Geotechnical Engineering Journal of the SEAGS & AGSSEA Vol. 51 No. 2 June 2020 ISSN 0046-5828
Geotechnical Engineering Journal of the SEAGS & AGSSEA
Vol. 51 No. 2 June 2020
ISSN 0046-5828
Honouring Prof. Harry G Poulos Lead Guest Editor: Prof. John Carter
Liquefaction Induced Downdrag for the Juan Pablo II Bridge at the 2010
Maule Earthquake in Chile, after Fellenius et al., 2020. Some Factors that Influence the Prediction of the Behaviour of Piled Rafts
via Simplified (Numerical) Analyses, after Cunha et al., 2020.
Biodegradable Prefabricated Vertical Drains: from Laboratory to Field Studies, after Thanh Trung Nguyen et al., 2020.
P-Cone: A Novel Cone Penetration Test Device for Deep Foundation Design, after Hai and Anand, 2020.
Numerical and Simplified Methods for Soil-Pile Interaction Analysis, after Dezi et al., 2020.
Evaluation of Analytical and Numerical Techniques to Simulate Curtain Pile Walls in a Tropical Soil of the Federal District of Brazil, after Jacazz et
al., 2020.
0
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Pile-toeLoad-movementPivot Graph
SoilPile
Long-termResistance
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Sustained Load
Drag
Force, Qn
At TestRt = 380 kNδt = 15 mm
Rt = 750 kN
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Long-termLoad Curve
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Figure 6 Long-term distributions of load and resistance for a single pile
Journal of the Sponsored by
GEOTECHNICAL ENGINEERING
Note:
GOUW Tjie liong and Anthony GUNAWAN paper is on page 9 onward of this PDF.
Geotechnical Engineering Journal of the SEAGS & AGSSEA Vol. 51 No. 2 June 2020 ISSN 0046-5828
Prof. Harry G. Poulos obtained a Civil Engineering degree from the
University of Sydney in 1961, and then went on to do a Ph.D. degree
in Soil Mechanics, graduating in 1965. He worked with the consulting
firm of McDonald Wagner and Priddle for a year before joining the
Department of Civil Engineering at Sydney University in 1965. He
was appointed a Professor in 1982, a position which he held until his
retirement in 2001. In 1989, he joined the consulting firm of Coffey
Partners International and is currently a Senior Principal with the
Coffey Group. He is also an Emeritus Professor at the University of
Sydney, and an Adjunct Professor at the Hong Kong University of
Science and Technology.
He has published books and technical papers on foundation
settlements, pile foundations, and offshore geotechnics. His main research interests continue to be in deep
foundations and their application to high-rise buildings, and to problems relating to ground movements near
foundations.
He has been involved in a large number of major projects in Australia and overseas including the Docklands
Project in Melbourne, the Crown tower development in Sydney, Egnatia Odos highway project in Greece,
high-rise foundation problems in Hong Kong, the Emirates twin Towers in Dubai, the Burj Khalifa tower
in Dubai, the Incheon 151 Tower in Korea, the Dubai Creek Tower in Dubai, the MahaNakon building in
Bangkok, and the Dubai tower in Doha, Qatar.
In 1993, he was made a Member of the Order of Australia for services to engineering. He was elected a
Fellow of the Australian Academy of Science in 1988, a Fellow of The Australian Academy of
Technological Sciences and Engineering in 1996, and an Honorary Fellow of the Institution of Engineers
Australia in 1999. In 2010, he was elected a Distinguished Member of the American Society of Civil
Engineers, the first Australian to receive this honour, and in 2014, he was elected as a Foreign Member of
the US National Academy of Engineering.
He has received a number of awards and prizes, including the Kevin Nash Gold Medal of the International
Society for Soil Mechanics and Geotechnical Engineering in 2005. He was the Rankine Lecturer in 1989
and the Terzaghi Lecturer in 2004, and was selected as the Australian Civil Engineer of the Year for 2003
by the Institution of Engineers Australia. In 2017, he received the ASCE Outstanding Projects And Leaders
(OPAL) award for design.
Prof. John Carter has more than 30 years’ experience in teaching,
research and consulting in civil, geotechnical and offshore engineering.
His research interests include analytical and numerical modeling, soil-
structure interaction, rock mechanics, the behaviour of cemented and
uncemented carbonate soils, soft soil engineering, tunnelling, and
offshore foundations. He has attracted more than $5 million in
competitive research funding and been associated with development
projects attracting additional grants of more than $4 million. He is the
author of several hundred refereed technical papers in geotechnical
engineering and engineering mechanics, covering a diverse range of
topics from theoretical mechanics to experimental applications. His
research output includes a significant body of work on the engineering
behaviour of seabed carbonate sediments.
Because of the expertise acquired during his research career in geotechnics, Prof. John Carter has been
called upon to consult widely to industry on a range of geotechnical projects, including soft clay foundations,
Honouring Prof. Harry G. Poulos
Lead Guest Editor: Emeritus
Professor John Carter
Geotechnical Engineering Journal of the SEAGS & AGSSEA Vol. 51 No. 2 June 2020 ISSN 0046-5828
offshore foundations, retaining walls, and buried structures. He has also been retained as an expert
consultant on numerous offshore foundation problems for a number of major oil and gas companies,
including BHP, Esso, Woodside, Wapet, Bond Oil, Amoco, and Exxon. He is currently a consultant director
of Advanced Geomechanics, a geotechnical consultancy based in Perth, providing specialist advice to the
offshore industry on foundation problems and on-shore and offshore site investigations. He has also been
involved in the commercialization of research and the marketing of its outcomes, including his own
specialist geotechnical software.
Between 1997 and 2000 he was a director, representing the interests of the University of Sydney, of Benthic
GeoTech Pty Ltd, a $10 million joint venture company that conceived, designed, built and now operates
PROD, the Portable Remotely Operated Drill, which is used to penetrate the ocean floor, conduct in situ
tests and recover core samples. Prof. John Carter's experience with engineering projects has required him
to work in Australia, Britain, and the USA. He has authored more than 60 major consulting reports for a
range of clients, including mining companies, oil companies, other engineering consultancies, and lawyers.
Geotechnical Engineering Journal of the SEAGS & AGSSEA Vol. 51 No. 2 June 2020 ISSN 0046-5828
GEOTECHNICAL ENGINEERING
EDITOR-IN-CHIEF
2020 - Present
Dr. Kuo Chieh Chao
Asian Institute of Technology
Thaliand
2010 - 2019
Dr. Teik Aun Ooi (Malaysia)
Prof. A.S. Balasubramaniam (Australia)
________________________________________
EDITORIAL ADVISERS
Prof. Za-Chieh Moh (Taiwan)
Dr. Teik Aun Ooi (Malaysia)
Prof. A.S. Balasubramaniam (Australia)
Dr. Edward W. Brand (U.K.)
Prof. Kwet Yew Yong (Singapore)
Prof. Harry G. Poulos (Australia)
Dr. Chin-Der Ou (Taiwan)
Dr. Suttisak Soralump (Thailand)
Dr. Wen Hui Ting (Malaysia)
Dr. John Chien-Chung Li (Taiwan)
Dr. Chung Tien Chin (Taiwan)
Prof. Pedro Seco E Pinto (Portugal)
Prof. Dennes T. Bergado (Philippines)
________________________________________
EDITORIAL PANEL
Prof. Paulus P. Rahardjo
Parahyangan Catholic University
Indonesia
Dr. Limin Zhang
Hong Kong University of
Science and Technology
Hong Kong
Dr. Erwin Oh
Griffith University
Australia
Dr. Dominic Ong
Griffith University
Australia
Dr. Apiniti Jotisankasa
Kasetsart University
Thailand
Dr. Jie-Ru Chen
National Chi Nan University
Taiwan
Dr. Phung Duc Long
Long GeoDesign
Vietnam
Dr. Darren Chian
National University of
Singapore
Singapore
Geotechnical Engineering Journal of the SEAGS & AGSSEA Vol. 51 No. 2 June 2020 ISSN 0046-5828
GEOTECHNICAL ENGINEERING
Paper Contribution, Technical Notes, and Discussions
Geotechnical Engineering is the official journal of the Southeast Asian Geotechnical Society and the Association of
Geotechnical Societies in Southeast Asia. It is published four times a year in March, June, September, and December
and is free to members of the Society. Please visit our website at http://www.seags.ait.ac.th for the membership
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SEAGS & AGSSEA encourage the submission of scholarly and practice-oriented articles to its journal. The journal
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of Geotechnical Societies in Southeast Asia, promote the ideals and goals of the International Society for Soil
Mechanics and Geotechnical Engineering in fostering communications, developing insights and enabling the
advancement of the geotechnical engineering discipline. Thus, the publishing ethics followed is similar to other
leading geotechnical journals. The standard ethical behavior of the authors, the editor, and his editorial panel, the
reviewers, and the publishers is followed.
Before you submit an article, please review the guidelines stated herein for the manuscript preparation and submission
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Geotechnical Engineering Journal accepts submissions via electronic. The manuscript file (text, tables, and figures)
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9. If experimental data and/or relations fitted to measurements are presented, the uncertainty of the results must
be stated. The uncertainty must include both systematic (bias) errors and imprecisions.
10. Authors need not be Society members. Each author’s full name, Society membership grade (if applicable),
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page of the paper.
Geotechnical Engineering Journal of the SEAGS & AGSSEA Vol. 51 No. 2 June 2020 ISSN 0046-5828
11. Journal papers submitted are subject to peer review before acceptance for publication.
12. Each author must use SI (International System) units and units acceptable in SI. Other units may be given in
parentheses or in an appendix.
13. A maximum of five keywords should be given.
14. References
American Petroleum Institute (API) (1993). Recommended Practice for Planning, Designing, and
Constructing Fixed Offshore Platforms – Working Stress Design, API Recommended Practice 2AWSD
(RP 2A-WSD), 20th edition, 1993, p 191.
Earth, J.B., and Geo, W.P. (2011). “Asian Geotechnical amongst Authors of Conference Publications,”
Proceedings of Int. Conference on Asian Geotechnical, publisher, city, pp 133-137.
Finn WDL and Fujita N. (2002). “Piles in liquefiable soils: seismic analysis and design issues,” Soil
Dynamics and Earthquake Engineering, 22, Issues 9-12, pp 731-742.
15. Discussions on a published paper shall be made in the same format and submitted within six months of its
appearance and closing discussion will be published within twelve months.
For additional information, please write to:
Dr. Kuo Chieh Chao
Hon. Secretary-General
Southeast Asian Geotechnical Society
Email: [email protected]
Website: http://www.seags.ait.ac.th
Ir. Peng Tean SIN
Hon. Secretary-General
Association of Geotechnical Societies in Southeast Asia
Email: [email protected]
Website: http://www.agssea.org
Geotechnical Engineering Journal of the SEAGS & AGSSEA Vol. 51 No. 2 June 2020 ISSN 0046-5828
GEOTECHNICAL ENGINEERING
TABLE OF CONTENTS List of Papers Page
1. Liquefaction Induced Downdrag for the Juan Pablo II Bridge at the 2010 Maule Earthquake in Chile 1 - 8
By Bengt H. Fellenius, Babak Abbasi, and Balasingam Muhunthan
2. Deep Compaction of Sand Causing Horizontal Stress Change 9 - 21
By K. R. Massarsch and B. H. Fellenius
3. Some Factors that Influence the Prediction of the Behaviour of Piled Rafts via Simplified 22 - 29
(Numerical) Analyses
By Renato P. Cunha, Harry G. Poulos, and John C. Small
4. Evaluation of Analytical and Numerical Techniques to Simulate Curtain Pile Walls in a Tropical 30 - 38
Soil of the Federal District of Brazil
By S. Jacazz, Y. M. P. de Matos, F. F. Monteiro, R. P. Cunha, J. C. Ruge, and G. Gassler
5. Biodegradable Prefabricated Vertical Drains: from Laboratory to Field Studies 39 - 46
By Thanh Trung Nguyen, Buddhima Indraratna, and Pankaj Baral
6. P-Cone: A Novel Cone Penetration Test Device for Deep Foundation Design 47 - 53
By Hai M. N. and Anand J. P.
7. Analysis of Stiffened Granular Piled Raft 54 - 64
By Madhav Madhira, Jitendra Kumar Sharma, and Raksha Rani Sanadhya
8. Can a Pile Load Tested to ‘Failure’ be used as a Working Pile? 65 - 72
By T. L. Gouw and A.Gunawan
9. Displacement of Piles from Pressuremeter Test Results - A Summary of French Research 73 - 82
and Practice
By R. Frank
10. Effect of Seismic Action on Settlement and Load Sharing of Piled Rafts Based on Field Monitoring 83 - 94
By K. Yamashita, J. Hamada and T. Tanikawa
11. Model Vibration Tests on Piled Raft and Pile Group Foundations in Dry Sand 95 - 102
By Anh-Tuan Vu, Tatsunori Matsumoto, and Kohei Kenda
12. BEM and FEM Approaches to the Analysis of Negative Skin Friction on Piles 103 - 110
By Gianpiero Russo
13. Effective Stress Friction Angle of Normally Consolidated and Overconsolidated Intact Clays from 111 - 116
Piezocone tests
By Zhongkun Ouyang and Paul W. Mayne
14. Numerical and Simplified Methods for Soil-pile Interaction Analysis 117 - 129
By Dezi F., Carbonari S., Morici M., and Leoni G.
15. The Behaviour of Pile Group and Combined Piled-Raft Foundation in Liquefiable Soil under 130 - 138
Seismic Conditions
By Aniruddha Bhaduri, Vansittee Dilli Rao, and Deepankar Choudhury
16. Foundation Investigation and Analysis for Tall Tower Developments 139 - 149
By C. M. Haberfield, J.E. Finlayson, and A. L .E. Lochaden
Geotechnical Engineering Journal of the SEAGS & AGSSEA Vol. 51 No. 2 June 2020 ISSN 0046-5828
17. Effects of Cyclic Behaviour during Pile Penetration on Pile Performance in Model Load Tests 150 - 158
By S. Moriyasu, T. Matsumoto, M. Aizawa, S. Kobayashi, and S. Shimono
18. FD Analysis on Piled Raft Foundation Settlements under Vertical Loads 159 - 165
By D. W. Chang, H. W. Lien, and M. H. Hung
19. Analysis for Laterally Loaded Offshore Piles in Marine Clay 166 - 171
By S. Jeong, and Y. Kim
20. Pile Design in Seismic Areas: Small or Large Diameter? 172 - 178
By R. Di Laora
Cover Photograph
1. Liquefaction Induced Downdrag for the Juan Pablo II Bridge at the 2010 Maule Earthquake in Chile
By Bengt H. Fellenius, Babak Abbasi, and Balasingam Muhunthan
2. Some Factors that Influence the Prediction of the Behaviour of Piled Rafts via Simplified (Numerical) Analyses
By Renato P. Cunha, Harry G. Poulos, and John C. Small
3. Biodegradable Prefabricated Vertical Drains: from Laboratory to Field Studies
By Thanh Trung Nguyen, Buddhima Indraratna, and Pankaj Bara
4. P-Cone: A Novel Cone Penetration Test Device for Deep Foundation Design
By Hai M.N. and Anand J. P.
5. Numerical and Simplified Methods for Soil-pile Interaction Analysis
By Dezi F., Carbonari S., Morici M., and Leoni G.
6. Evaluation of Analytical and Numerical Techniques to Simulate Curtain Pile Walls in a Tropical Soil
of the Federal District of Brazil
By S. Jacazz, Y. M. P. de Matos, F. F. Monteiro, R. P. Cunha, J. C. Ruge, and G. Gassler
Geotechnical Engineering Journal of the SEAGS & AGSSEA Vol. 51 No. 2 June 2020 ISSN 0046-5828
65
Can a Pile Load Tested to ‘Failure’ be Used as a Working Pile?
T. L. Gouw1 and A. Gunawan2
1Universitas Katolik Parahyangan, Bandung, Indonesia 2Bina Nusantara University, Jakarta, Indonesia
1E-mail: [email protected] 2E-mail: [email protected]
ABSTRACT: There are a few available loading test methods to obtain a load-settlement curve of a pile. Likewise, there are many definitions
to determine the ‘ultimate’ pile capacity from a load-settlement curve. Although pile load tests have been widely used over the past decades,
there are still many questions regarding its practice and interpretation. Frequently asked questions include: when does a pile test considered to
have failed? From an economic point of view, a failure in pile loading test can cost quite a lot of money. To what load can the pile be loaded
till it is considered to have failed? Can a pile loaded to failure still be used as a working pile? What is a bidirectional pile load test (BD-test)?
When should a BD-test be used? Can a pile tested with a BD be used as a working pile? What are the differences between kentledge or reaction
piles static loading test with the bidirectional test? Do the different pile tests produce the same results? This paper aims to shed light on these
questions, one case history where the pile tested to ‘failure’ and later used as working piles is presented.
KEYWORDS: Pile static load test, Bidirectional test, Ultimate pile capacity, Fail Pile
1. INTRODUCTION
Foundation piles have been used for over one hundred years. There
are many methods to construct the piles. Likewise, there are also
many methods to test the pile capacity. In Indonesia, foundation piles
are very common, and engineers in Indonesia are willing to adopt
state-of-the-art testing methods. From the common kentledge loading
test, static load test with reaction piles, dynamic loading test (also
known as PDA - pile driving analyzer), to the more recent one,
bidirectional test (BD-test). Although these testing methods have
been widely adopted in Indonesia, there are still questions regarding
these testing methods. Often, engineers have different perspective on
the practice of these testing methods. This paper aims to shed light to
the following frequently asked questions:
• A pile load test should not be determined as failure as the project
owner has spent thousands or tens of thousands of US dollars for
it. So, in what scenario does a pile load test considered to have
failed?
• Can a pile tested to “failure” still be used as a working pile?
• What is a bidirectional load test or O’ Cell? When is it necessary
to apply this test method?
• Can a pile tested by bidirectional load test still be used as a
working pile?
• Will a pile tested by kentledge load test, static load test by
reaction pile, and bidirectional test give the same results?
The paper first discusses what “ultimate” pile capacity is, the
principles of each pile tests, followed by answers to the above
questions.
2. ULTIMATE PILE CAPACITY
Eurocode 7 (BS EN 1997-1, 2004) defines ultimate pile capacity, also
known as ultimate limit states, as compressive or tensile resistance
failure of a single or piles system. However, according to Fellenius
(2017), “Ultimate pile capacity” is a very imprecise concept in most
soil conditions. This can be seen from a typical load-settlement curve
shown in Figure 1. As shown in Figure 1, pile “capacity” continues
to increase the further it is loaded. So, when does a pile fail? Figure 2
shows the 3 types of load-settlement curves that can be obtained in
the field. The first type is a general failure, which as stated previously,
the pile capacity continues to increase with pile settlement. The
second type is punching failure with a relatively constant capacity, in
which pile continues to move under constant load. The third type is
punching failure with a reduction in capacity. Geotechnical pile
failure only occurs when type 2 or type 3 occurs. For types 2 and 3, a
true “ultimate” capacity can be defined. It is important to differentiate
the peak and ultimate capacity for type 3. These three types of curves
obtained can be explained with ultimate shaft resistance and toe
resistance.
Figure 1 Typical load-settlement curve from a pile-load test in
medium dense sand (Zhang and Tang, 2001)
Figure 2 Three types of load settlement curve: 1 – general failure, 2
– punching failure with constant capacity, 3 – punching failure with
reduction in the pile capacity
Geotechnical Engineering Journal of the SEAGS & AGSSEA Vol. 51 No. 2 June 2020 ISSN 0046-5828
66
2.1 Ultimate Shaft Resistance
Development of shaft resistance is the consequence of relative
movement between the pile and soil. If the pile settles more than the
soil, a positive shaft resistance is generated. Whereas, when the soil
settles more than the soil, a negative shaft resistance is generated. To
fully mobilize shaft resistance, very small relative movement is
required, often only a few millimeters (Fellenius, 2017). The relative
movement required is independent of pile size but depends on soil
type and roughness of the pile.
Shaft resistance is a function of the magnitude of relative
movement and soil type as observed from direct shear test results
shown in Figure 3. At first, the shear stress vs. movement increases
more or less linearly, then, for loose sand or normally consolidated
clay, after some magnitude of movement has been reached, the slope
gets flatter and, finally, the shaft resistance becomes approximately
constant. For dense sand or overconsolidated clay, the shaft resistance
usually reaches a peak value, thereafter it decreases with movement
to a residual strength. Some will define the ultimate shaft resistance
as the peak value, others prefer to define it as the residual strength.
Figure 3 Shear stress versus shear displacement on dense and loose
sand (Modified after Das, 2014)
2.2 Toe Resistance
Unlike shaft resistance, toe resistance does not have an ultimate value.
The load-movement of pile-toe is a function of the stiffness and
effective stress of the soil. Figure 4 shows an example of load versus
pile toe movement measured in a 1.5 m and 1.8 m diameter piles.
Even after a large movement of 150 mm, which is nearly 10% the pile
diameter, the load-movement curve does not indicate reaching
“failure”.
Figure 4 Unit toe resistance measured on a 1.5 and 1.8 m diameter
bored pile constructed in silty sandy clay and clayey sand
(Fellenius, 2017)
2.3 Failure in Pile
The three types of failure shown in Figure 2 can be explained from
the ultimate shaft and toe resistance. For general failure, although
ultimate shaft resistance has been mobilized, the toe resistance can
continue to develop resistance as load is added. A Type 3 punching
failure can occur, when the shaft resistance reduces more than the
increase of toe resistance. Punching or plunging failure with relatively
constant capacity or with reduced resistance is rather rare. For general
failure, there is no obvious pile capacity. If a capacity value is
necessary, a specific definition must be used and agreed on by the
parties involved in the evaluation of the static loading test.
2.4 Failure Criterion
For pile which experience general failure, specific criterion to derive
pile capacity is needed. In the early days (1960s-1970s), pile capacity
is defined by identifying the initial relatively gentle part of the curve
and the latter steeper part of the curve. Examples include Hansen 80%
and 90% criteria (1963), Chin-Kondner extrapolation (Chin, 1971;
Kondner 1963), DeBeer intersection load (1968), and many others.
A straighter forward method to define a pile capacity is by taking
the pile load under certain displacement, usually based on the pile
diameter. Eurocode 7 defines pile capacity as the load that resulted in
a movement equal to 10% of the pile-toe diameter (BS EN 1997-1,
2004). Indonesian standard applies similar criterion, in which pile
capacity is taken as the load that produced 25 mm movement in a pile
with a diameter smaller than 800 mm, and a movement equal to 4%
pile diameter for piles with a diameter larger than 800 mm (SNI
8640:2017).
There is also pile capacity derivation which includes elastic
shortening of pile from the axial load. This method is adopted by
Davisson (1973), AS2159 (2009), Ng et al. (2001), etc.
From the numerous different approaches available, many
different pile capacities can be derived. As shown in Figure 1, the
difference can be more than 150%! Naturally different approach also
has their own respective accepted factor of safety. Engineers should
abide by their respective local standards, unless for special reasons
stricter settlement is required.
Before understanding the different types of pile load tests, an
engineer needs to understand the basis of determining pile capacity.
In essence, the capacity does not exist until it is defined. With this
appreciation, one can have a clearer picture of the advantages and
disadvantages of each testing methods, as well as their
appropriateness in different situations.
3. THE STATIC LOADING TEST
A static loading test is a test whereby tested pile is loaded axially,
either using dead-weights (kentledge) or reaction piles/frames. The
choice of pile tested is usually based on the pile installed in the most
adverse soil conditions. This is to ensure that the obtained results are
most conservative and that there is no overestimation of pile capacity
in other areas.
The main purpose of the static loading test is to obtain load versus
movement relationship of the test pile. The pile capacity can be
derived from the results based on the specific criterion. Some also
assess a creep response of movement versus time under constant load.
Another useful information that can be obtained through a static load
test is the rebound behavior, when the pile tested is unloaded (BS EN
1997-1, 2004). More useful information can be obtained by using
instrumented piles, e.g. separating shaft and toe resistance (Fellenius,
2017). In the next sections, the procedure of static loading test by
kentledge and reaction piles are discussed.
3.1 Kentledge System
Figure 5 and 6 shows a schematic diagram and photograph of static
load test with kentledge system, respectively. A pile capacity can
range from a hundred of kN to thousands of kN. To load a pile to that
level, a sufficient reaction force is required. One method to provide
Geotechnical Engineering Journal of the SEAGS & AGSSEA Vol. 51 No. 2 June 2020 ISSN 0046-5828
67
the reaction force is by kentledge, where blocks of concrete are placed
on a platform to act as a reaction to loading of the pile. ASTM D1143
states that the total weights should at least be 10% larger than the
maximum load that is going to be applied. The center of the cross
beams needs to be in the center of the pile to prevent eccentric
loading. Only 1% eccentric loading and an eccentric distance of 25
mm is allowed. To stabilize the cross beams, temporary support of the
platform, such as timber or concrete cribs, need to be built. Care must
be taken in determining the clear distance between the pile to the
cribs. The distance is important because the kentledge load is
transferred to the soil underneath the cribs adding stress to the ground
and the supports must be placed far enough to not let the change of
vertical stress affect the shaft resistance of tested pile. As a general
guideline, ASTM D1143 states that the clear distance should not be
less than 1.5 m.
Figure 5 Schematic diagram of static load test with kentledge
system (ASTM D 1143, 2007)
Figure 6 Photograph of static load test with kentledge system
(Courtesy of Khmer D&C Technical Consultant, 2018)
3.2 Reaction Piles or Anchors
Alternative to kentledge, reaction piles or anchors can be used to
provide the reaction force for pile loading. Figure 7 and 8 shows a
schematic diagram and photograph of reaction pile system. Care must
be taken to ensure sufficient resistance from anchors or reaction piles.
Movement of anchors or reaction piles also must be measured to
calculate the net movement of the tested pile. Another thing to note is
the different requirements in clear distance between the tested pile
and its anchors or reaction piles. ASTM D1143 states that the required
clear distance is 5 times the largest pile/anchor diameter (can be the
test pile or reaction pile) or 2.5 m, whichever is larger. The required
clear distance is larger than the kentledge system, because for the
kentledge system, the larger the load applied on the test pile, the lower
the load on the cribs. However, when reaction piles or anchors are
used, the larger the load applied on the test pile, the larger the opposite
load acts on the reaction piles or anchors.
Figure 7 Schematic diagram of a static load test with anchored
reaction frame (ASTM D 1143, 2007)
Figure 8 Photograph of static load test with reaction piles
(Courtesy of Structville, 2018)
3.3 Loading Procedure
Ideally, the load applied should reach a “failure” that reflects the axial
static compressive capacity of the pile. Care must be taken that the
load applied does not exceed the axial structural strength of the pile.
As pile capacity changes with time (setup effect, when strength is
gained; relaxation, when strength decreases) a qualified engineer
should specify the waiting period before testing. Moreover, for a cast-
in-place pile or a bored pile, sufficient time should be given for the
concrete to gain adequate strength.
ASTM D1143 lists 7 loading procedures that can be adopted for
static loading tests. In Indonesia, the most commonly used loading
procedure is the maintained test (ASTM D1143, 2007). The test pile
is loaded to a minimum of 200% design load in 25% increments, the
pile is then unloaded in four or five equal decrements. When higher
capacity is anticipated, the pile can be reloaded to a higher load level.
Figure 9 shows an example of a test pile loaded to 100%, 200% then
300% design load performed by the authors.
Figure 9 Static loading test result
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3.4 Results, Failures in Execution of Static Load Test
Results from a non-instrumented pile static loading test comes in the
form of load-settlement curve (an example is shown in Figure 1 and
9). From the load-settlement curve, the pile capacity can be
determined using a definition based on local national standards.
However, without any geotechnical instrumentation, it is not possible
to separate the shaft or toe resistance. The importance of
instrumentation is discussed in the next section.
Failures in the execution of static loading tests cost a lot of time
and money. Causes of failures include bearing capacity failure of the
concrete block supports/cribs, e.g. in Figure 10; instrumentation
errors; insufficient reaction force; support platform located too close
to the pile. These failures can be prevented and should not be allowed
to occur.
Figure 10 Failure of kentledge system before loading
(Courtesy of Profound BV, 2017)
3.5 Importance of Instrumentation
The most common instrumentation installed in a pile are strain gages.
Strain gages provide the load distribution along the pile shaft, e.g. in
Figure 11. From the axial load distribution, it is possible to derive the
shaft resistance by differentiating the curve. It is also possible to
estimate the toe resistance from the bottom-most strain gage. From
the results, design can be verified, and optimization can be carried
out.
Figure 11 Development of axial load distribution with load steps
4. BIDIRECTIONAL TEST
The bidirectional test (BD-test) was first used in the 1980s in Brazil
and the USA (Fellenius, 2017), and widely accepted internationally
from 1990 onward (Osterberg, 1998). Because of Dr. Jorj Osterberg’s
pioneering work, the bidirectional cell (BD-cell) is also known as the
Osterberg Cell test, or O-cell test. Figure 12 shows a schematic
diagram of a bidirectional test. The BD-cell is in principle a hydraulic
jack placed at some depth within the pile shaft. The cells are
sacrificial, as they cannot be retrieved after the test completion. When
pressure is applied to the O-cell, the cell expands, pushing the upper
part of the test pile upward, and the lower part downward. The BD
test can be used for both cast-in-place and precast piles.
Figure 12 Schematic diagram of a bidirectional test (ASTM, 2018)
4.1 O-cell Test Apparatus, Instrumentation and Installation
Currently, there is no guideline available for bidirectional tests in the
Indonesian Standard. For guideline, one can refer to ASTM D8169
(2018). For an O-cell test, the only apparatus required are the O-cell
itself and hydraulic pump. Required instruments are pile head
measuring device, e.g. digital survey, or reference beam with dial
gauges, the BD-cell top, and bottom plate movement measuring
device which are in the form of either electronic displacement
indicators or telltales. Optional instrumentation are strain gauges
along the pile shaft.
For cast-in-place pile, the reinforcement cage is separated into 2
sections. The first section is welded onto the top bearing plate of BD-
cell, while the second section is welded onto the bottom bearing plate
(see Figure 13). The bearing plate needs to have sufficient spacing to
allow grouting to flow through.
For precast pile, the BD-cell can be prefabricated with the pile.
Alternatively, the precast pile can be separated into two segments,
that are spliced in the field with the segments attached to one of the
BD-cell’s bearing plates (Figure 14). The installation of precast pile
with BD-cell attached is the same as normal precast piles.
4.2 Loading, Measurement of O-cell and Results
The BD test is carried out by applying hydraulic pressure using a
hydraulic pump at the ground surface (refer to Figure 12). The applied
pressure expands the BD-Cell, pushing the upper shaft upward, and
the lower downward.
Figure 15 shows the typical results from a BD test. During the
initial loading phase, the BD-cell shows zero movement as it has to
overcome the buoyant weight of the upper length of the pile, as well
as any residual load. As the BD-cell is further loaded, the shaft and
toe resistance start to get mobilized until either the shaft or toe
ultimate resistance is reached. The difference between the pile head
movement and the top bearing plate movement is the shortening of
the upper length of the pile. From the measurements, one can obtain
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69
a load-movement curve for both the pile shaft and pile toe. Therefore,
the shaft and toe resistance can be evaluated separately.
Figure 13 Reinforcement cage welded onto bearing plates of BD-
cell (Courtesy of Foundation Alliance, 2018)
Figure 14 Installation of BD-cell in precast pile
(Courtesy of YJack, 2018)
Figure 15 Typical result of a BD-cell test (Fellenius, 2017)
4.3 Failures in Execution of BD-cell test
Ideally, the BD-cell should be placed at a level that allows full
mobilization of the upper length of the pile, and as much toe
resistance as possible. Therefore, in most cases, the BD-cell is placed
either at the pile toe, or very close to the pile toe. However, in cases
where the pile sits on very soft soil, and depends mostly on the shaft
resistance, it may be necessary to place the BD-cell higher up the pile.
5. CASE HISTORY
The case history is based on the authors’ work at a project in the
central business district area of Jakarta, the capital city of Indonesia.
Two bored piles of 1.0 m diameter and embedded to 52.5m depth
below ground were tested up to 300% of its design load. The design
load is 6400 kN. The subsoil condition is as shown in Table 1 below.
Table 1 Subsoil Layers and Their Properties
Both piles were instrumented with vibrating wire strain gauges
(VWSG). Eight layers of VWSG were installed, i.e. at 0.7, 8.0, 15.3,
23.1, 30.0, 37.2, 44.8 and 52.0 m depths; with 3 numbers of VWSG
at each layer. The static loading tests were carried out following
ASTM 1143.
With a safety factor of around 2.5, a preliminary estimate gave an
allowable axial pile capacity of 6400 kN. To optimize the design, it
was decided to carry out preliminary load tests on two piles placed at
a presumably weaker area as revealed by the boreholes. The two piles
were tested to 300% of their design load.
Before the loading test is carried out the integrity of the piles were
tested by sonic logging. Figure 16 shows the test pile no. 1 has good
integrity. Test pile no. 2 also has good integrity.
Figures 17 and 18 show the load distribution along the pile shaft.
The graphs show that with 300% design load, i.e. up to 19,200 kN,
the shaft resistance more or less already fully mobilized, except the
segment below 45m depth where the shaft resistance and the end
bearing has been not fully mobilized. Figure 19 shows the pile
settlement curve along with the ‘ultimate’ capacity derived by various
methods. The load settlement curves show type 1 behavior as defined
in Figure 2, which means the pile bearing capacity increases with its
settlement.
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Figure 16 Sonic logging test result show good pile integrity
Figure 17 Load distribution curve of test pile no. 1
Figure 18 Load distribution curve of test pile no. 2
Figure 19 Load settlement curve of TP-01 and TP-02
19,200
14,672
11,227
5,341
4,812
4,253
3,505
372
-55
-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
0 1,0
00
2,0
00
3,0
00
4,0
00
5,0
00
6,0
00
7,0
00
8,0
00
9,0
00
10,0
00
11,0
00
12,0
00
13,0
00
14,0
00
15,0
00
16,0
00
17,0
00
18,0
00
19,0
00
20,0
00
Dep
th (
m)
Load (kN)Load Distribution - TP 2 - Last Test Cycle
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The ultimate capacity derived by using various definitions is
tabulated in Table 2. The average ‘ultimate’ capacity of the two test
piles is around 18,000 kN. Taking the minimum safety factor of 2.5
as defined by the Indonesian National Standard (SNI 8640:2017), the
allowable capacity of the pile is 7200 kN. At the 7200 kN allowable
load, the settlement of the test piles are still less than 6 mm, which is
also one of the criteria set in the Indonesian standard where at design
load under non-seismic condition, i.e. the pile head settlement should
be less than 6 mm. With these results, the initial design load of 6400
kN was increased to 7200 kN, and these two test piles were also used
as working piles without any problem to the building constructed.
Table 2 Pile ‘Ultimate’ Capacity
6. DISCUSSION
The pile geotechnical ‘failure’, capacity, or ultimate resistance is
basically a definition determined in the design stage, specifically by
its magnitude of settlement (movement) at a certain load.
6.1 Using Pile Loaded to Failure as Working Pile
As discussed in section 2, in most cases, piles will not reach
‘geotechnical’ failure during pile load tests. In most soils, a pile’s toe
resistance continues to increase the further a pile is loaded. What is
meant by pile loaded to ‘failure’ is when the tested pile is loaded
beyond a certain failure criterion, e.g. pile head settle more than 4%
pile diameter or other definition.
Therefore, as long as the tested pile is not structurally damage, a
pile loaded to ‘failure’ does not mean it become unusable. In other
words, a pile loaded to reach a failure criterion can still be used as a
working pile as long as there is no structural damage. Furthermore,
when a pile experience unloading, the next time it is loaded, it will
show a stiffer response, until the previous maximum load is exceeded
(see Figure 20). This behavior is very much like loading an
overconsolidated soil.
However, one must pay attention when punching failure with a
reduction of pile capacity occurs (type 3 failure in Figure 2). When
reusing such a pile, the ultimate pile capacity has to be used instead
of peak pile capacity. However, for other piles which weren’t loaded,
the peak pile capacity can be used as long as sufficient factor of safety
is given to ensure that the pile will not be loaded beyond its peak
capacity during its design life.
Figure 20 Load-settlement curve in cyclic pile load test
(Trishna, 2018)
6.2 Using Pile Tested by Bidirectional Test as Working Pile
Similar to that discussed in Section 6.1, a pile tested by a bidirectional
test can be reused as a working pile. Although there is a fracture zone
in the pile, the upper and lower reinforcement cages are connected by
the BD-cell’s bearing plates. Besides, the fracture zone is always
grouted, making the pile acts as one body.
It is also very costly to not use a pile tested by a bidirectional test.
Bidirectional tests are common for large piles and offshore piles. This
is because building a kentledge system or reaction piles would be
time-consuming and costly. Therefore, due to economical reason,
most piles tested by bidirectional tests are reused as working piles. Of
course, this is also because conducting a bidirectional test does not
significantly diminish the tested pile performance.
6.3 Similarity of Results from Static Load Test and BD-Test
The main objective of conducting pile load tests, regardless of the
methods is to obtain the ‘ultimate’ capacity of the tested pile. Despite
the difference in the measurement system, provided the same
definition is used to determine the ‘ultimate’ capacity, theoretically,
the static loading test and BD-test should produce more or less the
same ultimate pile bearing capacity. This is because the bidirectional
test is essentially a static load test as well. Bidirectional tests can
provide information on both the shaft and toe resistance, while
conventional static load test can only produce the total pile capacity.
Fellenius (2017) considers the bidirectional tests to be superior as
compared to conventional static load tests.
7. CONCLUSION
The ‘ultimate’ or ‘failure’ capacity is a definition which has to be
defined and agreed upon in its design stage. A pile tested to its
‘ultimate’ or ‘failure’ load, either by a kentledge static loading test or
by a bidirectional test, can still be used as working piles as long as the
tested pile is not structurally damaged. Geotechnically speaking there
is no difference between static loading test and bidirectional loading
test.
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