, water abstraction and environmentalmonitoring and remediation.

The method requires fairly sophisticated equipment and toolingand the experience of skilled operators. While it has its advantages,there are limitations for which the technique is suitable and it can befraught with problems if undertaken by inexperienced contractors orwith inadequate equipment.

Since it was first implemented, a great deal of research has beenundertaken and significant developments have been made in themachinery, tooling, tracking equipment and slurry design, and HDD hasnow reached a level of advancement that makes it a viable, competitiveand cost-effective alternative to conventional subsurface installationmethods. Projects can now be undertaken which, for social, environ-mental or financial reasons, would not otherwise have been possible.

For various reasons the method has yet to receive sufficient recogni-tion and application in South Africa, which has placed limitations onthe number of contractors carrying out HDD work, and on the num-ber and size of drilling rigs and tooling available.

SLAKING AND DISINTEGRATION in Karoo Mudstones is a wellknown, extensively documented geotechnical problem, especiallywhen ongoing disintegration in rock cuttings results in underminingof more resilient overlying sandstone, with concomitant crashing ofthese onto the roadway. Recent investigations into continuous ravel-ling and loose rock falling onto National Route N2 in the Kei Cut-tings of the Eastern Cape have resulted in innovative and cost-effec-tive methods of stabilising rockmass exposures susceptible to thismode of failure.

DISINTIGRATION IN MUDROCKOne of the major engineering problems associated with the rapidweathering of mudrock surface on exposure is when disintegratingor slaking rock in cuttings is overlain by more resilient rock such assiltstone or sandstone. Over time, cavities expand beneath compe-tent rock until a vertical joint is intersected, or until the cantileverstrength of the overlying rock is breeched, at which time catas-trophic failure occurs and masses of rock plummet down to theroad. There is usually very little warning and the condition isalways potentially life-threatening.

CONCHOIDAL FRACTURING IN SANDSTONEConchoidal fracturing in sandstones of the Adelaide Subgroup;Beaufort Group; Karoo Sequence, is a phenomenon observed in thefield by the authors, and appears to be particularly prevalent in theBorder and former Transkei areas of the Eastern Cape. Yet the phe-nomenon is poorly referenced. A literature survey has providedonly one reference, namely from Brink (1983), in which he refers towork by Haughton (1969) that ‘certain sandstones in the lowerBeaufort Group are also liable to disintegrate with a small-scalespheroidal type of pattern’. Haughton suggests, in one oblique ref-erence, that ‘both the lower beds of the Beaufort and the underly-ing Ecca sediments contain bands of spheroidally-weatheringgreenish or bluish sandstones, greenish flagstones, and calcareousconcretions’. Important here is not so much the ‘spheroidal’ refer-ence, but rather the stratigraphic locality, that is, as ‘lower’ Beau-fort, placing these particular sedimentary units in the Border andformer Transkei areas.

Dr G V Price, investigating reasons for a large sandstone rock collapse in the Barberskrans area of the N10 near Cradock, discov-ered that certain sandstones – on weathering – produced not ‘small-scale’ spheroidal fracturing as suggested by Brink, but relatively large-scale arcuate or ellipsoid fracturing which Price hastermed conchoidal fracturing of weathered sandstone. Furtherinvestigations in the Kei Cuttings of the N2 reveal the problem toexist there, too. Here, newly exposed sandstone in certain rock cutslopes indicate rock to be initially free of any visible deformation, yet in time dark lines appear on the rock surface,which lines appear to demarcate planes of weakness along whichmoisture is being absorbed and lost. In time relatively large-scalebreakup of the rock occurs along these, now elliptical lines, to produce a smooth curved fracture – hence the term ‘conchoidalfracture’.

GEOTECHNICAL ANALYSESInvestigations into rockmass cutslopes in the Kei Cuttings revealmoderately to slightly weathered, grey, pale yellow and brown, close-ly jointed sandstone with minor intercalations of olive brown mud-stone in some cuttings. In others, mudstone occupies the entire cuts-lope. Mudstone rock disintegrates on exposure, with continuousaccumulation of gravel/pebble-sized fragments of mudstone in theside drain creating an ongoing maintenance problem. Exposed sand-stone, on the other hand, undergoes conchoidal fracturing, whichcould give rise to large-scale, even catastrophic, rockmass failure,although measured failures to date have been relatively small. Thisproblem is exacerbated by a joint pattern capable of localized top-pling and wedge failure. Scaling by barring down loose material hasimproved stability but this is only a temporary measure since ongo-ing disintegration and conchoidal fracturing upon exposure will cre-ate the same poor rockmass conditions over and over.

Long-term, more permanent solutions, such as battering back,topsoiling and vegetating the slope, or stabilising with rockbolts,mesh and shotcrete, are either impractical or too costly. Cutslopesare high and extensive, which would require excavating half themountainside in the former, and the latter, besides being aesthetical-ly unattractive and environmentally intrusive, would be prohibitive-ly expensive. A more innovative and cost-effective solution wasrequired, leading to the installation of a ‘cable-mesh anchorage’ trialsection on one of the larger cutslopes in the Kei Cuttings.

CABLE-MESH ANCHORAGE – THE SYSTEMThe use of rockfall netting fixed to cutslopes has seen widespread useinternationally, particularly in mountainous countries where rockfailures are prevalent. Here in South Africa, rock catch-fences andmeshnet stabilisation have been successfully utilised, notably alongChapman’s Peak Drive. However, to the authors’ knowledge, this isthe first application of rockfall netting specifically to control near-vertical disintegrating/conchoidally fracturing mudstone and sand-stone rockmasses.

Cable-mesh anchorage comprises a system of mesh and cablesanchored into the rock face and revolves around three major ele-ments, namely mesh, cabling and anchorage pins.

DESIGN AND CONSTRUCTIONGeotechnical investigations required for the design include joint sur-veys to determine the extent of any rockmass instability plus esti-mates of strength/disintegration and fracturing of the rock substance.The kinematic instability is estimated based on stereographic projec-tions and stability analyses determined from these projections.

The cable-mesh anchorage system installed in the Kei Cuttings atN2 Section 17, km 1.2 (immediately north of Kei Bridge) comprisesthe following components:

Mesh: 2,7 mm diameter hot-dip galvanised and uPVC-coated,hexagonal woven double-twisted wire mesh, with 80 mm x 100mm mesh openings, installed in 2 m widths hung off the summitcable and tied to the base cable. Mesh laced together along alljoints, using 2,2 mm diameter uPVC-coated binding wire.


Innovative solution for fracturing rockmass

Text Dr G V Price Terreco Consulting East LondonN North-Coombes Goba Moahloli Keeve Steyn (Pty) Ltd DurbanR Damhuis South African National Roads Agency Port Elizabeth

Special thanks to the South African National Roads Agency for permission to publish this article

Cables: 10 mm woven steel cables strung diagonally across the faceof the cutting, connected to 12 mm horizontal cables installed atthe summit of the cutting and 2,5 m above the toe (height chosento discourage theft of mesh).Anchors: 16 mm diameter galvanised and threaded gewi bar dowels,grouted 500 mm into the rock face in pre-drilled holes, with 1 200mm long bars installed above the summit to anchor the top cable.Rock face anchors installed at a bi-directional grid spacing of 5 m,with diagonal cables strung through them and secured to top andbottom cables. Note that anchorage dowels can also perform a sta-bilising function and be designed as rockbolts where appropriate.Summit drainage: Desirable, but not provided in this case, due inpart to the difficult terrain and in part to the presence of existingestablished vegetation. The binding effects of existing root systemsand the water attenuating effects of the vegetative cover weredeemed to be integral to the stability of the summit area and weretherefore not compromised. In addition the contributing flow fromthe summit catchment is relatively small.Catchwall: Desirable where the possibility of larger boulders slip-ping through the bottom of the mesh is high – not required orprovided in this case.

CONCLUSIONThe cable-mesh anchorage system has been implemented and testedin the Kei Cuttings with outstanding results. Rock debris alongsidethe road has been reduced to virtually zero with most of the looserock trapped by the mesh. A small quantity of finer fragments slipdown the face and onto the toe verge, where they are removed asnecessary. There is therefore also a maintenance cost benefit. A sig-nificant bonus has been the ‘greening’ effect in the exposed rockface. Debris accumulation acts as a filter with larger fragments trap-ping smaller ones and resulting ultimately in localised islands of soilwhere vegetation has established. This will result in partial revegeta-tion of even very steep slopes and with it, added stability and a boonto environmental aesthetics. Indeed, proprietary eco-friendly filterfabrics can be installed below the mesh to mitigate the erosive effectsof wind and water and to accelerate the greening of the slope.

Cable-mesh anchorage is not, however, the panacea for all ills. Itrequires a specific geological set of mudstone/siltstone and sandstoneassemblages; state of weathering is fundamental; and is more applica-ble to areas of existing road located immediately adjacent to the roadverge where space for alternative measures is limited. The rockmassmust be largely homogenous, whether it be sandstone or mudstone,and large ledges of unweathered rock undermined by rapidly slakingmudstone would, for example, not be an appropriate condition. Anexcessively weathered rockmass would also not be appropriate as atsome point the rockmass stability defining characteristics – disconti-nuity relationships; joint condition; hardness; rock disintegration;etc – are superseded by the rock substance properties which revolvearound soil mechanics characteristics such as shear strength; pres-ence or absence of moisture, and so forth.

These apart, the use of cable-mesh anchorage for disintegrating orfracturing rock is a very viable tool of rockmass support. Conchoidal

fracturing of sandstone rockmasses in the Eastern Cape – and possi-bly elsewhere – is a relatively poorly known mechanism of rockmassinstability, with little documentation yet there is, as shown, substan-tive proof and recognition of this malady, which has potential forlarge scale mass movement. Cable-mesh support has in the mean-time proved capable of supporting such rockmass. The method isinnovative, economically sound, aesthetically enhancing, and envi-ronmentally effective.

ReferencesBrink, A B A 1983. Engineering geology of southern Africa; Volume 3; The KarooSequence. Pretoria: Building Publications.

Haughton, S H 1969. Geological history of southern Africa. Cape Town: GeologicalSociety of South Africa.

Venter, J P 1980. The engineering properties and road-building characteristics ofmudrocks with special reference to southern Africa. DSc thesis, University of Pretoria.

Before During After

GEOLOGYThe general area of the proposed miningdevelopment is along the eastern flank of amajor area of geological upheaval known asthe Vredefort Dome Impact site. The Vrede-fort Dome was formed an estimated 2 000million years ago when an asteroid some 10 km in diameter hit the earth close thewhere the town of Vredefort is situatedtoday. The area is primarily underlain bysedimentary lithologies of the Ecca Groupof the Karoo Supergroup, particularly thoseassociated with the Vryheid Formation.Dolerite intrusions in the form of sills aregenerally present in the upper horizons ofthe Karoo Sequence. The Block 13 coaldeposits cover an area of approximately 12 km from north to south and 10 km fromwest to east.

INITIAL INVESTIGATIONS ARQ Consulting Engineers undertook ageotechnical investigation of various aspectsof the proposed development at the feasibili-ty stage. This included general infrastructuresuch as offices, change rooms, stores, waterhandling dams, storage silos and some 18 km of conveyor route. In addition, themine entrance area was investigated bydrilling rotary core boreholes as well as per-cussion boreholes logged by traditional andgeophysical methods. Based on the findingsof this investigation, recommendations were

formulated on the most appropriate way toaccess the coal reserves.

ADIT EXCAVATIONSasol decided that an open-voided, aditexcavation was the most cost effective andpractical means of accessing the coalreserves. The initial plan was to excavate a500 m long decline at a slope of 8 degrees toterminate at a square base 52 m belowground level. An extensive geotechnicalinvestigation into the feasibility and detaildesign of the various components of theaccess route to the coal was undertaken bymeans of geo and hydro exploratory rotarycore boreholes supplemented by an exten-sive programme of geophysical probe log-ging. Two-dimensional finite element soft-ware was used to model stresses and defor-mations of actual and planned excavations.

Assessment of stresses and strains in rock mass by finite element methods

Three-dimensional view of a digital terrain model used in the planningstages of the adit excavation

The layout of the adit excavation, blast-ing patterns and required lateral supportwere greatly influenced by the highly weath-ered and fractured nature of a near surface,hard rock dolerite sill (UCS around 200MPa) characterised by steeply dipping dis-continuities that opened up very soon afterexcavation. This problem was solved bytrimming back cut slopes excavated into thedolerite sill to 45 degrees and in this processremoving most steeply dipping discontinu-ities, thus drastically minimising thepropensity for toppling failure.


Text Pieter OosthuizenARQ Consulting Engineers (Pty) Ltd

Geotechnical aspects of the development of the Sigma

MOOIKRAAL UNDERGROUND COLLIERYSigma Colliery has been the sole supplier of coal to Sasol Infrachem Industries (SII) in Sasolburg since1952. Several alternatives to this supply have been investigated and having natural gas piped fromMozambique is probably the most viable long-term solution. Coal, however, is still required to producethe steam that is needed for the SII processes. The current coal reserves of Sigma Colliery in Sasolburgare not sufficient to supply needs in the long term and several other alternatives were investigated. Themost viable solution to supplying SII with coal was to establish a new operation, Sigma MooikraalUnderground, in the Block 13 portion of the Sigma Colliery reserves

Excavation through the upper, hard rock dolerite sill produced manychallenges

That problem having been circumvented,the underlying sandstone formations provedequally problematic. The exposed sandstonewas much softer (UCS around 20 MPa) andmore friable than expected and degradedrapidly on exposure to atmospheric condi-tions. Great difficulty was experienced indrilling the pre-split holes into this material.A decision was taken to use a tracked exca-vator to remove as much as possible of thesoft, overlying sandstone, mostly in theform of loose sand.

Pre-split and bulk blasting drilling intosandstone soon commenced. Owing to thesoftness of the sandstone, the first blastcaused large-scale damage to the rock face tosuch an extent that it was decided to aban-don the deepening of the adit excavation.The deepening of the adit excavation wassubsequently terminated at a final depth ofapproximately 22 m below surface.

Extensive damage to sandstone rock after pre-split and bulk blasting


Sector CH along c/l Rock Discontinuity Average dip Average dipNo of tunnel (m) spacing (degrees below direction(s)

Start End horizontal)1 0 150 Sandstone Slightly to mode- 17 to 24 120 and 260

rately fractured2 150 185 Siltstone/shale Moderately to 38 to 42 130 and 190

highly fractured3 185 234 Sandstone Moderately 22 90 and 270

fractured

Typical summary of information gathered from the results of the geophysical logging

Layout of the four parallel access tunnels relative to the adit excavation and mineable coal deposits

An example of a portion of a geophysical log giving rock type, rock hardness, spacing and inclination of discontinuities. An acoustic scanner image ofthe borehole wall is included

ACCESS TUNNELSSasol Mining has extensive experience in theunderground mining of coal in the Mohlolounderground section of Sigma Colliery.Based on this experience and because similarrock conditions were expected at the newsite, a preliminary layout of tunnel dimen-sions and spacing, rock bolt spacing andother rock support measures were proposedfor the new tunnels. ARQ was approached toundertake an independent assessment of theproposed support measures based on exist-ing information and the drilling of addition-al rotary core boreholes and geophysical log-ging along the proposed route. Data gath-ered during the geophysical probing of theboreholes was used to assess the quality andcutability of the rock material along theroute of the tunnels.

The assessment of the proposed supportmeasures was undertaken with the Phase2software platform; an elastic and plastic,finite element program for calculating stress-es and displacements around undergroundor surface excavations. Various rock supporttypes and configurations as well as liner sup-ports were incorporated into the models.

One of the four parallel tunnel entrances at the base of the adit excavation

Rock support during and after installation

Movement along discontinuity in exposed rock face

FINAL REMARKS At present the excavation of the access tun-nels is ongoing. Although large volumes ofgroundwater and soft rock conditions havebeen encountered in certain areas, only iso-lated and small instabilities have beenrecorded. All is on track for the first extrac-tion of coal from the newly developed minein September 2005.


Typical output from a plastic analysis undertaken of an access tunnelindicating expected deformations, contours of strength factors andfailed elements

TRENCH SHORING

ONE OF THE MAJOR DILEMMAS on a con-struction site, in particular where the workinvolves excavations, is achieving optimumproduction without in any way compromis-ing the safety of workers. Shoring a trenchor excavation in South Africa usually meansinstalling timber planks and props in theexcavation. This is a time-consuming processand is extremely limiting, as it involvesworking within a congested timber-proppedexcavation.

In Europe, the USA and Middle East, tim-ber shoring has, for many years now, beenreplaced by prefabricated, portable and re-usable trench-shoring systems. These sys-tems not only vastly improve safety on con-

struction sites, but achieve substantialincreased productivity.

Time saved for completion of a shoredtrench installation using prefabricatedshoring systems is at least three-fold. Forexample, a 100 m length of 4 m deep pipeinstallation in a timber-shored trench couldtake 15 days to complete, whereas the samejob shored with prefabricated trench boxescould take five days.

Krings Verbau, of Germany, pioneered anexcellent range of prefabricated shoring sys-tems some 30 years ago. These shoring sys-tems are designed to stringent Europeansafety standards and for ease of use. Kringsproduces a wide range of shoring elementssuited to different excavation applications,ranging from lightweight systems to with-stand earth pressures of 17 kPa and depthsof 1,5 m, to systems withstanding earthpressures of 120 kPa and depths of 5–7 m.Corner elements for pit shoring and adapta-tions for manhole widenings on pipelinesalso form part of the range. These trench-shoring products have re-use factors of 250and more.

Transportation to site is on a flat-bedtruck and assembly is undertaken with a siteexcavator or TLB. The installation procedurecomprises an initial shallow excavation fol-lowed by the insertion of the shoring ele-ments, followed by further excavation andpushing downward on the elements untilfinal depth is reached. Extraction of theshoring system is undertaken while backfill-ing is in progress.

The timber-shoring system currently usedin South Africa requires that the constructionworker must enter the previously excavatedtrench or pit to install the shoring elements,thus working in a dangerous situation tomake the trench or pit safe. By contrast, theKrings shoring systems are installed duringexcavation and extracted during backfilling,and thus the worker never enters an excava-tion which is not shored.

The South African civil engineering con-struction industry should be looking toachieve the same safety and productivityadvantages offered by prefabricated shoring.The promulgation of the new ConstructionRegulations in July 2003 now require that anengineer-designed shoring system must beused to make safe all man entry excavationsdeeper than 1,5 m below ground level. Thenew regulations also place a large degree ofresponsibility for ensuring safety on site onthe client, and therefore on the professionalteam employed by the client.

Krings shoring products may be pur-chased or rented in South Africa throughAject Africa (Pty) Ltd. In order to optimisethe use of the trench-shoring systems, AjectAfrica and Krings Germany offer a designservice to ensure the client gets the rightproduct for the job.

ContactHugh Feely

Adject [email protected]

Prefabricated shoring systems

RADAR’S EVOLUTION FROM RESEARCHTOOL TO MAINSTREAM APPLICATIONSGround penetrating radar (GPR) systemshave been in use for over 30 years, mostcommonly in geophysical applications, suchas mapping bedrock layers and water tables.Because of advances in electronics and soft-ware, GPR has rapidly evolved into a valu-able investigative tool for mainstream appli-cations. Today GPR is used to study, evaluateand solve a wide range of infrastructureproblems such as locating and mappingburied utilities; determining road layerthickness, material characteristics and sub-base and sub-grade conditions; assessing themagnitude and location of deteriorationinside reinforced concrete structures; andinvestigating the condition of railway tracksystems and components. Such GPR-basedinformation can be used to provide an effi-cient and effective method of identifyinginfrastructure problems.

Although early GPR systems were com-plex and required an experienced operatorto collect and interpret data, current systemsemploy advanced analysis software andimproved user-interfaces, making them sig-nificantly easier to operate. Radar is nolonger just a tool for researchers. It is anaccurate, cost-effective and non-intrusivetool that is practical for mainstream mainte-nance and inspection.

A BRIEF REVIEW OF THE TECHNOLOGYA GPR system emits a pulse of electromag-netic energy into a surface and measures theenergy reflected from any buried targetswithin that structure. As the system ismoved across the surface, a series of reflect-

ed signals are used to create a profile imageof the sub-surface. Collecting multiple paral-lel profile lines allow the creation of 3Dimages. The total power of transmitted puls-es during system operation is only about 1/1 000th that of a mobile phone, so GPRposes no adverse health problems for theuser or interference with existing communi-cations systems.

A typical GPR system consists of a con-trol unit, antenna and survey cart. The con-trol unit contains electronics that produceand regulate the pulse of radar energy thatthe antenna sends into the ground, andrecord and store the data. Antenna frequen-cy is a major factor in depth penetrationand target resolution, and should be selectedbased on the application. A higher frequen-cy antenna will locate smaller targets, butwill not penetrate as far into the surface,while a lower frequency antenna will pene-trate deeper, but will have lower resolution.

GPR APPLICATIONS FOR UTILITYDETECTIONSpeed and accuracy are critical in locating ormapping underground utilities. Simplymarking known utilities from as-built mapsis often a risky approach, as many of thesedocuments are incomplete or outdated.Since the consequences of making an errorare potentially huge – ranging from thefinancial costs of interrupting communica-tion or electrical services to loss of life – pro-fessional locating contractors are beingcalled upon with increasing frequency toverify what lies below the surface. GPRoffers superior ability to determine the loca-tion and depth of utilities and identify voids

and buried objects. Unlike other locatingtechnologies such as radio frequencyidentification, GPR can detect utilities ofall material types, including PVC, andenables the user to map closely spacedutilities in 3-D. When integrated withGPS technology, an accurate map of thearea can be produced and archived forfuture reference.

GPR APPLICATIONS FOR CONCRETESTRUCTURE INSPECTIONIn many situations, inspection of con-crete structure using traditional non-

destructive testing (NDT) methods such asacoustic emission and radiography (X-ray) isnot practical. The processes can be time-con-suming to complete, require evacuation ofthe area being tested, and demand consider-able set-up time before the inspection caneven begin. All of these factors can be unap-pealing to customers who need a fast, reli-able, unobtrusive method.

GPR quickly and accurately locates rebar,tension cables, plastic conduits and voids toa depth of 40–50 cm in existing concretestructures (for example tunnels, walls, floors,slabs, decks, balconies and garages). In addi-tion, it is used to detect and map the rela-tive condition of concrete so that rehab pro-jects can be prioritised and planned moreeffectively. For QA on new concrete struc-tures, radar is used to inspect and measureslab thickness.

GPR APPLICATIONS FOR ROADWAYINSPECTIONGPR systems are now able to collect roadwayinformation at speeds up to 100 km/h sothat traffic flow is minimally affected. A highscan rate permits imaging of small voids andpipes underneath the road. Concrete road-way (up to 40 cm) and bituminous/asphaltroadway (up to 90 cm) can both be surveyedwith a high degree of accuracy.

On new projects, accurate roadway thick-ness profiles collected continuously alongroadways provide an excellent method ofverifying adherence to QC/QA specifica-tions. Roadway thickness accuracy is criticalfor establishing valid load capacities – a fac-tor that greatly enhances the life of anyroadway network. The digital ‘infrastructure


GPR technology in concrete and road structure inspection and

Text Terry Odgers Red Dog Scientific Services

profiles’ can be archived for immediateaccess, and can facilitate the planning oflong-term maintenance programmes.

Radar is ideal for the identification andinventory of older roadway systems whoseconstruction history is often unknown. Lackof good data presents an expensive chal-lenge in determining whether to spot repaira stretch of roadway or to partially or fullyreconstruct it.

GPR APPLICATIONS FOR BRIDGE DECKINSPECTIONGPR can be used on overlaid and bare con-crete decks reinforced with longitudinal andtransverse steel (upper and lower mesh) toidentify deterioration quantities (delamina-tion, punky concrete, corroded rebar) andtheir locations on the deck structure.

As in other applications, radar can also beused for QC/QA verification on new bridges.If there is not enough rebar coverage, theconcrete can wear away, leaving the rein-forcements accessible to the elements, forexample salt and moisture can cause corro-sion, degrade the integrity of the concrete,and lead to unscheduled and costly repairs.An excessive amount of rebar coverage canhave a negative impact, as excessive surfacecracking can result. Accurate measurementof concrete cover (depth of rebar fromexposed concrete or asphalt surface) on newconstruction allows engineers to better pre-dict the service life of a bridge deck, reduc-ing the likelihood of future problems.

In bridge maintenance, radar comple-ments and enhances traditional engineeringevaluations. Radar-imaged deterioration

maps can be used to guide the optimal useof corrosion potential testing, chloride test-ing and coring – minimising the deck arearequired for sampling. The resulting dataprovides an accurate overall deteriorationthreshold, which separates critical mainte-nance zones from areas not requiring imme-diate attention.

CONCLUSIONGPR technology continues to evolve andimprove, offering benefits in a wide range ofpractical NDT investigation and damage pre-vention applications. It has proven to beone of the most efficient and accurate meth-ods available to the marketplace.

utility location

TERRATEST, THE GEOTECHNICAL andenvironmental consulting firm establishedin 1990, has undergone significant changesin 2005. Mrs Jan Norris, who joined thecompany in 1996 as a geotechnical engineerand became a director in 2004, has nowbeen appointed managing director and Pro-fessor Deneys Schreiner, formerly dean ofthe Faculty of Engineering at the Universityof KwaZulu-Natal, took over as head ofgeotechnical engineering as from 1 March2005. Peter Waldron, the project leader ofthe very successful Schools Play-pump Pro-gramme (which recently received theSAACE commendation for EngineeringExcellence for projects with a value of lessthat R5 million) continues at head of theearth sciences section.

With a professional team of engineers,environmental scientists, hydrogeologists,geophysicists, geologists, project managersand GIS specialists, Terratest provides aunique service to the industry.

‘Terratest’s strength lies in the synergybetween our environmentalists, geohydrolo-

gists and geotechnical specialists,’ says Norris.‘The integration of our services allows us

to view each project holistically and provideoptimum solutions to our clients, whichinclude municipalities, consulting engineers,the mining sector and developers.’

The firm is involved in a variety of pro-jects, including the implementation of theZululand Groundwater Supply Programme,for which an average of 20 boreholes arebeing drilled every week. The programmehas been carefully planned, with input froma variety of sources, including the ZululandDistrict Municipality’s planning division,groundwater consultants, engineering con-sultants, local government structures andcommunity representatives. This is a rudi-mentary programme which is not seen as thefinal method of water delivery to the localcommunities, but rather as an interim mea-sure to supply water quickly, cost-effectivelyand efficiently to recipients who will receivebulk water only several years from now.

A recent challenging geotechnical projectwas a large lateral retaining wall on the

North Coast Road, Durban, undertaken forEthekweni Municipality City Engineers Unit.Owing to the widening of this road theexisting Metro rail line had to be supportedin a complex and unstable geology. Thesolution involved ground anchors, piles, androck bolts, and on completion, great empha-sis was placed on the aesthetic appearanceof the area. A terrace block wall, plantedwith indigenous vegetation, was erected,and on the upper slope a terracotta pigmen-tation were used in the schokcrete to createan environmentally appealing look.

Terratest is also busy with the strategicenvironmental assessment (SEA) for theAbaqulusi Municipality in the Vryheid area.An SEA aims to integrate natural environ-mental concerns into the planning processat the same level at which social, economicand institutional considerations areaddressed. It serves as a tool for the practicaltranslation of the idea of sustainability intoprogrammes and projects in the integrateddevelopment planning (IDP) process.

Female engineer heads up geoscience consultancy

JAN NORRISJan Norris was born in Liverpool in 1965. Aftercompleting her B(Eng)Hons in civil engineeringat Birmingham Universityin 1989 she spent a yearworking in Zimbabwe as asite agent for the con-struction of earthembankment damsthroughout the country.

She returned to Eng-land the following year and joined Thames Water in their geotechni-cal division. Most of her time there was spent on the geotechnicalinvestigation for the London Water Ring Main – a large 3,5 m diame-ter, 80 km long tunnel 50 m underground.

Thames Water sponsored her part-time MSc studies in geotechni-cal engineering at Surrey University, from which she graduated in1994. She was then promoted to Thames Water’s head office in Read-ing to join the project management team (their engineering disciplinewas 500 strong). It was during this time that she met her husband,Craig, and moved to South Africa.

In 1996 she joined Terratest as a geotechnical engineer. She waspromoted to associate in 2000 and executive associate in 2002, andappointed a director of the firm in 2004.

She regards herself as ‘lucky’ to have been involved in a diversearray of projects – embankments over highly compressible clays, later-al support design, constructions over old landfill sites in Ireland, and(as part of the independent engineers team) the recent rehabilitationof Chapman’s Peak Drive.

Jan became a member of the Pietermaritzburg SAICE branch com-mittee in 2003, was elected chair in 2004, and is now responsible forthe branch’s continued professional development portfolio.

PROFESSORDENEYSSCHREINERAfter 20 years as an aca-demic, including five yearsas dean of the Faculty ofEngineering at the Univer-sity of KwaZulu-Natal,Professor Deneys Schrein-er is re-establishing him-self in the consulting fra-

ternity. In March this year he took on the role of head of geotechnicalengineering at Terratest.

Schreiner believes that engineers can find technical solutions toany foundation problem. The challenge, as he sees it, is to marry thetechnical solution to the financial viability of the project, thus provid-ing the most cost-effective solution for the client.

‘There is little benefit in providing a cheap solution which will leadto significant maintenance costs in the future,’ he says.

‘Likewise there is little to be gained from a solution so expensive

that the client’s project becomes unprofitable. Equal attention mustbe paid to the three key requirements of adequate strength, continu-ing functionality and economic viability.’

Schreiner has spent most of his working life alternating betweenthe UK and South Africa. After obtaining his MScEng in geotechnicalengineering under Ken Knight at the University of Natal in 1976, heworked as a soils engineer for Des Webb with extensive service on theSasol 2 piling project. In 1979 he was awarded the Confederation ofBritish Industry Scholarship and left for the UK to work on the con-struction of an earth dam in Yorkshire and then on the analysis anddesign of piled and gravity base foundations for offshore oil platforms.In 1980 he returned to Johannesburg where he joined Ove Arup &Partners as a geotechnical engineer. He soon moved to their Durbanoffice, becoming the associate responsible for foundation engineeringin that region, dealing with various projects such as the PlayhouseTheatre and the Marine office block. In 1983 he was enticed back toBritain by McClelland Limited to continue his work on offshore foun-dations but in 1985, frustrated by an industry slow-down, he resumedhis studies and obtained his doctorate under John Burland at ImperialCollege, London, studying the effects of expansive soils beneathAfrican roads. He has published a number of conference and journalpapers on this and other geotechnical engineering topics.

In 1991, encouraged by the political changes in South Africa andwanting to be part of the reconstruction process, Schreiner returnedto take up a post as senior lecturer in the Department of Civil Engi-neering at the University of Natal. He quickly moved up the academicladder to become full professor and dean of the Faculty of Engineer-ing in 2001. His deanship ended in 2004 with the merger of the engi-neering faculties from the universities or Natal and Durban-Westville.


YGEC 2005YOUNG GEOTECHNICAL ENGINEERS

CONFERENCEENVIRONMENTAL GEOTECHNOLOGY

– A CONTRADICTION IN TERMS?A conference organised by the SAICE Geotechnical Division in

collaboration with SAIEG, GIGSA & SANIRE

WHEN?13–15 June 2005

WHERE?Aventura Swadini, Mpumalanga. Swadini is situated in the

Drakensberg, on the banks of the Blyde River in the Blyde RiverCanyon Nature Reserve (www.aventura.co.za/swadini/swadini.htm)

HOW DO I GET THERE?The resort is situated 35 km from Hoedspruit in

Mpumalanga and is readily accessible by car, or by plane via Hoedspruit Airport

CONTACTLesley Stephenson

Tel 011-717-7031, Fax 011-339-7853E-mail [email protected]

THE GEOTECHNICAL DIVISION OF SAICE has been hosting localYGE conferences since the 1980s. The 1st International YoungGeotechnical Engineers Conference (iYGEC) was held at the Uni-versity of Southampton in the UK in 2000. At this event youngengineers from around the globe gathered to experience aninternational conference, share their knowledge and experiences,and build lasting friendships. In 2003 the division obtained theapproval of our international body (the International Society forSoil Mechanics and Geotechnical Engineering, ISSMGE) to hostthe 1st African Regional YGE Conference (aYGEC) in Swakop-mund, Namibia. This was followed later in the same year by the2nd iYGEC in Romania.

This event is aimed at bringing together young engineersand scientists working or studying in Africa in the fields of soilmechanics, geotechnical engineering and geology and to pro-vide an opportunity to

experience a conference of international standards, in afriendly environment, amongst his/her peerssubmit a technical paper for peer review and to present thispaper before an audience of his/her peersget feedback and positive criticism from the conference ‘Godfather’ (a senior and well-respected member of the SouthAfrican geotechnical community) andbe eligible for the best paper and best presentation awards,which involves sponsorship to attend and represent SouthAfrica at the next International YGE gathering in Osaka, Japan,in September 2005


LOCAL Young Geotechnical EngineersConference, YGE 2005Swadini, Mpumalanga13–15 June 2005

ContactLesley Stephenson

Tel 011-717-7031, Fax 011-339-7853E-mail [email protected]

INTERNATIONAL 2nd International Conferenceon Problematic SoilsMalaysia27–29 April 2005

ContactThe Secretariat

Tel +65 733 2922, Fax +65 235 3530E-mail [email protected]

www.cipremier.com

International Conference onDeep MixingBest Practice and RecentAdvancesStockholm, Sweden23–25 May 2005

ContactConference Secretariat Deep Mixing

Tel +46 13 20 18 00, Fax +46 13 20 19 14E-mail [email protected]

www.deepmixing05.se

International Symposium onGeology and Linear Infrastruc-tures, GEOLINE 2005Lyon, France23–25 May 2005

ContactPatrick Ledru


5th International Symposiumon Geotechnical Aspects ofUnderground Construction inSoft GroundAmsterdam, The Netherlands15–17 June 2005

ContactConference Secretariat

KIVI CongresorganisatieAtt J van der Kamp

Fax +31 (0) 70 391 98 40 E-mail [email protected]

www.tc28-amsterdam.org

11th International Conferenceof the International Associationof Computer Methods andAdvances in GeomechanicsPrediction, Analysis and Design inGeomechanical ApplicationsTorino, Italy19–24 June 2005

ContactE-mail [email protected]

www.iacmag2005.it

2nd International Conferenceon Geo-Environmental Engi-neeringUnited Kingdom22–24 June 2005


Tel +65 733 2922Fax +65 235 3530


6th International Conference onGround Improvement Tech-niquesCoimbra, Portugal18–19 July 2005


Tel +65 733 2922Fax +65 235 3530


International Symposium onGeotechnics in CitiesLille, France27–29 July 2005

ContactGeocityNet 2005

Tel +33 (0)3 20 43 45 66Fax +33 (0)3 28 76 73 31


2nd International Symposiumon Identification and Determi-nation of Soil and Rock Parame-ters for Geotechnical Design,PARAM 2005Paris, France20–21 August 2005

ContactFrancoise Bourgain

Tel +33 (0)1 44 58 28 22Fax +33 (0)1 44 58 28 30


16th International Conferenceon Soil Mechanics and Geotech-nical EngineeringGeotechnology in harmonywith the global environment Osaka, Japan12–16 September 2005

ContactChairman: Prof Toshihisa Adachi

Tel +81 3 3251 7661Fax +81 3 3251 6688

E-mail [email protected]/~16ICSMGE

Please refer to the GeoDiv website atwww.up.ac.za/academic/civil/geodiv/

for more information

Local and International Conferences and Symposiums 2005

Installing sheetpile cofferdam for deep liftshaft pit (Durban Point area)

Trench support for 1 800 mm dia stormwater pipe. Depth of excavation 5,5 m (Ballito, KwaZulu-Natal)

TRENCHING AND EMBANKMENT SUPPORT MADE EASIER AND SAFERWORKING INSIDE DEEP TRENCHES and at the foot of steep embankmentsand cuttings has now been made easier and safer with the availability of lightinterlocking sheetpiles and easy-to-use excavator-mounted vibratory hammerswhich both install and extract the sheetpiles.

These products have now been launched in South Africa by geotechnicalsupplier Pilequip SA.

Boyd Cousins, owner of Pilequip SA, identified the need for ashoring/trenching system that was safe yet affordable to the South Africanmarket. The first excavator mounted vibrator – an ICE EM328 – was landedhere in April 2004.

The Dutch manufacturer ICE BV ranks among the largest in the world andoperates in 45 countries. South Africa is seen as a potential growth marketand hence Pilequip was signed up as its southern African agent.

The light sheetpiles needed to complement the vibrator arrived in August2004 from world sheetpile leader Arbed (Luxembourg). The potential of thesystem was soon recognised and taken up by specialist civils contractor Leomatplant hire and construction, who has been involved with deep excavations forewer and water services as well as deep structures for over 2015 years.

According to Arnaldo Corbella (director of Leomat Durban), working withthe excavator-mounted vibratory unit took about a week to master, and nowdeeper excavation trenching solutions can be offered without having to callin specialist piling contractors with large crane units.

The Arbed PU 6 sheetpiles – in lengths of 6,0 m and 4,0 m – are relativelylight (75 kg/m2) yet surprisingly strong. They can support embankments of upto 2,5 m without props and simple propping for depths up to 4,0 m. Theinterlock makes for added strength and very good water retention in wet con-ditions. ‘The sheets are robust and since they are vibrated into the ground wedo not damage them like an impact hammer does,’ says Corbella.

Leomat are confident that they will get more than ten re-uses from a sin-gle set of PU 6 sheets, which makes the PU 6 solution quite affordable.

P R O J E C T S A N D P R O D U C T S

MAINTENANCE CONTRACT FORAFRICA’S GIANT EYE AWARDEDTHE SOUTH AFRICAN ASTRONOMICAL OBSERVATORY (SAAO) has chosenApplyIT’s Aurora-Maintenance software to manage the maintenance of theSouthern African Large Telescope (SALT) which, once complete in July 2005,will be the largest single optical telescope in the southern hemisphere.

Also known as Africa’s giant eye, SALT is under construction in Sutherlandin the Karoo, the SAAO’s main astronomical observation site renowned for itsclear weather and dark, cloud-free, unpolluted skies. The US$30 million tele-scope is a modified version of the Hobby-Eberly telescope in Texas. It isowned by the SALT Foundation, an international consortium initiated by theNational Research Foundation, which through South Africa’s Department ofScience and Technology, owns approximately 30 % of the shares. Partners inthe project include academic institutions from Germany, New Zealand,Poland, the UK and the US.

Aurora-Maintenance, which is used extensively in the process manufactur-ing industry, focuses on ensuring safe, reliable operations by supporting pre-ventative and reactive maintenance strategies, including the automatedscheduling of routine inspections and maintenance tasks.

The Aurora maintenance management system, which will go live at SALT atthe end of January, includes integrated modules for equipment management,work order management, scheduled maintenance and spares management.

‘SALT’s maintenance requirements are not unlike those of the processmanufacturing industry. The difference is that we don’t manufacture widgets,we process digits,’ says James O’Connor, Sutherland operations manager.‘The data we gather from our studies of the night sky is crucial for astronomi-cal research around the world and as such, our margin for error is extremelynarrow. Anything less than 100 % accuracy is simply not good enough. Toachieve this standard, our equipment needs to be well monitored and main-tained at all times.’

O’Connor says the SAAO’s choice of maintenance software was based ona number of factors. ‘The performance of the chosen system had to matchthe highest international standards of maintenance software. It was an addedbonus for us that the Aurora suite has been locally developed and as such,was priced competitively for us as a non-profit research organisation,’ he says.

The higher the capital investment in equipment, the greater the emphasisthat needs to be placed on maintaining equipment effectively through theimplementation of correct procedures, notes Gavin Halse, MD of ApplyIT.

‘Of equal importance is the appropriate automated monitoring and man-agement of the condition of equipment, reducing management’s dependenceon human interaction and ensuring consistent levels of control,’ says Halse.

Once the Aurora system has been rolled out for SALT, the SAAO intends intime to implement the software across all the telescopes stationed on theSutherland site.

EXPLORING NEW AVENUES TO MANY, LAKE MICHELLE is probably one of the most beautiful places in theworld. Set amidst Noordhoek’s tranquil wetlands, this incredible lakefrontdevelopment has inspired numerous investors to create breathtakingly mag-nificent homes. The R200 million residential initiative has been ongoing forthe last eight years, presenting many interesting challenges.

Lake Michelle’s heart is a salt marsh lake with indigenous fauna and flora.The area is home to over 126 species of birds and other fauna like the rareleopard toad and an extensive variety of ducks and fish. ‘Our greatest chal-lenge in this five phased project was to ensure that the venture remain ecofriendly. This required us to engage in many long discussions with environ-mental bodies like The Noordhoek and District Civil Association, The Develop-ers of the Environment for the Western Cape and the Noordhoek Environ-mental Action Group,’ says Peter Wium, senior partner at De Villiers SheardConsulting Engineers.

Although the project started eight years ago, it was suspended temporari-ly until a Cape Town developer bought the ground and resumed the ventureat its full pace. The delay placed tremendous time constraints on the team.They subsequently approached Knowledge Base Software to help with thepreliminary designs, feasibility studies and DTM, extending into the finaldesigns for the roads, services and pond structures. ‘It was comforting toknow that we were receiving help from the Civil Designer software expertsand we acquired a great deal of knowledge during this period. KnowledgeBase provided us with two technicians for a month and we were able to meetour deadline in time,’ notes Peter.

Besides the actual environment, the design itself was equally challenging.‘We were given specific requirements for the design of the sewer systems,being so close to the water body and with a ground surface that was veryflat. In addition, certain zones were restricted and we found ourselves havingto work around these environmentally sensitive areas.’

In order to maintain the quality and aesthetics of the estate, the landscapeguidelines specified that stormwater pass through reeded channels to aid thewater purification process before entering the lake. These reeded links formaccess points via bridges and paths, leading residents onto decks, boardwalks, jetties and bird hides.

InfoYolanda Desai, Knowledge Base

021-701-1850, [email protected].

ROCKFALL PROTECTIONROCKFALL PROTECTION SYSTEMS ARE A KEY ELEMENT in the design andmaintenance of infrastructure networks and have a direct impact on safety.The word ‘system’ correctly embraces the different structural componentsthat should be considered when taking on a problem of this kind.

A key distinction should be made between active and passive protectionsystems. Passive systems do not affect the process of the rock detaching, butfocus, rather, on containing falling debris, thereby averting danger to theinfrastructure and its users. These systems include drapery wire mesh, rockfall


protection barriers, and rockfall protection embankments. Active sys-tems, on the other hand, act on the rock-detachment process. Oneexample is armoured mesh, where different kinds of metal wire andcables form a mesh which is then anchored to the rock slope.

Marco Pauselli, technical manager of Maccaferri / African Gabions,says that Maccaferri’s concept behind a protection system is a combi-nation of good planning and the correct choice of system componentswhich depend primarily on the stresses the system will have to with-stand. The concept is one of ‘minimum energy level’, that is, aresponse proportionate with the problem, thereby avoiding overdesignand unnecessary costs.

Take for example the most basic of passive systems, a drapery ofwire mesh nets. Here the nets are anchored at the top of the cliff andleft unanchored on the rockwall, allowing rocks to fall to the foot of thecliff, in a contained fashion. Until recently, the mesh drapery and thesteel cable used for anchorage were installed in two separate processes,clearly a time-consuming exercise.

Maccaferri has developed a product midway between a cable-rein-forced mesh and a cable panel surface revetment known as ‘Steelgrid’.This system is typically applied to rock masses whose surface can breakdown into fragments not smaller than the apertures in the mesh, andin any case not larger than 0,5 m in diameter.

Steelgrid encompasses the flexibility of the double-twist mesh withthe strength of the steel cable by having the steel cable intrinsicallywoven into the double-twist mesh. However, the great economicbonus of Steelgrid comes from the fact that two different products canbe installed at the same time (mesh and steel cables).

Maccaferri have developed and perfected a host of systems, bothfor the passive and active cases. These innovations extend to the 250kJ to 3 000 kJ rockfall barrier systems capable of covering a wide rangeof energy spectrums, rockfall embankments and steel cable panels.

ALEC HAYIt is with greatpleasure that theSouth African Insti-tution of CivilEngineering con-fers an honoraryfellowship on astalwart of the civilengineering profes-sion and of thisinstitution –Alexander James

Hay, better known to most of us as Alec. As a young man Alec joined the Johan-

nesburg City Engineer’s Department as atrainee civil engineering assistant, but soonattended the University of the Witwater-srand, from where he graduated in 1969. Heremained with the City Engineer’s Depart-ment until 1991, rising from an assistantresident engineer on the South-Eastern Out-fall Sewer to assistant city engineer in 1983at the age of 36 and to deputy city engineerin 1987. As deputy city engineer he headedboth the Design and the Road Planning andTraffic Engineering branches of the Johan-nesburg City Council.

His career highlights while he was withthe Johannesburg City Council includedinvolvement in the design of the Diepslootarch bridges, which were to carry the Diep-sloot Outfall Sewer, the investigation intoaggregate alkali reaction, which had affectedcertain structures on the Johannesburgmotorway and which led to, for example,the reconstruction of a portion of a portalon the double-decker section of the M1 in1991. Alec was involved with the design ofmany reservoirs to meet the requirementslaid down by Rand Water, which at the timedoubled the storage capacity of Johannes-

burg. With the advent of implosions ofbuildings in South Africa, led the team thatformalised this method of demolition with anew chapter in the National Building Regu-lations.

At the end of 1991 the City Engineer’sDepartment ceased to exist, ending the firsthalf of Alec’s professional career. At thetime the industry was in the deepest reces-sion it had ever experienced, so that twodifficult years followed before he wasappointed assistant chief civil engineer atRand Water, where he assumed responsibili-ty for the administrative management ofthe Civil Engineering Design Section ofRand Water.Major projects that were beingundertaken included elements of the ‘1992Scheme’, a project that enhanced supplycapacity to the Gauteng Region in conjunc-tion with the Lesotho Highlands WaterTransfer Scheme.

Alongside his successful professionalcareer, Alec contributed enormously toSAICE from 1978, when he became secre-tary, and later chairman, of the then Munic-ipal Engineering Division. In 1987 he waselected to Council and in 1996 becamepresident of the Institution. In the yearssince his presidency Alec has remained atrusted and valued member of variousSAICE committees. His involvement overthe years with ECSA Council and commit-tees, such as the Central Registration Com-mittee, the Registration Committee for Pro-fessional Engineers, the Professional Adviso-ry Committee for Civil Engineers, and theInternational Committee, in manyinstances as chairman, as well as his contri-bution to the Engineers Mobility Forum andthe establishment of agreements of mutualrecognition with sister engineering bodiesoverseas, has greatly benefited the institu-tion and the profession.

BINGLE KRUGERIt is an honour forthe South AfricanInstitution of CivilEngineering toconfer an honoraryfellowship onPieter Willem Bin-gle Kruger.

Bingle Krugeroriginally intendedto become a sheepfarmer, but in 1959

was one of the first nine graduates from thenewly established engineering faculty at theUniversity of Pretoria. He furthered his edu-cation at the University of California inBerkeley, where he obtained his master’s (in1962) and doctorate (in 1964) in transporta-tion and traffic engineering. The Universityof Pretoria honoured him with the Tuk-sAlumni Laureatus Award in 2000 and aDEng (Honoris Causa) in 2003. He was invit-ed by the engineering institutions to deliverthe 2000 Hendrik van der Bijl Lecture at theUniversity of Pretoria.

In 1965 Dr Bingle co-founded the con-sulting engineering firm Bruinette, Kruger,Stoffberg and Hugo, later known as BKS. Formany years he was responsible for the tech-nical management of the firm’s work in thefield of transportation engineering. With hismanagerial skills and expertise in this field,which includes traffic engineering, road andairport planning and design, public trans-port, and comprehensive transport plan-ning, Dr Bingle was instrumental in hiscompany’s international operations in morethan 20 countries and contributed to pro-jects of national importance, such as theMohale Dam and roads on the LesothoHighlands Water Project, toll road studies

S A I C E A N D P R O F E S S I O N A L N E W S

RECIPIENTS OF HONORARY FELLOWSHIPS

and the planning of several toll roads, indus-trial complexes, large sports stadia, theNational Water Resource Strategy, the SouthAfrican Large Telescope, the Nelson MandelaBridge, and the Sasol gas pipeline fromMozambique to Secunda. Dr Bingle acted asexpert witness for a large number of town-ship board hearings on matters concerningthe traffic implications of proposed largedevelopment schemes such as Menlyn Shop-ping Centre in Pretoria and Sandton City inJohannesburg. He has been a member of thePWV (now Gauteng) Transportation Consor-tium since 1973 and is still the chairman.

Not surprisingly, in 1989 Dr Bingle wasappointed by the Minister of Transport tothe South African Roads Board, the TollRoads Committee and the Urban TransportPlanning Committee. The eight-memberSouth African Roads Board is responsible forthe direction and approval of all nationalroad projects. The Minister also appointedhim to the Civil Engineering Advisory Coun-cil, of which he was acting chairman in1998/99. He served on the steering commit-tee of the former National Institute of Roadand Transportation Research of the CSIR fora time. As a member of the South AfricanAssociation of Consulting Engineers heserved on the National Liaison Committeebetween SAACE and the Department ofTransport for several years as well.

Dr Bingle’s involvement with SAICE isclosely linked to his leadership and manage-ment skills, and his interest in transporta-tion. In 1988 he was the chairman of theorganising committee of the Eighth Quin-quennial Convention for SAICE in conjunc-tion with the Annual Transportation Con-vention, which was held in Pretoria. He wasthe honorary treasurer and chairman of theFinance and Administration Committeefrom 1989 to 1994. In 1995 he served SAICEas its president.

Although Dr Bingle has now retired, heremains active, notably as the president ofthe multi-disciplinary South African Acade-my of Engineering, which has a membershipof around 100 eminent engineers. Theacademy aims to serve the nation at policy

decision-making level through the applica-tion of engineering and technology in itsbroadest sense. It is fitting that a civil engi-neer of the dignified and professional statureof Dr Bingle Kruger is leading the way.

ROSS PARRY-DAVIESIt is with greatpleasure that theSouth African Insti-tution of CivilEngineering con-fers an honoraryfellowship on anindividual who is aunique combina-tion of distin-guished academic,leading contractor

and consultant, having spent 40 years in thecontracting industry and 20 years as a con-sultant – Dr Ross Parry-Davies.

Ross Parry-Davies graduated from UCT in1945, and spent the next nine years con-tracting, mainly on water supply projectsand dams, before he worked for two yearswith F E Kanthack & Partners on the designof the Kafue hydroelectric project, whichincorporated dams, tunnels, penstocks andunderground power stations. In 1956 hejoined the Cementation Company and wasinitially involved in aspects of the Karibascheme where he began developing tech-niques for the stressed strengthening ofdams, which he later applied at 13 dam sitesin southern Africa, using anchors up to 6 000 kN capacity.

He returned to the Cape to build theApostles Tunnel and various harbour works,but at the same time he was working oninnovative techniques, such as vibroflota-tion, dynamic consolidation, specialisedgrouting and ground improvement tech-niques. He was the first person in the worldto use ground anchors to provide lateral sup-port for basement excavations, which wereinitially used on the SA Mutual basement inPort Elizabeth. His subsequent work with

Ruben Stander, in which grout jacking wasused for the first time to provide a lateralsupport system for the Trust Bank basementexcavation in Johannesburg, at the time thedeepest in the world, won wide acclaim. Heused soil nails to reinforce slopes on DeWaal Drive in Cape Town, 20 years beforethe ‘new’ techniques of soil nailing wereclaimed, and built a unique through-flowrockfill dam in Lesotho.

In 1970 he created Ground Engineering,which he sold to LTA in 1974, Here hebecame involved with, among other pro-jects, the Drakensberg Pumped Storagescheme and the Huguenot Tunnel, whereground-freezing techniques smoothed theway for construction.

Since his retirement from LTA in 1987 hehas been involved with consulting on main-stream engineering projects, has appeared asan arbitrator and expert witness, and hasbeen a specialist consultant on the acclaimedrehabilitation of Chapman’s Peak Drive.

In 1991, when he was well into his six-ties, he was awarded a doctorate from theUniversity of Pretoria.

Dr Ross Parry-Davies served on the SAICECouncil for six years. His mission was tounify the profession by incorporating allmembers of the civil engineering industry,including professional technologists andtechnicians, into SAICE. He was chairman ofthe sub-committee that updated the SouthAfrican Code of Practice for Lateral Support,for which he received the Jennings Awardand the Geotechnical Medal for meritoriousservice. In 2002, with Brenda Sudano, heorganised the funding and publication of thebook The Romance of Cape Mountain Passes byGraham Ross, making possible a splendidtribute to South African engineering.

Dr Ross Parry-Davies has brought distinc-tion to the profession of civil engineering.He has been a leading contractor, distin-guished academic and consultant, a loyalservant of the profession, and a definitiveexample of the species ingenior and the inno-vators who makes things happen and solveproblems through bright ideas and lateralthinking.


At the awards ceremony: Mr Bouathong Vong Lorkham (Acting Minis-ter of Communications, Transport, Ports and Construction), Kevin Walland Mr Somphone Dethoudom (Director-General of the Department ofHousing and Planning)

KEVIN WALL FROM CSIR Building and Con-struction Technology won a joint award forthe best paper presented at the Water, Engi-neering and Development Centre (WEDC)

Conference in Vientiane, Laos, South EastAsia. Kevin’s paper is entitled ‘An investiga-tion of the franchising option for water ser-vices in South Africa’.

The WEDC has for the last three decadesbeen organising international conferenceson the provision of infrastructure servicesfor low- and middle-income countries.These have grown in stature, and are nowregarded by developing countries’ waterand sanitation services practitioners andadvisers as ‘the’ conferences to attend. Theconference location alternates each yearbetween Africa and Asia, and is jointlyorganised by staff from WEDC and a localorganising committee.

The 2004 conference took place in Laos(more correctly ‘the Lao People’s DemocraticRepublic’), a country of six million peoplethat is bordered by Vietnam, Cambodia,Thailand, Myanmar (formerly Burma), andChina. The capital, Vientiane, is on theMekong River, which fortunately has verybroad shoulders and can accept the pollu-tion from this city of 800 000 people

The 2005 conference will be held in Kampala, Uganda.


CSIR RESEARCHER WINS BEST PAPERAWARD AT WEDC CONFERENCE

DIARISE THIS!

EventBusiness Finances for Built Environment Professionals

Coastal Engineering and Management Course

Handling Projects in a Consulting Engineer’s Practice

Technical Report Writing

Concrete Technology(C&CI Level 3)

Concrete Practice(C&CI Level 2)

Introduction to Concrete (C&CI Level 1)

South African Society for Intelligent Transportation SystemsSASITS Conference 2005

EcoSan 2005Third International Conference on Ecological Sanitation

Mortars Plaster and Masonry

Young Geotechnical Engineers ConferenceYGE 2005Concrete Repairs

Obtaining Environmental Authorization: A Strategy

Assertiveness and Conflict Resolution for Managers

Date9–10 June

18 & 19 April21 & 22 April

4–5 August 2005

21 & 22 April4–5 July13–14 July11–12 August3–7 October 2005

31 May – 3 June 200515–18 August 2005

6–7 June 20055–6 September 20057–8 November 200510–13 May 2005

23–27 May 2005

24 May 200520 October 2005

13–15 June 2005

14 June 2005

13–14 July 2005

2–3 August 2005

VenueSAICE National OfficeThornhill Office Park MidrandCape TownSaldanha

SAICE National OfficeThornhill Office ParkMidrandSAICE National Office, MidrandCape TownSAICE National OfficeDurbanContest Concrete TechnologyServicesWestmead, Pinetown, DurbanContest Concrete TechnologyServicesWestmead, Pinetown, DurbanContest Concrete TechnologyServicesWestmead, Pinetown, DurbanCape Town International Con-vention Centre, Cape Town

International Convention Centre, Durban

Contest Concrete TechnologyServicesWestmead, Pinetown, DurbanSwadini, Mpumalanga

Contest Concrete TechnologyServicesWestmead, Pinetown, DurbanMidrand

Midrand

ContactLungelwa LamaniTel 011-805-5947, Fax [email protected] LamaniTel 011-805-5947, Fax [email protected] LamaniTel 011-805-5947, Fax 011- [email protected] LamaniTel 011-805-5947, Fax 011- [email protected]

Antoinette MaraisTel [email protected] MaraisTel [email protected] MaraisTel [email protected] de JagerTel 011-805-5947, Fax 011- [email protected] de JagerTel 011-805-5947, Fax 011- [email protected] MaraisTel [email protected]@ebe.wits.ac.za

Antoinette MaraisTel [email protected] LamaniTel 011-805-5947, Fax 011- [email protected] LamaniTel 011-805-5947, Fax 011- [email protected]

civil eng april 2005 web

Documents

geotechnical field

geotechnical aspects

thornhill office park

twintower office

koker secretariat

menlo park

south african piling

innovative solution