Pile-supported Structures Research Articles

Progressive failure mechanism of existing-supplementary double-layer piles retaining excavation beneath existing underground space

The increasing degree of urbanization has resulted in traffic and space congestion. When there is no longer any aboveground space for development, the existing space underground is excavated, and the construction of underground buildings is expected to solve the above problems. In the excavation of an underground layer, it is necessary to drive supplementary and existing piles into the soil to form a double-layer pile-supported structure. Aiming at an existing–supplementary double-layer pile-supported structure and considering the pile spacing of the supplementary piles, use of crown beams, and other factors, this study performed a series of indoor model tests and an simulation analysis in combination with finite element analysis software to reveal the bearing characteristics of this structure. The results showed that the installation of supplementary piles could effectively inhibit soil slippage after pile driving, redistribute the soil pressure load of the existing piles, and reduce the number of soil cracks between the piles. With the increase in the supplementary pile spacing, the deformation of the existing–supplementary double-stacked piles gradually intensified, and the bending moment of the pile body and the horizontal displacement at the top of the piles increased. The installation of crown beams in the existing piles could strengthen the connection between the existing and supplementary piles, reduce the number of soil cracks between these piles, and change the force mode of the pile body. Considering the geological conditions and the influence of existing buildings, the deformation laws of the supporting structure and the soil around the foundation piles during the excavation of an underground layer of an L-shaped foundation pit were revealed. The research results are expected to provide a scientific and theoretical basis for the design and construction of downward additional support structures for existing buildings, along with socio-economic significance.

Optimization of H-type Anti-slide Pile Support Structure Based on RSM-NSGA-II

The parameters of an h-type anti-slide pile are optimized and analyzed with respect to its structural characteristics. Based on laboratory model tests, further analysis of its stress characteristics is carried out through numerical simulation methods. Then, the response surface methodology (RSM) combined with the NSGAII algorithm was employed to perform multiobjective optimization of the reinforcement performance and engineering cost for h-type anti-slide piles regarding landslide consideration. Finally, the entropy weight TOPSIS method was used for comprehensive evaluation to obtain the optimal structural parameters. The results show that the bending moment distribution of the front and rear rows of h-type piles first increases and then decreases with increasing depth, and the front soil pressure of the pile gradually increases. Using RSM-NSGA-II instead of finite element modeling can shorten the optimization time, and the accuracy of the surrogate model reaches 94.8%. NSGA-II is much stronger than that of the particle swarm optimization algorithm. The entropy weight method combined with the TOPSIS method can obtain the unique optimal solution from the Pareto solution set without prior knowledge. The h-type anti-slide pile with the best structural parameters reduces the cost by 75.19%, while the slope safety factor increases by 47.39%. This method provides a new idea for structural optimization.

Analyses of Pile-Supported Structures with Base Isolation Systems by Shaking Table Tests

The dynamic behavior of a pile-supported structure with a base isolator was investigated by using 1 g shaking table model tests considering soil–structure interaction (SSI). The emphasis was placed on evaluating the effect of the with/without developed base isolator on the dynamic behavior of end-bearing piles and structures. The experiment was performed through sweep tests and sinusoidal wave tests. As a result of the tests, the developed base isolator was found to effectively reduce the structure’s resonant frequencies and damped the response acceleration under resonance frequencies. According to sweep tests, the base shear force of the pile-supported structure system tends to decrease as the relative density of the soil increases during resonance. It showed that the base isolator tends to reduce significantly the response acceleration of not only the rigid-based structure but also the pile-supported structure. It was shown that although the isolated superstructure recorded large horizontal displacements, piles experienced reduced horizontal displacement and bending moments, regardless of soil conditions.

Neural networks-based spring element for second-order analysis of pile-supported structures with nonlinear soil- structure interaction

This paper proposes a novel structural analysis approach, the neural networks-based spring element (NNSE) method, to synergize machine learning (ML) techniques with the line finite element method (LFEM) for the second-order analysis method of pile-supported structures. Traditional LFEM, widely used in upper structure design, showcases limitations in efficiently modeling complex Soil-Structure Interaction (SSI) along piles since it requires dense element mesh for accuracy. Conversely, ML offers a mesh-free alternative for analyzing single piles but struggles in simulating pile-supported structures as the training sample collection for large-scale problems might be unbearable. This paper addresses these challenges by proposing a new analysis framework to utilize the neural network (NN) model, which only describes structural responses of single piles, for the simulation of entire pile-supported structures. In the proposed method, the NN model is not directly used for structural analysis but employed to formulate a new spring element named the NNSE to model single piles in pile-supported structures. This NNSE can be seamlessly implemented within the existing LFEM framework to analyze pile-supported structures, eliminating the dense mesh requirement for single piles and thereby significantly improving the computational efficiency. Extensive examples are provided to verify the effectiveness of the proposed method, indicating its potential in promoting the second-order analysis method to the design of pile-supported structures.

Influence of Relative Lateral Stiffness and Dynamic Characteristics of Pile Foundation and Superstructure on SSPSI Response of Pile-Supported Structure: Experimental Study Using Shake Table

Influence of Relative Lateral Stiffness and Dynamic Characteristics of Pile Foundation and Superstructure on SSPSI Response of Pile-Supported Structure: Experimental Study Using Shake Table

Preliminary analysis of the influence of changing distance between piles on horizontal acceleration elastic response spectra for pile-supported structure

Preliminary analysis of the influence of changing distance between piles on horizontal acceleration elastic response spectra for pile-supported structure

Refined three-dimensional pile element formulation for second-order analysis of pile-supported structures accounting for complex loading conditions

The second-order analysis method is a simulation-based design method but less utilized for pile-supported structures due to the current inaccurate and unstable analysis methods for piles, especially for those under complex loading conditions in pile-supported structures. A refined Three-dimensional Pile Element (3DPE) formulation is proposed to promote the application of the second-order analysis method in pile-supported structures. The proposed refined 3DPE formulation can efficiently capture the nonlinear Soil-Structure Interaction (SSI) that is over-simplified in the conventional analysis method. Compared with the existing Pile Element formulation, the proposed refined 3DPE formulation can more accurately capture the structural behaviors of piles under complex loading conditions, including the shear effect and axial-torsional coupled response. Furthermore, three soil stiffness matrices are firstly proposed to improve the numerical stability of the spatial analysis using the existing element formulation. Extensive examples are provided to validate the effectiveness of the refined 3DPE formulation, indicating its applicability in extending the second-order analysis to pile-supported structures.

Study on the Influence of Excavation of Superlarge and Ultra-Deep Foundation Pits on the Pile Foundation of Existing Viaducts

The rapid development of urban above- and underground transportation has brought an increasing number of deep foundation pit projects that close to existing urban viaducts. Excavation of the deep foundation pit projects leads to soil movement around the pile foundation, which adversely affects the adjacent existing pile foundation and seriously threatens the operation safety of the adjacent existing viaduct. In this paper, the three-dimensional numerical model of foundation pit excavation, viaduct, and pile foundation was established by using the MIDAS GTS against the background of the basement foundation pit project in the new Guangzhou Baiyun Station comprehensive transportation hub building, production, and life complex, where the interaction between foundation pit excavation and viaduct pile foundation was simulated. The influence of various excavation-related factors and different parameters of the pile foundation on lateral displacements of the pile body adjacent to the existing pile foundation was analyzed. The variables controlled in the numerical model included the different excavation depths of the foundation pit, the distance between the excavation surface and the adjacent pile foundation, the spatial effect of different excavation sequences, the diameter of the pile that adjacent to the existing pile foundation, and the elastic modulus of the bored occlusal pile support structure. The results indicated that the lateral displacement of the pile body of the bridge pile foundation was significantly affected by the excavation of the deep foundation pit. The excavation depth exerted the greatest influence on the lateral displacement of the pile foundation, followed by the distance between the pile foundation and the excavation surface, the excavation sequence of the foundation pit, and the elastic modulus and the diameter of the bored occlusive pile support structure. Among them, the pile foundation located at the corner of the foundation pit was negligibly affected by these influencing factors. The findings in this study can provide valuable experiences for similar projects.

Numerical Simulation Study on Application of T-Shaped Composite Pile Support System in Super-Large Foundation Pit Support Engineering

To reduce the impact of the one-time excavation of deep and large foundation pits on nearby subway tunnels, the excavation should be performed separately; thus, a T-shaped pile support system was studied. First, several foundation pit support structures were compared and selected, and a pile support system was proposed. In terms of space, a T-shaped support structure was formed to reduce the spatial requirements of the foundation pit. Through finite element software, a 1:1 restoration of the foundation pit using a T-shaped pile support system was carried out. The stress characteristics and support effect of the support structure were studied under two working conditions of symmetric and asymmetric excavation. The study found that there was a central effect on the foundation pit using a T-shaped pile support system, that is, the support piles farther away from the center of the T-shaped structure gradually increased the maximum pile bending moment and displacement owing to the constraints of vertical piles and the influence of the pit angle effect, respectively. In the case of symmetrical excavation, the T-shaped structure was simplified into a triangular structure, and the stress form of this type of structure could be reduced to a cantilever double-row pile structure, which met the requirements of pit excavation. The application of a T-shaped pile support structure can provide new design ideas for foundation pit engineering near regional subway lines.

Efficient numerical implementation for nonlinear analysis of pile-supported structures during soil liquefaction through adaptive pile element formulations

The structural behavior of pile-supported structures during soil liquefaction is sometimes insufficiently investigated properly due to the inefficiency in the existing line finite element method (LFEM), which is widely used in practice. The traditional LFEM to simulate pile response requires dense element mesh for accurate results, as it simplifies the continuous surrounding soil as discrete spring elements, resulting in high computational costs, especially for pile-supported structures with a significant number of piles. Additionally, analyzing pile-supported structures in different stages of soil liquefaction requires repetitive updating of p-y curves and tedious starting-over iteration processes. To address these issues, an innovative line element formulation named the pile element formulation is employed and improved to adaptively simulate the surrounding soil conditions at different stages during liquefaction within the element formulation, eliminating the need to model discrete soil springs and significantly improving computational efficiency. The adaptive pile element formulation is then implemented within a refined Newton-Raphson iteration procedure that is proposed for a more effective nonlinear analysis process to consider soil liquefaction without repetitive iteration processes from starting over. Through several examples, the computational efficiency of the proposed method is validated, which requires only 20% of the computational cost compared to traditional LFEM while still providing accurate results, highlighting the application potential of the present study.

Performance of Seismically Isolated Pile-supported Structures through 1 g Shaking Table Tests

This study fabricated friction pendulum (FP) and rolling pendulum (RP) seismic isolation systems using 3D printing to conduct 1g shaking table tests of pile-supported structure models incorporating these systems. The test results indicate that, when the FP bearing was applied to the pile heads, the acceleration response of the structure decreased once the FP bearing began to operate; as the input earthquake frequency increased (1, 3, and 10 Hz), the seismic isolation system engaged at lower input accelerations (0.16, 0.11, and 0.02 g, respectively), and the deck acceleration response decreased significantly (15, 37, and 65%, respectively) compared to that in the fixed pile head condition. Similarly, when the RP bearing was applied to the pile heads, a higher input earthquake frequency (1, 3, and 10 Hz) corresponded to a greater decrease in the deck acceleration response (82, 95, and 96%, respectively) compared to that in the fixed condition. However, a significant deck displacement was observed when using the RP bearing owing to the resonance phenomenon when the natural period of the structure was similar to the frequency of the input earthquake. Therefore, since applying RP bearing is not desirable in terms of structural displacement, it is appropriate to apply FP bearing, which can avoid resonance by changing the natural period during the operation of the seismic isolation system.

Review of the Double-Row Pile Supporting Structure and Its Force and Deformation Characteristics

The conventional support forms of foundation pit retaining piles include single-row piles, double-row piles, anchor-row piles, and so on. The double-row pile supporting structure is widely used in the deep foundation pit supporting the engineering of wharves, bridges, subways, tunnels, and high-rise and super-high-rise buildings. This study on double-row pile supporting structures mainly focuses on four aspects: (1) The influence of dimension parameters, such as pile diameter and pile length, and engineering parameters, such as pile spacing and row spacing, on the deformation control of a double-row pile structure and the stability control of foundation pits; (2) Influence of the soil arch effect on the stress and deformation of the double-row pile supporting structure; (3) Study on the deformation characteristics and rules of the components and the whole structure of the double-row pile supporting structure; (4) Study on the calculation model of pile-soil interactions. Based on the above four aspects, this paper summarizes the latest research status of the existing double-row pile supporting structure and its stress and deformation characteristics. The deformation characteristics and calculation model of the pile-soil interaction of double-row piles are reviewed and evaluated. Finally, the problems and deficiencies in the research on double-row pile support are summarized. These results provide a reference for future research on the double-row pile supporting structure of the foundation pit and the numerical analysis and calculation model and lay a solid foundation for further development of the theory.

Numerical Investigation on the Interaction between a U-Shaped Pile Supporting Structure and an Adjacent Gravity Retaining Wall in River Dredging

There is significant interaction between the new supporting structure and the existing adjacent retaining wall in the dredging and excavation project of urban rivers. In addition, the three factors, the spatial location, the stiffness of the structures, and the soil conditions of the two sides of the interaction will exert effects on the bearing properties of the two structures. Combined with an actual dredging project, FLAC3D software was applied to analyze the influencing rule of U-shaped concrete sheet pile (USCSP) section size, pile length, retaining wall height, and pile–wall spacing on the supporting structure and the bearing properties of the existing gravity retaining wall during dredging excavation. The results are that when the length of the sheet pile increases, the horizontal displacement of the pile gradually decreases, the horizontal displacement of the existing retaining wall declines, and the earth pressure at the wall’s back rises. With the increase in the section size of the sheet pile, its bending resistance enhances gradually, and the horizontal displacement of the existing retaining wall reduces, while the earth pressure slightly increases. When the pile–wall spacing grows, the interaction between the supporting structure and the retaining wall is gradually weakened under the process of excavation, the horizontal displacements of the sheet pile and the retaining wall decrease continuously, and the earth pressure at the retaining wall’s bottom continues to strengthen. Moreover, with the retaining wall growing, the passive resistance from the soil in front of the wall is greater for keeping the stability of the retaining wall, and the horizontal displacement and the stress of the sheet pile increase significantly after excavation. The above results indicate that the characteristics of the pile–wall interaction should be deeply considered in designing and constructing such projects in order to determine the overall stability of the retaining pile and the existing retaining wall. In this study, FLAC3D software was used to analyze the influence of various factors on the structure in order to provide reference for ensuring the safety of the whole structure.

Evaluation of Liquefaction-induced Lateral Force on Pile in Slope by Centrifuge Tests

Pile foundations in liquefied ground may be subjected to a substantial force induced by lateral soil movement, which is crucial in the seismic design of pile-supported structures. Thus, this study aims to investigate the liquefaction-induced lateral force to piles by conducting centrifuge tests. Pile–deck systems installed in liquefiable finite slope with an angle of 27° were constructed and tested with different base motions. Results show that the liquefied slope pushes the piles toward the downslope, causing a large bending moment. The linear and uniform distributions of lateral soil pressure, which have been previously suggested for pile analysis in liquefied ground, were examined and compared with the measured maximum bending moment. The linear soil pressure profile reasonably predicted the bending moment compared to the results of the uniform profile. The empirical gradient factor of the linear profile was calibrated for the single piles and then implemented in the pile group analysis. The calibrated factor improved conventional methods for predicting the bending moment profile of group piles.

Domain reduction method: Formulation, possibilities, and examples for analyzing seismic soil-structure interaction

The Domain Reduction Method (DRM) enables the analysis of seismic soil-structure interaction in a different way compared to other seismic methods. Additionally, it allows certain very important aspects of the mentioned interaction, which are ignored in the usual seismic methods for justified reasons, to be addressed. All this, as well as the fact that this method is still unknown to the professional public and has not been implemented in modern seismic standards, motivated the writing of a paper in which the formulation of the DRM was first presented in detail. Then, the possibilities and approaches to its application in engineering practice were analyzed. In the end, simple dynamic analyses of the seismic interaction of the foundation soil and the pile-supported structure are performed using the DRM, a very specific and insufficiently researched type of seismic soil-structure interaction. Among other things, the results of the performed linear-elastic analyses point to the eventual possibility that the Lateral force seismic method, which is recommended by the Eurocode 8 standard for regular structures and which is most often used in engineering practice, underestimates the level of the lateral seismic load of pile-supported structures. A correct assessment of the seismic load is a fundamental requirement for ensuring a sufficient level of seismic resistance in structures.

Field Test Study on Cantilever Circular Occluded Pile Supporting Structure

In order to explore the deformation of the pile body of the circular occluded pile retaining structure under earth pressure, this paper carries out on-site monitoring in combination with the actual project, and obtains the deformation characteristics and change rules of the occluded pile by measuring the strain and displacement of the pile body. The research conclusion can provide a certain reference value for the pile body design of bite pile in similar projects.

The Filtering Effect of Pile Foundations in Clay

This paper reports the results of a series of centrifuge experiments exploring the dynamic response of pile foundations. The model tested in a centrifuge at 50g consisted of an isolated pile and two pile groups embedded in a kaolin clay, subjected to a sequence of quasi-sinusoidal waves with different amplitudes and frequencies. The results are back-analyzed through a two-step procedure. First, a one-dimensional ground response analysis is performed, in which the small-strain shear modulus is evaluated using data from air hammer tests, while a literature model is used to account for nonlinearity of soil behavior. Second, a three-dimensional finite-element analysis of the model foundations is carried out using the mobilized soil damping ratio and shear modulus determined from the previous step. The aforementioned procedure allowed to reproduce satisfactorily the response of the model foundations tested in the centrifuge, showing that the response of these models is strongly affected by the inertial oscillation of the cap connecting piles necessary to accommodate the measurement devices and to rigidly connect the piles’ heads of the groups. The same numerical model was then adopted to evaluate the change of seismic motion due to pure kinematic interaction effects by setting the pile cap mass equal to zero. This allowed to check the prediction capability of simplified methods of analysis for the evaluation of the base excitation of pile-supported structures. In addition, a number of issues related to the execution of centrifuge tests aimed at investigating the kinematic interaction between pile and soil are highlighted and discussed.

Numerical evaluation of slope effect on soil–pile interaction in seismic analysis

This study aims to evaluate the slope effect on the behavior of soil–pile interface in the lateral direction, which is a factor governing the seismic response of pile-supported structures. A series of numerical simulations of a single pile in cohesionless soil subjected to lateral loading were performed by considering various slope configurations, soil densities, and loading directions. The lateral and confining forces acting at the soil–pile interface increased at a comparable rate under increasingly lateral loading. The ratio of the ultimate lateral force to the ultimate confining force was defined as a lateral interface-force ratio, which was introduced to quantify the slope effect on the strength parameter of the lateral soil–pile interface. The lateral interface–force ratio increased together with embedment depth and maintained a constant value below a certain depth corresponding to the change in failure mechanism from the wedge mode to the flow mode. In addition, an interface model of the soil–pile separation due to the slope failure was developed for the numerical analysis of piles in the cohesionless soil. Finally, the proposed lateral soil–pile interface was implemented via a three-dimensional numerical simulation of a dynamic centrifuge test for the validation work. The good agreement between the numerical simulation and experimental data indicates the reasonable applicability of the proposed interface properties.

Review of the Deformation Mechanism and Earth Pressure Research on the Double-Row Pile Support Structure

As a new support structure system, the double-row pile is widely used in foundations in pit engineering, slope engineering, water conservancy engineering, and other fields. It has a big horizontal stiffness and strong anti-overturning ability and has less impact on the surrounding neighboring existing buildings (structures) when it is applied. It must be mentioned that the design experience of the double-row pile is ahead of the theory, and some research has been carried out on double-row pile support structures. This work reviews and evaluates the force deformation and earth pressure on piles of double-row piles, including pile deformation damage mechanism, soil pressure distribution law, and double-row pile structure form. In addition, the problems and shortcomings of the current double-row pile research are concluded. These results have enriched the study of the mechanism of double-row piles, provided the theoretical guidance for double-row pile support structures, and laid the foundation for further theoretical research.

Problems and Countermeasures of Double Row Pile Support Structure of Deep Foundation Pit in Geotechnical Engineering

With the development of geotechnical engineering, the double row pile support technology of deep foundation pit in geotechnical engineering has also been improved. However, at present, there are still problems, which affects the quality and safety of the whole geotechnical engineering, and requires measures to deal with them. This paper first describes the characteristics of double row pile support of deep foundation pit in geotechnical engineering, then analyzes the problems laying in it, and finally puts forward some countermeasures.