Geosynthetic-reinforced Pile-supported Embankment Research Articles

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.

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.

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.

Influences of number of geosynthetic reinforcement layers on soil arching under cyclic loading

Geosynthetic-reinforced pile supported (GRPS) embankments have been widely used in highways and railways on soft subsoil. During the operation period, these embankments are often subjected to cyclic loading, such as traffic loading. Considering that soil arching is a key load transfer mechanism in these embankments, the development of soil arching under cyclic loading is vital important to operational safety of these embankments. Conventional trapdoor system cannot represent actual conditions of soil arching in GRPS embankments because it have a forcibly-moved trapdoor and cannot simulate load-induced subsoil settlement. Hence, this paper used a self-moving trapdoor supported by compression springs that moved up and down dependent on its overburden pressure. To investigate influences of number of geosynthetic reinforcement layers on soil arching under cyclic loading, two self-moving trapdoor tests were conducted, including a single layer and two layers, where the total reinforcement stiffness were approximately same. The trapdoor test results show that the inclusion of two reinforcement layers with a fill layer of a certain height in between reduced surface settlement of the fill and tensile forces of reinforcement, as compared with a single reinforcement layer. It also enhanced soil arching effect and improved the stability of soil arching under cyclic loading.

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.

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

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

A Mechanical Model and Solution for Dynamic Response of Geosynthetic-Reinforced Pile-Supported Embankment under Traveling Loads

A Mechanical Model and Solution for Dynamic Response of Geosynthetic-Reinforced Pile-Supported Embankment under Traveling Loads

Dynamic Analysis of Geosynthetic-reinforced Pile-supported Embankment for a High-Speed Rail

Dynamic Analysis of Geosynthetic-reinforced Pile-supported Embankment for a High-Speed Rail

Experimental and Numerical Investigation of Geosynthetic-Reinforced Pile-Supported Embankments for Loose Sandy Soils

This research focuses on advancing the geosynthetic-reinforced pile-supported embankment technology over loose sandy soil. A small-scale laboratory model supported by floating piles and a geotextile layer was constructed, and a numerical model was validated against laboratory measurements. This study aims to achieve a more uniform distribution of the load over all piles of the system via a parametric study that analyzes the influence of embankment fill material, horizontal reinforcement scenarios, pile cap shape, and pile type. The results demonstrate that using embankment fill with high cohesion and internal friction properties leads to a significant reduction of 46% and 37% in maximum settlements, respectively, and similarly, results in a noteworthy reduction of 48% and 50% in differential settlements. The incorporation of two geotextile layers contributes to a reduction of up to 30% in maximum settlement. The utilization of plus-shaped caps in small areas, with an area equal to three times the cross-sectional area of the pile, has been substantiated as the preeminent approach for the reduction of settlements. Piles with caps also present better behavior regarding differential settlements compared to longer piles and piles with bigger diameters under the same volume condition.

Performance Evaluation of Design Methods for Geosynthetic-Reinforced Pile-Supported Embankments

Geosynthetic-reinforced pile-supported (GRPS) embankments are widely used in soft soil regions to support roadways. Various design methods for GRPS embankments have been developed; however, engineering experience and recent research have shown that the performance of these design methods varies case by case. This paper systematically evaluates the performance of several empirical GRPS embankment design methods, which include the BS8006 method, the Nordic method, the EBGEO method, the FHWA method, and the CUR226 method. A preliminary assessment of these methods using three field case studies confirms that their performances differ from each other and from field measurements, the differences sometimes being quite significant. To enable a more systematic evaluation of the design methods, a validated finite element model (FEM) was first used to conduct a comprehensive parametric study considering typical soft soil conditions and various geometrical parameters, the results of which served as a baseline for the evaluation of the design methods. The efficacy, stress concentration ratio, maximum differential settlement, and maximum reinforcement tension were used as indicators for the method evaluation. The results show that, overall, the CUR226 method outperforms other design methods. The percentage difference between the CUR226 method and FEM can be as small as 5%, and the maximum value is 130%. It was also found that the Nordic method does not apply to small embankment heights, and that the BS8006 method provides a large overestimation of reinforcement tension when pile spacing is large (>4 ft) for all embankment heights considered.

Investigation on the long-term strain of geogrid in GRPS embankment under cyclic loading

Geogrid is a horizontal reinforcement material that is used in geosynthetic-reinforced pile-supported (GRPS) embankments in freeways with soft soil. Nevertheless, the long-term deformation mechanics of geogrid in the GRPS embankment under cyclic loading is not clear enough. This paper presents a laboratory model study of a GRPS embankment to study the long-term geogrid strain under cyclic loading. The effects of parameters such as number of load cycles, load frequency, geogrid layer numbers, and length of supporting piles on the long-term strain of geogrid were investigated. The results showed that geogrid strain increased with the number of load cycles, mainly developed in the first 10 000 load cycles and increased slowly in the later period. When the frequency was increased from 1 to 5 Hz, geogrid strain increased dramatically. When compared with the condition of a single geogrid layer, the upper layer of two geogrid layers caused a less geogrid strain. Compared with long piles and short piles GRPS embankments, a sufficient membrane effect of geogrid was found for long-short piles GRPS embankments. Finally, the 95% prediction interval proposed in this paper could be expressed using a logarithmic function, providing a theoretical foundation for future engineering applications.

Proposed Method for the Design of Geosynthetic-Reinforced Pile-Supported (GRPS) Embankments

Soft soils with unfavorable properties can be improved using various ground-improvement methods. Among these methods, geosynthetic-reinforced pile-supported (GRPS) embankments are considered a reliable option for challenging ground conditions and time-bound projects. Nevertheless, the intricate load transfer mechanism of the GRPS embankment presents challenges due to the multiple interactions among its components. To overcome the limitations of current design methods that do not fully account for all interactions, a simplified design method has been developed for GRPS embankments. This method uses numerical analysis to predict pile load efficiency and geosynthetic tension. In this study, a validated model of the GRPS embankment, which incorporates certain simplifications for design purposes, was adopted. Based on this simplified model, a database of load efficiency and geosynthetic tension was collected to derive the design equations. The design method employed six parameters, namely, pile cap width, pile spacing, embankment height, oedometric modulus of the subsoil, geosynthetic stiffness, and embankment fill unit weight. The design process utilized Plaxis 3D and Curve Expert software. The results showed reasonable agreement between the findings of the proposed design method and the field measurements of eight case studies.

Recent advances in subgrade engineering for high-speed railway

Abstract In the last decade, the design and construction technologies of subgrade in high-speed railway (HSR) developed significantly. This article reviews corresponding development in five aspects, including mechanical properties of fill materials, dynamic performance of subgrade, foundation treatment, retaining structure, and smart construction technologies. It shows that for unbonded granular materials, it is acceptable to use static strength for subgrade design, but for clayey soil it would be more appropriate to base on shakedown theory. The mechanism for lime modified clay has been thoroughly reviewed, and the effect of lime content, curing age, and curing conditions on the behavior of lime-treated clay is discussed. The dynamic response of subgrade, especially the long-term deformation and dynamic stability analysis are important to understanding the behavior of HSR subgrade. The effect of track types, operation speed, etc. on the dynamic response of subgrade are reviewed first. Then, the prediction methods, influencing factors, and corresponding issue for long-term deformation of subgrade are presented, followed by the methods used for dynamic stability analysis. Three types of foundation treatment methods, including geosynthetic-reinforced pile-supported (GRPS) embankment, pile-raft structure, and pile-plate structure are reviewed for the corresponding load transmission mechanism, and application scenario. The static and dynamic behavior of four types of retaining structures are presented, including cantilever retaining wall, geosynthetic reinforced soil retaining wall, anchored retaining structure, and retaining wall reinforced by soil nailing. Finally, a series of new technologies correlated to smart construction are introduced, relating to the survey, design, construction, detection, and management of subgrade.

Physical model study of pile type effect on long-term settlement of geosynthetic-reinforced pile-supported embankment under traffic loading

In coastal area, the long-term settlement of high-way embankment is seriously concerned. Geosynthetic-reinforced pile-supported (GRPS) embankments have been widely adopted for the construction over soft soils to solve the large settlement problem. However, the long-term performance of GRPS embankment under traffic loadings is not fully understood. In this study, a series of physical model tests were conducted. Different pile types (rigid pile, rigid-flexible pile, flexible pile) and geosynthetic layers (single-layer and double-layer) were comparatively investigated. Two stages of long-term cyclic loadings were applied to simulate the traffic loadings. Based on the results, it is found that the model test with rigid pile has the least settlement, whereas the model test with flexible pile experiences the largest settlement when subjected to both 1 Hz and 2 Hz cyclic loadings. In the view of long-term settlement control, the rigid pile is the best choice for the GRPS system. The applied cyclic loadings have the lowest effect for the pile strain distribution in rigid pile model but much higher effects in both flexible pile and the rigid-flexible pile models, which demonstrates that the traffic loading after the construction of GRPS embankments may leads to unneglected stress redistributions. The findings of this study would provide the reference to consider the traffic loading effects on different pile types of GRPS embankment.

Optimized Design of Piled Embankment Using a Multi-Effect Coupling Model on a Coastal Highway

This study presents a multi-effect coupling model to optimize the design of a geosynthetic-reinforced pile-supported embankment (GRPSE) considering the coupling effects of soil arching, membranes, and pile–soil interaction on a coastal highway. The developed model could optimize the design of the GRPSE to fulfill the design and construction requirements at a relatively low project cost. This was achieved by adjusting the critical factors that govern the settlement of GRPSEs, such as pile spacing, tensile stiffness of geosynthetic reinforcement (GR), arrangement of piles, pile cap size, and cushion thickness. The model predictions were validated by a series of field tests using a range of geotechnical sensors. The results show that model predictions agreed with experimental measurements reasonably well. In addition, the results indicate that in comparison to a square arrangement of piles, a triangle net arrangement can decrease the differential settlement of pile soil. Furthermore, this study demonstrates that a change in the GR’s tensile stiffness has little impact on the settlement of GRPSEs. This study can help to improve the stability of roadbeds of coastal highways.

Seismic performance of near-fault geosynthetic-reinforced pile-supported embankment

The seismic performance of embankments is an important consideration for the design and construction of high-speed railways (HSRs) in near-fault areas. Incorporating geosynthetics into embankment soil can improve seismic resistance. However, the effect of different reinforcement methods on the seismic performance of embankments is not well understood. In this study, two 1 : 20 scaled embankment models (full-length-geosynthetic-reinforced pile-supported embankment (FRPE) and turn-back-geosynthetic-reinforced pile-supported embankment (TRPE)) were tested on a shaking table to compare their seismic performance and failure characteristics. The results show that under near-fault bidirectional seismic excitation, the pile foundations of both embankments exhibited bending deformation, with the largest bending moment in the middle of the pile body. The TRPE reduced the vertical dynamic response of the embankment slope but exhibited a more remarkable horizontal dynamic response than the FRPE. Furthermore, the embankment deformation and excess pore water pressure of the TRPE were generally larger than those of the FRPE. Nonetheless, the TRPE has potential application in practical engineering as it ensures earthquake resistance, with higher economic benefits.

Reinforcement load in geosynthetic-reinforced pile-supported model embankments

The stress conditions of geosynthetic reinforcements (GRs) are crucial in achieving the accurate serviceability design of geosynthetic-reinforced pile-supported (GRPS) embankments. However, the sensitivity of load distribution to the settlement process has been reported in geosynthetic-reinforced embankment overlying cavities. In this study, a three-dimensional model embankment was used to perform experiments and evaluate the load acting on the GR. A flexible pressure-mapping sensor was introduced to investigate the pressure distribution for two types of supporting conditions: partitioned displacement by multiple movable trapdoors and even trapdoor settlement underneath different subsoil materials. The results showed that the load on the GR was concentrated on the strip areas between adjacent pile heads along with the settlement. The measured load on the GR strip area was related to the settlement process and finally exhibited a U-shaped distribution after detachment from the support underneath. The soil arch height in the subgrade continuously increased with the settlement; meanwhile, the pile head load increased rapidly at first and then decreased slightly or remained stable depending on the foundation support stiffness. For both types of settlement behaviours, soil arching exhibited stress history-related characteristics that influence the load transfer in GRPS embankments.

Analytical solutions of the dynamic response of a dual-beam model for a geosynthetic reinforced pile-supported embankment under moving load

To analyze the dynamic response of geosynthetic-reinforced pile-supported (GRPS) embankment, a dual-beam model that includes an upper Euler-Bernoulli beam under moving concentrated load and a lower Euler-Bernoulli beam to simulate pavement structure and geosynthetic reinforcement respectively are established in this paper. Furthermore, the embankment fill layer is idealized as continuous spring-dashpot systems supporting the pavement structure. The pile improved foundation is idealized as a series of periodically distributed pile-soil spring-dashpot systems supporting the geosynthetic reinforcement. The governing equations of the dual-beam system are derived based on the assumptions above. The steady-state solutions are solved by Fourier series and verified by periodicity condition and Finite Difference Method. A detailed parametric study has been performed to analyze the effects of load velocity, pile stiffness and reinforcement moduli. The results show that the deflection and stress distribution of GRPS embankment are related to the load location. The influence of load velocity on deflection and stress distribution cannot be ignored. The deflection and stress increase as load velocity increases. Increasing pile stiffness and reinforcement modulus can reduce the influence of load velocity on the GRPS embankment. Piles and geosynthetic reinforcement play a significant role in GRPS embankment deflection and making GRPS embankment more stable.

Effect of Different Reinforced Load Transfer Platforms on Geosynthetic-Reinforced Pile-Supported Embankment: Centrifuge Model Test

Geosynthetic-reinforced pile-supported (GRPS) embankment has been widely utilized in the railways and highways subgrade of soft clay area. The load transfer platform (LTP), consisting of sand layers and one or more layers of geosynthetic, is constantly used at the base of embankment to increase the load transfer to piles and reduce the differential settlement of embankment surface. However, the effect of different reinforced LTPs on the performances of GRPS embankment has not been fully understood. Eight centrifuge model tests were conducted to investigate the effect of five influence factors on deformation and load transfer of embankment, and tensile force of geogrid: placing geogrid or not, the number of geogrid layers, geogrid reinforced position, geogrid stiffness, wrapped-back geogrid setting in LTP. The results showed that the wrapped-back geogrid setting in the LTP was equivalent to anchoring the geogrid at the slope toe of embankment, which strengthened the reinforcement-soil interaction and restricted the pull-out displacement of geogrid to enhance the stiffness for LTP. The LTP reinforced with stiffer geogrid or multi-layer geogrid contributed to increase the stability and load transfer of embankment due to the increase of the integrity stiffness for LTP. When the geogrid was set at the middle of LTP, the performances of the GRPS embankment was enhanced due to the more interfaces between the geogrid and soil to improve the integrity stiffness of the LTP. The two-layer geogrid reinforced in the LTP could be the best choice to enhance the performance of the GRPS embankment under the comprehensive consideration of the performance and economy. The five setting ways of the reinforcement in LTP increased the integrity stiffness of LTP, which provided more methods to enhance the performances of the GRPS embankment.

Two-dimensional soil arching evolution in geosynthetic-reinforced pile-supported embankments over voids

Soil arching and tensioned membrane effects are two main load transfer mechanisms for geosynthetic-reinforced pile-supported (GRPS) embankments over soft soils or voids. Evidences show that the tensioned membrane effect interacts with the soil arching effect. To investigate the soil arching evolution under different geosynthetic reinforcement stiffness and embankment height, a series of discrete element method (DEM) simulations of GRPS embankments were carried out based on physical model tests. The results indicate that the deformation pattern in the GRPS embankments changed from a concentric ellipse arch pattern to an equal settlement pattern with the increase of the embankment height. High stiffness geosynthetic hindered the development of soil arching and required more subsoil settlement to enable the development of maximum soil arching. However, soil arching in the GRPS embankments with low stiffness reinforcement degraded after reaching maximum soil arching. Appropriate stiffness reinforcement ensured the development and stability of maximum soil arching. According to the stress states on the pile top, a concentric ellipse soil arch model is proposed in this paper to describe the soil arching behavior in the GRPS embankments over voids. The predicted heights of soil arches and load efficacies on the piles agreed well with the DEM simulations and the test results from the literature.