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

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.

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.

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.

Soil arching exists in many geotechnical applications, including tunnels, buried pipes, and geosynthetic-reinforced pile-supported (GRPS) embankments. Soil arching has been mostly investigated using trapdoor tests under soil self-weight and/or uniform surcharge. In real applications, localized surface loading, such as traffic loading, may be applied onto soil and affect or degrade soil arching. Geosynthetic reinforcement is used in GRPS embankments or over buried pipes and may have effects on soil arching mobilization and degradation under localized surface loading. The effects of surface traffic loading and geosynthetic reinforcement on soil arching have not yet been well investigated. This study investigated the effects of static surface footing loading on soil arching mobilization and degradation in geosynthetic-reinforced and unreinforced embankments using trapdoor model tests under a plane-strain condition. These model tests consisted of both trapdoor and loading stages, which were used to evaluate the mobilization and the degradation of soil arching, respectively. The trapdoor test results show that the displacement of the trapdoor induced progressive mobilization of soil arching and geosynthetic reinforcement minimized soil arching mobilization due to the change of the soil deformation. Localized surface loading degraded soil arching. Single and double layers of geosynthetic reinforcement helped maintain soil arching under localized surface loading. The test results also show that the biaxial geogrid was more effective than the uniaxial geogrid with similar tensile strength and stiffness in carrying the load due to its better lateral restraint. Geosynthetic reinforcement increased the applied surface load required to fully degrade soil arching and eliminate the benefit of the geosynthetic.

A geosynthetic-reinforced pile-supported (GRPS) embankment that consists of embankment fill, geosynthetic, piles, and foundation soils is a complex soil–structure system. Its key load transfer mechanisms include soil arching and tensioned membrane effects and subsoil resistance. Type of embankment fill (cohesive or cohesionless) and type of pile (end-bearing or floating) are expected to affect these load transfer mechanisms; however, their influence has not been well investigated. Six scaled model tests were conducted in this study to investigate the influence of the embankment fill properties, the clear spacing of pile caps, and the pile type on soil arching and tensioned membrane effects. This study used cohesive and cohesionless embankment fills and end-bearing and floating piles. The test results show that the cohesive embankment fill strengthened the soil-arching effect, increased the pile efficacy, and reduced the settlements of the subsoil between pile caps and the embankment crest under the same load as compared with the cohesionless embankment fill. The soil arching-effect was inversely proportional to the clear spacing of pile caps. Soil arching initiated at a low ratio of the embankment height to the clear spacing of pile caps (i.e. 0.5 to 0.7) and became stable at a higher ratio (i.e. 1.1 to 1.5). The embankment height when the soil arching becomes stable is also referred to as the critical height, at which full soil arching is formed. The measured vertical earth pressures at the edges of the pile caps were higher than those in the middle of the pile caps in all six model tests. When the end-bearing or floating piles were used, the loads on the piles (i.e. the pile efficacy) increased during the construction of the embankment. However, when the floating piles started to penetrate into the underlying soil under a higher load; the pile efficacy decreased with the embankment and the surcharge load. Floating piles resulted in less soil arching and larger settlement.

Geosynthetic-reinforced pile-supported embankments have been increasingly used as a rapid construction technique to reduce total and differential settlements and enhance load transfer from soil to piles for embankments over soft soils. Most studies have been done so far to investigate this embankment system under static loads. However, highway and railway embankments are subjected to cyclic loading. The behavior of this embankment system under cyclic loading is not well known, therefore, it deserves further research. In this study, the discrete element method incorporated in the Particle Flow Code (PFC) 2D was adopted to investigate the movement of soil particles above pile caps and the geogrid layer. A cyclic load was applied on the top of the assembly and the contact stresses and the tension in the geogrid under cyclic loading were monitored and analyzed. The DEM analysis shows that the geogrid reduced the permanent deformation under cyclic loading and increased the stress concentration ratio as compared with the unreinforced embankment. The flexural stiffness of the geogrid influenced the magnitude and distribution of the tension along the geogrid.

Piles or columns have been used successfully in combination with geosynthetics to support embankments over soft soil. The inclusion of geosynthetic reinforcement over piles enhances load transfer from soil to piles, reduces total and differential settlements, and increases slope stability. It creates a more economical alternative than that without the geosynthetic. An existing geosynthetic-reinforced pile-supported embankment in Berlin was selected for numerical modeling and analysis. This embankment was constructed to support railways over deep deposits of peat and soft organic soils. Precast piles and caps were installed with a load transfer platform formed by three layers of geogrid and granular materials installed between the piles and the embankment fill. Instrumentation was installed to monitor the settlements of the embankment and the strains in the geogrid layers over time. A finite difference method, incorporated in the fast Lagrangian analysis of continua three-dimensional software, was used to model this embankment. In the numerical analysis, piles were modeled with pile elements, and caps were modeled as an elastic material. Geogrid elements built in the software were used to represent the geogrid reinforcement. Embankment fill, soft soil, firm soil, and platform fill material were modeled as linearly elastic perfectly plastic materials with Mohr–Coulomb failure criteria. The embankment was built by a number of lifts to simulate its construction. Numerical results and comparisons with field measurements on the vertical and lateral displacements, the tension along the reinforcement, and the axial forces and moments on piles are presented.

In 1980s, when digital technology flourished, computer was used solely as drawing tool, while in today's architectural environment, digital technology has undertaken the role of being the main component of the architectural production process. Parametric design, algorithmic design and similar digital design methods, gathered under the title of computational design, have been an important tool in the emergence of contemporary architectural products. With its alternatives, parametric design has been one of the most important current architecture’s problem solvers, enabling control of all criteria, from production of forms to efficient use of topography and natural conditions to reflection of local cultural architectural texture. Parametric design with its ability to use all the criteria limiting design as a forming tool has become an instrument that arranges relations of architecture with different disciplines such as ecology, climatology, engineering, geography, sociology, history, archeology, lighting. In this context, parametric design with its potentials such as reinterpretation of traditional architectural forms, understanding of cultural infrastructure with its all layers and considering it as a form source has become a preferred approach in societies expressing their social and cultural changes through architecture, especially in buildings such as museums and libraries they construct. On the other hand, structures’ harmony designed by using parametric design with cultural and environmental factors has been another reason for preference of this method. In UAE, which is a newly established country and attempt to create its cultural memory together with its economic power, in China, which weakened its ties with past after the Mao Revolution and is struggling to change its existing culture to contemporary one to support its economic power, in Istanbul/Turkey which has multilayered historical structure, the parametric form creation methods have been utilized for the museum building’s design. In this study, firstly, parametric design’s role method in memory space design will be discussed theoretically. Subsequently, it is aimed to embody the discussion over three pillars that deal with parametric design method with different approaches. In this sense, the Abu Dhabi Louvre Museum in UAE, which endeavors to create its social and cultural memory, the Yinchuan Museum in China, whose ties with the past have been weakened due to political reasons, and attempts to reconstruct its ancient culture with contemporary understanding of culture, and Istanbul City Museum, which uses parametric design method to present the stratified structure of its local and cultural memory, will be reviewed as model architectural structures of the study. One of the main objectives of the study is to show how parametric design is benefited in these three structures’ designs, how parametric-based form creation methods varies with these three structures, and how the relationship between cultural memory and space is configured differently with parametric methods. Additionally, in the context of the possibilities provided by parametric design, an analysis of the artefact-form relations with the environmental factors of all three museums and discussion of these relations are among the objectives of the study. In the study, descriptive survey method was pursued, and an interview was conducted with Alper Derinboğaz, architect of the Istanbul City Museum (ICM). In the conclusion, information use provided by the parametric design as a form source in formation of societies’ cultural memory, cultural-environmental adaptation possibilities and flexible design understanding were assessed, and the fact that non-euclid and topological form understanding strengthens the monumentality of museum structures were discussed. Keywords: memory, memory space, museum, parametric design.

Soft clayey soils are generally improved by the consolidation process. The different improvement techniques which are in vogue include the use of stone columns, sand drains with and without preload and prefabricated vertical drains. Upon improvement, the soft soil attains a higher strength and better resistance to excessive settlement. The extent of this improvement of the soft soil is measured through different in-situ tests including Standard Penetration Test (SPT), Cone Penetration Test (CPT) and Pressuremeter Test. Most of these tests are invasive and require boreholes for the collection of soil samples. Geophysical tests can scan the entire area within a short time and can accurately interpret the extent of the improvement depending on the expertise of the investigators. Sometimes a combination of two or more geophysical tests is suitable for an accurate prediction of any change in soil properties. The present study is an attempt to measure the effect of ground treatment by implementing two types of geophysical tests, namely, Electrical Resistivity Tomography (ERT) and Multichannel Analysis of Surface Wave (MASW) near a by-pass road in Silchar, Assam. The tests were conducted on a newly constructed road embankment that had undergone excessive settlement and was subsequently treated with stone columns with a preload. Both the geophysical tests showed improvement in soil properties as well as in the bearing capacity of the original soft soil. A bore log survey was also carried out before the improvement work to validate the results of the geophysical tests. Existing correlations among geophysical properties and soil properties were used to obtain the effect of improvement. It has been observed that geophysical tests can easily be carried out to accurately calculate the effect of improvement of soil properties. A combination of two or more geophysical methods yields a better understanding of the post-treatment results.

We conducted a centrifugal model test to investigate the deformation and failure mode of a geogrid-reinforced and pile-supported (GRPS) embankment. The embankment filling was simulated using the incremental acceleration method, and the surcharge was subsequently applied using an inflatable airbag on the embankment. By installing different types of instruments, the displacement of the soil, the axial force and bending moment of the piles, and the earth pressure and pore water pressure of the foundation were monitored. The test results revealed that the embankment tended to slide in a circular-arc manner from shallow to deep, and the stress distribution of the piles varied with the locations. The stress concentration ratio of the embankment was higher, which indicates a more efficient load transmission. Additionally, the excess pore water pressure in the GRPS embankment was lower compared with that in conventional piled embankments.

Model tests on 3D soil arching in pile-supported embankments with and without geotextile

Background: Soft soils present significant challenges in civil engineering practice due to their high compressibility, low shear strength, and susceptibility to excessive settlement under structural loading. Accurate characterization and prediction of settlement behavior are therefore essential for safe and economical foundation design, particularly in regions underlain by soft cohesive soils. Methodology: In this study, soil samples were obtained from three locations, with two trial pits per location, at depths of 0.5 m and 1.0 m, using a systematic site investigation approach. Laboratory testing was conducted in accordance with relevant ASTM standards to determine key geotechnical parameters, including moisture content (MC), optimum moisture content (OMC), cohesion (C), internal friction angle (∅), maximum dry density (MDD), unconfined compressive strength (UCS), shear strength (SS), void ratio (e₀), hydraulic conductivity (K), and consolidation characteristics. Principal Component Analysis (PCA) was applied to identify dominant soil parameters controlling behavior, while multivariate linear regression models were developed to predict total settlement, unconfined compressive strength, shear strength, and permeability Results: The results indicate pronounced spatial variability in soil properties across locations and depths, reflecting heterogeneity typical of soft soils. Correlation analysis, regression modeling, and PCA consistently identified moisture content, void ratio, permeability, and compressibility-related parameters as the primary controls on settlement behavior. The regression models exhibited high predictive accuracy, with coefficients of determination (R²) ranging from 97.0% to 99.9%, confirming strong quantitative relationships between soil properties and measured responses. PCA revealed that the first principal components are dominated by void ratio and hydraulic conductivity, representing a compressibility–permeability mechanism, while strength- and density-related parameters govern secondary components, reflecting soil compactness and structural resistance. Conclusion: This study demonstrates that integrating laboratory-based soil characterization with statistical tools provides both predictive and interpretative insights into soft soil behavior. While PCA–regression techniques are established in geotechnical analysis, their application to site-specific soft soils enables a clearer identification of critical parameters influencing settlement. The developed regression models and PCA framework offer practical decision-support tools for foundation design and settlement risk assessment in soft soil environments, while highlighting the need for broader datasets to enhance regional generalization.

The construction of pavements is usually based on different national and international standards. The overall thickness of the pavement construction depends on many different parameters. Especially during construction of pavements across soft soils, large settlements occur which often results in damages to the pavement layers. Besides improvement of the soft subgrade material by different methods, the vertical loads on the soft subgrade can be reduced by the use of light infill materials. One of those materials is called glass foam gravel and is produced from recycled glass. FilterPave™ can be used as an alternative for the asphalt and concrete layers. This material is also manufactured from recycled glass. The main advantage of this product compared to asphalt and concrete is its high permeability without any loss of bearing capacity. Both sustainable materials for the construction of pavements are described in the paper.

Embankments are often required in many civil engineering construction projects involving infrastructure development to elevate the ground level. Due to the limitation of land availability for infrastructure projects in many countries, a large number of projects are now being carried out on soft ground. However, embankment construction over soft ground is a challenging task due to several undesirable characteristics associated with soft soils such as local instability, inadequate bearing capacity and large settlements, which can occur over a long period of time. These problems can generally result in expensive remedial measures and long construction delays. The conventional soft ground improvement methods based on consolidation such as vertical drains and preloading are not suitable when projects have to be completed within a short period of time or the ground improvement has to be carried out in contaminated ground. In such situations, reinforced pile-supported embankments are increasingly used as an alternative construction method due to the shorter construction time required compared to consolidation based methods and due to the higher reliability of the method when the subsoil properties cannot be relied upon. . This paper presents a comprehensive numerical study carried out using the finite element method in order to investigate the performance of reinforced pile supported embankment. A detailed parametric study is presented inthree-dimensional conditions incorporating the full geometry of embankment system. The influence of pile embedded length, pile diameter, elastic modulus of piles, height of the embankment, construction rate of the embankment were investigated on the performance of the selected embankment.

ABSTRACT: The soil reinforcement method, which consists of placing a granular mattress above a set of rigid inclusions, is used to transfer part of the surface load to the piles through arching. The addition of an extensible geosynthetic layer at the base of the mattress increases load transfer. A small-scale centrifuge model, the mobile tray device, is used to simulate the foundation behaviour by modelling soft soil settlement between the inclusions. A parametric study was conducted to examine the influence of the mattress thickness and of the pile spacing. The different test configurations are compared with regard to the stress transmitted to soft soil, to differential settlement and to the efficiency of load transfer. With thicker mattresses and/or closer pile meshing, load transfer increases and surface settlements are reduced. Geosynthetic maximum experimental and analytical deflections are also examined. For the analytical study, conducted using the EBGEO German standard, three different distributions of the vertical stress applied to the geosynthetic layer are compared: uniform, triangular and inverse triangular. All three scenario results fall within the range of the experimental results. The inverse triangular distribution reveals some deflection values that were lower than the uniform one. The triangular distribution gives the highest deflection values.