Geosynthetic-reinforced Pile-supported Research Articles

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.

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.

Mechanical mechanism of soft soil foundation improved by geosynthetic-reinforced pile-supported technology based on field experiment

Geosynthetic-reinforced pile-supported (GRPS) technology is an effective method for improving soft soil foundations. Conducting field tests is crucial for accurately assessing the mechanical behavior of GRPS technology. Based on the fourth expansion project at Pudong Airport, field tests were conducted to investigate the effects of GRPS technology on soft-foundation treatment. Specifically, the tests examined the changes in the pile and soil settlement, pore water pressure, and pile and soil stress. The results showed that the settlement of the GRPS foundation mainly occurred during the loading period, accounting for approximately 65% of the total foundation settlement. Increasing the pile modulus and reducing the pile spacing decreased the total foundation settlement. The filling load was mainly transferred to the piles through the soil arching effect, resulting in a large excess pore water pressure in the soil layer near the pile tip. In addition, when the filling height was low, the load transfer relied predominantly on the tensile membrane effect of the geogrid, which was more pronounced near the piles. However, as the filling height increased, the soil arching effect surpassed the tensile membrane effect and played a key role in load transfer.

Case Study on Instrumenting and Monitoring Geosynthetic-Reinforced Pile-Supported Mechanically Stabilized Earth Wall Built over Soft Soil

This paper presents a case study on instrumenting, monitoring, and finite element modeling (FEM) of geosynthetic-reinforced pile-supported (GRPS) mechanically stabilized earth (MSE) walls. The GRPS-MSE wall was monitored using various instruments such as piezometers, earth pressure cells, shape-acceleration arrays (SAAs), and strain gauges. The performance criteria included efficacy, stress concentration ratio (SCR), differential settlement, and reinforcement tension. Collected data, such as excess pore-water pressures, contact pressures on pile and soft soil, differential settlements, and lateral displacement of MSE wall, were analyzed thoroughly. A 3D FEM was also developed to simulate the GRPS MSE wall, and the results are in good agreement with field data. The results demonstrated significant load transfer from soil to piles as a result of soil arching, yielding 30–32 SCR. The field efficacy was measured at 37.69 %, while the FEM efficacy was estimated as 42.4. Strains in geogrids within the geosynthetic-reinforced load transfer platform (GLTP) system were under 1%, less than the 5% maximum recommended by FHWA. The maximum differential settlement measured between pile cap and soft soil from SAAs is 7.1 mm, while it is estimated to be 8.3 mm from FEM. The MSE wall exhibited low lateral displacement (<25 mm), indicating enhanced stability because of GLTP. The comparison between five analytical GLTP design methods showed that the CUR226 methods gave the closest results to field measurements and FEM results. This study offers crucial insights into leveraging GLTP and MSE walls in highway construction.

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.

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.

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.

Review of Geosynthetic-Reinforced Pile-Supported (GRPS) embankments - parametric study and design methods

Embankment construction on soft soil may result in excessive settlement, loss of bearing capacity, or sliding instability. However, geosynthetic-reinforced pile-supported (GRPS) embankments offer an effective technique to overcome the problems resulting from soft foundations soils. This paper presents a review of the most important parameters affecting the behaviour of GRPS embankments as well as design methods that estimate tensile forces in the geosynthetic layers and load efficiency. Results highlight the importance of using GRPS embankments, but also reveal the inconsistencies between design methods. Finally, general conclusions about the design and construction of GRPS systems are presented.

Long-Term Stability of High-Speed Railway Geosynthetic Reinforced Pile-Supported Embankment Subjected to Traffic Loading Considering Arching Effect

Geosynthetic reinforced pile-supported (GRPS) embankment is widely used in the construction of high-speed railways on soft foundations. Arching effect, which is a common phenomenon in the system involving soil-structure interaction, is considered a key factor in the design of GRPS embankment. Its performance has been found inevitably to affect the post-construction settlement and bearing capacity of the embankment. However, the existing design methods are mainly based on static loading condition; soil arching effect under high-cycle loading has not been fully understood. In this study, a series of numerical simulations were conducted to study the long-term behavior of GRPS embankment under traffic loading, with the consideration of arching effect in soil. An implicit–explicit transition calculation algorithm was implemented to predict the permanent deformation under high-cycle traffic loading through the data transfer and conversion between implicit and explicit numerical stages, in which the mixed “implicit” and “explicit” calculation strategy were carried out based on the high-cycle accumulation (HCA) model. By using the proposed algorithm, a cross-section of high-speed railway GRPS embankment was selected as a case for discussion. Results indicate that the affected areas of stress concentration over piles in the embankment are reduced under traffic loading. With different levels of stability, the variation of stress concentration ratio of the arching effect can be mainly classified into three groups: stable, gradually weakened, and destroyed. Through parameter study, the effect of subsoil stiffness is discussed and a reasonable modulus ratio between pile and subsoil is suggested for the design reference.

A computation model for pile-soil stress ratio of geosynthetic-reinforced pile-supported embankments based on soil consolidation settlement

The pile-soil stress ratio (PSSR) is the key to the design and construction of geosynthetic-reinforced pile-supported (GRPS) embankments. However, the computation models for the PSSR which takes account of the effect of consolidation settlement of soil among piles (SAP) is not complete. This paper splits the piles and the SAP into multiple small elements for iterative calculation, according to the principle of the collaborative actions between pile, soil, embankment and reinforcement. The calculation method for pile-soil interaction was improved by Davis’ 1D nonlinear consolidation theory, and the hyperbolic load transfer model of pile-soil interface proposed by Wong and Teh. Then, a novel computation model for the PSSR of GRPS embankments was established, under the joint impact of soil arching effect, tension membrane effect and improved pile-soil interaction. Finally, this proposed computation model was proved reasonable by the comparison with tests and other methods, and the effects of key parameters were investigated. The results show that the settlement difference between piles and SAP increased with the degree of consolidation of the SAP and the elapse of time; the PSSR below the reinforcement net (RN) is slightly higher than that above the RN; the PSSRs above and below the RN are both positively correlated with the degree of consolidation and initial bulk compressibility of the SAP.

Geosynthetic-reinforced pile-supported embankment: settlement in different pile conditions

Three centrifuge model tests were conducted on geosynthetic-reinforced pile-supported (GRPS) embankments with side slopes to investigate the influence of pile end-bearing conditions and pile modulus on their performance. This study found that when end-bearing piles were used, differential settlement occurred at the base of the embankment and the majority of the embankment load was transferred to the piles. Floating piles, however, behaved as rigid inclusions and formed a composite foundation with their surrounding soil, which shared the total load under an approximately equal-strain condition. The use of end-bearing piles with low modulus increased the total settlement of the piles and the foundation soil at the base of the embankment and promoted lateral movement of the side slopes. Two theoretical methods were adopted with some modifications to calculate pile head settlement compared with the measured data. When the end-bearing piles were used to support the geosynthetic-reinforced embankment, the modified Vesic method considering negative skin friction along pile shafts was used to calculate the pile head settlement close to the measured one. When floating piles were used to support the geosynthetic-reinforced embankment, the modified equivalent footing method was used to calculate the settlement, matching reasonably well with the measured one.

3D modeling of geosynthetic-reinforced pile-supported embankment under cyclic loading

Geosynthetic-reinforced pile-supported (GRPS) embankments are an attractive soft soil improvement technique. They are broadly used in infrastructure projects. Most previous studies focused on investigating reinforced piled embankments under static loading. There is a paucity of studies on structure behavior under cyclic loading. In the study, three-dimensional numerical modeling using the finite element method (FEM) was performed with the objective of better understanding the cyclic behavior of GRPS embankments in terms of load transfer mechanisms and settlements. An advanced constitutive model based on the hypoplasticity concept was employed for the embankment fill to simulate the cumulative strain during each loading cycle. Parametric studies related to the embankment height, traffic loading parameters (amplitude and frequency), and number of geosynthetic reinforcement layers are presented. The numerical results obtained indicate that the presence of a geosynthetic reinforcement decelerates the reduction in the arching effect within the embankment fill and decreases the cumulative settlements. The rate of the cumulative settlements decreases with the number of load cycles. The number of geosynthetic reinforcement layers does not appear to influence the soil arching and cumulative settlements.

Analysis of geosynthetic-reinforced pile-supported embankment with soil-structure interaction models

Abstract A geosynthetic-reinforced pile-supported (GRPS) embankment is a complex soil-structure system. The response of a GRPS system is affected by the interactions among its five linked elements, namely the geosynthetic (a synthetic product used in civil engineering to stabilise the terrain), foundation, granular platform, fill soil, and geological media underlying and surrounding the foundation. The key load transfer mechanism in a GPRS embankment is a combination of various phenomena that include arching in the fill layers, tensioned membrane effect of the geosynthetic, frictional interaction, and support of the soft subsoil. Referring to the current numerical and experimental studies, a new theory has been developed in this study by combining the arching theory for the soil layer and the tensioned membrane theory for the geosynthetic. The subsoil effect with both linear and non-linear models and the frictional interaction are also included in the proposed method, thereby providing a more comprehensive design approach than the earlier methods that considered only either the tensioned membrane theory or the arching theory. It is demonstrated in this work that the proposed method produces results that are in good agreement with the experimental observations.

Experimental Investigation of Geosynthetic‐Reinforced Pile‐Supported Composite Foundations under Cyclic Loading

A series of model tests were conducted in this study to investigate the deformation characteristics of geosynthetic‐reinforced pile‐supported (GRPS) composite foundations under cyclic loading. The effects of the applied load, the number of geogrid layers, and types of piles on the performance of the GRPS composite foundation were studied through 1g physical models of composite foundation with well‐planned instrumentation. Furthermore, a numerical fitting method was used to assess the relationship between the foundation settlement and the number of load cycles. The results show that with the increase in the magnitude of cyclic load and the number of load cycles, the settlement of GRPS composite foundations and the strain of the pile and geogrid increased accordingly. Adding rigid piles and increasing the number of geogrid layers both could reduce the settlement of GRPS composite foundations, while adding rigid piles was more effective. The relationship between the foundation settlement and the number of load cycles can be expressed by an exponential regression function. The pile strain varied from place to place that the strain of the upper part of the pile was greater than that of the lower part. The geogrid showed a significant impact on the load transfer mechanism of the composite foundation as the geogrid closer to piles endured larger strain. It is critical to consider the variation of the pile strain and the geogrid strain under cyclic loading in the geotechnical practice of composite foundation. The model test results also suggest that the use of GRPS system can effectively reduce the composite foundation settlement. This paper can provide useful references for developing the theoretical framework and design guides for GRPS composite foundations under cyclic loading.

Centrifuge tests to investigate global performance of geosynthetic-reinforced pile-supported embankments with side slopes

Three centrifuge model tests were conducted to investigate the influence of the number of geosynthetic layers and the pile clear spacing on the global performance of Geosynthetic-Reinforced Pile-Supported (GRPS) embankments with side slopes constructed on soft soil foundations. This study found that the change of the geogrid number from one to two did not significantly affect the foundation settlement, the geogrid deflection, and the vertical stress at the embankment base. For the GRPS embankment with a single geogrid layer, the geogrid strain distribution at the embankment base showed an “M” shape along the transverse direction with the maximum strain near the embankment shoulder. When two geogrid layers with sand in between were used, the upper and lower layers showed different strain distributions with the maximum strains happening near the embankment shoulder and at the center of the embankment for the upper and lower layers respectively. The strains of the upper geogrid were smaller than those of the lower geogrid. Smaller pile clear spacing reduced the geogrid deflection and the foundation settlement. Despite the change of the pile clear spacing, the progressive development of soil arching with the normalized displacement at the embankment base followed a similar trend without an obvious stress recovery stage.