Pile-supported Embankments Research Articles

Numerical investigation of soil arching and integral abutment bridge in a pile-supported railway embankment

ABSTRACT Rail transport plays a crucial role in promoting sustainable mobility and tackling environmental challenges. However, the construction of a railway track on soft soil poses significant challenges due to the inherent instability and potential for excessive settlement. To address these issues, this study numerically assessed a pile-supported embankment and an integral abutment bridge. Two different numerical models are simulated in two-dimensional (2D) plane strain conditions. Findings from numerical analyses of the pile-supported embankment revealed that soil arching is significantly influenced by embankment height and pile spacing. The maximum settlement of the embankment decreases with an increase in embankment modulus and friction angle. Furthermore, a correlation among soil arching indicators was established. Conversely, the analysis of integral abutment railway bridges (IARBs) indicates that the performance of the transition zone is significantly influenced by factors such as approach slab geometry and multiple axle passages.

3D Numerical Investigation of Soil Arching in Deep Cement Mixing and Stiffened Deep Cement Mixing Pile-Supported Embankments

3D Numerical Investigation of Soil Arching in Deep Cement Mixing and Stiffened Deep Cement Mixing Pile-Supported Embankments

Load transfer mechanism of floating pile-supported embankments under cyclic loading

Pile-supported embankments are one of the most commonly used techniques for ground improvement in soft soil areas. Existing studies have mainly focused on embankments supported by end-bearing piles under static loading, with limited research on floating pile-supported embankments under cyclic traffic loading. In this study, model tests for unreinforced floating, unreinforced end-bearing, geosynthetic reinforced floating, and geosynthetic reinforced end-bearing pile-supported embankments were conducted. Cyclic traffic loading was simulated using a three-stage semi-sinusoidal cyclic loading. Comparative analyses and discussions are performed under floating and end-bearing conditions to investigate the influence of floating piles on the soil arching evolution and membrane effect under cyclic loading. The results indicate that floating piles result in earlier stabilization of surface settlement. There is less arching and membrane effect induced by floating piles, and the arching does not continue to degrade under cyclic loading. Less membrane effect in floating pile-supported embankments results in less geosynthetic and pile strain. The degree of membrane effect in floating pile-supported embankment largely depends on the pile-end condition.

Scaled model tests on pile types influencing the stability of stiffened deep mixed pile-supported embankment over soft clay

Scaled model tests on pile types influencing the stability of stiffened deep mixed pile-supported embankment over soft clay

Performance of unreinforced and geogrid-reinforced pile-supported embankments under localized surface loading: Analytical investigation

An analytical solution is proposed to identify the performance of unreinforced and geogrid-reinforcement pile-supported embankments under localized surface loading at working stress conditions based on the total efficacy and efficacy induced by soil arching alone, average strain of geogrid reinforcement, and average settlement of subsoil. This solution considered interactively soil arching within the embankment fill, the load-deflection behavior of geogrid reinforcement (if existed), and subsoil settlement. Specifically, the soil arching consisted of a structural arch with different stress states (evaluated by the elastoplastic state coefficient K) and a frictional arch. The load-deflection behavior of geogrid reinforcement was modeled by a membrane, with due consideration of the skin friction between the geogrid and soil. The subsoil was idealized as a one-dimensional compression model. The effectiveness of the proposed solution was verified by comparisons with results from the collected literature. It is shown that geogrid reinforcement improved the performance of embankments with low subsoil stiffness significantly more than that of those with high stiffness subsoil. A high tensile stiffness geogrid was found to be inefficient because its contribution to reducing the subsoil settlement and enhancing the load transfer efficacy was minimal. This paper provides a significant reference for optimizing these embankment design.

Discrete element analysis of geosynthetic-reinforced pile-supported embankments

A discrete element trapdoor model was established using the MatDEM software, and the effects of different embankment and reinforcement heights on the soil arching effect of embankments under reinforced conditions were investigated by introducing a biaxial geogrid. The outcomes demonstrated that the inclusion of a geosynthetic reinforcement could enhance the load transfer efficacy of the embankment and thereby reduce the differential settlement of the embankment surface. The differential settlement could be reduced by approximately 50 % when the reinforcement height and the pile cap were close. The inclusion of the geosynthetic reinforcement helped reduce the development of the slip surface within the embankment above the reinforcement and prevented the vertical slip surface from continuing to move upwards, thus ensuring that the soil arching effect did not degrade too quickly and continued to play a role. In the case of a low embankment reinforcement, the soil arching effect was largely nonfunctional because of the rapid development of the vertical slip surface, and the load on the embankment in the soft soil was mainly transferred to the piles through the tensioned membrane effect of the geosynthetic reinforcement. For a high embankment with a low reinforcement height, the soil arch structure of the embankment was well maintained, the soil arching effect did not degrade, and the load on the embankment in the upper part of the soft soil was transferred to the piles via the soil arching effect along with the tensioned membrane effect. In the case of a high embankment with a high reinforcement, the reinforcement blocked the vertical slip surface only for the soil above the reinforcement height, whereas the vertical slip surface below the reinforcement height developed in line with that of the same height, when the tensioned membrane effect and soil arching effect worked together in the embankment above the reinforcement height, and the soil arching effect below the reinforcement height degraded and hardly played a role.

Numerical tests on dynamic response of pile-supported reclaimed embankment for high-speed railway in saturated soft ground using soil–water coupling elastoplastic FEM

High-speed train (HST) running in the saturated soft ground induces significant vibration that may threaten the running safety and serviceability of high-speed railway (HSR). Extensive studies have been conducted on the dynamic responses of HSR, yet, the soil–water coupling and plastic behavior in the saturated soft ground are rarely considered, and thus the build-up of excess pore water pressure (EPWP) and displacement cannot be accurately calculated. In this study, 2D soil–water coupling elastoplastic FEM was employed to investigate HST induced vibration in the pile-supported embankment using FE code called DBLEAVES. Dynamic soil stress, EPWP, acceleration and displacement under different cases were numerically analyzed in detail. Numerical tests confirm that liquid phase in soft ground plays important influence on the dynamic responses that vertical acceleration and displacement will be overestimated while the horizontal acceleration and displacement as well as EPWP will be underestimated if soil–water coupling is not considered. Single-phase analysis also exaggerates the acceleration attenuation and underestimate the vibration amplification in soft ground. The existence of piles can induce significant soil arching effect in the embankment, the distributions of vertical acceleration and EPWP are partitioned sharply by the piles while vertical displacement in soft ground becomes more uniform along the depth direction within the pile reinforced area. The existence of piles also induces stronger vibration beneath the pile end so that larger EPWP is generated below the pile end than around the pile body. The main influence area due to HST vibration for pile-supported embankment is overall 20 m away from the centerline of HSR track, therefore, it is reasonable to improve the ground by properly increasing the number of pile within this area. When the number of pile is determined, increasing the length of pile or reducing the pile spacing are two effective ways to mitigate the dynamic response.

Assessing the Settlement and Deformation of Pile-Supported Embankments Undergoing Groundwater-Level Fluctuations: An Experimental and Simulation Study

The intensification of extreme weather phenomena, ranging from torrential downpours to protracted dry spells, which trigger fluctuations at the groundwater level, poses a grave threat to the stability of embankments, giving rise to an array of concerns including cracking and differential settlement. Consequently, it is crucial to embark on research targeted at uncovering the settlement and deformation behaviors of pile-supported embankments amidst changes in water levels. In tackling this dilemma, a series of direct shear tests were carried out across a range of wet–dry cyclic conditions. The results confirmed that the occurrence of wet–dry cycles significantly impacted the resilience of silty clay. Additionally, it was observed that the erosion of cohesion and the angle of internal friction initially diminished sharply, subsequently leveling off, with the first wet–dry cycle exerting the most substantial influence on soil strength. Employing a holistic pile-supported embankment model, simulations revealed that variations in the groundwater level, fluctuations therein, varying descent rates, and periodic shifts in the groundwater level could all prompt alterations in soil settlement between embankment piles and could augment the peak tensile stress applied to geogrids. In summary, the orthogonal experimental method was utilized, indicating that, in terms of impacting embankment settlement under periodic water-level changes, the factors ranked in descending order were the following: pile spacing, pile length, embankment height, and the height of the groundwater table.

Analytical model of three-dimensional concentric ellipsoidal soil arching in geosynthetic-reinforced pile-supported embankments

The geosynthetic-reinforced pile-supported (GRPS) embankment is an effective method for improving soft ground, widely adopted in engineering applications. In this paper, a concentric ellipsoidal soil arching model was proposed to describe the stress distribution within the GRPS embankment. An analytical solution for soil arching efficacy was derived by solving the loads acting on the pile caps and geosynthetics under piles arranged in a squared pattern. Subsequently, finite difference models were established to verify the accuracy of the derived analytical solution. Meanwhile, four field tests were introduced to validate the analytical model. Finally, parametric studies were conducted on the concentric ellipsoidal soil arching model, considering parameters such as the embankment height, the pile spacing, the pile cap width, the unit weight, and the friction angle of fill soil.

Investigation of soil arching in GRPS embankments under localized loading: Multi-span spring-based trapdoor model test

A novel multi-span spring-based trapdoor apparatus has been developed to simulate more realistically the coupling of piles, soft soil, and geosynthetics, as well as the intricate interactions between adjacent soil arches under localized loading within geo-reinforced pile-supported (GRPS) embankments. By employing movable blocks with varying spring stiffnesses, this study advances the understanding of the coupling effect between piles, soft soil, and geosynthetics. Utilizing digital image correlation (DIC) technology, the research captures the dynamic evolution of soil arch shapes, providing new insights into stabilization mechanisms within GRPS embankments. It is found that lateral geosynthetics can effectively reduce the overall settlement of the embankment and mitigate the influence of trapdoor stiffness on the soil arch height. The geo-reinforcement enhances the stability of soil arches under localized loading by providing essential support to the arch feet of multiple internal soil arches. Four distinct stages in soil arch evolution under localized loading have been identified. The relationship between geo-reinforcement stiffness and trapdoor stiffness in affecting soil arching is complex and varies with different loading scenarios. The membrane effect plays a pivotal role in inter-span load transfer.

Evaluating the mechanisms and performance of Geosynthetic-Reinforced Load Transfer Platform of pile-supported embankments design methods

This study evaluates the existing design methods of Geosynthetic-Reinforced Load Transfer Platform for Pile-Supported Embankments (GLTP-PSE) through comprehensive 3D Finite Element (FE) analyses. It scrutinizes the assumed arching mechanisms, methodologies, design criteria (arching height, maximum strain, differential settlement, and T in geosynthetics), and overall performance of these methods. The 3D FE analysis results and measurements from two case studies were compared with six established GLTP-PSE design methods based on the four design criteria. Key findings include the identification of a progressive concentrated ellipsoid as the developed soil arching formation, with arching height dependent on the embankment equivalent height (including embankment and traffic load), pile spacing, maximum strain along the geosynthetics, and the number of geosynthetic layers. The load distribution on geosynthetic reinforcement was observed to align more closely with a non-linear inverse triangle. These insights led to recommendations for updating existing design methods, enhancing the accuracy and reliability of GLTP-PSE designs. The study's outcomes contribute significantly to advancing and refining GLTP-PSE design practices by providing a deeper understanding of soil arching mechanisms and the performance of geosynthetic reinforcements.

Centrifuge Modeling Investigation of Geosynthetic-Reinforced and Pile-Supported Embankments

Centrifuge Modeling Investigation of Geosynthetic-Reinforced and Pile-Supported Embankments

Settlement and stress analysis in stabilized slab- and pile-supported embankment based on double-equal settlement plane

PurposeThe soft stabilized slab and pile-supported (SSPS) embankment is an improvement technique to increase the efficiency of resources in road construction. To capture the effects of stabilized slabs on the stress transfer mechanism, the differential settlements and the lateral displacement of the embankment completely. A theoretical model of SSPS is proposed by considering the effect of soil arching and the interaction between the embankment fill, stabilized soil, pile, foundation soil and bearing stratum.Design/methodology/approachIn the theoretical model, the stress and strain coordination relationship of the system was analyzed in view of the minimum potential energy theory and equal settlement plane theory. Subsequently, the theoretical method was applied to field tests for comparison. Finally, the influence of the elastic modulus and the thickness of the stabilized slab on the stress concentration ratio and foundation settlement were examined.FindingsIn addition to the experimental findings, the method has been revealed to be reasonable and feasible, considering its ability to effectively exploit the stabilized slab effect and improve the bearing capacity of soil and piles. An economical and reasonable arrangement scheme for the thickness and strength of stabilized slabs was obtained. The results reveal that the optimum elastic modulus was chosen as 28 MPa–60 MPa, and the optimum thickness of the stabilized slab was selected as 1.5 m–2.1 m using the parameters of field tests, which can provide guidance to engineering design.Originality/valueAn optimization calculation method is established to analyze the load transfer mechanics of the SSPS embankment based on a double-equal settlement plane. The model’s rationality was analyzed by comparing the settlement and stress concentration ratios in the field tests. Subsequently, the influence of the elastic modulus and the thickness of the stabilized slab on the stress concentration ratio and settlement were examined. An economical and reasonable arrangement scheme for the thickness and elastic modulus of stabilized slabs was obtained, which can provide a novel approach for engineering design.

Investigation of Soil Arching Effect and Accumulative Deformation in Pile-Supported Embankments Subjected to Traffic Loading Using Numerical Modeling

Investigation of Soil Arching Effect and Accumulative Deformation in Pile-Supported Embankments Subjected to Traffic Loading Using Numerical Modeling

Finite Element Analysis on the Behavior of Solidified Soil Embankments on Piled Foundations under Dynamic Traffic Loads

Most research conducted so far has primarily focused on pile-supported gravel embankments. The ability of solidified soil used as an embankment filling material has been verified, and a clear view on the performance of solidified soil embankments on piled foundations is rather limited. The three-dimensional unit cell models of pile-supported embankments are conducted to investigate the performance of solidified soil embankments in comparison to gravel embankments under static and dynamic loads. Then, a systematic parametric analysis is performed to investigate the effects of various factors, including the cohesion and friction of solidified soil, the velocity and wheel load of vehicles, the pile spacing, the height of embankments. The results show that, compared with the results of gravel embankments, the heights of the outer soil arch plane in solidified soil embankments reduces under static and dynamic loads, and the piles bear more load. In addition, the total settlements of solidified soil embankments decrease with increasing cohesions, and there is an economical cohesion of 25 kPa. The vehicle wheel load, pile spacing, and the height of embankment significantly influence the load transfer mechanism and total settlement of solidified soil embankment, while the friction angles and velocities have little effect on the total settlements and vertical stress. The relationship between the soil arch height and various parameters in solidified soil embankments is established by multiple regression analysis. This investigation highlights the advantage of solidified soil in reducing total settlement and provides an insightful understanding of the load transfer mechanism of solidified soil embankment on piled foundation.

Upward soil arching effect under unloading: mechanism, theory and engineering application

Upward soil arching effect under unloading indicates the unloading part moves in a vertically downward direction, generating the arching zone and the loosened zone towards an upward direction. This study presents a summary of definitions, characteristics, theoretical models and engineering applications for the upward soil arching effect under unloading. The evolution of the upward soil arching effect is highly related to the unloading/differential displacement. The characteristics of the upward soil arching effect under unloading are comprehensively interpreted in terms of the normalized height of arching, the minimum soil arching ratio (at which state the maximum arching is developed) and the normalized unloading displacement to reach the maximum arching state. Two deformation-dependent theoretical models are introduced, to appropriately interpret and predict the variation of the soil arching ratio with the normalized unloading displacement (i.e., the ground reaction curve). Using the research findings for the upward soil arching effect under unloading, the settlement of the geosynthetic-reinforced pile-supported embankment as well as the face stability and ground settlement during tunnelling are proven to be precisely predicted and well controlled.

Dynamic soil arching effect in pile-supported embankment due to train passages at high speeds

Pile-supported embankment has been widely adopted for high-speed railways constructed over soft soils to reduce post-construction settlement. The role of soil arching effect in stress distribution inside pile-supported embankment under static weight load has been extensively studied, while the dynamic soil arching effect due to train moving loads has been paid little attention. In this paper, a sophisticated three-dimensional (3D) track-embankment-pile-subsoil finite element model (FEM) has been developed to analyze dynamic stress responses due to train passages at high speeds. The numerical model has been validated by experimental results on a full-scale pile-supported railway embankment model. The numerical analyses reveal that the dynamic soil stress distribution in the embankment near the track is almost consistent with the Boussinesq solution, but the presence of piles underneath the embankment leads to the redistribution of dynamic soil stresses inside the embankment due to the dynamic soil arching effect. The soil arch height under train load is 2 m (2.5 times of the clear space of piles), higher than the height 1.6 m (2 times of the clear space of piles) under embankment self-weight. Besides, the pile efficacy (ratio of load borne by the pile cap to the total applied load) caused by moving train load at 100 m/s is 0.6, which also is higher than the pile efficacy 0.57 caused by embankment weight. Train passage at high speeds significantly amplifies the dynamic stress intensity in the embankment but barely changes the pile efficacy.

Probabilistic three-dimensional finite element analysis of geosynthetic-reinforced pile-supported embankments

The current study focuses on a probabilistic three-dimensional finite element analysis of geosynthetic-reinforced pile-supported embankments. The probabilistic analysis utilizes a finite element technique and was executed using Python scripting in Abaqus. A deterministic model is established for both unreinforced and geosynthetic-reinforced pile-supported embankments, employing a basic linear elastic perfectly plastic Mohr-Coulomb constitutive model. This numerical model adopted a simplified methodology that eliminates the need to simulate actual piles and subsoil. The results are validated across different embankment heights and mesh sizes. Based on results from Monte-Carlo simulations, we aimed to show how results can vary even by considering only one random variable. Probability density functions for various parameters, including pile efficacy, maximum differential settlement, and maximum strain in the reinforcement, are shown. The findings illustrate the ability of probabilistic approaches to predict the most likely occurrences for different governing parameters of geosynthetic-reinforced pile-supported embankments. They also highlight the potential of probabilistic approaches to expand further into a full-scale comprehensive study which can offer deeper insights into the stability of these embankments considering various sources of uncertainties.

The effect of geosynthetic reinforcement on the load transfer mechanism of pile-supported low embankments subject to cyclic traffic loading

Pile-supported embankments are commonly employed for highways in soft soil areas. Extensive studies have been conducted on high embankments under static loading. However, low embankments with lower costs and carbon footprint have not yet been thoroughly studied. This study aims to investigate the performance of pile-supported low embankments under cyclic traffic loading by carrying out two large-scale model tests. The soft soil was constructed using Kaolin clay, and the cyclic traffic loading was simulated using a localized semi-sinusoidal function. The effect of geosynthetic reinforcement on the load transfer mechanism of pile-supported low embankments was investigated by comparing the measured data from unreinforced and reinforced cases. Test results show that geosynthetic reinforcement reduces settlement and leads to faster stabilization of settlement in low embankments. Pile-supported low embankments experience a rapid decrease followed by a stabilization in pile efficacy with increased cyclic loading, and geosynthetic reinforcement increase the pile efficacy and facilitate quicker stabilization. Geosynthetic reinforcement enhances the transfer of static and dynamic stresses to piles, resulting in less stress degradation under cyclic loading. Based on experimental results, pile-supported embankments should account for the adverse effects of cyclic loading, even if they are classified as high embankments according to existing analytical models.

Investigation on Load Transfer in Geosynthetic-Reinforced Pile-Supported Embankments

Investigation on Load Transfer in Geosynthetic-Reinforced Pile-Supported Embankments