Three-dimensional finite element analysis on effects of tunnel construction on nearby pile foundation

A three-dimensional finite element simulation was carried out to investigate the effects of tunnel construction on nearby pile foundation.The displacement controlled model (DCM) was used to simulate the tunneling-induced volume loss effects.The numerical model was verified based on the results of a centrifuge test and a set of parametric studies was implemented based on this model.There is good agreement between the trend of the results of the centrifuge test and the present model.The results of parametric studies show that the tunnelling-induced pile internal force and deformation depend mainly on the pile?tunnel distance,the pile length to tunnel depth ratio and the volume loss.Two different zones are separated by a 45° line projected from the tunnel springline.Within the zone of influence,the pile is subjected to tensile force and large settlement;whereas outside the zone of influence,dragload and small settlement are induced.It is also established that the impact of tunnelling on a pile group is substantially smaller as compared with a single pile in the same location with the rear pile in a group,demonstrating a positive pile group effect.

Verification of Seismic Performance of Pile Foundation in Composite Ground through Experimental and Numerical Methods

A new construction method of pile foundation in composite ground, in which, prior to installing piles, the ground is improved around the heads of the piles in soft ground or ground subject to liquefaction, which is introduced in this paper. This construction method uses a combination of pile foundation construction together with common ground improvement methods, including deep mixing, preloading and sand compaction piling, and it is referred to as the composite ground pile method. Since an artificial ground with relatively high rigidity comparing with that of the original ground was formed around the pile in this method, and the seismic performance has not been made clear, thus the seismic performance of piles in composite ground was systematically analyzed through a series of centrifuge model tests and numerical analyses by using dynamic nonlinear finite element method, and a verification method for the seismic performance of piles in composite ground was proposed on the basis of the experimental and numerical results.

Force analysis of pile foundation in rock slope based on upper-bound theorem of limit

Based on the characteristic that the potential sliding surfaces of rock slope are commonly in the shape of either line or fold line,analysis thought of conventional pile foundation in the flat ground under complex load condition was applied and the upper-bound theorem of limit analysis was used to compute thrust of rock layers with all possible distribution shapes. The interaction of slope and pile was considered design load in terms of slope thrust,and the finite difference method was derived to calculate inner-force and displacement of bridge pile foundation in rock slope under complex load condition. The result of example shows that the distribution model of slope thrust has certain impact on displacement and inner-force of bridge pile foundation. The maximum displacement growth rate reaches 54% and the maximum moment and shear growth rates reach only 15% and 20%,respectively,but the trends of inner-force and displacement of bridge pile foundation are basically the same as those of the conventional pile foundation in the flat ground. When the piles bear the same level lateral thrust,the distribution shapes of slope thrust have different influence on inner-force of pile foundation,especially the rectangle distribution,and the triangle thrust has the smallest displacement and inner-force of pile foundation.

Seismic response comparison and sensitivity analysis of pile foundation in liquefiable and non-liquefiable soils

Case history investigations have shown that pile foundations are more critically damaged in liquefiable soils than non-liquefiable soils.This study examines the differences in seismic response of pile foundations in liquefiable and non-liquefiable soils and their sensitivity to numerical model parameters.A two-dimensional finite element(FE)model is developed to simulate the experiment of a single pile foundation centrifuge in liquefiable soil subjected to earthquake motions and is validated against real-world test results.The differences in soil-pile seismic response of liquefiable and non-liquefiable soils are explored.Specifically,the first-order second-moment method(FOSM)is used for sensitivity analysis of the seismic response.The results show significant differences in seismic response for a soil-pile system between liquefiable and non-liquefiable soil.The seismic responses are found to be significantly larger in liquefiable soil than in non-liquefiable soil.Moreover,the pile bending moment was mainly affected by the kinematic effect in liquefiable soil,while the inertial effect was more significant in non-liquefiable soil.The controlling parameters of seismic response were PGA,soil density,and friction angle in liquefiable soil,while the pile bending moment was mainly controlled by PGA,the friction angle of soil,and shear modulus of loose sand in non-liquefiable soil.

Effects of liquefaction-induced large lateral ground deformation on pile foundations

The pile-soil system interaction computational model in liquefaction-induced lateral spreading ground was established by the finite difference numerical method.Considering an elastic-plastic subgrade reaction method,numerical methods involving finite difference approach of pile in liquefaction-induced lateral spreading ground were derived and implemented into a finite difference program.Based on the monotonic loading tests on saturated sand after liquefaction,the liquefaction lateral deformation of the site where group piles are located was predicted.The effects of lateral ground deformation after liquefaction on a group of pile foundations were studied using the fmite difference program mentioned above,and the failure mechanism of group piles in liquefaction-induced lateral spreading ground was obtained.The applicability of the program was preliminarily verified.The results show that the bending moments at the interfaces between liquefied and non-liquefied soil layers are larger than those at the pile＇s top when the pile＇s top is embedded.The value of the additional static bending moment is larger than the peak dynamic bending moment during the earthquake,so in the pile foundation design,more than the superstructure＇s dynamics should be considered and the effect of lateral ground deformation on pile foundations cannot be neglected.

Parameter analysis of composite pile foundation in bridge foundation

In the current theory of bridge foundation design,all of the loads above the cap are loaded by the pile,and the bearing capacity of the soil among piles is not taken into account.In order to analyze the bearing capacity of the soil among piles in bridge pile foundation,a model of pile foundation is established based on a bridge foundation which is under construction,and by the finite element analysis software ANSYS.According to the results of finite element analysis(FEA)and current bridge foundation design theory,a feasible composite pile foundation which can be applied in the design of bridge foundation,is recommended.Additionally,a number of modifications are made to the original design.It was confirmed that these modifications derived from numerical simulations can improve the performance of the foundation.

Finite element analysis on impact of foundation treatment in bridgehead transition section upon bridge piles

In order to decrease relative settlement, foundation treatment plays an extremely important role in bridgehead transition section, especially, the situation of building the bridge piles firstly, and then processing piles. On the basis of engineering practice, the authors analyzed the influence of foundation treatment on bridge piles in bridgehead transition section by finite-element method (FEM). This research has positive significance in predicting displacement of bridge pile, directing construction of foundation treatment, and improving quality of engineering and so forth.

Pile-clayey soil interaction analysis by boundary element method

This paper is an attempt to solve the soil-pile interaction problems using the boundary element method（BEM）.A computer package called PGroupN,which deals mainly with the analysis of the pile group problem,is employed in this study.Parametric studies are carried out to assess the impacts of the pile diameter,pile length,ratio of spacing to diameter and the thickness of soil stratum.The external load is applied incrementally and,at each increment,a check is made that the stress state at the pile-soil interfaces does not violate the yield criteria.This is achieved by specifying the limited stresses of the soil for the axial pile shaft capacity and end-bearing resistance.The elements of the pile-soil interface yielded can take no additional load,and any increase in load is therefore redistributed between the remaining elements until all elements have failed.Thus,by successive application of loading increments,the entire load-displacement relationship for the pile group is determined.It is found that as the applied load reaches the ultimate bearing capacity of the pile group,all the piles will share the same amount of load.An exception to this case is for the center pile in a group of 9 piles embedded in clay,which is not consistent with the behaviors of the other piles in the group even if the load reaches the ultimate state.For the 4 piles group embedded in clay,the maximum load carried by the base does not exceed 8% of the load carried by each pile with different diameters.This low percentage ascertains that the piles embedded in cohesive soils carry most of the load throughout their shafts.

Three-dimensional elasto-plastic finite element analysis of a soil-pilebridge interaction

The soil-pile-bridge interaction of super-large pile groups is a very complex issue for the design of deep pile group foundations. In this paper, the load distribution on the pile top of a super large bridge foundation and its influential factors are analyzed comprehensively using a three-dimensional elasto-plastic finite element method. The adopted model and its input parameters are firstly verified by comparing the numerical results with the measured data of static loading tests of a single pile. Numerical analysis is then performed to investigate the load distribution and the load-settlement characteristics of super-large pile groups, and the models are verified using centrifuge laboratory model testing data. The mechanism of the interaction between pile groups and soil under different conditions is explored.

Effect of constructing twin tunnels under a building supported by pile foundations in the Sydney central business district

In congested cities such as Sydney,competition for underground space escalates within the built environment because various assets require finite geotechnical strength and support.Specific problems such as damage to buildings may develop when high-rise buildings on piled foundations are subject to ground movements as tunnels are constructed.This paper focuses on the risks of tunneling beneath Sydney’s Martin Place and how buildings are subject to additional loads caused by tunneling.The key objective of this study is to improve the understanding of tunnel-rock-pile interactions and to encourage sustainable development.A finite element model is developed to predict the interaction between tunnel construction and piled foundations.The tunnel,rock,and pile components are studied separately and are then combined into a single model.The ground model is based on the characteristics of Hawkesbury Sandstone and is developed through a desktop study.The piles are designed using Australian Standards and observations of high-rise buildings.The tunnel construction is modeled based on the construction sequence of a tunnel boring machine.After combining the components,a parametric study on the relationship between tunnel location,basements,and piles is conducted.Our findings,thus far,show that tunneling can increase the axial and flexural loads of piles,where the additional loading exceeds the structural capacity of some piles,especially those that are close to basement walls.The parametric study reveals a strong relationship between tunnel depth and lining stresses,while the relationship between tunnel depth and induced pile loads is less convincing.Furthermore,the horizontal tunnel position relative to piles shows a stronger relationship with pile loads.Further research into tunnel-rock-pile interactions is recommended,especially beneath basements,to substantiate the results of this study.

New method of designing anti-slide piles——the strength reduction FEM

At present,the thrust of an anti-slide pile can be worked out with some calculation methods. However,the resistance in front of the pile,the distributions of resistance and thrust,and appropriate pile length cannot be easily obtained. In this paper,the authors applied the strength-reduction finite element method (FEM) to several design cases of anti-slide piles. Using this method,it is possible to take the pile-soil interactions into consideration,obtain reasonable resistance in front of pile and the distributions of thrust and resistance,and reasonable lengths of anti-slide piles. In particular,the thrust and resistance imposed on embedded anti-slide piles can be calculated and composite anti-slide pile structures such as anchored piles and braced piles can be optimized. It is proved through the calculation examples that this method is more reliable and economical in the design of anti-slide pile.

Numerical Analysis of the Settlement of Composite Foundation Reinforced with Crushed Stone Grouting Pile and Rigid Bearing Plate

This paper deals with a new type of crushed stone grouting pile with a rigid bearing plate. The load transfer characteristics were analyzed, and a settlement model of the composite foundation reinforced with crushed stone grouting pile and rigid bearing plate was built by FEM program. The effects of replacement ratio of capping plate, replacement ratio of pile, replacement ratio of grout diffusion zone, pile-soil modulus ratio, and serous-soil modulus ratio, on the composite foundation settlement were discussed. It is concluded that the proposed crushed stone grouting pile with a rigid bearing plate is effective in decreasing the settlement of composite foundation.

Innovative Techniques Unveiled in Advanced Sheet Pile Curtain Design

This thorough review explores the complexities of geotechnical engineering, emphasizing soil-structure interaction (SSI). The investigation centers on sheet pile design, examining two primary methodologies: Limit Equilibrium Methods (LEM) and Soil-Structure Interaction Methods (SSIM). While LEM methods, grounded in classical principles, provide valuable insights for preliminary design considerations, they may encounter limitations in addressing real-world complexities. In contrast, SSIM methods, including the SSI-SR approach, introduce precision and depth to the field. By employing numerical techniques such as Finite Element (FE) and Finite Difference (FD) analyses, these methods enable engineers to navigate the dynamics of soil-structure interaction. The exploration extends to SSI-FE, highlighting its essential role in civil engineering. By integrating Finite Element analysis with considerations for soil-structure interaction, the SSI-FE method offers a holistic understanding of how structures dynamically interact with their geotechnical environment. Throughout this exploration, the study dissects critical components governing SSIM methods, providing engineers with tools to navigate the intricate landscape of geotechnical design. The study acknowledges the significance of the Mohr-Coulomb constitutive model while recognizing its limitations, and guiding practitioners toward informed decision-making in geotechnical analyses. As the article concludes, it underscores the importance of continuous learning and innovation for the future of geotechnical engineering. With advancing technology and an evolving understanding of soil-structure interaction, the study remains committed to ensuring the safety, stability, and efficiency of geotechnical structures through cutting-edge design and analysis techniques.

Stochastic Response Analysis of Piled Offshore Platforms to Earthquake Load

In this paper, using the theory of stochastic analysis of the response to earthquake load, a stochastic analysis method of the response of piled platforms to earthquake load has been established. In the method, the strong ground motion is considered as three dimensional stationary white noise process and the pile-soil interaction and water-structure interaction are considered. The stochastic response of a typical platform to earthquake load has been computed with this method and the results compared with those obtained with the response spectrum analysis method. The comparison shows that the stochastic analysis method of the response of piled platforms to earthquake load is suitable for this kind of analysis.

Pile-up现象对材料本构关系反演计算的影响

针对商用纳米压痕测试中忽略凸起(Pile-up)现象的问题,开展了Pile-up现象对材料力学参数和本构反演计算结果影响的研究。推导能量法理论,选取5种不同材料进行了纳米压痕测试,利用商用Oliver-Pharr(O-P)法和能量法分别进行硬度和弹性模量计算,并比较测试误差率。推导极限分析法理论并进行反演计算,得到考虑材料Pile-up现象的应力应变曲线,并根据计算结果对纳米压痕过程进行仿真。结果表明:当纳米压痕测试中压痕残余深度与压入深度比值大于0.7时,Pile-up现象对商用O-P法测试影响明显,弹性模量和硬度值误差率达到20%以上;对发生塑性变形较大材料进行本构关系反演计算时,理论计算值和数值模拟结果均证明了Pile-up现象对应力应变曲线计算有一定的影响。研究结果可为纳米压痕测试本构关系的反演计算方法提供参考。

Time-dependent lateral response of pile embedded in elasto-plastic soil

A two-dimensional （2D） finite element analysis was carried out to assess the time-dependent behavior of single vertical pile embedded in elasto-plastic soil. The finite element analyses were carried out using the linear elastic model for the structure of the pile, while the Mohr-Coulomb model was used for representing the soil behavior surrounding the pile. The study includes cohesionless and cohesive soil to assess the lateral response of pile in the two types of soil. The whole geoteehnical model is suitable for problem of piles to determine the design quantities such as lateral deformation, lateral soil stress and its variation with time. The model is verified based on the results of published cases and there is good comparison between the results of published ease and the present simulation model. It is found that, the pile in cohesionless soil has more resistance in the rapid loading and less one in the long term loading. On the other hand, the pile in cohesive soil shows opposite behavior.

High-frequency interference waves in low strain dynamic testing of X-section concrete piles

Stress waves propagate along vertical,radial and circumferential directions when a non-uniformly distributed load is applied at one end of a three-dimensional shaft.As a result,the receiving signals are usually mixed with undesired interference components,often featuring as high-frequency fluctuations.Previous studies have revealed that sectional geometry(shape and size)greatly affects the high-frequency interference.In this study,low strain dynamic testing on full-scale X-section concrete is conducted in order to investigate the influences of high-frequency interference on velocity responses at the pile head.Emphasis is placed on the frequency and peak value of interference waves at various receiving points.Additionally,the effects of the geometrical,and mechanical properties of the pile shaft on high-frequency interference are elaborated on through the three-dimensional finite element method.The results show that the measured wave is obscured by interference waves superposed by two types of high-frequency components.The modulus and cross-sectional area are contributing factors to the frequency and peak value of the interference waves.On the other hand,the position with the least interference is determined,to some extent,by the accurate shape of the X-section.

DYNAMIC BEHAVIOR OF PILES EMBEDDED IN TRANSVERSELY ISOTROPIC LAYERED MEDIA

Dynamic behavior of single pile embedded in transversely isotropic layered media is investigated using the finite element method combined with dynamic stiffness matrices of the soil derived from Green's function for ring loads. The influence of soil anisotropy on the dynamic behavior of piles is examined through a series of parametric studies.

Finite Element Simulation of Residual Stress Determination Based on Spherical Indentation Accumulation Morphology

The introduction of residual stress during the processing of materials has an important impact on the properties of the materials, so it is important to accurately measure the residual stress of the material. This paper established a finite element model of spherical indentation under the action of non-equivalent biaxial residual stress. Then we extracted the full-field accumulation state near the indentation under different stress states from the simulation results and summarized the pile height distribution near the indentation under different stress states. From the simulation, we found that the maximum pile-up height near the indentation point presented a regular trend.

Strength reduction and step-loading finite element approaches in geotechnical engineering

The finite element limit analysis method has the advantages of both numerical and traditional limit equilibrium techniques and it is particularly useful to geotechnical engineering.This method has been developed in China,following well-accepted international procedures,to enhance understanding of stability issues in a number of geotechnical settings.Great advancements have been made in basic theory,the improvement of computational precision,and the broadening of practical applications.This paper presents the results of research on（1） the efficient design of embedded anti-slide piles,（2） the stability analysis of reservoir slopes with strength reduction theory,and（3） the determination of the ultimate bearing capacity of foundations using step-loading FEM（overloading）.These three applications are evidence of the design improvements and benefits made possible in geotechnical engineering by finite element modeling.