Deep Foundations and Geotechnical In Situ Testing

Theoretical and experimental studies on the bearing capacity and deformation characteristics of uplift piles have received much attention due to extensive use of uplift piles in underground structures in soft ground. Shanghai World Expo 500kV Underground Transformer Substation and Shanghai Hongqiao Comprehensive Transportation Hub are typical examples. Both types of uplift piles, i.e. uniform-section piles with side-grouting and enlarged-base piles, are often used in engineering practice. Despite of their extensive applications, theoretical studies have lagged far behind engineering practice. Presented in this paper was a comprehensive study on the simplified method for predicting the ultimate bearing capacity of enlarged-base piles with various pile lengths before and after deep excavation, and load-displacement responses of uniform-section piles with side-grouting based on the load transfer method. The good agreement between theoretical predictions and field pile load test results was obtained. The proposed method provides reliable estimates in a simple way for the bearing capacity and deformation characteristics of uplift piles.

This paper presents a case history of design and performance of a piled raft supporting a 162 m high residential tower. The 47-story building is a reinforced concrete structure and the average contact pressure over the raft is 600 kPa. The raft is founded on diluvial sand-and-gravel at a depth of 4.3 m below ground surface. Because the building has a base isolation system, differential settlement of the foundation is rigorously restricted. To reduce the differential settlement, a piled raft foundation consisting of thirty-six 50-m long cast-in-place concrete piles was adopted. To confirm the validity of the foundation design, field measurements were performed on the settlement of the foundation, axial loads of the piles, contact pressures between raft and soil and pore-water pressure beneath the raft from the beginning of construction to eight months after the end of construction. Based on the field measurement results, the foundation design was found to be appropriate.

In this paper effect of pile configuration and loading type on piled raft foundations performance was studied. The parametric study presented in this research work was carried out with a computer program ELPLA. Three basic pile configurations and three load distribution types were considered and the effect of loading type for each pile configuration on maximum moment in the raft, piles bearing factor (percentage of total load carried by piles) and piled raft settlement was studied. Pile configuration 1 has the pile uniformly distributed under whole raft area. Pile configuration 2 has piles under central area of the raft as well as under the edges of the raft. In pile configuration 3 the piles are placed only in the central area of the raft. It has been found that pile configuration and load distribution are very important and effective in piled raft settlement, maximum moment and piles bearing factor.

On the soft grounds, effects of consolidation on performance of the system of piled rafts as well as superstructures cannot be overlooked due to nonlinear interaction characteristics. Conventional methods of engineering design and numerical procedures of two-dimensional interaction analysis cannot realistically simulate loading and deformation mechanism of the interaction system and cannot completely predict variations of deformations and internal forces of both structure and piled raft foundation. Therefore in order to well understand long-term behavior of the interaction system, time-dependent effect of soil deformations on performance of the interaction system of piled rafts and foundations as well as superstructure is evaluated in this paper. The nonlinear deformation and strength behavior of foundation soils are taken into account by using the elasto-plastic constitutive model based on Mohr-Coulomb's yield criterion while the consolidation effect of subsoil under loading is incorporated by numerically solving the coupling Biot's equations of consolidation. Numerical analyses are conducted for the structure-raft-foundation interaction system by using the finite element methods. Based on numerical analyses for a given interaction system, both the features of variation in time of internal forces, settlements and the characteristics of compatibility mechanism of interaction system are examined. It is shown that both nonlinear behavior of soft soils and consolidation characteristics of foundation remarkably affect the time-dependent performance of the interaction system. Such dependency is intimately related to variation of excess pore water pressure of subsoil.

As the first large-scale wind farm of Asia, the wind turbine foundation of Donghai-bridge Offshore wind farm is in possession of the following four engineering characteristics such as marine structure, tower structure foundation, dynamic equipment foundation and complex soft subgrade foundation, which makes the foundation design a key technical issue. The common issues of offshore wind turbine foundation design are discussed in this paper. , while the characteristics of wind turbine foundation, the nonlinear dynamic interaction of foundation and subgrade, dynamic simulation of the system comprised of wind turbine-tower-subgrade-foundation and the fatigue analysis of foundation structure are emphatically analyzed.

This paper proposes a simple method to include superstructure stiffness in foundation analyses. The method involves extracting a small "condensed structural matrix" from finite element models of the superstructure, which can then be incorporated into pile group or piled raft analyses using common approaches such as elastic continuum or load transfer methods. The matrix condensation method directly couples structural and geotechnical analyses, and eliminates the need for iterative analyses between structural and geotechnical engineers. Effectiveness of the approach is illustrated through analyses of several buildings designed with a typical floor plan but with varying heights. The parametric study illustrates that superstructure stiffness can have a significant influence on foundation settlement estimates, and the stiffening effects are dominated by the lower stories of the superstructure. The proposed method aims to bridge the gap between structural and geotechnical analyses. Also, being a computationally simple and accurate approach, it is applicable to parametric or optimization studies that would otherwise involve large amounts of analyses.

Two phenomena characterize cyclic axial loaded piles: accumulation of plastic pile displacements and degradation of pile capacity with increasing load cycles. The reason for this complex pile-soil-interaction is still not well understood. Hence, load and displacement controlled small-scale model pile tests were performed to investigate pile and soil behaviour from a qualitative point of view. Particle Image Velocimetry (PIV) was used to visualize the grains movement near the pile. A volume change was generally observed in all the tests depending on the mode of cyclic load. Shear localization appears in a small shear zone parallel to the pile shaft and remains approximately constant with increasing load cycles. Next to the shear zone a shear band can be observed which expands outwards with increasing load cycles. Moreover, a different pile and soil behaviour was observed under cyclic load compared to the static load test.

Scour removes soil and reduces the capacity of a pile foundation, and thus may cause instability of a bridge. An analysis of bridge response under scoured conditions requires consideration of water-soil-pile-structure interaction. However, limited research has been done to integrate the analysis of water-soil-pile-structure interaction for a bridge due to scour. In this study, an attempt was made to consider such integration. A pile group was treated as an equivalent single pile, and the nonlinear response between soil and the equivalent single pile was modeled usingp-y The curve. influence of water flow was considered by applying stream pressure to the bridge piers and the pile foundation at different scour depths. Interaction between the piles and superstructure was analyzed by performing iterative calculations of their respective stiffness matrices until convergence was obtained. Kansas Bridge 45 was selected as a case study for evaluation of a typical scour-susceptible bridge under scoured conditions. The results show that scour significantly increased lateral deflection of the pile head. Considering pile cap had positive effects on the decrease of the lateral deflection of the pile groups. The investigation was also made into the influence of boundary conditions of bridge abutment on the lateral bridge responses.

Micropiles are grouted and small diameter piles that are often used in foundation retrofit. Experimental evidences have indicated that micropiles behave well under seismic loading due to their high flexibility. Moreover, observations in the 1995 Kobe Earthquake indicate a good performance of friction piles under seismic loading. However, the seismic behavior of micropiles is not fully understood due to the limited number of full and model-scale tests, as well as the limited amount of numerical modeling studies for micropiles. This paper focuses on Finite Element modeling of single and micropile groups under both static and dynamic loading. The micropile/soil interface was modeled either with perfect bonding or with frictional interface elements. The lateral vertical boundaries of the soil were set up in such a way that the reflection of the arrival waves at the boundaries was avoided. The problem includes soil non-linearity, gapping and slippage between the micropile and the soil, complex boundary conditions and possible pile non-linearity. The structure is described by a single degree of freedom system composed of a concentrated mass and a column. The results of this study show the influence of micropiles inclination on dynamic amplification and on the seismic-induced internal forces in micropiles.

This study presents the results of modeling the soil-pile interaction phenomenon under acceleration-time history seismic loading. The studies are carried out for three sets of single piles with different diameters which consider the effect of gapping between soil and pile in more details. The Drucker-Prager soil constitutive law is used to model soil behavior while the behavior of the concrete piles is assumed to be elastic. Analyses were conducted by the commercial program ABAQUS 6.8 and the results were converted to the corresponding frequency magnitudes that are of more interest for the frequency dependent transfer and impedance functions regarding the kinematic and inertial interactions, respectively. The results showed that the effect of gapping on the kinematic interaction is to increase the displacement of the pile head compared to free-field. In addition, gapping causes reduction in the stiffness and damping of the system in general.

In this paper, nonlinear pile-soil-structure interaction under dynamic loads is formulated by using free-field soil analysis and beam on Winkler foundation. The free-field motions are calculated separately through a site response analysis using DYFRA program which was developed by the author to prepare the data in the form of displacement time history. Linear beam column finite elements are used to model the piles and structural elements. Nonlinear modeling of soil media is done by introducing a rational approximation to continuum with nonlinear interface springs along the piles. In order to calibrate the parameters used in the model and also verify the proposed formulation, the result of a shaking table tests are used. The numerical analyses-show good consistency with the test results, in terms of recorded spectral acceleration of soil layers and acceleration time history of superstructures above the piles.

The influence of pile geometry on internal sand movement around a laterally loaded pile was visualized in this paper by utilizing transparent soil and digital image correlation (DIC) methods. Transparent sand was made of amorphous silica gel and a pore fluid with a matching refractive index. An optical system consisting of a laser light, a camera, a loading frame, and a computer was developed to illuminate a targeted section inside a transparent soil model. A distinctive laser speckle pattern was generated by the interaction between the laser light and transparent soil. Two laser speckle images before and after deformation were used to calculate the displacement field using DIC. Two different cross-sectioned piles were used in the tests: a square-sectioned pile and a circular pile. Both piles were made of acrylic and had a diameter or width of 12.7 mm. Two different failure planes were observed in the tests, where a larger zone was mobilized by the circular pile compared to the one in the square-sectioned pile.

Group-pile foundations are used extensively for supporting buildings, bridges, and other structures to transfer structural loads safely to the ground and to avoid excess settlement or lateral movement. Therefore, it is necessary to understand the behaviors of the group-pile foundations and superstructures during a major earthquake. In this paper, numerical simulation of real-scale group-pile foundation subjected to horizontal cyclic loading is conducted using a program named as DBLEAVES. In the analysis, nonlinear behaviors of ground and piles are described by subloading t_ij model (Nakai and Hinokio, 2004) and axial force dependent model (AFD model, Zhang and Kimura, 2002) which considered the axial-force dependency in the nonlinear moment-curvature relations. The purpose of this paper is to verify the applicability of the proposed numerical method by comparing the numerical results with the test results.

Piles installed in seismically active regions are subjected to predominantly lateral loads due to earthquakes. Design of laterally loaded pile is mainly governed by its bending behaviour, which may be amplified under earthquake load compared to static loads. The influence of pile diameter on seismic response of single pile embedded in clay is investigated with a help of a three-dimensional finite element model. The model developed was validated through experimental/numerical results reported in literature. Subsequently a comprehensive parametric study was carried out by varying soil and pile parameters. The results of the numerical study are interpreted to estimate bending behaviour of piles under earthquake loads. It is found that the soil/pile characteristics, particularly, pile diameter have pronounced effect on seismic response of piles in clay.

A growth-rate based model has been briefly introduced to predict pile setup for the south Louisiana clayey soils based on the PDA data collected by the Louisiana Department of Transportation and Development (LADOTD) from the construction of the LA-1 relocation project. This paper presents the development procedures of the rate-based model. Predictability of this model was evaluated by using the dynamic, static, and statnamic testing results, and by comparing it with the conventional Skov-Denver model. In the paper, preliminary work was done to incorporate the pile setup into the regular LRFD method by providing independent resistance factors for the rate-based and the Skov-Dever prediction models, respectively.

To investigate the effect of pile-rock adhesion condition and rock stiffness on both socket friction in rock and side friction in the overlying soil of piles socketed into rock, pile load tests were performed on four instrumented model piles with hanging bases (i.e. the pile ends were unsupported). Cement grout and lean concrete were used to simulate strata of weak and hard rock, respectively; and slurries of different concentrations were applied to the pile-rock interfaces to simulate different pile-rock adhesion conditions. The overlying soil layer was comprised of compacted silt. The load test results indicate that the side resistance of the piles in the soil layer could fully develop even when the pile tip displacement was relatively small; the side resistance distribution was of a saddle shape in general with higher values at the top and bottom and lower values in middle of the soil layer.

Many piled foundations have been destroyed under significant cyclic loads in earthquakes. Centrifuge modelling of a single pile subjected to cyclic loads has been conducted to investigate the influence of cyclic loads on the axial performance of the single pile. Different pile installation procedures were applied to compare the axial behaviour of different piles under cyclic loads. Pile head permanent settlements accumulated due to cyclic axial loads, and these increased with the increasing load amplitude. Also the pile head axial secant stiffness decreased with the increasing number of axial load cycles, and with increasing amplitude. Furthermore, the axial pile performance is influenced significantly by different installation methods.

This paper presented a comparison of pile capacity from axial load tests and that from empirical equations. Additionally, a correlation was developed based on the load test database to estimate skin friction and end bearing of piles based on cone penetration resistance or undrained shear strength. Up to 1000 pile load tests on displacement piles, such as precast concrete, cast in place, steel, and screwed cast in place piles, micro piles, etc. are evaluated. The result of this study has been already integrated in the national German recommendations for piles "EA-Pfähle".

A deformation measurement system based on the digital image correlation method has been developed for studying the work mechanism of a single pile with a cap. A digital camera with high resolution is used to capture the gradual deformation failure process of the pile foundation under vertical load. Reliability and precision of this measurement system are validated by an example, which presents sub-pixel precision. The test results indicate that the settlement of the pile foundation varies gradually with total load. As the load increases, the ultimate state of the pile is earlier reached than that of the soil under the cap, and the additional increase in load is taken mainly by the soil. The displacement pattern of a pile with a cap is similar to that of a single pile without a cap. The plastic region of soil beneath the cap is developed after the pile reaches the ultimate state and the plastic region is transformed from cap edge to center as the load increases. A triangular compression zone beneath the cap occurs and is similar to those proposed by Terzaghi using the limit equilibrium method. The pile foundation is presented as the general shear failure. The test results indicate that this deformation measurement system is a useful tool for geotechnical physical model test to study global and localized deformation problems.

The stability of super-long piles that are supported laterally along part of their length or their entire length by an elastic Winkler foundation is investigated for the case when the coefficient of subgrade reaction is the general power distribution and the skin friction develops along the embedded pile length. Based on the potential energy method, taking into account the characteristic of load-transfer of super-long pile, the deflection functions for six different boundary conditions developed using the Rayleigh-Ritz method are analyzed in this paper. The applicability of the proposed analytical solution is validated against results of pile load tests reported in the literate. Therefore, the proposed method is considered promising for practical use.

To study the buckling stability of piles with high-rise cap widely used in bridge and harbor engineering, the advantages as well as the insufficiency of traditional analysis methods (e.g., the method using the minimum potential energy theory and variational method by treating the pile shaft as ideal axially-compressed bars) were first discussed. Then, based on the second type of stability problem (i.e., the pile shaft is viewed as an unideal bar with initial quality defects) and the nonlinear finite element method (FEM), a new method was presented to consider the nonlinear pile-soil interaction. And influencing rules of various factors especially those initial defects on the critical buckling load P_cr were discussed through the numerical analysis model by ANSYS. The analysis result shows that, with the increase of the free length at the pile top from 2.5m to 5.0m, the P_cr will decrease to a relative extent of 32.5%, and similar changing rules are also found with the increasing degree and location of initial bending and necking along the pile shaft. Moreover, the increasing inclination degree of pile shaft will result in an obvious linear cut down of P_cr. Finally, the present method is applied to analyze the data from a site loading test, which found a good agreement between the calculated buckling load 18.27MN and the measured failure load 17.28MN with a relative error of 5.7%.

This paper aims at calculating the transfer behavior of negative friction of single pile in two-layer soil in pile foundation. Based on the traditional load transfer function method, a model for calculating the transfer behavior of negative friction on a single pile in a two-layer soil profile is presented in this paper. In this model, the settlement of soil is assumed to follow bi-linear distribution; the transfer function is linear elastic and full plastic; the pile toe resistance is assumed to vary linearly with movement. By solving the model equations, the analytic solution of relative displacement and axial force of pile have been obtained. Moreover, a case history from literature is used to validate the proposed theoretical model. The prediction of negtive friction from the theoretical model agrees well with the measured value from the case history.

Polymer fluids have been used in foundation drilling for many years and yet no previous studies have been reported which assess their sensitivity to shear such as is induced by pumping equipment. A field study has been carried out on two specific polymer products under actual site conditions. It is found that there is a significant loss of viscosity when partially hydrolyzed polyacrylamide (PHPA) fluids are circulated through a centrifugal pump in a loop system. This behavior is quite distinct from that of bentonite slurries which require high shear mixing and recirculation to ensure good hydration. At first sight the sensitivity of PHPA fluids to shear may be perceived as a disadvantage but in fact if shear can be reduced so can on-site energy consumption. A reduction in fluid viscosity was also observed over a standing period between mixing and use, suggesting that a second mechanism may be contributing to the properties change. From the trial results, recommendations are given on pump selection and on the maintenance of fluid properties.

In this paper, an analytical method is proposed to transform the results of Osterberg-Cell pile testing (OPT) to conventional load-settlement curve of pile, which is loaded downward at the pile top. First, a tri-linear load transfer function representing pile side resistance was used to analyze the OPT of the pile segment above the Osterberg Cell. Parameters needed for the transfer function were obtained by fitting the OPT data. The self-weight of the upper pile segment was taken into account. As the friction between soil and pile in OPT has opposite direction compared to that of the conventional test, the downward transfer function has been transformed into the upward function. The OPT data of the lower pile segment was considered as boundary conditions of the upper segment of the equivalent top-loaded pile to transform the OPT data into conventional results with the upward friction obtained above. Case histories were used to validate that the conventional pile load-settlement curve obtained using this analytical method compared well with the measured data.

The axial load-displacement-capacity response of drilled shaft and bored pile foundations can be evaluated during the analysis and design stage using an elastic continuum framework and results from in-situ testing methods, in particular, the seismic piezocone test (SCPTù). The SCPTù is an optimal and economical means for collection of geotechnical data because the same sounding provides up to five separate measurements with depth: cone tip resistance (q_t), sleeve friction (f_s), porewater pressure (u₂), time rate of consolidation (t₅₀), and shear wave velocity (V_s). Moreover, the SCPTù provides information on soil behavior at both ends of the stress-strain-strength curves, namely the peak strength and geostatic stress state for evaluating axial pile capacity and the small-strain stiffness (G_max = ρ_t⋅V_s2) for the initial soil-pile deformations. Using a Randolph-type analytical elastic pile model, the approach can handle either traditional top down compression loading by dead-weight or reaction beam systems, or the more recent Osterberg cell that juxtaposes base and side resistances in opposite directions. A case study involving O-cell tests on a drilled shaft in Piedmont residuum and partially-weathered rock in Atlanta are presented.

This paper presents six case histories of load tests on reverse circulation method installed drilled shafts, with or without tip grouting, under axial load. Shaft displacement readings based on both telltale/extensometer and rebar strain gage are presented first. Subsequently, effect of loading cycle on shaft elastic modulus estimation is evaluated. The load versus displacement relationships at the shaft head, the t-z curves of the clay layer and of the gravel layer and the tip resistance versus displacement relationships are other important concerns and are compared in this paper. In addition, revised adhesion factor α and the parameter β based on the pile load test results are proposed in the paper.

A design phase load test program was performed at the Broadway Viaduct bridge site to evaluate load carrying capacity and constructability of post grouted drilled shafts. Three strain gauge instrumented test drilled shafts were installed in medium dense sand. Two drilled shafts included sleeve port and plate base grouting apparatus and were post grouted. The third drilled shaft was un-grouted and served as a control drilled shaft for comparison of the un-grouted end bearing. All drilled shafts were 1.52 m (5 feet) in diameter. The control drilled shaft was 16.76 m (55 feet) long. Post grouted drilled shafts were 16.76 m (55 feet) and 20.12 m (66 feet) long. The three drilled shafts were tested including integrity testing using the crosshole sonic logging method on each shaft, post grouting, and statnamic load testing. The test results were used to evaluate the axial capacity increase and an existing design method for post grouted drilled shafts.

During the construction of deep foundations there are different circumstances that are likely to affect the final shape of piles that tend to affect the designed depth, cross section and material quality. For quality control assurance of these elements pile integrity test (PIT) is often used. PIT as a method that involves the impact of a hammer on the head of the pile generating a low strain compression wave that propagates along the pile and afterwards is reflected at the bottom of the pile, or where there are changes of impedance related with variations in cross section or density of the material. In this paper a numerical solution is presented for the problem of one dimension wave propagation along a concrete pile. The problem consider a longitudinal element with a piece wise varying section, friction forces along the element and a reaction force at the tip, with a transient stress pulse applied at the top. This problem is representative of low strain pile integrity tests. Different alternatives for the solution of the problem were considered, and the spectral analysis method was chosen and implemented using Matlab. The test was modeled for several cases, comparing the results with actual PIT measurements. The parameters for the analytical model were obtained from numerical models of soil-pile interaction.

Due to the complicated construction condition, i.e. formidable natural conditions and complicated geological conditions and the large scale of bay bridges, the design and construction of Hangzhou bay bridge have inevitably encountered numerous obstacles, among which the construction of large scale pile foundation is a crucial one. In this paper, the key technology and countermeasures of construction of large scale pile foundation in rich shallow-buried gas in offshore zone of the south shore beach area are introduced. Deformation of the steel casing pipe and countermeasures project was studied in the pile construction of south and north channels bridge piers. In addition, such technologies as installation of cathode protection, large-sized pile-sinking barge performance and pile-sinking hammer model, are studied in steel-pipe pile foundation construction of water area. The results will serve as a theoretical foundation and guidance for successful construction, operation safety and sufficient durability of Hangzhou bay bridge, and also as a reference for design and construction of other bay bridges in China.

During the penetration process of jacked pile installation, the soil around pile will move laterally and heave. The existing structures and facilities were often damaged due to the soil movement resulted from jacked pile installation. To reduce those accidents, it is important to study the law of the lateral soil movement and upward heave due to compaction. This paper describes results from a series of experiments that investigated the radial soil displacement due to jacked piles in layered soils. A number of jacked piles were installed in a test chamber filled with dry sand and rubber powders, which was used to simulated soft soil. Closed-ended piles with 40-mm diameters were used. The experiments were carried out to study how radial displacement and vertical displacement changed as the pile penetration depth varied. We determined how the displacement value changed at different soil interfaces during the pile pressing process. The results revealed the soil displacement behavior produced by different position and penetration depth of the pile. We found that a lag effect existed between the maximum displacement and the pressed pile depth. The experimental results allow for a better understanding of the inherent mechanism of compaction of the jacked pile during the penetration process. These results are important for estimating the influence of pile installation and guiding jacked pile design.

Groove of preventing the compacting effect was an effective construction measure of decreasing compacting effects of jacked pile. An appropriate finite element model adopting the Drucker-Prager failure criterion and finite deformation theory was proposed according to the actual process of jacked pile. This model can simulate the interaction of pile and soil and continuous penetration. Displacement fields on the measure of groove were studied through the finite element model, and the simulation results were compared. The results show depth and situation of groove are important influencing parameters of the compacting effect of jacked pile. The compacting soil displacement of jacked pile can obviously be decreased due to the use of groove. Therefore, when the building and underground utilities need to be protected, the depth of grooves preventing the compacting displacements should be larger than that of protected surroundings.

This paper reports the response of embedded circular plate anchors to varying frequencies of cyclic loading. It also highlights the effect of pre-loading on anchor movement and post-cyclic monotonic pullout behavior using model circular plate anchor, buried at embedment ratio of six in soft saturated clay. The frequencies of loading cycle are found to have considerable effect on anchor movement. For a given duration of loading, high frequency cycle causes more anchor movement than that caused by low frequency cycles. Pre-loading causes a reduction of anchor movement in subsequent loading stages. Anchors subjected to cyclic loading and then monotonic pullout, show stiffer load-displacement behaviour at an initial stage compared to anchors not subjected to any cyclic loading. Pre-loading causes a reduction of anchor movement in subsequent loading cycles. When anchors are recycled at a load ratio level less than the pre-cycling load, the anchor movement in the recycling phase is very much reduced, but if the recycling is done at a higher load ratio level, the effect is not that pronounced, and the anchors behave as if they were not subjected to any cycling load in the past. The relative post-cyclic stiffness of anchors for the present test conditions varies from 1.169 to 1.327.

This paper presents a scaled-model test on sand displacement field during anchor uplifting. An in-house data acquisition system is developed to acquire the force, the anchor displacement, and soil images during anchor uplifting. The sand displacement is calculated using the digital image correlation (DIC) method from two images: one is taken at the initial stage and the other is at the peak pullout load moment. The failure plane is identified by locating the maximum shear strains deduced from the displacement field. Two distinctively different shear bands are observed in loose and dense conditions: 1) in loose sand, the shearing bands start at the edges of the anchor plate and converge and form a bell above the anchor; 2) while in dense sand these shear bands extend outward to the ground surface with an inclination angle with the vertical of approximately 1/2 to 1/3 the friction angle of soil.

An analysis of uplift capacity of pile anchors in cohesionless soil is proposed in which Kötter's equation is employed to obtain the distribution of soil reaction on the axisymmetric failure surface, assumed to be the frustum of a cone with a characteristic angle of inclination with the pile-soil interface. A closed form solution for the uplift capacity of pile anchor is obtained with no requirement of any charts or tables. The results are compared with experimental data for a total 28 cases, ranging from loose to dense cohesionless soil, with maximum embedment ratio of 40, vis-à-vis available theoretical solutions. The proposed method leads to the predictions that are very close to the experimental results in 75% cases and this demonstrates the successful application of Kötter's equation for the estimation of the uplift capacity of pile anchors.

Stiffened Deep Cement Mixed (SDCM) pile technique has provided a new approach for treating soft. soil. The main focus of this paper is the bearing behavior and capacity prediction of single SDCM pile. Static load tests data of 67 piles collected from six different districts in China are analyzed in this paper. The bearing capacity, load-settlement curve and failure modes of SDCM piles are studied. According to the bearing mechanism of SDCM pile, a new approach to predict the capacity, Sectioning and Summarizing method, is proposed. To calculate the capacity, one SDCM pile should be divided into two segments: the upper segment with core pile and the lower segment without the core pile. The total shaft resistance of SDCM pile is the summation of the two segments. Finally the dominate factors influencing the pile resistance are analyzed. The study results show that the capacity of SDCM pile is mainly affected by the parameters of the core pile. The resistance provided by the pile shaft including core pile was 1.0∼2.9 times that of bored and cast-in-place concrete pile. The proposed Sectioning and Summarizing method can be used to estimate the capacity of the SDCM pile and get more logical result than the currently used methods.

Rammed concrete pile is the development of columnar-hammer rammed and expanded technique. Due to the twice compaction effect during installation process and high compression strength of pile shaft, rammed concrete pile has the advantages of high bearing capacity and relatively low cost. The main purpose of this paper is to study the installation procedure, the bearing behavior of rammed concrete pile and compaction effect on the surrounding soil. The indoor tests results indicate that the rammed concrete specimens take only 14 days, only half of the common concrete, to achieve the design strength, which is favorable to shorten the construction period of foundation. Additionally, the compression strength of rammed concrete is about 10 to 50 percent higher than the regular concrete with the same cement content ratio. Field tests results show that rammed concrete pile offers greater capacity than driven and cast-in-place pile. Finally a case history is introduced that further verified the compaction effect of the rammed concrete pile to the surrounding soil.

In order to investigate the behaviors of the support systems and the associated ground deformations, centrifuge model test is adopted to simulate the excavation of ultra-deep foundation pit in soft ground. In this test, the geometrical scale is 1:120, and the soil layer thickness, excavation depth and retaining wall height are 60 cm, 31.6 cm and 54.2 cm respectively. The model ground consists of two types of soil, including silty clay and sandy silt. The aluminum alloy plate and aluminum alloy pipes are used to simulate reinforced concrete diaphragm wall and braces respectively. The retaining wall deformation, bending moment, brace axial force, earth pressure around the retaining wall, ground surface settlement, etc. are measured and discussed in detail in this paper. This can be used to comprehensively assess the stability of pit excavation support system. The findings from the centrifuge study are particularly useful for practical engineering.

Recently, a construction method for installing a precast pile nearby an existing driven pile has been developed considering the drainage of buried soil excluding the embedded soil of the ground. This type of displacement pile may affect the behavior of the surrounding ground. This study examines the influence of the displacement pile on the behavior of the surrounding ground with axisymmetric elastoplastic finite element analysis. In the analysis, increment of volumetric strain is applied to simulate the construction of the displacement pile. The behaviors of the ground consisting different types of soil characteristics such as cohesive soils, sandy soils and mixing of different soils are discussed.

During the installation of a displacement pile the surrounding soil is pushed away and distorted. For a driven pile the process is even more complex, due to vibrations caused by the installation process. In engineering practice the installation effects are accounted for empirical or analytical design method. For more complex geotechnical constructions, especially in cases with complex load combinations or strong interaction with neighboring structures, the use of the finite element method is common, in order to reach an optimal and economical design. However, when the modeling of displacement piles is attempted in finite element code, the installation phase is often not taken into account. Considering effects of pile installation is a challenging task for numerical simulations of displacement piles. This paper presents 2-D axysimmetric finite element analysis of one mini-pile in sand. For initializing the effects of installation, stress-controlled cavity expansion is considered. It is shown that realistic stress fields can be obtained by stress controlled cavity expansion up to the appropriate value of K, which is later pressure parameter ( later soil pressure to vertical stress). The method is considered as a feasible method for engineering practice to simulate the effects of installation.

Monopiles are open-ended steel pipe piles with diameters of usually 3 to 5m, which are used as foundation structures for offshore wind energy towers. Such foundations are subject to intensive cyclic horizontal loading due to wind and wave loads. In the practical design different requirements regarding the minimum embedded pile length are used in order to limit the lateral deformation under static and in particular cyclic loads. Such are the "critical length", "vertical-tangent" and "zero-toe-kick" criteria. For piles of very large diameter and thus high stiffness like monopiles these criteria lead to very large and hardly realistic required lengths. In this study, the different design criteria are compared with respect to piles of very large diameter. By means of the stiffness degradation method, a method which makes the determination of displacement accumulation with cyclic loading possible, the different criteria are assessed. With that, the suitability of adopting the mentioned design criteria for monopile foundations is discussed.

The Large Diameter Cast-in-place Concrete Pipe Pile (referred as PCC pile) has been used primarily in soft ground improvement applications such as for bridge abutment support piling. To assist design of PCC pile group, this paper investigates the influence of pile spacing on the embankment settlement control based on a series of numerical analysis. The pile spacing was varied from 3D to 5D. The induced horizontal displacement on neighbouring piles upon loading was also presented. It was found that settlement reduces as pile spacing reduces. Pile spacing of 3D is reasonable in terms of settlement control and economic purposes.

The results of a site investigation on the soft, normally to slightly overconsolidated, Lixia River Lagoonal clay deposit underlying several expressway lines based on seismic piezocone penetration tests (SCPTUs), undisturbed soil sampling from an adjacent borehole, and laboratory tests, are reported here. SCPTU data were used both in the determination of soil profile and the interpretation of strength and deformation properties. The investigation demonstrated a close agreement between strength parameters derived from the field vane tests, and laboratory tests and interpreted SCPTU parameters with a cone factor of N_kt = 16.5. Comparison of the results reveals the validity of SCPTU tests to interpret the strength and deformation properties of Lixia River Lagoonal clay deposits.

The neutron probe has proven to be an effective means for long-term monitoring of in-situ soil moisture variations. However, correlation of neutron probe data (i.e. neutron counts) with moisture contents to give accurate absolute values is a very difficult task, particularly for expansive soils due to problems associated with soil volume changing and shrinkage cracks. In this study, a numerical model of neutron diffusion in soils is used to calibrate neutron-probe data collected in a field site over a period of 5 years. The envelopes of soil moisture content derived from the neutron probe, representing the extreme observation at various depths are reported. The effects of tress and covers on soil moisture changes are also examined.

When using vane strength to evaluate the stability of soft clay slopes in Tianjin Harbor area, the calculated safety factors are often much less than 1.0 for stable slopes. A reasonable explanation is given to this phenomenon and a new way of using vane strength is presented for slope stability analysis. A correlation between the in-situ vane shear strength and undrained shear strength parameters is proposed based on the considerations that the vane strength is anisotropic and that the vane strength increases with depth linearly. Stability analysis was performed for several existing slopes. The results indicate that the safety factors calculated using the correlated shear strength parameters are more reasonable than those calculated with the vane strength directly.

Characterization of the in-situ critical shear stress of cohesive soils plays a vital role in bridge scour design. This stress is closely related to the undrained shear strength, which is conventionally obtained using a field shear vane (FSV) in situ or an erosion function apparatus (EFA) in laboratory. However, neither method is appropriate for assessing the erosional resistance of top surface layer of soft clays in streambeds, because: (1) FSV lacks sufficient sensitivity for the strength of very soft clays; (2) it is very difficult to obtain high-quality samples from such soft clays to be tested in laboratory; and (3) the properties of cohesive soils vary significantly with consolidation, organic matter content, microorganisms and biofilms, and seasonal changes. This paper describes the development of a new Louisiana Scour Vane (LSV) for in-situ measuring the undrained shear strength of surficial soft clay layer. Laboratory testing on a reconstituted clay was conducted to validate the LSV's capability of measuring shear resistance changes at small depth intervals. This new portable and easy-to-operate apparatus will act as a suitable supplement to the FSV for geotechnical engineers.

The shear strength of soils is key design property that governs the stability of geotechnical structures. For clays, the undrained shear strength is commonly adopted in design, while the friction angle is a soil property that represents the shear strength of sands. Estimation of these properties is a challenging task, and the challenge is even greater for sandy soils since the strength is highly state-dependent and undisturbed soil sampling is difficult. As a result, various empirical correlations based on in-situ test results, such as SPT and CPT, have been proposed. However, further investigation is still necessary for the consideration of the state-dependent dilatancy and soil constitution. In the present study, a CPT-based method for the estimation of the in-situ strength for granular soils is investigated. Various field variables such as fines content, soil density and confining stress are considered. A series of laboratory test results obtained for various soil conditions are used in the analysis and investigation.

The paper reports results of an extensive piezocone testing campaign performed at the Treporti Test Site (Venice, Italy) within a long-lasting research project aimed at developing a reliable geotechnical model of the heterogeneous and highly stratified Venetian lagoon subsoil. The analysis and the interpretation of the large amount of piezocone data in terms of compressibility and consolidation properties of the Venetian silty sediments reveal limitations of standard approaches for the characterization of such intermediate soils. Potentially dilative behaviour as well as partial drainage effects during cone penetration in silts must be taken in careful consideration in order to derive reliable soil parameters from in-situ measurements. According to recently proposed procedures, a preliminary attempt to assess drainage degree during piezocone tests is finally proposed.

Solutions of cavity expansion have many practical applications in geotechnical engineering. In the large body of literature on the cavity expansion models for cohesive frictional materials, the solutions have mostly been derived by adopting a finite logarithmic strain definition in the plastic zone. A more rigorous alternative approach using the rate formulation for cylindrical cavity expansion from a finite radius is presented in this paper. The material is assumed to behave as elasto-perfectly plastic, obeying a Mohr-Coulomb yield criterion and the associated or nonassociated flow rule. The "time" (or evolution) variable is chosen to be the current cavity radius. The solution for the onset of plasticity serve as both the continuity condition for the elastoplastic interface and the initial condition for cavity expansion. The pressure-expansion relationship obtained is a first order ordinary differential equation and converges to a self-similar solution for expansion at a large radius.

This paper presents a well recorded case history of cone penetration test with pore water pressure measurement (CPTU) in the soft deposit of Shanghai. In China, stratigraphy for soft deposit is obtained through physical properties (e.g. grain size and color) and mechanical properties (e.g. cohesion and inner friction angle from direct shear test) from borehole samples. Identification of soil stratigraphy with CPTU was developed 30 years ago. The field data at test site of Yan'an Road Tunnel in Shanghai is used in the analysis. The soil classification chart proposed by Robertson is employed to identify soil strata. The results are compared with that from plasticity index and grain size distribution of borehole samples (refer to code method). The results show that Robertson's chart can identify the stratigraphy of the soft deposit in Shanghai. However, there are some discrepancies of the results from Robertson's chart and the code method. The reason of the discrepancies is also discussed in the paper.