bored pile/drilled shaft synthesis project: an overvie · five subtopics of bp/ds industry: design,...

AUTHOR

slow. It has often taken decades to move a

skill set from Europe to North America or

even to move a technology from another

industry to the construction sector.

Through this project, the hope was that the

movement of innovations or underutilized

practice from one jurisdiction to another

could be accelerated.

To address these questions, a task force

met at the DFI Annual Conference in Phoenix,

Ariz., in October 2013. It was agreed that

the task force would examine the following

five subtopics of BP/DS Industry: Design,

Construction, Quality Assurance/Quality

Control (QA/QC), Innovative Technologies

and Trends, and Procurement Methods.

Authors/ResearchersEach of these subtopics was examined by a

pair of authors, one knowledgeable with

North American practice, and the other

knowledgeable with European practice.

The following author pairs were

developed:

DEEP FOUNDATIONS • NOV/DEC 2016 • 103

Alan Macnab, P. Eng., D.GE

The Bored Pile/Drilled Shaft (BP/DS)

Synthesis Project, endorsed by the DFI

Dril led Shaft Committee, was the

brainchild of James Johnson, trustee liaison

to the committee. Johnson felt that DFI

members in the European Union (EU) and

North America (NA) would benefit from a

comparison of the state of practice for

drilled shafts (called bored piles in Europe)

in those two regions.

Johnson posed several key questions:

• Is the design and construction of BP/DS

similar in both regions?

• If not, why not? Is it because of

regulatory drivers, environmental

drivers or financial drivers?

• Or is it just different and could those

differences offer opportunities to learn

from those differences?

From past history in the geotechnical con-

struction industry, transfer of knowledge

bases and technology is often painfully

Bored Pile/Drilled Shaft Synthesis Project: An Overview

Topic North American Author European Author

Design Dr. Dan Brown, D.GE., P.E. Maurice Bottiau, ir (Belgium)

(Tennessee)

Construction Dr. Antonio Marinucci, P.E. Vince Jue (Italy)

(Rhode Island)

QA/QC Bernie Hertlein, FACI (Illinois) Gerald Verbeek (Netherlands)

Innovation Ray Fassett (California) Dr. Michael Arnold (Germany)

Procurement David Coleman, P.E. (New York) Arthur Tipter, Dipl. Ing. (Germany)

Installing bored piles in Dresden, Germany (photo courtesy Zueblin)

104 • DEEP FOUNDATIONS • NOV/DEC 2016 DEEP FOUNDATIONS • NOV/DEC 2016 • 105

Alan Macnab, P.Eng., D.GE.

public private partnerships or Build, Oper-

ate, Transfer) many, if not all, risks are borne

by the DB contractor, who then either shares

them within its team on an ability-to-pay

basis or finds insurance protection for them.

DB contractors in NA tend to be larger

conglomerates that coordinate design,

construction, testing and often financing

issues as well as long-term maintenance. In

the end, decisions are made based on

economic reasons. Short-term efficiencies

often do not equate to long-term

economies. Even conventional contracts,

which are awarded based on a value rather

than price basis, usually come with

increased builder liability and responsibility.

If one accepts the premise that, to the

DB contractor, the long-term economic

decision is paramount, then some of the

differences identified in this study are easier

to understand. It is a basic assumption

contained herein that this premise governs

DB in both the EU and NA.

For example, slurry protected shafts are

often cheaper to construct than cased

shafts, but suffer a higher incidence of

anomalies. Anomalies drive schedule

losses, which are often not considered by

DBB contractors. However a DB contractor,

who is responsible for financing, has a

different perspective. If cased shafts are

practice using fewer diameters for its

designs and, in general, the diameters used

in the EU tend to be smaller than in NA.

The use of Design Build (DB) or variations

thereof as opposed to Design Bid Build

(DBB) are far more prevalent in the EU than

in NA. In addition, the EU seems more

advanced in selecting contractors based on

value versus price. QA/QC testing is

performed on a smaller percentage of shafts

in the EU than in NA. The EU depends

more on analytical design and in some

cases load testing rather than integrity

testing for design assurance.

Why do we see these differences? The

task force concluded that many of these

differences can be attributed to risk issues

including: quality, productivity, safety,

schedule, cost, public disruption and

sustainability.

Risks are often the direct result of

decisions related to specialty subcontractor

selection, and/or design type selection.

Influence of Project Delivery MethodsIn the NA low bid environment of DBB,

risks are shared or volleyed between the

various entities. In contrast the DB

environment (including such things as

Bored pile construction in Switzerland (photo courtesy BAUER Spezialtiefbau GmbH)

Drilled shafts to support a concrete plant in Calgary, Canada (photo courtesy BAUER Spezialtiefbau GmbH)

Some authors recruited additional con-

tributors for their sections. Alan Macnab,

P.Eng., D.GE. (Canada) was appointed chair.

A follow-up meeting was held at the

EFFC (European Federation of Foundation

Contractors) Conference in Stockholm,

Sweden, in May 2014. Preliminary reports

were presented at the DFI Annual Confer-

ence in Atlanta, Ga., in October 2014. A

presentation of the final findings was made

at the International Foundations Congress

and Equipment Exposition (IFCEE) in San

Antonio, Texas, in March 2015.

The DFI Journal, Volume 10, Issue 2,

includes four papers that represent the

findings of the task force. Because of

significant overlap in the subject matter the

papers for QA/QC and Innovative Tech-

nologies and Trends were combined and

are presented as one paper.

Challenges FacedOne of the challenges the task force

encountered was defining the state of prac-

tice in each region and determining

whether it was possible to define a single

state of practice for each region. North

America, including Central America and

the Caribbean Islands, consists of 38

countries, 22.5 million sq km (8.7 million

sq mi) and 556 million people. Europe

consists of 50 countries, 12.5 million sq km

(4.8 million sq mi) and 742 million people.

It became apparent that it was unrealistic to

expect that practice in either North America

or Europe would be consistent, and it was

also not possible to accurately define

overarching behaviors in such large regions.

It was conceded that the task force

would compare Canada/U.S. and the EU.

The EU consists of 28 countries, 4.3 mil-

lion sq km (1.6 million sq mi) and 507

million people. By comparison, Canada

and the U.S. appear to be similar, however

practices are very regional and diverse;

both have weak central governments and

many operat ions, regulat ions and

practices are performed independently by

states or provinces. As such Canada/U.S.

combined consist of 60 states/provinces,

19.8 million sq km (7.6 million sq mi) and

352 million people. These are staggering

numbers and to describe unique trends or

discrete behaviour patterns required some

gross generalizations.

The task force knew from the start that

the U.S. has the American Association of

State Highway and Transportation

Officials (AASHTO) publications, which

guide transportation sector work, a very

large piece of the drilled shaft market, and

that the EU has the Eurocode for

guidance/regulation in its bored pile

market. The group also knew that there

was unprecedented entry into each

other’s markets from equipment manu-

facturers, which should give some clues

as to any differences which might exist.

The key was to concentrate on these

differences, explaining why they existed,

and determine if these explanations

warranted using the “idea” in other

jurisdictions.

In order to research the variations in

practice in the subject areas, a survey was

distributed to members of DFI, DFI

Europe, ADSC (International Association

of Foundation Drilling) and EFFC. Initial

returns were quite low and heavily

skewed toward NA. The survey was

modified and sent out again. This elicited

more EU response, but the results were

still heavily dominated by feedback from

NA. In order to reconcile this problem,

interviews were carried out with select

European construction representatives

and the task force eventually had

sufficient data to proceed.

FindingsPractice in both NA and the EU is governed

by overarching design and construction

documents that are heavily influenced by

local practices and local codes. Both regions

utilize the same equipment and similar

design methodologies, and both are

developing new innovations. EU innovation

is more focused on drilling and construction

site activities such as in-boom locating

devices. Representatives from the EU are

currently examining concreting practices

and plan to publish their conclusions in the

near future. In NA, the innovations are

focused on QA/QC, or post process needs

such as in-cab readouts, hole measurement

devices, and Thermal Integrity Profiling.

Although many of these measurement

devices are more widely used in NA, often

they were developed in Europe. Both

regions exhibit less conservatism in design

when stronger, more realistic geotechnical

investigation materials are available.

In general, the EU utilizes a larger

percentage of cased shafts while NA

constructs a higher percentage of shafts

using slurry protection. In the slurry

practice, the use of mineral slurries is

predominant in the EU while polymer is

prevalent in NA. The EU has standardized (Top Row L-R) Dr. Michael Arnold, Dr. Dan Brown, P.E., D.GE., Maurice Bottiau, ir, David Coleman, P.E., Ray Fassett(Bottom Row L-R) Bernie Hertlein, FACI, Vince Jue, Dr. Antonio Marinucci, P.E., Arthur Tipter, Dipl. Ing., Gerald Verbeek

106 • DEEP FOUNDATIONS • NOV/DEC 2016

regimes of the fluid concrete stream.

Additionally, bored pile or drilled shaft

concrete can be subjected to stringent test

methods not used on concrete structures

poured in environments that permit visual

inspection. Added research in the field

joining EU and NA knowledge and

resources is underway as a result of the

collaboration of this task force.

In conclusion, the onset of added DB

contracting in NA will probably bring

changes to the methods of contractor

selection as well as design type selection.

From the EU perspective, some of the work

done in NA on slurry techniques has raised

the reliability levels of this technique. This

may present opportunities for financial

economies not previously taken.

To read more details about the findings of the task force, see DFI Journal Volume 10, Issue 2, available for DFI members at MyDFI on the DFI website. Others can join

DFI or subscribe to the Journal at www.tandfonline.com/pricing/journal/ydfi20#.V1B55cr2Y0M.

Drilled shaft construction at Goethals Bridge, NY-NJ (photo courtesy Dan Brown and Associates)

Bored piles in Berlin for the State Opera (photo courtesy BAUER Spezialtiefbau GmbH)

more expensive, but more dependable

from a production schedule point of view, it

is quite easy to understand the EU bias for

cased shafts. There is anecdotal evidence

that the incidence of anomalies is

decreasing in both NA and the EU among

experienced specialty contractors. To

overcome some of the anomaly concerns,

owners have instituted increased use of

integrity testing and shaft measuring

devices, which explains the higher use of

QA/QC testing in NA.

Shaft installation on the Route 1 Gateway project in Canada (photo courtesy BAUER Spezialtiefbau GmbH)

One of the risks associated with DBB is

that the low bidder usually gets the work

regardless of subtrade competency. Drilled

shaft/bored pile contractors are almost

always subcontractors. In the mad dash to

become low bidder, decis ions on

subcontractor selection are often based

entirely on price. In that environment, it is

not surprising that owners would then

require a high degree of QA/QC testing.

When a DB contractor has most of the risk,

its selection of specialty subtrades is

probably based on more rational criteria.

Selecting a specialty subcontractor of

higher competency allows one to focus on

design improvements rather than chasing

quality mistakes.

While no evidence was presented, one

explanation for smaller shafts in the EU

may be that the use of nonredundant

structures such as mono foundations is not

as prevalent in the DB world when the risk

of failure is more catastrophic with

nonredundant structures. It may also be the

result of the use of more load testing in the

EU, which may either lower the assumed

design safety factors or increase the unit

capacity of the drilled shaft/bored pile.

Common Work, Common ProblemsIt became apparent during the work of this

task force that the contractors of the EU and

NA carry a common problem. A core

business activity is one of sophisticated

concrete placement. The specialty

contractors are often called “drillers,” but

that can be the simple part of the work. The

placement of higher-slump, high-strength

concrete in challenging environments

utilizing tremie methods is very difficult.

Problems arise in this type of work that are

often the result of a poor understanding of

critical characteristics necessary for drilled

shaft/bored pile construction by the ready

mix supply industry and inconsistent flow

properties of the resultant product. Some of

these issues are caused by the variation in

materials from supplier to supplier, or even

the variation in ingredients used by the

same supplier. In addition, we have been

placing concrete as an industry by tremie

methods for decades but still really don’t

understand the mechanics and flow