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GroundImprovementforRail,PortandRoadInfrastructure--FromTheorytoPractice

CONFERENCEPAPERinGEOTECHNICALSPECIALPUBLICATION·MAY2014

DOI:10.1061/9780784413401.001

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CholachatRujikiatkamjorn

UniversityofWollongong

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SanjayShrawanNimbalkar

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Ground Improvement for Rail, Port and Road, Infrastructure - From Theory to Practice

Buddhima Indraratna1 FASCE, Cholachat Rujikiatkamjorn2 and Sanjay Nimbalkar3

1Professor of Civil Engineering, Director, Centre for Geomechanics and Railway Engineering, Faculty

of Engineering and Information Sciences, University of Wollongong, Wollongong City, NSW 2522,

Australia, email: indra@uow.edu.au 2Associate Professor, Centre for Geomechanics and Railway Engineering, Faculty of Engineering and

Information Sciences, University of Wollongong, Wollongong City, NSW 2522, Australia 3Research Fellow, Centre for Geomechanics and Railway Engineering, Faculty of Engineering and

Information Sciences, University of Wollongong, Wollongong City, NSW 2522, Australia ABSTRACT: The transportation infrastructure in coastal regions of Australia has been expanded in recent years due to high population density and increased traffic volumes. Such expansions require the application of ground improvement techniques to improve performance and sustainability of the infrastructure. In this paper, innovative ground improvement techniques applicable to railway embankments, port reclamation and embankment fills are discussed. For ballasted rail tracks, the performance of different types of geosynthetics for improving the stability and drainage of railway tracks under high cyclic loading is investigated. Instrumented tracks were conducted to measure the in-situ stresses and deformations of ballast at Bulli, New South Wales (NSW), Australia. Furthermore, stabilization of soft formation soils underneath rail tracks using prefabricated vertical drains (PVDs) is also studied through finite element analyses and field measurements at Sandgate. The innovative use of the mixtures of coal wash (CW) and steel furnace slag (SFS) as the reclamation fill is demonstrated through laboratory and field investigations at the Outer Harbor extension of Port Kembla in Wollongong, NSW. The optimum CW-SFS mixtures that may meet most of the geotechnical specifications are proposed to be used as an effective structural fill. Finally, the design of the combined vacuum and surcharge fill system and the construction of the road embankment are described using a case study from the Pacific Highway upgrade project. Field data are presented and interpreted to demonstrate how the embankments performed during construction in both vacuum and non-vacuum areas.

1Ground Improvement and Geosynthetics GSP 238 © ASCE 2014

INTRODUCTION

Ground improvement techniques have been employed to improve road and railway embankment conditions and reclaimed lands in Australia. Ballasted rail tracks are the largest transportation infrastructure catering for public and freight transport in Australia. Railway industries are continuing to improve their efficiency and to decrease costs related to construction and maintenance. Rail embankments are usually subjected to large cyclic stresses due to heavier and faster trains inducing large deformations and degradation of the ballast layer. Several studies in the past have highlighted ballast breakage and confining pressure are key parameters controlling the behavior of ballasted rail tracks (Marsal 1973, Indraratna et al. 2005a, Lackenby et al. 2007). The potential use of geosynthetics to enhance track stability is demonstrated in several laboratory studies (Selig and Waters 1994, Raymond 2002, Indraratna and Salim 2003, Indraratna et al. 2010a, Indraratna and Nimbalkar 2013). Nevertheless, limited studies have quantified the relative performances of geosynthetics and shock mats under in situ track conditions. The details of field instrumentation and monitoring processes along with the preliminary findings of these unique studies are discussed.

Soft clays (estuarine or marine) along coastal regions in Australia have undesirable geotechnical properties such as low bearing capacity and high compressibility. In the absence of appropriate ground improvement (Indraratna and Redana 1998; Bergado et al. 2002; Indraratna et al. 2009; Indraratna et al. 2010b), excessive settlement and lateral movement adversely affect the stability of buildings and port and transport infrastructure including highway and rail embankments built on such soft ground (Indraratna and Redana 2000; Indraratna et al. 2011b). In this paper, finite element analysis of a rail track stabilized with relatively short prefabricated vertical drains (PVDs) is presented and discussed to show performance of short PVDs to dissipate cyclic load induced pore pressures, limit horizontal movements and increase the bearing capacity of the soft subgrade.

Attributed to our environmentally conscious society, waste minimisation and waste recycling are given a high priority in Australian industry today. Byproducts of the coal mining and steel industry including coal wash (CW) and steel furnace slag (SFS) are typically treated as wastes and disposed of in stockpiles occupying usable land. Innovative use of these granular wastes through civil engineering applications such as reclamation is vital for the local environment and economy. However, given the variability of these materials and the complex behavior especially under saturated conditions, the understanding and quantification of their load bearing capacities, stability and settlement characteristics are vital when used as harbor reclamation fill.

To enable the construction of road embankment in soft clay areas, adequate ground improvement techniques are required to eliminate excessive settlement and lateral movement which may affect the stability of infrastructure built on such soft ground (Indraratna et al. 2008; Indraratna et al. 2010; Indraratna et al. 2012). To reduce the embankment height and accelerate consolidation, a vacuum pressure can be applied and sustained via PVDs system (Rujikiatkamjorn and Indraratna 2009). Sathananthan et al. (2008), Ghandeharioon et al. (2010) and Ghandeharioon et al. (2012) showed that installing drains creates a disturbed region known as a smear zone where the structure of the clay layer is changed such that the horizontal permeability is reduced and the

2Ground Improvement and Geosynthetics GSP 238 © ASCE 2014

compressibility is increased. Once the soil shear strength has mobilized, the long term settlement will be significantly less, thereby eliminating any risk of instability of the overlying infrastructure (Shang et al. 1998). The ground improvement provided by prefabricated vertical drains combined with vacuum pressure is now proven to be an economically attractive alternative in the stabilization of deep soft clay sites (Gao, 2004).

USE OF GEOSYNTHETICS AND MATS FOR RAIL INFRASTRUCTURE

Application of Geosynthetics at Bulli Track

In order to investigate track performance including train-induced stresses, ballast

deformations and the effects of geosynthetics, an experimental track section was built in Bulli along RailCorp’s South Coast Track, NSW. The instrumented track section was subdivided into four sections, @ 15 m long. Sections 1 and 4 were constructed using fresh and recycled ballast without geosynthetic reinforcement. A geocomposite was placed at the ballast-sub-ballast interface in Sections 3 and 4. The thicknesses of the ballast and sub-ballast layer were 0.3 and 0.15 m, respectively. Track Instrumentation

The performance of the experimental section was monitored using a series of sophisticated instruments. The vertical and horizontal stresses developed in the ballast were measured by rapid response hydraulic earth pressure cells with thick, grooved active faces based on semi-conductor type transducers. Vertical and lateral deformations were measured by settlement pegs and electronic displacement transducers, respectively. These transducers were placed inside two, 2.5 m long stainless steel tubes that can slide over each other, with 100 mm × 100 mm end caps as anchors. The settlement pegs consisted of 100 mm × 100 mm × 6 mm stainless steel base plates attached to 10 mm diameter steel rods. The settlement pegs and displacement transducers were installed at sleeper-ballast, and ballast-subballast interfaces, respectively, as shown in Figure 1.

Figure 1. Installation of settlement pegs and displacement transducers at Bulli (after Indraratna et al. 2010)

3Ground Improvement and Geosynthetics GSP 238 © ASCE 2014

Particle size distribution of fresh ballast follows Technical Specification TS 3402 (RailCorp, Sydney). Recycled ballast was collected from spoil tips of a recycled plant in Chullora yard, Sydney. The sub-ballast material was categorized as a sand-gravel mixture. The geocomposite layers were formed by placing biaxial geogrids above the nonwoven geotextile layers. Technical specifications of various materials used during construction are reported in Indraratna et al. (2011a). The performance of the experimental sections was monitored using various instruments. Vertical and horizontal deformations were obtained by settlement plates and digital displacement transducers, respectively. They were installed at the sleeper-ballast and ballast-subballast interfaces, respectively.

Traffic induced stresses in ballast

Figure 2(a) shows the maximum cyclic vertical (v) and lateral (h) stresses measured at Section 1 during the passage of from a passenger train (20.5 ton axle load) travelling at 60 km/h. It is evident that vertical stress decreases considerably with depth, while lateral stress decreases only slightly with depth. The maximum vertical stress under the rail reduced by 73% and 20% at the base of the ballast layer and capping layer, respectively. Whereas the maximum vertical stress at end of sleepers showed a reduction of 64% and 45% at the base of ballast layer and capping layer, respectively. Figure 2(b) shows the maximum stress recorded in the ballast for a coal train (25 ton axle load). As expected, cyclic stresses (v, h) measured in the layer of ballast and subballast were higher for a coal freight train than a passenger train. It was evident that higher v and h exerted by coal train resulted in a greater deformation and degradation of the ballast, implying the need for earlier track maintenance.

(a) (b)

Figure 2. Cyclic stresses induced by (a) passenger train (82 tons), (b) a coal train (100 tons) (Indraratna et al. 2010a).

Ballast deformations

Vertical and horizontal deformations were measured in the field, against time. A relationship between the annual rail traffic in million gross tons (MGT) and axle load was used to determine the number of load cycles (Selig and Waters, 1994). Vertical

450

300

150

00 25 50 75 100 125 150 175 200 225 250

Maximum cyclic stresses under rail, v ,

h (kPa)

BA

LL

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elow

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eper

, z (

mm

)

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N = 9.1 X 105

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Maximum cyclic stresses under rail, v ,

h (kPa)

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eper

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)

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h

N = 9.1 X 105

SU

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AL

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ST

BA

LL

AS

T

4Ground Improvement and Geosynthetics GSP 238 © ASCE 2014

deformations of ballast against the number of load cycles (N) are shown in Figure 3(a). The recycled ballast section showed less deformations compared fresh ballast section because the former has moderately graded particle size distribution (Cu = 1.8) compared to the very uniform fresh ballast (Cu = 1.5). Recycled ballast often has a lesser amount of breakage because the individual particles are more rounded. This can lead to the prevention of corner breakage at high contact stress locations.

(a) (b)

Figure 3. Deformations of the ballast layer: (a) vertical; (b) lateral (Indraratna et al. 2010a).

Figure 3(b) indicates that geocomposite reduced lateral deformation of fresh ballast

by half and that of recycled ballast by approximately 10%. This is because the apertures of the geogrid enhance mechanical interlocking with the ballast. This leads to an increase in the capacity of the ballast layer to distribute a load which substantially reduced settlement under high repeated loading. The ability of geosynthetics to reduce the rate of track deterioration is appealing to the railway industry because the cost of installation is low, and more resilient behaviour by the ballast.

Design Process for Short PVDs under Railway Track

The Sandgate Rail Grade Separation Project is situated at Sandgate in the Lower Hunter Valley, NSW (Figure 4). Field and laboratory testing was conducted to obtain relevant soil parameters. Site investigation was comprised of 6 boreholes, 14 piezocone tests, 2 in-situ vane shear tests and 2 test pits. Laboratory testing included soil index property, standard oedometer and vane shear were also performed.

A soil profile presents that soft compressible formation varies from 4 m to 30 m thick. The lightly overconsolidated soft residual clay is underneath the soft soil layer and followed by shale stratum. The soil properties are shown in Figure 5. The groundwater is located at the ground level. The moisture contents are similar to their liquid limits. The average soil unit weight was approximately 15 kN/m3. The undrained shear strength varied between 10 and 40 kPa. The coefficient of

103 104 105 106

18

15

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0

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tica

l def

orm

atio

n of

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last

, Sv

Fresh Ballast Recycled Ballast Fresh Ballast with Geocomposite Recycled Ballast with Geocomposite

Number of load cycles, N

103 104 105 106

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Number of load cycles, N

5Ground Improvement and Geosynthetics GSP 238 © ASCE 2014

consolidation in horizontal direction (ch) is 2-10 times that in the vertical direction (cv). Based on preliminary numerical analysis conducted by Indraratna et al. (2010b) and Ni et al. (2013), short PVDs were suggested and installed at 2 m spacing in a triangular pattern up to 8m in depth. The objectives of the field instrumentations were to: (a) monitor the track stability; (b) assess the performance of the new railway stabilized by PVDs; and (c) investigate the accuracy of the numerical analysis through Class A predictions, where the field monitoring data were unavailable at the time of finite element modeling.

Figure 4. Map showing site location (adopted from Hicks, 2005).

0 20 40 60 80

Atterberg Limit (%)

30

20

10

0

Dep

th (

m)

12 14 16 18

Unit weight (kN/m3)

10 20 30 40

Undrained shear strengthobtained from

in-situ Vane test (kPa)

2 3 4

OCR

Plastic limit

Liquid limit

Water content

Figure 5. Soil properties at Sandgate Project (Indraratna et al. 2010b).

6Ground Improvement and Geosynthetics GSP 238 © ASCE 2014

Preliminary Design

Due to time limitation, rail tracks were constructed right after the PVDs installation. The train traveling at very low speed was employed as the only external surcharge. The equivalent dynamic loading considering an impact load factor was adopted for the numerical analysis. A static pressure of 104 kPa with an impact factor of 1.3 was applied according to the low train speed for 25-tonne axle load, based on the Australian Standards AS 1085.14-1997. The Mohr-Coulomb model was employed to represent the overconsolidated fill layer, whereas the soft formations were modeled using the Soft Soil model with the finite element code, PLAXIS (Brinkgreve 2002). The soil parameters are given in Table 1.

Table 1. Selected parameters for soft soil layer used in the FEM (Indraratna et

al. 2010b)

Soil layer

Depth (m) c (kPa)

e e

e kv (×10-4 m/day)

kh (×10-4 m/day)

1 1.0-10.0 10 25 2.26 0.131 0.020 0.70 1.4 2 10.0-20.0 15 20 2.04 0.141 0.017 0.75 1.5

Note: Back-calculated from Cam-clay M value. A mesh discritisation of the formation beneath the rail track is shown in Figure 6. A

plane strain finite element analysis employed triangular elements with six displacement nodes and three pore pressure nodes. Four rows of PVDs were used in the analysis. An equivalent plane strain analysis with appropriate conversion from axisymmetric to 2-D was adopted to analyze the multi-drain analysis (Indraratna et al. 2005b). In this method, the corresponding ratio of the equivalent smear zone permeability to the undisturbed zone permeability for plane strain analysis is:

75.0ln/ln ,,,,,

,

skksnkkk

k

axsaxhaxhpshpsh

pss (1)

1/67.0 23 nnsn (1a)

1/133.0112 22 nnsssnns (1b)

we ddn (1c)

ws dds (1d)

where, dε = the diameter of the unit cell soil cylinder, ds = the diameter of the smear zone, dw= the equivalent diameter of the drain, ks = horizontal soil permeability in the smear zone, kh = horizontal soil permeability in the undisturbed zone and the top of the

7Ground Improvement and Geosynthetics GSP 238 © ASCE 2014

drain and subscripts ‘ax’ and ‘ps’ denote the axisymmetric and plane strain condition, respectively. The ratio of equivalent plane strain to axisymmetric permeability in the undisturbed zone is given by:

75.0ln/167.0 22,, nnnkk axhpsh (2)

Figure 6. Vertical cross section of rail track and foundation (Indraratna et al. 2010b).

Comparison of Field Results with Class A FEM Predictions The field monitoring data were given to the Auhtors by the track owner (Australian

Rail Track Corporation) a year after the analysis. Therefore, all predictions can be classified as Class A (Lambe 1973). The calculated and measured vertical settlements at the centre line are shown in Figure 7. The predicted settlement is in agreement with the field data. The in situ horizontal displacement at 6 months at the rail embankment toe is presented in Figure 8. As expected, maximum lateral displacements are measured within the upper clay layer i.e. the softest formation below the 1 m crust and are is restricted to the topmost compacted fill (depth 0-1 m). The Class A predictions of lateral displacements also agree well with the field observation. The effectiveness of PVDs track stability through the reduction in lateral movement is demonstrated here.

0 50 100 150 200 250 300Time (days)

0.25

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Figure 7. Predicted and measured settlements at the centre line of rail tracks (after Indraratna et al. 2010b)

 104 kPa @ 2.5m width (including impact factor of 1.3)

20m

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Crust

Soft Soil 1

Soft Soil 2

8Ground Improvement and Geosynthetics GSP 238 © ASCE 2014

0 10 20 30 40Lateral movement (mm)

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th (m

)

Field Data

Prediction-Class A(PVD Spacing @2m)

Crust

Soft Soil 1

Soft Soil 2

Figure 8. Measured and predicted lateral displacement at the embankment toe at 180 days (after Indraratna et al. 2010b)

USE OF BLENDED MIXTURES OF COAL WASH AND STEEL FURNACE SLAG FOR PORT INFRASTRUCTURE AS A STRUCTURAL FIELD

As an option to the conventional freshly quarried or dredged sand fills, the potential use of CW and SFS as the predominant reclamation fill was examined at the reclamation project for the Outer Harbor extension of Port Kembla, Wollongong. Detailed laboratory investigations shown that there are optimum CW-SFS mixtures that may meet most of the geotechnical requirements to be adopted as an alternative structural fill above the high tide level. Geotechnical characterization of blended waste materials

The determination of geotechnical properties of blended wastes is fundamental for assessing their potential use as construction fills (Indraratna et al. 1991, Indraratna et al. 1994, Kamon 1997, Lim and Chu 2006). According to the Unified Soil Classification System, CW and SFS samples can be classified as well-graded gravel (GW) and sand (SW), respectively. To avoid the boundary effect, the reduced parallel gradations predominantly sand fractions were used in laboratory tests (Figure 9). The average specific gravity (Gs) of CW and SFS samples is 2.1 and 3.5, respectively. The Gs value of CW is lower due to the presence of coal and the higher Gs value of SFS is due to the presence of iron.

Compaction, permeability and shear strength

Standard Proctor compaction tests shows that as the SFS portion increases from 0% to 100%, the maximum dry density (MDD) increases from 15 kN/m3 to 22 kN/m3. The

9Ground Improvement and Geosynthetics GSP 238 © ASCE 2014

optimum moiture content somewhat decreases from 10.8% to 9.5% (Figure 10). The variation in MDD is essentially controlled by the significant increase in Gs when SFS content increses. MDD of mixtures containing 40-60% SFS are equivalent to the MDD of typical compacted sandy fills (18 kN/m3).

Figure 9. Particle size distributions of CW and SFS for field and laboratory conditions (Rujikiatkamjorn et al. 2013).

Figure 10. Compaction curves of blended mixtures (Rujikiatkamjorn et al. 2013).

Constant head permeability tests were carried out on different mixtures compacted at their optimum moisture content (OMC) using standard compaction energy. From Figure 11, when the percentage of CW increases from 0% to 100%, the permeability decreases considerably from 3 × 10-5 m/s (similar to gravel fills) to 2 × 10-9 m/s (similar to clayey fills). The permeability coefficients of blended specimens with 40-60% CW are comparable to those of typical compacted sandy fills (1 × 10-7 m/s).

0.01 0.1 1 10 1000

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/m3 )

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10Ground Improvement and Geosynthetics GSP 238 © ASCE 2014

The shear strength of blended mixture was assessed by conducting (consolidated) drained compression triaxial tests. The specimens with a density exceeding 95% of MDD were sheared at 0.003 mm/s strain rate. The friction angles () for CW and SFS were found to vary between 39° and 44°, which are relatively greater than those of conventional fills (> 30°).

Figure 11. Variation of permeability with coal wash percentage and friction angle (Rujikiatkamjorn et al. 2013).

Waste fill design and Field trial tests

To optimize the use of waste materials as effective reclamation fill, the following permeability and strength specification generally adopted for conventional fills may be considered: (i) Placed fill material to have a friction angle more than 30°; (ii) Placed fill material to possess a permeability coefficient between 1 × 10-7 m/s and 1 × 10-5 m/s to guarantee fast dissipation of excess PWP, as well as to minimize internal erosion (Chiaro et al. 2014). To satisfy the above stated design criteria, the blended waste mixtures should have a content of CW > 50%. The actual performance of a compacted fill in the field can be quite different from that observed in the laboratory for much smaller specimens with reduced gradations enclosed within a rigid boundary of the compaction chambers. As a result, it is important to validate the laboratory findings with the actual field behavior of CW-SFS mixtures and establish the most appropriate compaction method and associated machinery. For this purpose, field trial tests were carried out.

In September 2012, a field trial was conducted at Port Kembla reclamation site to evaluate the performance of two selected CW-SFS mixtures and to establish an appropriate compaction method for CW-SFS fills. Nevertheless, the field trial was an essential part of this investigation to properly assess in-situ swelling and to recognize the advantages and limitations of blended mixtures as compacted fill material. A pit with dimensions of 55 m long, 14 m wide and 1.4 m deep was provided for the field trial. The area was divided in two equal subsections having a volume of 540 m3 and

0 20 40 60 80 10010-7

10-6

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10-1 Experimental data Fitting curve

(' =43°)

Acceptable range of permeability for

fill materials

Typical permeability for sands

Per

mea

bilit

y (c

m/s

)

Percentage of CW (%)

Typical permeability for gravels

Mixturesfor field trial

(' =39°)

11Ground Improvement and Geosynthetics GSP 238 © ASCE 2014

filled by CW-SFS 50/50 by volume and CW-SFS 33/67 by volume. Approximately 1200 tonnes of CW and 1600 tonnes of SFS were used. Compaction of 300-mm thick layers was achieved by means of 13-tonnes smooth steel drum rollers (Figure 12). Based on a number of field density tests, including sand cone replacement and nuclear density techniques, it was concluded that 4 passes were adequate for attaining a fill density > 90% standard Proctor compaction. Dynamic cone penetration tests CPTs confirmed that compacted CW-BOS fills have greater strength compared to compacted sandy fill.

Volumetric expansion was also measured for a period of about 180 days. Swelling was found to be substantial for both the blends. According to field trial and laboratory investigations, although the strength of CW-BOS blend with SFS content > 50% may be better compared to most conventional fills, such considerable level of swelling (i.e. > 3%) should be employed with caution for CW-SFS mixture when used as structural fill, unless the live load exceeds the swell pressure (about 100 kPa for BOS).

Figure 12. Port Kembla construction site: (a) prior fill placement; and (b) during compaction (Chiaro et al. 2014)

(a)

(b)

12Ground Improvement and Geosynthetics GSP 238 © ASCE 2014

SOFT SOIL FOUNDATION IMPROVED BY VACUUM AND SURCHARGE LOADING

The Pacific Highway was built to support the transportation demand in the eastern coastal belt of Australia. The route has to cross a floodplain comprising of highly compressible and saturated estuarine and alluvial soft formation up to 30m in. Vacuum assisted surcharge loading together with prefabricated vertical drains was employed to stabilize ground before the road embankment can be built. At the site in Ballina, the installation of 34 mm diameter circular drains at a spacing of 1.0m in a square pattern over an area of approximately 9.5ha was carried out. Figure 13 presents the locations of field instrumentation, which included surface settlement plates, inclinometers and piezometers. The embankment was separated into 2 sections, i.e. Section A: conventional surcharge and Section B with vacuum pressure. The design embankment height was varied from 4.3m to 14.0m to limit the long term settlement. A vacuum pressure of 70 kPa (suction) was applied and removed after 400 days. Geotechnical parameters of the three subsoil layers obtained from standard oedometer tests are listed in Table 2.

Figure 13. Instrumentation layout for the test embankments at Ballina Bypass (Indraratna et al. 2010)

Table 2. Soil parameters at SP12 (Indraratna et al. 2010)

Depth (m)

Soil Type kN/m3 0e axhk ,

10-10 m/s OCR

0.0-0.5 Clayey silt 0.57 0.06 14.5 2.9 10 2 0.5-15 Silty Clay 0.57 0.06 14.5 2.9 10 1.7 15.0-24 Stiffer Silty Clay 0.48 0.048 15.0 2.6 3.3 1.1

Recorded settlements and associated pore pressure are shown in Fig. 4 with an

embankment construction schedule. Initially the embankments were built to a height of 4-8m in 3 months. Afterwards, the vacuum was applied and varied from -70 kPa to -80

13Ground Improvement and Geosynthetics GSP 238 © ASCE 2014

kPa for 200 days. No air leaks were detected during vacuum application. After 660 days, the second stage of embankment construction was commenced. The surcharge preloading was ceased after 3 years.

Only selected surface settlements are plotted (i.e., SP1 SP3, SP5, SP7, SP9 and SP11). SP1 is located in a non-vacuum area, whereas the others were installed in the vacuum applied area. The variations of time-settlement curves are significantly different because of the variation of clay depth and the fill thickness. The maximum vertical strain was about 24%, implying that the calculation of the settlement would need to capture large strain considerations. The dissipation rate of the excess pore pressure in non-vacuum areas was lower than that of the vacuum areas. The peak excess pore pressure in vacuum area (120 kPa) was less than the applied surcharge load (160 kPa). This could be attributed to the effect of applied vacuum pressure which increased the effective stress without developing excess pore pressure in the soft soil layers.

14Ground Improvement and Geosynthetics GSP 238 © ASCE 2014

0 400 800 1200 16008

6

4

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SP3

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0 400 800 1200 1600Time (days)

-100

0

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Exc

ess

pore

pre

ssu

re(k

Pa)

P1 (-1.3m)

P2 (-8.3m)

P3 (-4.8m)

Vacuum guageVacuum applicationperiod

Figure 14. Embankment stage construction with associated surface settlements and excess pore pressures (Indraratna et al. 2010).

Figure 15 presents the measured lateral displacement plots at 2 years. Inclinometer I1 was located at the border of the conventional area, whereas the inclinometers I2-I4 were installed at the boundary of the vacuum area. The lateral displacement normalized to the embankment height is shown in Fig. 15b. It clearly shows that the application of vacuum pressure reduces the lateral displacement. The embankment in non-vacuum area (SP1) experienced a higher change in lateral displacement in comparison with that in the vacuum areas, suggesting that the application of vacuum offers increased stability when constructing high embankments.

15Ground Improvement and Geosynthetics GSP 238 © ASCE 2014

0 200 400Lateral displacement (mm)

-20

-10

0

Dept

h (

m)

I1

I2

I3

I4

0 0.04 0.08 0.12

Lateral displacementnormalised by

embankment Height

I1

I2

I3

I4

(a) (b)

Figure 15. Measured lateral displacement and lateral displacement normalised with embankment height after 750 days (Indraratna et al. 2010).

CONCLUSIONS The performance of instrumented ballasted tracks at Bulli was assessed where

different ballast types and geosynthetics were used and installed. The results of the Bulli study showed that the use of geocomposite at the ballast and sub-ballast interface was proved to be a feasible and effective option for recycled ballasted tracks. A Class A prediction of the track behavior using finite element analysis confirmed with field data validation showed that short PVDs can increase track stability by significantly decreasing the buildup of excess PWP during train passages and facilitate the dissipation of excess PWP during the rest period. The dissipation of PWP increases the track stability for the next loading stage. Both the predictions and field data showed that the lateral displacement can be curtailed.

The potential use of the optimum blended CW and SFS was demonstrated as an alternative reclamation fill to the conventional fills at the Outer Harbor extension of Port Kembla in Wollongong via detailed laboratory and field investigations. While CW-SFS fills possess shear resistance, and permeability properties similar or superior to conventional sandy fills, their use may still be controlled by excessive swelling. For the case study presented here, only CW-SFS blends with CW content between 70 and 55% are able to meet the stringent port reclamation requirements, in terms of swelling

16Ground Improvement and Geosynthetics GSP 238 © ASCE 2014

(< 3%). It is important to note that, the results presented in this paper are only indicative and not necessarily valid for other types of CW-SFS mixtures owing its significant variation in properties of both materials.

The performance of the combined vacuum and surcharge fill system and construction of the embankment at Ballina Bypass, Australia was presented in this paper. The embankment heights together with vacuum application were designed to vary in each section depending on the clay thickness. The settlement magnitudes in all sections become more as a result of the increase in soft clay thickness, embankment height and the vacuum application. The measured excess pore pressure showed that the vacuum pressure can minimize the generation of excess pore pressure during embankment construction. The normalized lateral displacement in the vacuum areas was found to be less than that in non-vacuum areas. This clearly suggested the greater stability achieved in vacuum areas in view of lateral displacement control.

ACKNOWLEDGEMENTS

The Author wishes to thank the Australia Research Council, CRC for Rail

Innovation, RailCorp, ARTC, ARUP, John Holland, Penrith Lake Development Corporation, Coffey Geotechnics, Queensland Rail National, Douglas Partners, Port Kembla Port Corporation, Road and Maritime Services (NSW), Queensland Transport & Main Roads, Menard Bachy and BHP Billiton for their continuous support. The assistance of David Christie (formerly Senior Geotechnical Consultant, Rail Infrastructure Corporation (NSW)), Tim Neville (ARTC), Michael Martin (QR National), Dr Richard Kelly (Coffey) and Geoff McIntosh (Douglas Partners) is gratefully acknowledged. The advice and help over a long period of time by Professor A Balasubramaniam, Griffith University (Qld) is appreciated. A number of current and past doctoral students, including Dr Joanne Lackenby, Dr Wadud Salim, Dr Iyathurai Sathananthan, Miss Ana Heitor, Mr Ali Tasalloti and University of Wollongong colleagues, Dr Xueyu Geng, Dr Pongpipat Anantanasakul and Dr Gabriele Chiaro have all contributed to the contents of this paper. A significant portion of the contents have been reproduced with kind permission from the Journal of Geotechnical and Geoenvironmental Engineering ASCE, An International Journal of Geomechanics and Geoengineering and Canadian Geotechnical Journal.

REFERENCES Brinkgreve, R.B.J. (2002). PLAXIS (Version 8) User’s Manual. Delft University of

Technology and PLAXIS B.V., Netherlands. Bergado, D.T., Asakami, H., Alfaro, M.C. and Balasubramaniam, A.S. (1991). “Smear

effects of vertical drains on soft Bangkok clay”. J. Geotech. Eng. ASCE, 117(10): 1509–1530.

Chiaro, G., Indraratna, B., Tasalloti, S.M.A. and Rujikiatkamjorn, C. (2014). “Optimisation of coal wash – slag blend as structural fill”, Ground Improvement Journal, ICE (Accepted August 2013).

Gao, C. (2004). “Vacuum preloading method for improving soft soils of higher permeability”, Ground Improvement, 8(3):101-107.

17Ground Improvement and Geosynthetics GSP 238 © ASCE 2014

Ghandeharioon, A., Indraratna, B., and Rujikiatkamjorn, C. (2010). Analysis of soil disturbance associated with mandrel-driven prefabricated vertical drains using an elliptical cavity expansion theory”. International Journal of Geomechanics, ASCE. 10(2), 53-64.

Ghandeharioon, A., Indraratna, B., and Rujikiatkamjorn, C. (2012). Laboratory and Finite-Element Investigation of Soil Disturbance Associated with the Installation of Mandrel-Driven Prefabricated Vertical Drains”. J. of Geotechnical & Geoenvironmental Engineering, ASCE. 138(3), 295-308.

Hicks, M. (2005). Environmental impact statement for the Sandgate Rail Grade Separation, Hunter Valley Region, Australia.

Indraratna, B. and Redana, I. W. (1998). “Laboratory determination of smear zone due to vertical drain installation”, J. Geotech. Geoenviron. Eng.., 125(1): 96-99.

Indraratna B. and Redana I.W. (2000). “Numerical modeling of vertical drains with smear and well resistance installed in soft clay”. Can. Geotech. J. 37(1): 133-145.

Indraratna B. and Salim W. (2003). “Deformation and degradation mechanics of recycled ballast- stabilised with geosynthetics”. Soils and Foundations 43(4): 35-46

Indraratna, B., Aljorany, A., and Rujikiatkamjorn C., (2008). “Analytical and Numerical Modelling of Consolidation by Sand Drains beneath a Circular Embankment.” International Journal of Geomechanics, ASCE. 8(3), 199-206.

Indraratna, B., Attya, A., and Rujikiatkamjorn, C. (2009). “Experimental investigation on effectiveness of a vertical drain under cyclic loads”. Journal of Geotechnical and Geoenvironmental Engineering, ASCE, 135(6), 835-839.

Indraratna, B., Gasson, I. and Chowdhury, R.N. (1994). “Utilisation of compacted coal tailings as structural fill”, Can. Geotech. J. 31(5): 614-623.

Indraratna, B., Lackenby, J. and Christie, D. (2005a). “Effect of confining pressure on the degradation of ballast under cyclic loading”. Géotechnique, 55(4): 325-328.

Indraratna, B., Nutalaya, P., Koo, K.S. and Kuganenthira, N. (1991). “Engineering behavior of low carbon, pozzolanic fly ash and its potential as a construction fill”, Can. Geotech. J. 28(4): 542-555.

Indraratna, B., Rujikiatkamjorn C. and Sathananthan, I. (2005b). “Analytical and numerical solutions for a single vertical drain including the effects of vacuum preloading”. Can. Geotech. J., 42(4): 994-1014.

Indraratna B., Salim W. and Rujikiatkamjorn, C. (2011a). Advanced Rail Geotechnology – Ballasted Track, CRC Press/Balkema.

Indraratna B., Nimbalkar S., Christie D., Rujikiatkamjorn C. and Vinod J. S. (2010a). “Field Assessment of the Performance of a Ballasted Rail Track with and without Geosynthetics”, J. Geotech. Geoenviron. Eng. 136(7): 907-917.

Indraratna, B. and Nimbalkar, S. (2013). “Stress-Strain Degradation Response of Railway Ballast Stabilized with Geosynthetics”, J. Geotech. Geoenviron. Eng. 139(5): 684-700.

Indraratna, B., Rujikiatkamjorn, C., Balasubramaniam, A. S. and McIntosh, G. (2012). “Soft ground improvement via vertical drains and vacuum assisted preloading”. Geotextiles and Geomembranes, 30(1), 16-23.

Indraratna, B., Rujikiatkamjorn, C., Ewers, B. and Adams, M. (2010b). “Class A prediction of the behaviour of soft estuarine soil foundation stabilised by short vertical drains beneath a rail track”. J. Geotech. Geoenviron. Eng. 136 (5): 686-696.

Indraratna, B., Rujikiatkamjorn, C., Kelly, R. and Buys, H. (2010) “Environmentally Sustainable Soft Soil Improvement via Vacuum and Surcharge Preloading”. Ground Improvement 163 (1), 31-42.

18Ground Improvement and Geosynthetics GSP 238 © ASCE 2014

Indraratna, B., Rujikiatkamjorn, C., Ameratunga, J. and Boyle, P. (2011b). “Performance and prediction of Vacuum Combined Surcharge Consolidation at Port of Brisbane”. J. Geotech. Geoenviron. Eng, ASCE,137(11): 1009-1018.

Kamon, M. (1997). Geotechnical utilisation of industrial wastes. Proc. 2nd International Congress on Environmental Geotechnics, Osaka, Japan, 1293-1309.

Lackenby, J., Indraratna, B. and McDowel, G. (2007). “The Role of Confining Pressure on Cyclic Triaxial Behaviour of Ballast”. Geotechnique, 57(6): 527-536.

Lambe, T.W. (1973). Predictions in soil engineering. Geotechnique, 23: 149-202. Lim, T. and Chu, J. (2006). “Assessment of use of spent copper slag for land reclamation”,

Waste Manage, 24(1): 67-73. Marsal, R.J. (1973). Embankment dam engineering - mechanical properties of rockfill,

Wiley Publication, New York, 109-200. Ni, J., Indraratna, B., Geng, X. Y. Carter, J. P. and Rujikiatkamjorn C. (2013). “Radial

consolidation of soft soil under cyclic loads”, Computers and Geotechnics, 50 (1), 1–5.

Raymond, G.P. (2002). “Reinforced ballast behaviour subjected to repeated load”. Geotext. Geomembr. 20(1):39-61.

Rujikiatkamjorn C. and Indraratna, B. (2009). Analytical solutions and design curves for vacuum-assisted consolidation with both vertical and horizontal drainage”. Canadian Geotechnical Journal 46(3), 270-280.

Rujikiatkamjorn C, Indraratna B and Chiaro G (2013). “Compaction of coal wash to optimize its utilization as water-front reclamation fill”. Geomechanics Geoengineering: an International Journal 8(1): 36-45.

Sathananthan, I., Indraratna, B., and Rujikiatkamjorn C., (2008). “The evaluation of smear zone extent surrounding mandrel driven vertical drains using the cavity expansion theory”. International Journal of Geomechanics, ASCE. 8(6), 355-365.

Selig, E.T. and Waters, J.M. (1994). Track Geotechnology and Substructure Management, Thomas Telford, London. Reprint 2007.

Shang, J. Q., Tang, M. and Miao, Z. (1998). “Vacuum preloading consolidation of reclaimed land: a case study”. Canadian Geotechnical Journal, 35: 740-749.

T. S. (3402). “Specification for Supply of Aggregates for Ballast”. Rail Infrastructure Corporation of NSW, Sydney, Australia, 2001.

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