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Flooding occurrences have become increasingly severe, posing a serious danger to end-user safety and bridge resilience. As flood fragility assessment is a valuable tool for promoting the resilience of bridges to climate change, it is of great importance to push the development of such methods. However, flood fragility has not received as much attention as seismic fragility despite the significant amount of damage and costs resulting from flood hazards. There has been little effort to estimate the flood fragility of bridges considering various flood-related factors and the corresponding failure modes. To this end, a fragility-based approach that can explicitly address the scour-hole geometry and flood-induced lateral load is presented. First, a three-dimensional finite-element model with pile foundations and surrounding soil was established to estimate the failure mode under various flood scenarios. The loadings on pile foundations were characterized by vertical loading from the superstructure, horizontal loading from the flood-induced lateral load, and the scour effect simulated through a time-history analysis. Then, all potential failure modes of bridge pile foundations in various flood scenarios were summarized. Based on extensive parameter investigations using the deterministic method, the dominant failure mode of penetration failure was determined, and a failure envelope was fitted to guide the design of the pile foundation. Upon establishing the failure mode, a probabilistic fragility analysis considering uncertainties in hydraulic, structural, and geological parameters was finally conducted using the Latin hypercube sampling (LHS) method. The results showed the effects of variation on the fragility of the pile foundation, highlighting that the deterministic analysis without considering the uncertainties in model parameters leads to underestimating the risk due to the penetration failure and the significant influence region. [ABSTRACT FROM AUTHOR]

The physical and mechanical properties of red clay have a significant influence on the bearing characteristics of pile foundations. Therefore, this paper conducted model tests to study the influence of different red clay water content (16~−20%) and different compaction degrees (88~−92%) on the bearing characteristics of pile foundations. The results show that the load–displacement curves of the test pile generally exhibit a steep type. The ultimate bearing capacity of the test pile increases gradually with the compaction degree from 86% to 92%. However, the ratio of load borne by the side of the pile increases from 54.8% to 67.8%, while the ratio of load borne by the end decreases from 45.2% to 32.2%. The ratio of load borne by the pile end to that borne by the pile side also decreases gradually from 0.825 to 0.476. The ultimate bearing capacity of the test pile decreases gradually with the moisture content from 17% to 26%, showing a decreasing trend. However, the ratio of load borne by the pile side decreases from 69.5% to 51.9%, while the ratio of load borne by the end increases from 30.5% to 48.1%. The ratio of load borne by the pile end to that borne by the pile side also increases gradually from 0.439 to 0.927. This indicates that increasing the compaction degree or reducing the moisture content has a more significant effect on increasing the side resistance. In this paper, the ultimate bearing capacity of test piles are calculated by the Mohr–Coulomb criterion (M-CC) and Duncan–Chang hyperbolic model (D-CHM), respectively. The results show that M-CC and D-CHM methods can accurately calculate the bearing capacity of the pile foundation in red clay. The conclusion of this study can provide a reference for the design and construction of pile foundations in red clay areas. [ABSTRACT FROM AUTHOR]

This document discusses a research paper that proposes a modified method for evaluating the stability of deep excavations in soft clays. The discussion raises concerns about the proposed method and questions the assumptions made by the authors. It suggests alternative explanations for the observed behavior of excavations in soft clays and criticizes the models used in the study for not accurately representing actual ground movement patterns caused by excavation. The author invites the study authors to respond to these criticisms. [Extracted from the article]

Although end-bearing energy pile foundations subjected to symmetrical thermal cycles have been extensively studied in the laboratory and in the field, the mechanisms underlying the thermo-hydro-mechanical (THM) interactions in floating energy pile groups and rafts, especially when subjected to asymmetrical thermal loads, are not well understood. In this study, an advanced thermo-mechanical bounding surface model was implemented in finite-element (FE) code to investigate the THM interactions of a two-by-two floating energy pile group and pile raft, focusing on asymmetrical thermal cycles. Computed results are compared with published centrifuge model test results in soft clay. It is revealed that the irreversible volumetric contraction of the soil adjacent to the energy piles accumulates with each thermal cycle, resulting in a decrease in the horizontal stress and hence shaft resistance of the floating piles. During thermal cycles, the stress states of the soil around the energy pile shaft and the soil beneath the pile toe approach the critical state line along different paths. The induced temperature in the soil adjacent to the non-energy pile (NEP) is 5°C lower than that in the soil at the energy pile EP1, which is flanked by the other two energy piles EP2 and EP3. Consequently, the induced excess pore pressure in the soil at the NEP is approximately 20% smaller than that in the soil at EP1. The irreversible volumetric soil contraction at the NEP is about half that at EP1, resulting in approximately 45% less toe settlement. The thermally induced ratcheting settlements of the head and toe of the NEP are less than those of the energy piles, resulting in unacceptable ratcheting tilting of the floating energy pile group. However, the excessive tilting can be reduced by the use of a pile raft. [ABSTRACT FROM AUTHOR]

This study aims to prepare an anti-washout grout using marine soft clay to stabilize the wind power pile foundations. The cement, hydroxypropyl-methyl cellulose ether (HPMC), and sodium silicate were chosen as the main materials to modify the marine soft clay, and the fluidity, bleeding rate, setting time, rheology, anti-washout characteristics, and compressive strength were investigated. The results showed that high cement content, HPMC, and sodium silicate decreased the workability of grout while enhancing the washout resistance. The addition of HPMC and sodium silicate would increase the yield stress and plastic viscosity of the grout. The sodium silicate content was the key factor influencing the early strength, while the cement content and HPMC affect the later strength. The microstructures including the morphology of C-S-H gels and the content of ettringite and calcium hydroxide significantly changed with the addition of sodium silicate, and Friedel's salt was observed through the microstructure analysis. This study can provide effective guidance for the utilization of marine soft clay, the preparation of anti-washout grout, and the control of pile foundation stability. [ABSTRACT FROM AUTHOR]

Skirt–pile foundations have gained widespread attention in the field of offshore engineering due to their ease of installation and high bearing capacity. In this study, the ultimate bearing capacity, pile bending moment distribution and development, cumulative deformation characteristics, and cyclic stiffness development of skirt–pile foundations were investigated using physical model tests. The experimental results indicate that the ultimate bearing capacity and deformation resistance of the foundation can effectively be improved by increasing the skirt diameter. The cumulative deformation of the skirt–piles exhibited rapid development during the initial stages of cyclic loading, eventually stabilizing. Under long-term cyclic loading, the existence of the skirt can share the bending moment, which then affects the internal force distribution of the pile foundation along the axis. The pile foundation's cyclic stiffness reduces as the loading cycles increase and increases as the skirt diameter and length grow. Meanwhile, the horizontal cyclic stiffness decreases as the number of cycles increases, stabilizing after 3000 cycles. This study can not only deepen the understanding of the deformation laws of skirt–pile foundations in clay soil but also offers some references for the design of offshore pile foundations. [ABSTRACT FROM AUTHOR]

Although three-dimensional finite-element analysis has been introduced to foundation design for years, simplified computer-based calculations based on the spring analogy of soils and structural elements are also frequently used in many engineering projects. Using coefficients of subgrade reactions and pile stiffness is a straightforward way to design and analyze a piled raft foundation. This paper discusses the determination of the coefficients of pile reactions for embedded piled raft foundations in soft clays subjected to vertically uniform loads through a series of finite-element analyses. The geologic property was assumed to be composed of homogeneous soft clays with the shear-wave velocities varying at 100–140 m/s. The foundations with a square raft ranging from 16 to 36 m and embedment depths of 8 and 12 m were studied. Load intensity approximating 1.5 times the excavated soil pressures was considered where the maximum uniform load was applied to the foundation. The foundation settlements and reactions of the piles were obtained first from a three-dimensional finite-element analysis. For design convenience, the dimensionless pile displacements, pile reactions, and coefficients of pile reactions were developed and presented in plots. The embedment depth-to-raft size ratio, pile slenderness ratio, and pile-to-pile spacing distance-to-pile diameter ratio were examined to find their optimized correlation. Finally, a design example was given to verify the proposed suggestions. We conclude that the proposed method can be an alternative to the piled raft foundation design. [ABSTRACT FROM AUTHOR]

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Under the framework of Biot porous media theory, a fractional order Kelvin model is used to describe the rheological effects of soil skeletons, and a coupled vibration model of saturated clay and a pile foundation is constructed. The Laplace transform is used to derive the analytical solution of the control equation in the transformation domain, and then the time–domain solution is obtained through numerical inversion. By analyzing numerical examples, the displacement and internal force response of pile foundations under horizontal vibration loads, as well as the influence of parameters, are studied. The results show that the displacement and internal force response of pile foundation vibrations in saturated clay foundations have a delayed effect. The stronger the rheological properties of the foundation soil, the more obvious the delay, the lower the load frequency, and the more significant the influence of the rheological properties on the delayed effect. The stronger the rheological properties of the soil, the smaller the displacement amplitude of the pile foundation vibration, and the higher the load frequency, the greater the decrease in displacement amplitude. The stronger the rheological properties of the soil, the smaller the positive bending moment of the pile body, while the negative bending moment increases. Both positive and negative shear forces increase, but the shear force at the top of the pile is not affected. Therefore, when designing pile foundations in saturated clay foundations, it is necessary to appropriately increase the pile foundation or increase the reinforcement to meet the shear resistance of the pile foundation. The results of this study can provide a valuable reference for geotechnical and seismic engineers in pile foundation design. [ABSTRACT FROM AUTHOR]

Major structures like offshore platforms, wind turbines, transport infrastructure, tall buildings, etc., resting on soft compressible clays, are often supported by pile foundations. Apart from usual vertical loading (dead load, live load, etc.), these piles are subjected to significant cyclic loads arising from actions of waves, ship impacts, winds or moving vehicles. Under such circumstances, the lateral mode of cyclic loading is predominant and affects the overall foundation stability. Such repetitive loading leads to stress reversal in adjacent soft clay initiating progressive degradation in soil strength and stiffness, deteriorating the pile capacity with unacceptable displacements. Although several past studies investigated the response of single pile under lateral cyclic loading, a detailed investigation on pile group in clay subjected to cyclic lateral loading, which is of immense practical interest to field engineers, is yet to be carried out. In this paper, in-depth study has been carried out by developing a three-dimensional dynamic finite element model. Comparison of the computed results with available test data validates the numerical model. Extensive parametric studies with field data indicate that both the axial and lateral pile capacities and displacements have been significantly influenced by the cyclic loading parameters. Relevant design curves are also constructed. [ABSTRACT FROM AUTHOR]

Adding the skirts around shallow foundations is a method for increasing the bearing capacity of these foundations, and skirted foundations can be considered a suitable alternative to other types, such as shallow, semi-deep, and deep foundations. In this study, the vertical bearing performance of skirted circular foundations located on clay is analyzed by the stress characteristics method, and the Martin method is employed to determine the surface roughness of the foundation with soil interface. For obtaining the skirted circular foundation's bearing capacity, superposition principle is utilized, and the depth factor is evaluated with a three-point technique. It is necessary to pay attention to the effective parameters on skirted circular foundation performance for determination of bearing capacity. Sensitivity analysis on the skirted circular foundation model is performed with various methods as input/output correlation, standard regression coefficients, perturbation method, Cotter's sensitivity indices, Morris elementary effects, Sobol's sensitivity indices, and Borgonovo sensitivity indices. The obtained results show that the order of importance of parameters is the same in all sensitivity analysis methods except the Morris method, and skirt depth is a highly effective parameter for the range of parameters considered in this study. [ABSTRACT FROM AUTHOR]

This study focused on the effect of trapped water on the bearing capacity of PVC pipe pile foundations. This research is divided into two models. The first model (pressure cap pipe pole) and the second model (open press pipe pole) each consist of four variations of PVC pipe diameters of 5.08 cm, 6.35 cm, 7.62 cm, and 10.16 cm (standard size PVC pipe diameter) with the same length of 30 cm. In the first type, all pipes are tightly closed at their upper ends. In the second type, all upper-end caps are given two holes, each with a diameter of 0.5 cm. Each pipe pile is alternately piled into soft soil with a moisture content of 98.8% is in a glass box measuring 120 cm x 20 cm x 60 cm. The test results of the load against decrease were analyzed using the Mazurkiwicks interpretation method. The bearing capacity of the end of the pole (Qp) along with the air trapped in the pipe pile (QA) can increase the carrying capacity of important poles compared to the carrying capacity of the pole side (Qs). PVC pipe poles belong to the floating pile foundation group due to the influence of air trapped inside the pile. [ABSTRACT FROM AUTHOR]

A method for the estimation of the non-linear, time-dependent settlement of piled raft foundations (PRFs) embedded in saturated clayey soils subjected to uniformly distributed load under the single-drainage condition was developed. A total of 20 different rectangular PRFs resting on four different types of normally consolidated to moderately overconsolidated clays (overconsolidation ratios of 1, 2 and 5) were analysed to quantify their short- and long-term settlements. Rigorous three-dimensional, elasto-plastic finite-element (FE) analyses were performed with the critical-state-based modified Cam Clay soil constitutive model. Biot's coupled consolidation theory was used to model the time-dependent dissipation of excess pore pressure under the single-drainage condition. The FE analysis results were used to investigate systematically the influence of time and various soil and PRF parameters on the settlement responses of piled rafts. Fitted equations correlating PRF settlements and the degree of consolidation with various influencing parameters were developed. The proposed equations predicted the immediate and primary consolidation settlements and the degree of consolidation with reasonable accuracy and can be used in initial design stages. [ABSTRACT FROM AUTHOR]

The performance of marine clay (MC) treated with embedded polyurethane (PU) piles under vertical load is assessed through three-dimensional finite element (FE) simulations. The results of the FE analyses were validated using small scale physical model tests. The influence of pile length ratio and area ratio of the embedded PU piles in MC were also investigated. Additionally, the failure modes of the PU piled rafts were studied and safety analysis using c/ϕ reduction method were performed to determine the safety factor of the foundation. Results revealed that the bearing capacity of the MC treated with PU piled raft improved due to the increase in length and area ratio of the PU pile. The bearing capacity of MC that was stabilized with PU piles using an area ratio of 0.28, increased by 42%, 157%, 197% and 259%, with a length ratio of 0.25, 0.50, 0.75 and 1.00, respectively compared to the untreated MC. The untreated MC exhibited bearing capacity failure pattern that was characterised by an upward heave at the side of the footing. The side heave decreased by 91% when the MC was treated with PU pile using length and area ratios of 0.5 and 0.13, respectively. The result shows that increasing in the length ratio of the floating pile improves the safety factor of the stabilized soil. The safety factor improves from 1.1 to 1.2 and 1.3 when the length ratio increases from 0.25 to 0.50 and 0.75 respectively. [ABSTRACT FROM AUTHOR]

The development of foundation excavations in congested urban areas inevitably induces stress release and soil movements, resulting in additional lateral deflections in adjacent pile foundations, commonly referred to as passive loading piles. Prior research on pile deflection resulting from nearby excavations primarily focused on single-pile behavior and paid little attention to the characteristics of pile groups. This paper presents a two-step approach to predicting the behavior of pile deformation resulting from nearby excavation. Firstly, Mindlin solution in combination with the double Gauss-Legendre formula is employed to calculate the additional lateral stress acting on the centerline of the passive pile resulting from nearby excavations. Secondly, the equation governing the deflection of the passive pile is determined using the Pasternak foundation model and solved using the finite difference method. On the basis of the Mindlin equation, shielding influence among piles is developed and applied to the analysis of a laterally loaded passive pile group. Last but not least, the accuracy of the presented approach is validated by comparing the results from two published centrifuge model tests with single piles and pile groups, and good agreements are obtained. Generally, the recommended two-step approach presents effective insight into the interaction between the excavation, soil, and pile, taking into account the influence of the shielding effect between piles. It can be applied as an alternative method for the conservation evaluation of the deformation tendency of pile foundation deformation in the pre-design of nearby excavations. [ABSTRACT FROM AUTHOR]

Pile foundations are often subjected to lateral pressures in addition to axial loads due to earthquakes, ground pressure, and wind pressures in various buildings. As a result, pile foundations have gotten more research than any other type of foundation. Furthermore, estimating the lateral load capacity of a pile (LLCP) accurately is a difficult undertaking, and there has been relatively little study in this field. To overcome these problems, in this study, the adaptive neuro-fuzzy inference system (ANFIS) was ustilized to construct forecasting models for the indirect assessment of LLCP embedded in clay in this work. The fuzzy c-means clustering technique (FCM) and the subtractive clustering method (SCM) were implemented as ANFIS models. The data from open-source literature were used to evaluate the two ANFIS models. In these models, pile length (L), pile diameter (D), undrained shear strength of soil (Su), and eccentricity of load (e) were used as the inputs, while the measured LLCP in clay was the output. To compare the performance of the estimating models, several statistical performance measures were used. The modeling results show that the relationships determined for estimating the LLCP in clay by ANFIS models (ANFIS-SCM and ANFIS-FCM) are accurate and close to the real value. It can also be concluded that the use of ANFIS models to predict the LLCP in clay is very efficient. [ABSTRACT FROM AUTHOR]

Torsional load arising from horizontal load eccentricity has a significant effect on the ultimate horizontal load carrying capacity of tripod bucket foundations in clay. In this paper, the effect of torsional load on the failure mechanism and ultimate horizontal capacity of tripod bucket foundations in undrained clay was studied using 3D finite-element analyses. Three single buckets were connected to form a rigid tripod bucket foundation system. Two different shear strength profiles, that is, uniform and linearly increasing with depth were considered. A detailed parametric study was conducted by varying the bucket spacing and embedment depth to explore the effects of different governing parameters. All the analyses were carried out for smooth and rough interface conditions. The influence of torsion on horizontal capacity is presented in the form of combined horizontal-torsional (H-T) failure envelopes. Reductions in ultimate horizontal capacity with increasing load eccentricity were quantified for the ease of practice. Finally, an expression for estimating combined H-T capacity is provided as a function of normalized spacing and embedment. Additional analyses were also performed to evaluate the effect of moment arising from vertical eccentricity on the combined H-T capacity. [ABSTRACT FROM AUTHOR]

Rapid urbanization has led to the construction of important structures like bridges, flyovers and high rise buildings, mostly supported by pile foundations. In view of recent scarcity of land avoiding a particular construction site with poor soil deposit may not be a viable option. Hence, ground improvement has become an important remedial solution in the field of geotechnical engineering. Optimum depth of ground improvement required to achieve maximum lateral capacity of pile under seismic conditions is very much needed for practicing engineers. In the present study, Finite Element (FE) approach has been utilized to propose a simplified method to study the lateral response of pile under combined vertical and lateral load, installed in virgin as well as improved clayey deposit subjected to seismic motion. Nonlinear behavior of clay has been simulated using cyclic p-y curves. The number of equivalent uniform cycle for soil stiffness degradation has been considered based on earthquake magnitude. Stochastic simulation has been used to generate site specific earthquake accelerograms, considering different source to site distances. Comparison of pile behavior under different seismic motions of varying PBRA (Peak Bedrock Acceleration) have been done considering two different types of soil profile. The study reveals that with increased source to site distance, PBRA reduces whereas, PBRA increases with increased magnitude of earthquake. Maximum horizontal acceleration of soil (MHA) increases with increased earthquake magnitude and reduces with increased depth of ground treatment. Lateral pile head stiffness reduces with increased PBRA and increases with increased pile slenderness ratio up to L/D ≤ 20 , beyond which further increase of slenderness ratio reduces lateral pile capacity. Optimum depth of ground improvement for pile under seismic motion may be taken as about 6D to 8D for free head pile and 8D to 10D for fixed head pile. [ABSTRACT FROM AUTHOR]

This document is a discussion of a research paper titled "Numerical Study of the Effect of Ground Improvement on Basal Heave Stability for Deep Excavations in Normally Consolidated Clays" by Ari Surya Abdi and Chang-Yu Ou. The authors conducted a three-dimensional finite-element method analysis to investigate the impact of ground improvement on the stability of deep excavations in soft clays. They proposed a modified Terzaghi's method based on their findings. However, the discussion raises concerns about the reliability of the authors' numerical simulation results and suggests the need for validation through field or experimental data. It also questions the use of an elastic-perfectly plastic Mohr-Coulomb model and the absence of mention of dewatering in the original paper. The discussion further examines the displacement patterns and deflection profiles of retaining walls during excavation. The author requests a response from the original authors. [Extracted from the article]

This summary discusses the article "Installation Effects and Behavior of a Driven Prestressed High-Strength Concrete Nodular Pile in Deep Saturated Soft Clay" by Jian-lin Yu, Jia-jin Zhou, Ri-hong Zhang, and Xiao-nan Gong. The authors conducted a full-scale experimental study to investigate the behavioral characteristics of a driven prestressed high-strength concrete (PHC) nodular pile in deep-saturated soft clay. They compared the installation effects and shaft frictional resistance of the nodular pile to a similar nonnodular pile. The study found that nodular piles had higher load-bearing capacity and improved shaft resistance compared to nonnodular piles. The authors also discussed the influence of pile installation on the surrounding soil and provided information on pile spacing and pore-water pressure. [Extracted from the article]

The surrounding surcharge has an adverse impact on the service performance of buildings and bridges, and it can endanger their structural safety, especially in soft soil areas. As one case study, the inclination accident of an expressway ramp bridge and its rectification are investigated in this study. Through the three-dimensional (3D) finite element (FE) analysis of the overall structures composed of the bridge span, the pier, and the pile foundation, the whole process of the inclination by the adjacent dumped earth, partial recovery by the unloading, and the lateral pushing rectification of the bridge structure were simulated. The results show that the surcharge load leads to soil displacement near the bridge pile, and the pile-soil interaction leads to the pile deformation, which further causes the inclination of the pier, and the movement of the bridge span. The severity of the accident can be measured by the inclination of the piers and the opening widths of the bridge expansion joints. Due to the plastic deformation and drainage consolidation of the soft clay foundation under the surcharge load, the inclination of the piles and piers cannot be fully recovered after unloading. In order to capture these processes, the FE simulation was divided into three steps. First, the drainage consolidation of the soil foundation were identified by FE simulation and the field measurement of the recovery of the structure after unloading. Second, the effects of soil properties, the surcharge time and surcharge strength on the bridge inclination and the recovery capacity after unloading are discussed. Finally, the rectification of the bridge by lateral pushing was simulated, and the deformation and stress in the pier and pile were calculated to evaluate the safety of the structures. These analyses provided understanding towards the prevention of the bridge inclination under surcharge load, prediction of the recovery by the unloading, and the methods to reduce the residual deformation to meet the specifications. [ABSTRACT FROM AUTHOR]

In the present study, laboratory model tests and numerical analysis are carried out to study the immediate, and consolidation settlement of shallow foundations rested on clayey soil. The purpose is to evaluate the immediate and consolidation settlement of different cases and compares them with the calculated values using theoretical equations; the numerical analysis is utilized by the Plaxis-3D program for developing the finite element model, whereas the soft soil model was used for simulation. It was studied the effect of three parameters on the behavior of the foundation for immediate and consolidation settlement, these parameters are soil cohesion, the pressure applied on the foundation, and layer thickness. The obtained results indicated that the simulation using the soft soil model underestimates the immediate settlement by about 30 % and gives excellent results for predicting consolidation settlement. The total settlement of shallow raft foundation rested on a clay layer of depth three times raft width to one time was increased by about 66 %. The consolidation settlement is much higher than the immediate in clayey soils, however, the average of immediate to consolidation settlement is equal to 0.3 % for pressure 20 kPa, and increases with rising applied pressure until it reaches 1.2 %. The numerical analysis revealed a lower value than the calculated using the theoretical equation for immediate settlement, while for consolidation settlement, the results are close except for the soft clay condition cu = 20 kPa. [ABSTRACT FROM AUTHOR]

Clay soil is a common building foundation material, and its permeability is very important for the safety of foundation pits and the later settlement of buildings. However, the traditional Kozeny-Carman (K-C) equation shows serious discrepancies when predicting the permeability of clay in building foundation treatment. Therefore, solving the application of K-C equation in clay is a problem faced by the engineers and scholars. In this paper, the influence of clay mineralogy on pore structure and permeability is analyzed, and then the effective e (eeff) and effective SSA (Seff) are proposed. Based on the eeff and Seff, the permeability prediction model modified on Kozeny-Carman is built. Then, seepage experiments are conducted on two types of clay samples to test this prediction model; at the same time, the MIP combining freeze-drying methods are used to obtain the Seff and eeff. Through the discussion of the test results, three main conclusions are obtained: (1) there are invalid pores in clay due to the influence of clay mineral, this is the reason for which K-C equation is unsuitable for clay; (2) the eeff and Seff can reflect the structural state of clay during seepage; (3) the results of the permeability prediction model in this paper agree well with the test results, which indicates that this prediction model is applicable to clay. The research results of this paper are significant to solve the academic problem that K-C equation is not applicable to clay and significant to ensure the safety of building foundation pits in clay areas. [ABSTRACT FROM AUTHOR]

The soil–water characteristic curve (SWCC) is a key input for the numerical simulation of geotechnical engineering. It contains the basic information needed to describe the mechanical behavior of unsaturated soil. In order to study the variation of the SWCC characteristics and its mechanism after the freeze–thaw (F–T) process of low-liquid-limit silty clay in seasonally frozen regions, the SWCC of the soil samples subjected to zero, one, three, five, and seven F–T cycles at three dry densities were measured; then the microstructure was scanned by scanning electron microscopy (SEM) to analyze the relationship between the characteristic parameters of the SWCC and the microstructure after F–T cycles. Finally, according to the mathematical law of characteristic parameters, the prediction equation for the parameters of the SWCC considering the F–T cycles was established, which has a suitable fitting effect with the experimental data. The result shows that with the increase in F–T cycles, the air-entry value (AEV) and residual saturation (RS) decrease gradually, while the saturated water content and the moisture-losing rate of the transition section slightly increased. According to the microstructure analysis, it is due to the F–T process that the compacted soil sample has cracks, the entire plate structure is destroyed, and thus the arrangement between the soil particles becomes looser, and the porosity and average pore size increase. This study can provide data support and references for the design of low-liquid-limit silty clay foundation engineering in seasonally freezing regions. [ABSTRACT FROM AUTHOR]

Accurately predicting the installation resistance is of great benefit to a rational and economical design of foundations. This research performs a large-deformation finite-element analysis to investigate the effect of soil stiffness on the end bearing resistance in uniform clay. Different types of geotechnical structures and foundations, e.g., cone penetrometer, strip foundation, bucket foundation, and deep piled foundation are considered. Results show that soil stiffness has a negligible impact during shallow penetration but becomes pronounced at deep penetration. It is found that for strip footings, effect of soil stiffness is minimal, whereas the end bearing resistances of CPT and deep piled foundation with a partial plug are highly dependent on the soil stiffness. For a rough pile foundation, the resistance factor N c,pf increases by approximately 30% as soil rigidity I r increases from 50 to 500. For a bucket foundation, the effect of soil stiffness on the end bearing resistance falls between that of "shallow" and "deep" foundations. Based on the numerical results, empirical expressions are proposed to predict the end bearing resistance factor accounting for the effect of soil stiffness. [ABSTRACT FROM AUTHOR]

Offshore wind turbines are often constructed on the foundation of soft clay, which often experience strength and stiffness weakening and internal plastic strain under cyclic loading. These changes in the mechanical properties of soft clay foundation can negatively impact the normal operation of the upper turbine. Due to the complexity of the mechanical properties of soft clay, most of the existing cyclic pile-soil load transfer models for soft clay foundations are based on hyperbolic models, which are more complicated and less efficient. To address this problem, this paper introduces a mechanical model that can describe the cyclic weakening characteristics of soft clay in pile-soil interaction, and realizes the weakening characteristics of the soil with the cyclic loading by using ABAQUS subroutine secondary development. By introducing the cyclic weakening model of soft clay into the numerical simulation of pile-soil model, the weakening law of side resistance of pile with the number of cycles is obtained. The pile side load transfer model under the traditional static condition is improved, and a trilinear model of pile side load transfer that can consider the cyclic weakening effect of soft clay is proposed; in addition, the calculation method of pile foundation vertical bearing capacity is established according to the load transfer method which can consider the cyclic weakening effect of soft clay, and compared with the model test results in the existing literature, the correctness and effectiveness of the calculation method of pile foundation vertical bearing capacity considering the cyclic weakening effect of soft clay proposed in this paper are verified. Finally, the method is applied to the actual project of an offshore wind power pile foundation, and the vertical bearing capacity of offshore wind power pile foundation is calculated. [ABSTRACT FROM AUTHOR]

The settlements and corresponding soil reactions of a surface raft foundation subjected to vertically uniform load at the sites of granular or cohesive soils have been qualitatively introduced to engineers in the past. This study intends to verify the foundation load-response mechanism using three-dimensional finite-element analyses. The Mohr–Coulomb soil model was used to simulate the nonlinear effects of the granular and cohesive soils. The coefficients of subgrade reactions of the soil were back-calculated and compared to those obtained from the rigid foundation model. For all the square surface rafts studied, non-uniform settlements with the largest value at the center can be found. For the smallest rafts located in clay, the soil reactions were found to be rather consistent. For larger rafts in clay, the soil reactions would be changed according to the soil stiffness and raft dimensions. For surface rafts in sand, the effects of soil stiffness on soil reactions appeared to be insignificant. The soil reactions were generally higher at the center and varied with raft dimensions. For the smallest raft in sand, large soil reactions can be found at the edge. The coefficients of subgrade reactions were found to be more consistent with the smallest values occurring at the center. The results of this study indicate that the load-response mechanism of the raft foundation is rather complicated. Such load-response mechanisms are strongly affected by the relative rigidity of the foundation depending on soil stiffness and foundation dimensions. [ABSTRACT FROM AUTHOR]

Time-dependent response of piled raft foundations (PRFs) in saturated, normally consolidated and moderately overconsolidated clayey soils under the single-drainage condition is investigated using three-dimensional, elastoplastic finite-element (FE) analysis with the modified cam clay (MCC) soil constitutive model. Four different types of clay (Boston Blue Clay, San Francisco Bay Mud, London Clay, and Shanghai Clay) with different values of overconsolidation ratio (OCR) (OCR=1 , 2, and 5) and 20 different configurations of rectangular PRFs are considered for the study. The settlement response and load sharing of PRFs are investigated. Regression analyses are performed with the FE analysis results to obtain fitted equations for immediate settlement, primary consolidation settlement, and degree of consolidation of PRFs. These equations are applicable to PRFs with cast in situ bored piles similar in size to those considered in this study. The proposed equations can be used to estimate time-dependent PRF settlement in normally consolidated and moderately overconsolidated clay as part of preliminary design calculations. [ABSTRACT FROM AUTHOR]

Time-dependent settlements of piled raft foundations embedded in consolidating clays were studied using three-dimensional (3D) finite-element analysis and critical state-based soil constitutive modified Cam-Clay (MCC) model. In this study, different small to large rectangular rafts connected to circular bored cast-in-situ piles resting on four different types of clays and with varying overconsolidation ratios (OCRs) (1, 2, and 5) for each clay under a single drainage condition were analyzed. The influence of various piled raft parameters (pile length, pile spacing, pile diameter, raft thickness) and soil parameters (Poisson's ratio of soil, soil critical state parameters, stress history of soil or OCR) on immediate and consolidation settlements of piled rafts were investigated. The detailed parametric study shows that critical state parameters and soil elastic properties have important roles in piled raft immediate and consolidation settlements. However, the pattern of parametric influence on immediate settlement and consolidation settlement is different. To capture the total settlement at the end of primary consolidation, a simple and quick calculation method for estimating the average soil subgrade modulus below the piled raft in consolidating clays is proposed through regression analysis and defining a combined influence parameter based on soil parameters, area ratio, and normalized loading. The results of the proposed method were compared with five case studies of piled raft foundations in various normally or overconsolidated clays showing satisfactory matches. It is believed that the proposed method will be very useful for design practitioners to get a quick estimate for the overall settlement of piled raft at the initial design stage. [ABSTRACT FROM AUTHOR]

Lithomargic clay is found along the Eastern and Western coasts of Southern India. Presence of weak soils like lithomargic clay below the foundations, cause serious problems when they come in contact with water, and non-availability of stronger fill materials locally, to replace them is a challenge to foundation engineers. An attempt has been made in this paper to improve the strength of lithomargic clay by chemical stabilization using Lime and Granulated Blast Furnace Slag (GBFS). Disposal of massive amounts of industrial waste, GBFS, has become an environmental problem and utilization of the same for soil stabilization would be a sustainable solution for disposal. To optimize the use of lime and understand the mechanism behind the gain in strength, laboratory experiments were conducted on lithomargic clay, by replacing it with varying amounts of GBFS and addition of different percentages of lime. The optimum lime and GBFS content were found to be 4% and 20% respectively. Further optimization was done by mixing lithomargic clay with 4% lime and 20% GBFS and a significant strength improvement was observed. SEM and XRD analyses were conducted on the stabilized soil and the increase in strength was established from structural changes and formation of compounds like CSH and CASH. PLAXIS 2D was used to understand the settlement behavior of both the unstabilized and stabilized soils below strip foundations of varying widths. From load settlement analysis, it was observed that the net allowable pressure increases with increase in GBFS content and further increases with addition of lime to soil stabilised with optimum GBFS. [ABSTRACT FROM AUTHOR]

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The article examines the formation and development of engineering and geological properties of the Paleogene clays of North Tamdytau. By examining the features of the geological and tectonic development of the North Tamdytau, we have defined the formation and development of clays within the arid lithogenesis, distribution, thickness, depth of occurrence of lithology and properties. Their study has an important theoretical and practical importance, as these sediments are most often the foundations for various engineering structures. [ABSTRACT FROM AUTHOR]

A simplified analytical approach based on the non-linear pile–soil interaction model under vertical load is employed to analyse settlement of piled raft foundations. The accuracy of the simplified method is verified through comparisons with the results from previous research. Furthermore, according to the calculation results of various pile configurations, a simple empirical equation for estimating long-term settlement of a piled raft foundation is proposed. The prediction equation is validated through comparison with published cases. The comparison results show that the ratio of long-term settlement to immediate settlement increases linearly with the square root of the number of piles (at the same pile spacing), whereas the influence of the length/diameter ratio of the pile is small. The settlement ratio is approximately 2 for a piled raft foundation, and 1·5 for a raft or box foundation, and this may be useful for preliminary assessment of the long-term settlement behaviour of piled raft foundations. [ABSTRACT FROM AUTHOR]

In the rigorous analysis using FEM, the load sharing of the piles between the shaft and base resistance increased with increase in limited number of piles i.e. limited to decrease in pile spacing. The load sharing depends upon their location and spacing. The load carried by the center pile reduces with the increase in the number of piles and piled area. For the edge piles, it increased with the increase in the number of piles, whereas decreased for the corner piles. The total load carrying capacity of the piles increased with the pile sizes and spacing. The piled raft settlement decreases with the increase in the number of piles. By rearranging the same number of piles, more settlement of piled raft is observed for less pile spacing, which concentrated at the center, and the settlement is decreased with increase in pile spacing, which scattered outwards. Increased in number of piles is not always advisable and expensive. Based on limitation in settlement as specified by the code, limited number of piles and pile spacing are recommended. The settlement profile along the centre line of the piled raft decreased with the increase in the number of piles and more flexible at larger pile spacing. [ABSTRACT FROM AUTHOR]

This article evaluates two distinct external effects on the settlement results from standard analyses of piled raft foundation systems. The influence of the excavation level and the influence of the number of piles underneath the pile will be separately assessed by two independent analyses for two published case histories, respectively a house located in Gothenburg and another in Uppsala, Sweden. They have been initially presented by Hansbo (1993) and Hansbo and Källström (1983). Both structures were founded over a soft, highly plastic marine clay of varying thickness, where the foundation was designed by using the concept of "creep piling", i.e., piles in a state of full load mobilization. The analyses were carried out with the numerical tools DEFPIG and GARP, by considering a series of simplified assumptions for the load pattern, raft and pile characteristics and subsoil profile. The soil, pile and load characteristics have been considered, with analyses that allowed (and not) the effect of the excavation level (1st case history), and with variation (optimization) of the number of piles (2nd. case history). The exercise emphasizes the importance of the consideration of the excavation level for the proper assessment of the settlement pattern underneath the raft, and the beneficial aspect on the optimization of the number of piles in the piled raft design. [ABSTRACT FROM AUTHOR]

When designing a piled raft foundation (PR) on clay, it is necessary to understand the timedependent behaviour of the foundation because stresses and strains in clayey ground will change for a long time after the construction, due to consolidation processes of the ground. This paper, therefore, aims to investigate the long-term behaviour of PRs through small-scale physical modelling. In the experiments, the model ground was prepared by consolidating a slurry mixture of Kasaoka clay and silica sand. The model foundations consisted of a square raft having a width of 125 mm and 4 or 9 piles having a length of 150 mm. For the loading test of PR, vertical load was increased by multiple steps and each load step was maintained to observe the long-term behaviour. The experimental results show that the piles effectively suppress the foundation settlement for relatively smaller loads. In the primary consolidation stage, the pile resistance increases with elapsed time while the raft resistance decreases. This is caused by the dissipation of pore water pressure and the corresponding increase of effective stresses of soils below the raft base. In the secondary consolidation stage, for the case of 4-pile PR, the resistances of both the raft and piles are stable although creep settlement continues. For the secondary consolidation stage of 9-pile PR, pile load reduces slightly under smaller applied loads and stable under larger applied loads. In general, the 9-pile PR reduces the foundation settlement significantly under smaller applied loads, compared to the 4-pile PR. [ABSTRACT FROM AUTHOR]

In this research, the effect of using piles on the behavior of the foundation located on the slope has been studied experimentally and numerically. In the laboratory study, 12 models with a scale of 1:20, and in numerical analysis, 72 models in full-scale and laboratory-scale have been studied. The analyzed soil was made of clay. The results showed that reinforcing the slope with piles can significantly improve its behavior, so by increasing the ratio of pile length to foundation width from 1 to 4, an improvement of about 5 to 70% of the bearing capacity of the foundation systems was observed. In all scenarios, the ratio of failure settlement to the width of the foundation is 3 to 5 percent. Evaluations also showed that the use of piles with a length equal to the width of the foundation has no significant effect on the behavior of the foundation. [ABSTRACT FROM AUTHOR]

Single pile foundation has been widely used for the most offshore wind turbines to resist the cyclic loading resulted from the wind and wave. The cyclic loading can result in the degradation of the shear strength and the stiffness of clays surrounding piles. This study proposed a practical framework for assessing the effect of cyclic softening of clays on the lateral response of piles. A 3D finite difference model was developed for the pile – soil interaction under cyclic loading and then verified by full-scale monotonic and cyclic lateral load tests conducted on the single pile in clay. The cyclic softening behavior of undrained clays was described by a nonlinear dynamic softening constitutive model developed by the authors. The effect of the loading type (i.e., one-way and two-way loading) and the loading amplitude on the cyclic lateral response of piles was investigated. Moreover, a prediction function was proposed and was demonstrated to be effective in estimating the evolution of cumulative peak lateral displacement of cyclically loaded single piles in clays. The proposed practical framework provides an alternative for predicting the cyclic response of single piles in clays based on the monotonic lateral load test of piles. • A nonlinear dynamic softening constitutive model was used to describe the cyclic softening behavior of undrained clays. • A 3D numerical model was developed for the lateral response of piles in clay under cyclic loading. • A prediction function was proposed to estimate the evolution of the cumulative peak lateral displacement of piles in clays. • The proposed practical framework provides an alternative for predicting the cyclic response of single piles in clays. [ABSTRACT FROM AUTHOR]

Large fixed vertical offshore wind turbine (OWT) tower structures are typically used to transfer complex loads to the foundations from a combination of wind, waves, and self-weight. These loads must be accommodated within a very small rotation envelope and natural frequency bands to allow the turbines to operate effectively. These challenging loading conditions and strict operational requirements can lead to extremely costly foundation designs. Several foundation options are available to support these turbines, with monopiles currently accounting for 80% of the installed capacity with routinely used diameters of 5–8 m and depths of penetration of 30–80 m. To limit monopile diameters and penetration depths, an improved monopile design: the 'hybrid foundation' comprising a plate and centrally located pile, is proposed as an alternative to monopiles. A series of scaled physical model centrifuge tests were conducted to investigate the benefits of the hybrid foundation system and compare its behavior with the typically used monopiles. This type of foundation system can enhance the performance of an OWT since the turbines are subjected to high lateral loads and overturning moments. Centrifuge modeling has been used to investigate the lateral capacity and stiffness of the foundations under lateral monotonic and cyclic loading conditions. Two models were tested: a standard monopile (MP) and a hybrid foundation (HF). Lateral loads were applied with eccentricity for both models to replicate prototype (field) conditions. Models were tested at 50g in over-consolidated clay beds. These soil samples were prepared using inflight consolidation and subjected to a sand surcharge, to increase the shear strength in the zone of influence of the model foundations. Monotonic lateral loading results indicated that the addition of a plate improves the relative lateral ultimate capacity, whilst enabling a reduction of monopile penetration depth and diameter for similar capacities. Specifically, similar capacity/stiffness was realized for the HF system compared to the MP. One-way cyclic lateral loading indicated both the HF and the MP had a shakedown response under fatigue loading of up to 10000 cycles, which indicates the potential use of this novel system for future developments. • HF offered a similar capacity to MP although with a smaller and shorter monopile size. • Damage accumulation relationships are proposed describing the rotation evolution versus the number of cycles for various loading magnitudes. • Under cyclic lateral loading, the HF continued to record increased rotations; however, at decaying rates. • The rotation magnitude increased with the increase of cyclic loading ratio ζ. [ABSTRACT FROM AUTHOR]

Soft clay soils are problematic soil that causes bearing capacity failure and excessive settlement, leading to severe damage to buildings and foundation. In this study, bottom ash is used to replace the natural aggregate while quicklime is used to increase the bonding between bottomash particles. This research is aimed to investigate the role of single encased lime bottom ash column (ELBAC) in improving the shear strength by using laboratory scale model. Kaolin is being used as soil sample while lime bottom ash as the reinforced column and the column is encased with non-woven geotextile. Laboratory tests are conducted to determine the physical properties of bottom ash, kaolin clay, and quicklime sample. Unconfined Compression Test (UCT) also used to test the shear strength of the reinforced kaolin samples. There are 21 kaolin samples being tested in this study and the dimension of the specimen used is 50mm in diameter and 100mm in height. However, there are two different types of the diameter of single lime bottom ash column being used which are 10mm and 16mm. The heights of the column are 60mm, 80mm and 100mm. The improvement of shear strength of single encapsulated lime bottom ash column with area replacement ratio of 4.00% (10mm column diameter) and 10.24% (16mm column diameter) are 43.58%, 50.00%, 49.17% and 38.08%, 42.67%, 32.75% at sample penetration ratio, Hc/Hs of 0.6, 0.8 and 1.0 respectively. It can be concluded that the shear strength of soft clay could be improved by the installation of the single encapsulated lime bottom ash column. [ABSTRACT FROM AUTHOR]

The stability of skirted foundations subjected to combined vertical, horizontal and moment loading is of importance to the offshore engineering. The paper reports a computer-aided study on the effects of strength anisotropy and foundation embedment depth on the combined bearing capacity of skirted foundations. The results show that when the traditional load reference point, i.e. the base center, is utilized, the shape of failure envelope for skirted foundations is strongly dependent on embedment ratio, however independent of soil strength anisotropy. To gain a unified equation to describe the shapes of failure envelopes for skirted foundations with a range of embedment ratios, the searching algorithm for the optimal load reference point is implemented. Based on the optimal load reference point, the failure envelope obtained can be approximated as an ellipse in normalized moment-horizontal load space. Then a closed-form equation is proposed, which can be used to evaluate the bearing capacity of skirted foundations in soft clay considering strength anisotropy effect. [ABSTRACT FROM AUTHOR]

Skirted foundations have been widely applied as offshore foundations for several decades. In design, the use of failure envelopes is convenient for assessing stability under combined loading. A large number of studies on failure envelopes exist in the literature based on experiments and numerical analyses. Most of these studies focus on ultimate capacity and static loading. This paper presents a numerical study focusing on cyclic degradation and failure envelopes for skirted foundations subjected to combined cyclic and static loading. It was found that the shapes of the failure envelopes are little affected by degradation expressed by the number of equivalent cycles. In addition to failure envelopes, contours of displacements were computed in the three-dimensional load space (vertical, horizontal and moment load) for a more complete description of the response. As an example, the well-defined cyclic contour diagrams of Drammen clay were utilised to demonstrate how foundation response diagrams can be established. The database is accompanied by a simplified procedure to account for cyclic degradation through equivalent number of cycles, different normalised load-displacement response and variation in foundation geometry. The framework of procedures can be used to estimate foundation stiffness and capacity and the results can serve as a basis for the development of foundation macro-element models. [ABSTRACT FROM AUTHOR]

In this paper we investigate the effect of pile group geometry and loading direction on the ultimate lateral soil resistance developing on a tripod foundation, using numerical and analytical upper bound methods. Two distinct kinematic mechanisms are established, corresponding to different failure modes associated with wide and narrow pile spacing. A comparison of tripod group performance against other common pile group layouts suggests that the former results in optimal efficiency for cases when the direction of the lateral load is unknown, such as the foundation of offshore structures subjected to wind, wave and ocean current loads. [ABSTRACT FROM AUTHOR]

Rapid urbanization and the unavailability of suitable ground conditions escalated the demand for high-rise superstructures over the years. Challenges persuaded geotechnical engineers to think of a robust yet economical foundation system that can support these superstructures without compromising their safety and serviceability. The combined piled raft foundation (CPRF) has been distinguished as an effective foundation that regulates the total and differential settlements and considerably improves the overall performance of the whole structure. Substantial pieces of research have been conducted previously to understand the responses of this robust foundation under static vertical loading. A few static loading code provisions are also available to help engineers to practice such foundation systems in real field conditions. In fact, many South-East Asia and European nations have appreciated the conceptualization of CPRF based on their worthwhile functioning reported in various on-field projects. However, design provisions for CPRF under lateral loading are still terse. The present paper, therefore, attempts to critically review contemporary research on the responses of CPRF under lateral loading in different subsoil strata and discusses the importance of soil-structure interaction (SSI) consideration in the seismic design of CPRF. The emphasis of discussion is oriented to several important design aspects of CPRF such as load-sharing, bending moment, peak acceleration, lateral and vertical deformation, period lengthening, etc. A few case studies on the performance of CPRF under seismic conditions are also discussed. The significance of such a study lies in framing constructive design guidelines of CPRF under lateral loading and resting in different subsoil conditions. • The manuscript presents a state-of-the-art review of responses of CPRF subjected to lateral loading with an emphasis to seismic conditions. • The paper discusses the history of CPRF and how this has gathered confidence among practice engineers to use it for mega projects. • The paper emphasizes several important design aspects of CPRF such as load-sharing, bending moment response, peak acceleration, etc. • A brief insight into a few CPRF projects and the importance of SSI consideration in the seismic design of CPRF are also highlighted. • The significance of such a study lies in framing constructive design guidelines of CPRF for different subsoil conditions and load combinations. [ABSTRACT FROM AUTHOR]

Predicting the bearing capacity of a spudcan foundation under combined vertical ( V ), horizontal ( H ) and moment ( M ) loads is a challenging problem encountered by geotechnical engineers. In previous studies the combined VHM capacity was defined for a uniform soil profile, ignoring any variability in soil stratification and properties. In offshore conditions, however, both the soil profile and soil properties vary spatially. Therefore, it is of interest to account for the spatial variability of soil in the analysis of the bearing capacity of a spudcan. It is shown in this paper how the spatial variability of a clay affects the bearing capacity of a deeply buried spudcan foundation under combined loadings. Three-dimensional random fields are generated to model the spatial variability of undrained shear strength of clay and combined with a non-linear finite element analysis to investigate and define the VHM failure envelope of a spudcan foundation. Because of the random nature of soils VHM failure envelopes of different probability of occurrence are proposed. Results from this study provide guidance to the practical assessment of spudcan foundations in spatially varied soil conditions that can be encountered offshore. [ABSTRACT FROM AUTHOR]

Construction of an underground complex in congested urban areas calls for excavation of a group of foundation pits, referred to as a pit complex, which are usually surrounded by existing facilities. In such circumstances, the safety of the pit complex and facilities during the construction are of great concern. This paper presents a case of an underground complex construction in Shanghai soft clay. A pit complex composed of two deep excavations was excavated for a Comprehensive Transport Hub (CTH) and a commercial retail area and pedestrian concourse known as South Square (SS), which were connected to an operating metro station and a railway station. During the excavation, potential deformation of metro tracks and railway tracks were expected due to extensive soil unloading. To safeguard the railway and the subway, a zoned and staged construction technology was proposed, in which several temporary partition walls were constructed in addition to necessary supporting structures, to allow the large-scale deep excavations to be divided into several independent small-scale excavations. This paper discusses the rational construction sequence of these excavations as well as reinforcement measures in detail. The construction technology was examined by extensive field data. It is found that the maximum horizontal displacement of diaphragm walls ranged between 0.05% H e and 0.4% H e , where H e is the excavation depth. The vertical displacements of the railway tracks were well controlled, whereas the metro tracks heaved significantly due to unloading effect. [ABSTRACT FROM AUTHOR]

An elaborate three-dimensional nonlinear numerical model of a rail-tunnel-foundation system in a clay stratum was developed. The model closely represented an actual subway tunnel and described the rail, sleeper, track slab, inverted arch, lining and foundation. Operation of a subway train with six wagons traveling at 100 km/h was simulated. Large-scale nonlinear dynamic finite element computation for the system was performed. The analysis showed that the system is in a state of loading and unloading repeatedly as the train passes through the tunnel. The spatial distributions of dynamic displacement, velocity, acceleration and stresses in different parts of the system all vary simultaneously with time and space. The characteristics of dynamic stresses in the clayey stratum are much different from those in the inverted arch and lining. The dynamic stresses in the tunnel lining and inverted arch have small values, but the rate effects of dynamic stress for ballastless track slab, inverted arch and tunnel lining are much higher than that of the foundation clay. The rotations of principal stress axes in the XY and YZ planes are predominant for ballastless track slab, inverted arch, tunnel lining and foundation soil just below the tunnel lining, while rotation in the YZ plane is predominant for deeper foundation soil elements. These results justify a conclusion that the thickness of inverted arch and backfill concrete can be optimized. Much attention should be paid during design to the long-term stability of a clayey foundation. The results can be referred in the dynamic design of subways. [ABSTRACT FROM AUTHOR]