Advances In Deep Foundation
BALKEMA – Proceedings and Monographs in Engineering, Water and Earth Sciences PROCEEDINGS OF THE INTERNATIONAL WORKSHOP ON RECENT ADVANCES OF DEEP FOUNDATIONS (IWDPF07), PORT AND AIRPORT RESEARCH INSTITUTE, YOKOSUKA, JAPAN, 1–2 FEBRUARY, 2007
Advances in Deep Foundations Editors Yoshiaki Kikuchi Port & Airport Research Institute, Yokosuka, Japan Jun Otani Kumamoto University, Kumamoto, Japan Makoto Kimura Kyoto University, Kyoto, Japan Yoshiyuki Morikawa Port & Airport Research Institute, Yokosuka, Japan
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ISBN 13: 978-0-415-43629-8 (hbk)
Advances in Deep Foundations – Kikuchi, Otani, Kimura & Morikawa (eds) © 2007 Taylor & Francis Group, London, ISBN 978-0-415-43629-8
Table of contents Preface
Organizing Committee & Research Committee
D.J. White & A.D. Deeks
Centrifuge modelling of pile foundation
C.F. Leung Advanced modeling tools for the analysis of axially loaded piles
R. Salgado, M. Prezzi & H. Seo CPT-based design of displacement piles in siliceous sands
B.M. Lehane, J.A. Schneider & X. Xu Recent advances in designing, monitoring, modeling and testing deep foundations in North America
C. Vipulanandan Current design practice for axially loaded piles and piled rafts in Germany
C. Vrettos
Recent advances in the analysis of pile foundation in China
M. Huang, F. Liang & Z. Li
Current status of deep and pile foundations in Korea
S. Jeong, C. Cho, D. Seo, J. Lee, H. Seol, Y. Kim & J. Lee
Trend of research and practice of pile foundations in Japan
T. Matsumoto, P. Kitiyodom & T. Shintani Axial and lateral bearing capacity of piles
Vertical bearing capacity of large diameter steel pipe piles
Y. Kikuchi, M. Mizutani & H. Yamashita
Back analysis of Tokyo port bay bridge pipe pile load tests using piezocone data
J.A. Schneider, D.J. White & Y. Kikuchi
Pile foundation design of the connecting bridge for New-Kitakyushu airport
H. Ochiai, N. Yasufuku, Y. Maeda & S. Yasuda
Numerical prediction of long-term displacements of pile foundation
K. Danno, K. Isobe & M. Kimura
Side resistance of piles considering strain levels
M. Suzuki, M. Shirato, S. Nakatani & K. Matsui
V Evaluation of vertical and lateral bearing capacity mechanisms of pile foundations using X-ray CT
K. Morita, J. Otani, T. Mukunoki, J. Hironaka & K.D. Pham
Dynamic and static horizontal load tests on steel pipe piles and their analyses
P. Kitiyodom, T. Matsumoto, K. Tomisawa, E. Kojima & H. Kumagai
Press-in piling technology: Development and current practice
M. Motoyama & T.L. Goh
Centrifuge modelling of the base response of closed-ended jacked piles
A.D. Deeks & D.J. White
Development on battered pile with screw pile method (NS-ECO pile)
A. Komatsu
BCH method applicable to the construction under overhead restrictions
S. Tajima, T. Yoshikawa, S. Saito, H. Kotaki & M. Koda
Mechanical joint “KASHEEN” for large-diameter steel pipe piles
G. Mori & H. Tajika
Vertical bearing capacity of bored pre-cast pile with enlarged base considering diameter of the enlarged excavation around pile toe
K. Kobayashi & H. Ogura
Seismic performance of a group-pile foundation with inclined steel piles
K. Okawa, H. Kamei, F. Zhang & M. Kimura
Development of design method for a soft landing breakwater with piles
Y. Kikuchi
Settlement and load-sharing of a piled raft foundation combined with grid-form soil-cement walls on soft ground
K. Yamashita & T. Yamada
Earthquake resistant reinforcement method for pile foundations using effect of confinement of ground solidification body
Y. Adachi, K. Urano, T. Takenoshita, N. Tanzawa & M. Kawamura
A design approach for composite ground pile and its verification
K. Tomisawa & S. Miura
A study of reinforcing methods for existing bridges on soft ground with a solidification improvement
H. Fukada, K. Kato, N. Segawa, T. Ooya & Y. Shioi
Development of sheet-pile foundation combining footing with sheet-piles
H. Nishioka, M. Koda, J. Hirao & S. Higuchi
Recent technology development of steel pipe sheet pile foundation in Japan
T. Katayama
Development of three-dimensional frame analysis method for H-joint Steel Pipe Sheet Pile foundation system
M. Kimura, K. Isobe & Y. Nishiyama
Development of a composite pile system consisting of soil cement columns and H-beams
O. Kaneko Application of highcapacity micropiles for seismic retrofitting in Japan
Y. Otani & M. Hoshiya
Field experiment on installation of suction foundation
H. Yamazaki, H. Yoshinaga & K. Kaneda
Sample of proposal in consulting services using new technology/methods
M. Komatsu
Bearing capacity and settlement behavior of the spread foundation building on improved ground by non-vibratory sand compaction pile method
H. Yoshitomi, T. Ohnishi, Y. Yoshinari & T. Umeno
Centrifuge model tests on deep mixing column failure under embankment loading
M. Kitazume & K. Maruyama
Load transfer and failure mechanisms in the reinforced ground beyond vertically loaded pile
J. Hironaka, T. Hirai, Y. Watanabe & J. Otani
Ground improvement for the second phase construction of Kansai International Airport
Y. Morikawa, T. Tabata & T. Emura
Seismic design specifications for Japanese highway bridge deep foundations against large earthquakes
M. Shirato & S. Nakatani
New seismic design concept for port facilities
T. Sugano & T. Tanaka
Centrifuge tests on pile foundation-structure systems affected by liquefaction-induced soil flow after quay wall failure
T. Tazoh, M. Sato, G. Gazetas & J. Jang
Mechanical behaviors of sandy ground during or after liquefaction
B. Ye, A. Yashima, G.L. Ye & F. Zhang
Author index
Advances in Deep Foundations – Kikuchi, Otani, Kimura & Morikawa (eds) © 2007 Taylor & Francis Group, London, ISBN 978-0-415-43629-8
Preface
The emerging design methodology Reliability-Based Design has become today’s norm in Japanese structural design codes and will soon be included in the international standard codes. To meet this trend, methods for the design and construction of deep foundations have made large advances. As deep foundation construction is one of the most important and applied executions in geotechnical engineering worldwide, both research work by academics and the experience and ideas of practitioners are required to develop this field and meet future stan- dards.
The International Workshop on Recent Advances in Deep Foundations (IWDPF07, Yokosuka, Japan, 1–2 February 2007) was held to transmit the information on recent advances in deep foundations to an international audience and to provide academics and practitioners the opportunity to discuss the latest developments.
Every year more than thousand technical papers are presented at the Japanese National Conference on Geotechnical Engineering, but most of these articles are unfortunately not transmitted to other countries. As structural design codes are nowadays written with international standards, a significant amount of useful infor- mation would get lost if this information would not be published in a medium that is accessible to an interna- tional audience. For this reason, the IWDPF07 workshop has been focused on collecting the contributions that present Japanese technologies and experiences which are of interest to a broad, international audience. The result of this effort, this proceedings volume, comprises nine keynote lectures, prepared by outstanding inter- national experts and 34 technical papers. In addition to papers on recent research achievements and on case his- tories, a significant number of the technical papers is dealing with the practical development of deep foundations, seismic design methods, liquefaction problems, and ground improvements.
This workshop was held with the support of the Port and Airport Research Institute (PARI) and the Japanese Geotechnical Society (JGS). The research committee of JGS – “On the concept for evaluation of new technol- ogy on foundation structure design” – is the mother body of this workshop. We would like to express sincere gratitude to both organizations and the committee for their strong support of this workshop.
The editors hope that these proceedings will be interesting and fruitful to researchers and practitioners who are active in the development of deep foundation design methods and construction methods.
Yoshiaki Kikuchi
Co-chairman of IWDPF07
IX
Advances in Deep Foundations – Kikuchi, Otani, Kimura & Morikawa (eds) © 2007 Taylor & Francis Group, London, ISBN 978-0-415-43629-8
Organizing Committee Co-Chairmans
Dr. Yoshiaki Kikuchi, Port & Airport Research Institute Prof. Makoto Kimura, Kyoto University
Secretary
Dr. Yoshiyuki Morikawa, Port & Airport Research Institute
Members
Prof. Jun Otani, Kumamoto University Dr. Masahiro Shirato, Public Works Research Institute Dr. Kouichi Tomisawa, Civil Engineering Research Institute for Cold Region Dr. Hisashi Fukada, Fudo Tetra Corporation Dr. Ken-ichi Horikoshi, Taisei Corporation Mr. Masataka Tatsuta, Nippon Steel Corporation
Research Committee on the Concept for Evaluation of New Technology on
Foundation Structure Design (JGS) ChairmanProf. Makoto Kimura, Kyoto University
Secretary
Dr. Hisashi Fukada, Fudo Tetra Corporation
Members
Mr. Jiro Fukui, Public Works Research Institute Dr. Yozo Goto, National Research Institute for Earth Science and Disaster Prevention Mr. Motohisa Hara, Penta-Ocean Construction Dr. Ken-ichi Horikoshi, Taisei Corporation Mr. Akio Inoue, Obayashi Corporation Dr. Yoshiaki Kikuchi, Port & Airport Research Institute Dr. Masayuki Koda, Railway Technical Research Institute Mr. Masataka Komatsu, Japan Bridge & Structure Institute, Inc Mr. Yoshinobu Miura, Kyushukensetsu Consultant Dr. Katsunori Okawa, Mitsubishi Heavy Industries, Ltd.
Prof. Satoru Ohtsuka, Nagaoka University of Technology Prof. Jun Otani, Kumamoto University Dr. Masahiro Shirato, Public Works Research Institute Mr. Shinichi Tajima, Kajima Corporation Mr. Masataka Tatsuta, Nippon Steel Corporation Dr. Takashi Tazoh, Shimizu Corporation Mr. Kouichi Tomisawa, Civil Engineering Research Institute for Cold Region Mr. Kiyoshi Yamashita, Takenaka Corporation Prof. Feng Zhang, Nagoya Institute of Technology
Keynote lectures
Advances in Deep Foundations – Kikuchi, Otani, Kimura & Morikawa (eds) © 2007 Taylor & Francis Group, London, ISBN 978-0-415-43629-8
3
1 INTRODUCTION
1.1 Motivation for pile jacking technology The expansion of urban development into increas- ingly marginal sites, and the invention of new pile construction techniques, make the economics of deep foundations increasingly attractive. Recent techno- logical improvements have led to a proliferation of pile types and installation methods. Displacement piles, driven into the ground by hammering or vibration, remain widely used for offshore and nearshore foun- dations. For onshore foundations, non-displacement piles have increased in popularity during the past 50 years since these can be installed without the noise and vibration associated with conventional methods of pile driving.
Increasingly stringent environmental legislation now precludes the use of pile hammers in urban areas, and restricts the disposal of spoil created by the con- struction of conventional bored piles. In response, alternative construction methods for pile foundations have evolved. These developments have been driven by a desire either to improve the performance of the foundation or to reduce the environmental impact of its construction. Performance is quantified by the strength and stiffness of the foundation. Noise, ground vibrations and spoil material (particularly from urban brownfield sites) all have negative environmental impacts.
One such new construction technique is pile jacking, which is the subject of this review paper. Pile jacking has historically been used for the construction of small foundation piles, as are used for minor underpinning works. More recently, high-capacity jacking machines have been developed, which offer the opportunity for the foundations of large buildings or heavy structures to be installed without the noise and vibration associated with conventional methods of displacement piling. Some pile jacking systems can be supported on the pile wall under construction, rather than a piling mat, which reduces the need for temporary works leading to shorter construction schedules and reduced material use.
For displacement piles, the installation method – jacking, or dynamic driving – has an effect on the deformation of the soil during installation, and the resulting stress field around the pile. In turn, these fac- tors affect the pile behaviour during subsequent load- ing. In design practice, the effect of installation method is rarely considered when assessing the response of a pile foundation. In some cases, design codes and research papers recommend empirical factors to differ- entiate between the capacity of bored and driven piles (e.g. Bustamanate & Gianeselli 1982, De Beer 1988, Ghionna et al. 1993) but as pile jacking is a relatively new technology little advice exists for predicting the behaviour of jacked piles.
In addition to the short-term impact of noise and vibration during the construction process, the
Recent research into the behaviour of jacked foundation piles D.J. White Centre for Offshore Foundation Systems, University of Western Australia, Perth, Australia Cambridge University Engineering Department, UK A.D. Deeks Cambridge University Engineering Department, UK
ABSTRACT: Pile jacking technology uses static jacking force to install large pre-formed displacement piles without the noise and vibration associated with dynamic piling methods. Recent research into the mechanisms governing the shaft and base resistance of displacement piles is reviewed, and the differences between jacked and driven piles are highlighted. Methods for predicting the resulting pile stiffness and capacity are described, within the framework of recently-developed CPT-based prediction methods. Compared to driven piles, jacked installation leads to enhanced plugging and residual base load, and reduced friction fatigue. The resulting axial response is stiffer and can be stronger than an equivalent driven or bored pile. Recent applications of jacked H-piles to support axial load are reported, and a novel technique for optimising the ratio of axial capacity to installation force via plugging is described. environmental impact of foundation construction extends to the energy and resource use prior to instal- lation, and subsequent to the initial working life of the foundation. If dynamic installation is discounted in urban areas due to the unacceptable ground vibra- tions, the choice between jacked or bored installation methods is linked to the choice between steel or con- crete piles. The extraction and re-use of steel piles, which is made possible by pile jacking rigs, reduces the whole life cost of this type of foundation (Dawson, 2001, Chau et al. 2006).
If the environmental benefits of pile jacking are to become more widely exploited, research into the influence of installation method on pile behaviour must be disseminated amongst practitioners to estab- lish this knowledge in engineering practice.
This paper reviews recent research into the behav- iour of piles installed by jacking. The following topics are covered:
1. Pile jacking technology and the environmental impact of pile jacking compared to alternative pile construction techniques;
2. Recent research into the fundamental mechanisms underlying the installation and loading of dis- placement piles;
3. Recent guidance for predicting the axial capacity and load-settlement response of piles, with emphasis on the differences between driven and jacked piles;
4. Recent research into the use of H-piles, focussing on differences in behaviour of jacked and driven piles due to plugging. A significant proportion of the research reported in this paper is related to the ‘press-in’ method of pile jacking, reflecting the authors’ experiences in a long-term research programme at the University of Cambridge supported by Giken Seisakusho Co. Ltd. However, key outcomes from other major research projects into jacked piles are also reported.
Figure 1. ‘Silent piler’ jacking machines.
1.2 Machine development in the UK in 1960 for the installation of sheet piles. Pre-formed displacement piles can be installed by This machine stood on top of a row of sheet piles, and static jacking force alone if sufficient reaction force is gained reaction from a pair of piles on either side of available. Small rigs capable of pushing micro-piles the pile currently being jacked downwards. into the ground for underpinning are in wide use. The first machine of the type now referred to as a Reaction force is usually provided by the weight of ‘Silent Piler’ was produced by Giken Seisakusho the structure being underpinned. Co. Ltd. in 1975. This type of machine ‘walks’ along
Modern pile jacking machines operate by pushing the row of piles under construction, gaining reaction the pre-formed pile – made from steel or precast con- by gripping the previously-installed piles – an approach crete – into the ground with hydraulic rams, using which has been termed the ‘press-in method’. static force alone. Reaction is provided either by kent- Different types of Silent Piler are capable of installing ledge (deadweight) or by gripping the heads of adja- sheet piles (Fig. 1a), tubular piles (Fig. 1b) or precast cent piles that have already been installed. concrete piles.
The first large pile jacking machine was the An alternative to the ‘self-walking’ approach is Taylow Woodrow ‘Pilemaster’, which was developed to hang the hydraulic unit from the leader of a conventional piling rig, as used by the 2 MN capacity ‘Push-pull’ system produced by Dawson Construc- tion Plant Ltd, UK (Fig. 2). This system has been used for the installation of small groups of piles which act in unison as a single larger pile after construction (Filip 2006).
Since the Pilemaster, the Silent Piler and the Push- pull systems gain reaction from previously-installed piles, only closely-spaced groups of piles or continu- ous walls can be installed by these methods. An alter- native approach is to gain reaction force from either the deadweight of the machine, additional ballast or temporary ground anchors.
The use of a deadweight-reaction pile jacking machine was reported in Russia by Goncharov et al. (1964) (Fig. 3). The 350 kN weight of the tractor units of this machine was used as reaction force to drive precast concrete piles into clayey soils. More modern pile jacking machines that rely on kentledge for reac- tion are manufactured by Tianhe Machinery Ltd, China, and have been exported to Malaysia and Australia, where they are known as the ‘G-pile’ system (Fig. 4). The jacking unit of this machine can move horizontally within the footprint of the ballast, so multiple piles can be installed without unloading the deadweight.
The largest pile jacking machines of the Silent Piler type have a jack capacity of ⬃4 MN but weigh only ⬃400 kN. The largest Silent Pilers can install tubular piles of up to ⬃1.5 m diameter in strokes of length ⬃ 1 m. The largest G-pile machine has a jacking capacity (and a deadweight) of ⬃9 MN and can install
400 mm square precast concrete piles in 1.8 m jack strokes. When comparing these systems, the additional jacking capacity of the G-pile machine is offset by the operational complexity of moving 900 tonnes of dead- weight around a site. A substantial piling mat is needed for soft ground sites. The mean bearing pressure exerted by the fully loaded 9 MN G-pile machine dur- ing movement of the jacking unit is ⬃300 kPa. In con- trast, the ‘self-walking’ feature of the Silent Piler system extends to specially-designed pitching cranes and power packs. The resulting system requires no temporary works since all equipment is supported on the pile wall under construction (Fig. 5).
1.3 Applications of pile jacking Most current design guidance for the axial and lateral response of piles has been derived from experience with dynamically driven or bored piles. As new installation
Figure 2. ‘Push-pull’ rig-mounted pile jacking unit (Filip 2006).
Figure 3. Early Russian jacking unit (Goncharov et al. 1964).
Figure 4. Deadweight-based pile jacking system (GEO 2006). techniques have been developed, such as pile jacking, designers are required to assess whether current guidance is applicable, or whether modified methods are appropriate to reduce risk or exploit improved performance.
The installation method of a pile determines the stress state and level of disturbance of the soil imme- diately surrounding the pile, as described in Section 3 of this paper. These stresses and disturbance have a significantly influence on the axial response of the pile under working conditions. In contrast, the instal- lation method has less effect on the lateral response of the pile. During lateral loading, the strength of more distant soil is mobilised, which is unaffected by the installation method.
Therefore, jacked piles have been widely adopted for laterally-loaded applications such as retaining walls supporting river banks and excavations, designed by conventional methods. Long linear projects, such as riverbank reinforcement, are particularly suited to ‘self-walking’ pile jacking systems due to the elim- ination of temporary works. Case studies describing recent applications of pile jacking systems for appli- cations involving lateral loading are reported by Dubbeling et al. (2006).
In contrast, for axially-loaded applications, such as building or bridge foundations, designers have been cautious in adopting pile jacking technology, due to concerns that the installation procedure may not lead to the same capacity as conventional dynamic instal- lation methods. This uncertainty has been reduced by recent research programmes involving axial load test- ing of jacked piles.
Recent case studies in which jacked piles have been used to support axial loads are reported by Li et al. (2003), Mitchell & Mander-Jones (2004), White et al. (2003), Filip (2006) and Lehane et al. (2003).
A beneficial feature of pile jacking is that the installation force provides an indication of the static bearing capacity during subsequent loading. As dis- cussed later, it is important to recognise that consoli- dation and ‘set-up’ can cause changes in capacity after installation. Usually these effects lead to an increase in capacity, but in certain circumstances a loss of strength has been observed. Most pile jacking systems include direct measurement of the applied jack load during installation, and some systems have specific features to allow static maintained load tests to be conducted after installation, providing verifica- tion of the pile performance.
An additional requirement in order for jacked piles to be adopted for axially-loaded applications is the need for new acceptance or termination criteria in regions where the capacity of a pile must be con- firmed at the completion of driving. Hammer-driven piles are conventionally installed to a specified set per blow as confirmation – based on a dynamic pile driv- ing analysis – that the design capacity and stiffness requirements have been met.
2 ENVIRONMENTAL IMPACT
2.1 Noise emissions Noise emissions on construction sites present a health hazard to site operatives and cause annoyance to neighbours. Noise levels are expressed in decibels, which are related to the fluctuating air pressure, p (Equation 1).
Noise levels typically decrease with the logarithm of radius, r, from their source, due to spherical geo- metric spreading. The noise level of a source, N
source
, can be attenuated using Equation 2 to deduce the noise level, N, at a remote point (Sarsby 2000).
Guidance on acceptable noise levels during con- struction is given by British Standard BS5228 (1992). In urban areas N should not exceed 75 dB at the out- side of a noise sensitive building such a residential or office building. In rural areas a lower limit of 70 dB applies.
Noise emissions from traditional dynamic or vibra- tory piling rigs have been reduced in recent years through the development of improved cushioning and Figure 5. ‘Self-walking’ system without temporary works. isolation systems. In Figure 6, various environmental noise levels are compared with the source noise levels, N
source
, of typical piling equipment, including recent ‘quiet’ hammers and pile jacking machines. The human ear perceives a 10 dB increase in noise level as a doubling in loudness so the logarithmic scale obscures the true variation.
By plotting the theoretical attenuation of noise with distance (Equation 2), an indication of the min- imum acceptable separation is found. Modern ‘quiet’ hammers are rarely acceptable in congested urban areas, but are increasingly used for new-build devel- opments, where the minimum separation limits can be satisfied. The noise emissions from pile jacking machines do not exceed ambient urban noise.
2.2 Ground vibration Design codes specify limits on the permissible ground vibrations from construction operations. These limits are intended to prevent disturbance to people and damage to nearby structures. The limits preclude the use of conventional dynamic piling methods in certain locations, particularly urban areas.
Ground vibrations are usually quantified by the peak velocity of particles in the ground as they are disturbed by the passing wave. The instantaneous particle velocity consists of three orthogonal components which are usu- ally measured independently using a triaxial geophone. The most commonly used definition of peak particle velocity is the simulated resultant ppv. This is the vector sum of the maximum of each component regardless of whether these component maxima occur simultan- eously (Hiller & Hope, 1998).
Eurocode 3 (1992) provides guidelines for accept- able human exposure to ground vibrations depending on the length of the construction period (Fig. 7a). Structural damage thresholds are also specified, ran- ging from a ppv of 2 mm/s for buildings of architectural merit, to 15 mm/s for industrial buildings (Fig. 7b).
Ground vibration measurements near to pile jack- ing operations have been reported by Li et al. (2003), Rockhill et al. (2003) and White et al. (2002) (Fig. 8). The primary source of these vibrations is the elastic rebound of the pile head when the jacking load is released at the end of each stroke. If the pile is deviat- ing during installation, lateral vibration can result in addition to upwards movement.
Good operational practices can reduce these sources of ground vibration. For example, the Silent Piler sys- tem allows the jacking force to be reduced in a con- trolled manner at the end of a downstroke, and a skilled operator can correct for any deviation before releasing the pile head. Figure 9 shows the time record of ground vibrations during installation of a sheet pile using a Silent Piler jacking machine. Negligible vibra- tions are recorded whilst the pile is moving but four transient pulses are evident between jacking strokes. The largest of these events correspond to the opening and closing of the chuck that grips the pile, and from
Figure 6. Noise limits and emissions from piling operations.
Figure 7. Maximum acceptable transient ground vibrations. Figure 8. Ground vibrations near pile jacking operations.
Figure 10. Ground vibrations near pile driving operations.
Equation 3 (Attewell & Farmer (1973), BS5228 (1992), Eurocode 3 (1992)).
The constant A in Equation 3 depends on the proper- ties of the medium and the initial energy of the wave. If the medium is non-dissipative, the index n refers to the geometry of the wavefront. Geometric spreading of a cylindrical wavefront leads to n ⫽ 0.5, whilst for geometric spreading from a point source n ⫽ 1. Empirical guidance for the selection of A for dynamic pile driving methods is given by Eurocode 3 (1992), based on hammer energy and soil type. A value of n ⫽ 1 is recommended, reflecting that at relevant dis- tances from the pile, the upper portion from which the vibrations radiate is best idealised as a point source.
For the jacked pile data shown in Figure 8, Rockhill et al. (2003) proposed a bilinear fit as a sim- ple predictor for ground vibrations induced by pile
Figure 9. Ground vibration measurements during sheet jacking, linking ppv to the log of separation, r
pile installation using a Silent Piler jacking machine.(Equation 4). Close to the pile, the bilinear fit uses an index of n ⫽ 0.5, reflecting that the pile is better rep- resented as a line source at this close proximity. the impulse of hydraulic force at the start of the jack-
Further away, the index reverts to n ⫽ 1, indicative of ing stroke. spherical geometric spreading. For comparison, a database of previously pub- lished measurements of ground vibrations during dynamic piling is shown in Figure 10 (Head & Jardine, 1992). Figures 7–8 and 10 are plotted on iden- tical axes. The measured ground vibrations reduce in
By combining Equation 4 with the Eurocode 3 limits, an approximately linear fashion with log radius. A an indication of the minimum separation between pile number of empirical methods for predicting ground jacking and sensitive structures can be assessed. For vibrations follow this trend, taking the general form of residential structures this intersection corresponds to a nominal separation of around 0.5 metres. However, for practical purposes, the minimum separation is more likely to be limited by logistical constraints than the transmission of ground vibrations. For a separa- tion greater than a few metres, the ground vibrations from pile jacking are indistinguishable from vibra- tions arising from passing traffic and other construc- tion plant such as generators.
2.3 Sustainability: material and energy use In urban areas the most commonly-used pile material is concrete, due to the low cost of bored piling and the unsuitability of pile hammers. The recent introduction of high capacity jacking machines has made steel piles a feasible solution for urban areas, and the choice between steel and concrete is once again available.
s
vo
(as the pile base passed that horizon) more recently than the in situ stress σ⬘
bf
, experienced the load q
sf
, taking due account of the mechanisms that occur as the soil passes around the base of the advancing pile. Since the soil adjacent to the pile shaft, which governs τ
t
to q
sf
Instead, it is increasingly common to link τ
, but correlations between these parameters are hampered by the unreliability of sleeve friction measurements, which are often affected by wear and alignment of the sleeve, and by the reso- lution of subtraction cone devices.
sf
, is analogous to the unit shaft resistance, τ
. The relative size of the pile and the CPT must be accounted for, as discussed in Section 3.3. The CPT sleeve friction, f
As raw materials become scarcer, and environmen- tal concerns related to excessive energy use emerge, the choice between steel and concrete is increasingly influenced by environmental factors. In certain regions, these factors are having an increasing effect on the economics of construction through environmental taxes imposed by legislation.
bf
, and in turn this can be linked to the subsequent static base resistance at failure q
bf,install
, can be linked to the base resistance during installation, q
t
If a jacked pile is considered analogous to a CPT, then the CPT tip resistance, q
Most modern pile design methods directly link CPT parameters to pile capacity, taking advantage of their similar geometry and installation processes (Fig. 11). This analogy is particularly appropriate for jacked piles, which are installed by static force – in the same way as a CPT – in contrast to the dynamic installation of driven piles.
3.1 Pile – CPT analogy for design As discussed in Section 1.3, the installation method of a pile determines the stress state and level of disturbance of the soil, which in turn has a significant influence on the subsequent strength and stiffness under axial load. This section describes a simple framework for describing the stress changes that take place around a jacked or driven pile during installa- tion. This framework provides a simple basis on which to (i) formulate prediction methods for the strength and stiffness of jacked piles and (ii) under- stand how the installation process of a jacked pile can be optimised to maximise the axial strength and stiff- ness (or reduce the required jacking capacity).
3 INSTALLATION AND AXIAL CAPACITY
The facility to remove steel piles – unlike bored concrete piles – and release the site for subsequent alternative development is an additional consider- ation when comparing the long term impact of founda- tion piles (Dawson 2001).
emissions provide additional indica- tors to guide material selection, although standard input parameters and procedures for life cycle analy- sis assessments are not widely established.
2
Chau et al. (2006) describe a case study comparing the embodied energy of steel and concrete retaining wall systems. For the conditions considered, it was found that the embodied energy of a steel sheet pile wall is halved by the use of recycled steel, and is the optimal solution – from an embodied energy view- point – compared to reinforced concrete systems. Other indicators of environmental impact such as the embodied CO
Unlike concrete, steel piles can be easily recycled, although re-use in situ remains an option (Chapman et al. 2001). Embodied energy is a common indicator used to assess the energy use of an object or structure. In the case of foundation piles, this quantity includes the energy used to extract and process the raw mater- ials, then transport and install the foundations. For recycled steel piles the embodied energy is substan- tially reduced.
, it is Figure 11. Nomenclature for CPTs and piles. more logical to estimate shaft capacity from q
t
v
during a subsequent load test: (i) During installation, local heterogeneities in ground condition are smoothed out by the large size of a pile compared to a CPT. The zone of deformation around the base of a pile is larger than around a CPT, in proportion to the effective diameter of each. Measurements of q
t
are there- fore more sensitive to local variations in ground condition. (ii) The combined effects of the differences in diam- eter and penetration rate of a pile compared to a
CPT may lead to different drainage conditions. The degree of drainage during steady penetration is governed by the dimensionless group vD/c
v
, where v ⫽ penetration rate, D ⫽ diameter and c
is the relevant coefficient of consolidation. The diameter of a pile is typically an order of magni- tude larger than a CPT (D
during jacking, and q
CPT
⫽ 35.7 mm), whereas the installation rate of jacking machines is comparable to a CPT (v
CPT
⫽ 20 mm/s). There- fore, at sites where the CPT is drained, pile instal- lation may be partially drained, causing excess pore pressure generation and a difference in pene- tration resistance compared to a CPT.
(iii) During static loading after installation, the plunging, or steady penetration resistance may
Figure 12. Stages in the loading history of a soil element adjacent to a jacked pile.
bf
bf,install
than from σ⬘
, q bf
vo using a classical earth pressure method.
This approach of breaking down the stress history of a soil element during pile installation is described in detail by Poulos (1988) and White (2005), and is summarised below.
3.2 Soil element ‘life cycle’ for drained
penetration (installation in sand)
The key stages in the stress history of a soil element close to a jacked pile are illustrated in Figure 12. A simple stress path to represent these changes is given in Figure 13. These diagrams represent the case of drained installation – in a sandy soil – so neglect pore pressure effects. Each stage is described in sequence below.
3.3 Base resistance, q bf,install
3.3.1 Mechanisms linking q t
and q
, q bf,install , q bf
A soil element that will be in contact with the pile shaft after installation initially lies beneath the pile tip. As the pile or CPT tip approaches, the local stress rises from the in situ value until a stress of q
bf,install
or q
t
acts as the pile or CPT tip reaches that point. The following mechanisms can lead to differences between the profiles of q
t
Figure 13. Loading history of a soil element adjacent to a displacement pile. not be fully mobilised if q is defined by a settle-
bf
ment criterion. However, due to the high base stiffness of jacked piles (described in Section 4), the plunging base capacity is usually mobilised at the conventional settlement criterion of D/10.
3.3.2 Field measurements linking q c bf,install and q Field measurements at sand and clay sites generally indicate that a unit resistance similar to the CPT tip resistance is mobilised on the base of a closed-ended or plugged pile during jacked installation, such that α ⬃1 in Equation 5: where q is the CPT tip resistance, suitable averaged
t,av
over a vertical range, to account for the effect of local heterogeneities. At uniform sites a simple arithmetic average of q over a vertical range of ⫹/⫺1.5D is
Figure 14. Plug resistance during open-ended pile jacking t widely used to derive q (Randolph 2003, Jardine (Lehane & Gavin 2001). t,av
et al. 2005 and White & Bolton 2005). However, Xu & Lehane (2005) show that for sites with a strongly layered stratigraphy it is more appropriate to use the ‘Dutch Method’ (Van Mierlo & Koppejan 1952, Schmertmann 1978). This method gives additional weighting to regions of weaker soil, to which the deformation during penetration will be attracted.
Field tests reported by Dingle et al. (2007) showed that the Dutch method gave a lower bound prediction to q for a 320 mm diameter closed-ended tubu-
bf,install lar pile at a highly layered site in Japan. Lehane et al.
(2003) report measurements of q for a 350 mm
bf,install
square precast concrete pile installed through sands and silty clays. It was found that q was ⬃80%
bf,install
of the raw q profile, but in closer agreement with q
t t,av
found using the Dutch method. Good agreement between q and q has also been reported by
bf,install t
Chow (1997) and Lehane (1992) during installation of a 100 mm diameter closed-ended instrumented jacked pile at relatively uniform sites.
Figure 15. Annular resistance during open-ended pile
A plug usually forms within an open-ended jacked jacking (Lehane & Gavin 2001). pile after a few diameters of penetration, unless spe- cial measures are used, such as vertical cycling penetration, q /q
⬃1, but reduced values are
b,plug c
(‘surging’), water jetting, internal augering or the use measured with increasing incremental filling ratio of an internal pile shoe. During further jacking the (IFR) (Fig. 14). This observation confirms that when pile remains fully plugged unless a stronger layer is the internal shaft resistance is insufficient to hold the reached, at which point the penetration reverts to a plug in place against the steady penetration resist- coring manner until sufficient additional plug length ance, q , soil flows into the pile, lengthening the plug.
t
is mobilised to balance the increase in base resistance After sufficient lengthening, the increased internal (White et al. 2000, Randolph et al. 1991). shaft resistance balances the penetration resistance, It is difficult to measure the base resistance acting q , and the incremental filling ratio reverts to zero.
t
on the enclosed soil plug of an open-ended pile dur- Lehane & Gavin’s (2001) data of annular resist- ing installation. Lehane & Gavin (2001) present ance, q , confirms that the full local CPT resist-
b,ann
measurements of annular and plug resistance during ance, q is mobilised on the steel area of the pile
t
installation and load testing of a heavily instrumented (Fig. 15). It is usual to assume the same for open-section model jacked pile in sand. During fully plugged H-section or sheet piles.
A back-analysis by White et al. (2000) showed that a vertical arching analysis, following De Nicola & Randolph (1997), can capture the plugging behaviour of a pipe pile during jacking. However, the arching equations are very sensitive to the assumed profile of earth pressure coefficient within the soil plug. For most practical dimensions of tubular pile, a plug will form during jacking, and so the installed pile can be considered as closed-ended under subsequent static loading. This behaviour contrasts with dynamic pile installation methods, during which the inertia of the soil within the pile prevents formation of a plug (Liyanapathirana et al. 2001).
bf
Figure 16. Plugging and buckling of an H-pile (Li et al. 2003).
Compared to driven piles, jacked piles exhibit a stiffer base response – and a greater base capacity if defined by a settlement criterion – due to the stiffen- ing effect of the final jacking stroke and the resulting residual base load. For closed-ended driven piles in sand, the UWA-05 design method recommends a value of α ⫽ 0.6 in Equation 5 (Lehane et al. 2005a).