Geosynthetic-reinforced Pile-supported Embankment Research Articles

Experimental Investigation of Soil-Arching Development in Unreinforced and Geosynthetic-Reinforced Pile-Supported Embankments

AbstractSoil arching is one of the most important mechanisms in piled embankments. To investigate the development of soil arching in piled embankments, 14 unreinforced and 8 geosynthetic-reinforced...

Geosynthetic reinforcement of pile-supported embankments

Rigid piles are used to reinforce soft soil foundations and thus increase embankment stability. This technique is improved by placing one or more geosynthetic reinforcement (GR) layers inside or at the base of the embankment. A series of 33 small scale models were tested using a geotechnical centrifuge. Soft soil settlement was imposed by the downward displacement of a tray. First, a series of models were prepared to examine how the load transmitted to the pile network increased with the embankment thickness. Using the same configuration, two identical models were prepared to successively test two different types of GR (geosynthetic reinforcement). Another approach was used to study how the external surcharges applied on the embankment affect load transfer. The results showed that, compared to the piled embankment, the load transfer increased for the case of the geosynthetic-reinforced pile-supported embankment (GRPSE) due to the membrane effect. The membrane effect is higher when the GR is stiff and its vertical distance from the pile is reduced. Numerical modelling reveals that, when another GR layer is added, the second GR has an effect only if punching is sufficient. However, the second layer did not reduce embankment settlement.

Scaled model tests on influence factors of full geosynthetic-reinforced pile-supported embankments

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.

Review of existing design methods for geosynthetic-reinforced pile-supported embankments

Embankment construction over soft foundation soils is a challenging task for geotechnical engineers due to the undesirable characteristics of soft soils, such as excessive settlements and low bearing capacity. Among the various ground-improvement methods available for overcoming these undesirable characteristics, geosynthetic-reinforced pile-supported (GRPS) embankments are considered to be a reliable solution suitable for time-bound construction projects and difficult ground conditions. Various researchers have introduced methods to design GRPS embankments based on different load transfer mechanisms. However, among design engineers, there is uncertainty regarding the applicability of these design methods. This paper investigates the load transfer mechanism of GRPS embankments using two-dimensional and three-dimensional finite element analyses, and currently available design methods are compared with the results of the finite element modelling. A comparison of the design methods was carried out using the stress reduction ratio, the geosynthetic tension and pile efficacy, considering different pile diameters and spacing, and embankment heights, which govern the currently available design methods. Based on these model results, the inconsistencies in the currently available design methods are identified and discussed in detail.

Effect of geosynthetic creep on reinforced pile-supported embankment systems

ABSTRACT: Geosynthetic-reinforced pile-supported (GRPS) embankments provide an effective solution to the problems faced by geotechnical engineers when dealing with embankment construction on soft foundation soils. Introduction of piles will reduce the embankment load transferred to the soft soil and the addition of a geosynthetic reinforcement layer will enhance the load transfer to the piles while alleviating the uneven settlements at the crest of the embankment. Numerous studies have been carried out regarding GRPS embankments throughout the last few decades including both experimental work and numerical studies. However, the creep effects of the geosynthetic layer were not investigated in these studies. This paper presents a numerical analysis carried out on a GRPS embankment based on the finite-element method including the creep effects of the geosynthetic layer. The creep model used in the analysis was validated using experimental data from previous studies which involved a geosynthetic pullout test and uniaxial tensile tests. The analysis was carried out in three-dimensional condition and the interaction between the soil and the geosynthetic layer was also taken into account. Furthermore, results from a parametric study to investigate the significance of creep on the overall behaviour of GRPS by varying the creep model parameters are presented.

Role of geogrids in load transfer of pile-supported embankments

A series of physical model tests on a geosynthetic-reinforced pile-supported (GRPS) embankment were performed in the laboratory to investigate the role of a geogrid on the load transferred to the pile-supported embankment. Two geogrid types, which differ in tensile stiffness by a factor of 2, were used to study the effects of geogrid stiffness. Different embankment configurations having different total embankment heights were employed so as to allow a comparison of the effects of different relative settlements between the soft soil and the piles. From the test results, it was shown that the relative settlement between the soft soil and the piles is necessary to form soil arching. In particular, when the embankment was geogrid-reinforced, the additional vertical stress transferred to the piles by the reinforcement with the geogrid became significant only when this relative settlement was sufficiently allowed. Furthermore, a larger additional vertical stress transferred to the piles was achieved by reinforcement with a stiffer geogrid. However, the difference in the vertical stresses transferred to the piles was substantially smaller than the difference in the geogrid stiffness.

Comparison of Different Two-Dimensional Idealizations for a Geosynthetic-Reinforced Pile-Supported Embankment

AbstractEmbankment construction on soft ground has increased considerably over recent years as a result of the increase in infrastructure development activities and because of the unavailability of suitable land. Geosynthetic-reinforced pile-supported (GRPS) embankments provide an effective and reliable solution to the problem of constructing embankments over soft ground. The combination of geosynthetic reinforcement and piles can alleviate the uneven surface settlements on the embankment crest while reducing the embankment load transferred to the soft foundation soil. This paper presents a numerical analysis based on the FEM carried out on a GRPS embankment. Analysis was carried out in both a two-dimensional (2D) plane strain condition for different 2D idealizations of piles and in a three-dimensional (3D) condition. The interaction between geosynthetic and soil was taken into consideration during the analysis. The results obtained for the 2D models are compared with the 3D model results. The stress tran...

Load Distribution Form of Soil between Piles in Geosynthetic Reinforced Pile-Supported Embankment

The strict control standards for post-construction settlement of high-speed railway require high accuracy of settlement calculation. Harmonizing the contradiction that settlement calculation theory lags far behind the engineering practice, the computational method of additional stress of foundation urgently needs improvement. For Geosynthetic Reinforced Pile-Supported (GRPS) embankment, as the stress caused by the load acting on soil between piles is an essential part of the whole, the computed results of additional stress of foundation largely depend on the load magnitude and load distribution form of soil between piles. Starting with the mechanical behavior of GRPS embankment, this paper analyzes the classic assumptions of soil arch form and their computation theory of load acting on soil between piles, and then deduces the distribution function of parabolic load, which can provide basis for further research on calculating the additional stress.

DEM Analysis of Stresses and Deformations of Geogrid-Reinforced Embankments over Piles

AbstractThe geosynthetic-reinforced pile-supported embankment is one of the favorable ground improvement techniques used in the construction of earth structures over a compressible soil when limited construction time is available and limited deformation is permissible. Various methods are available for the design of the geosynthetic-reinforced platform based on various load transfer mechanisms from the embankment to the piles and the compressible soil. The existence of the geosynthetic layer makes the mechanisms more complex. This study focuses on the behavior of geogrid-reinforced embankments over piles compared with the behavior of unreinforced embankments. The numerical simulations of the unreinforced and reinforced pile-supported embankments were conducted using the discrete element method (DEM). The embankment fill was simulated using unbonded graded aggregates of diameters ranging from 9.2 to 20.8 mm and the geogrid was simulated using bonded particles. This study investigated the changes of vertica...

Testing and Simulation Analysis on the Settlement of Geosynthetic-Reinforced Pile-Supported Embankments on Soft Ground for the High Speed Railway

The settlement of railway subgrade has an important connection with the quality, safety and natural life of the railway, the excessive settlement of subgrade will directly cause too many problems in the process of railway using. Especially in high speed railway, these problems will be more outstanding, thus affecting the development and progress of the railway. For the foundation of traffic infrastructure in areas with soft subsoil often embankments supported by piles are necessary due to the settlement requirements. For sufficient load transfer into the piles different construction methods are possible. For the construction of a high speed railway, a cement stabilization of the embankment material and geogrid reinforcement on top of the piles were used. Before the temporary load the settlement is monitored continuously for 10 months. In this paper, the method of construction is described and important field monitoring results are presented.

Mechanical Performance of Geosynthetic-Reinforced Pile-Supported Embankments

According to the characteristics of the soft soil subgrade reinforced by geosynthetic and piles, the deformation of geosynthetic was modeled as circular arc and the arching effect in embankments and the interaction of piles and soil are both considered in the calculation. The interaction mechanism of geosynthetic, pile and soil under the embankment load was analyzed. The method presented in this paper was validated by comparing with the testing results and three current design methods in the literature. The results show that the analytical solutions have agreement with the measured data and can be applied in engineering practice. Finally, four important parameter (the differential settlement, the diameter of pile, the width of pile cap, the height of equal settlement plane) were investigated.

Geogrid-Reinforced Pile-Supported Railway Embankments: A Three-Dimensional Numerical Analysis

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 ...

Geogrid-Reinforced Pile-Supported Railway Embankments

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.