Geosynthetic-reinforced Pile-supported Research Articles

Lateral Response and Failure Mechanisms of Rigid Piles in Soft Soils Under Geosynthetic-Reinforced Embankment

Previous studies regarding geosynthetic-reinforced pile-supported (GRPS) embankments over soft soils have mainly focused on load transfer mechanisms and design approaches. However, little attention was given to the lateral performance of rigid piles in GRPS embankment systems. This paper presents the results of 3D finite element analyses to examine and compare the lateral response and failure mechanisms of floating and end-bearing piles in soft soils under geosynthetic reinforced embankments. The effects of geosynthetic reinforcement and pile length on the stability of the embankments are also investigated. The results indicate that the induced lateral responses in the piles are distinctly different for floating and end-bearing piles. Failure of the floating pile is primarily caused by the inclination of the pile. However, for end-bearing piles, bending failure is clearly established as the principal mode of failure. The benefit of the geosynthetic layers in improving the stability of piled embankments is not particularly apparent. Moreover, the increase in pile length is significant in enhancing the stability of GRPS embankments. Specifically, when the normalized pile length varies from 0.75 to 1.15, the critical height of embankment increases from 6.2 to 11.8 m. However, the effect of pile length becomes negligible when the normalized pile length exceeds 1.15. The lateral movement and failure modes of GRPS embankments are strongly dependent on pile length. Therefore, it is essential to consider this aspect when analyzing the stability of the GRPS embankment.

A novel 2D-3D conversion method for calculating maximum strain of geosynthetic reinforcement in pile-supported embankments

For design of a geosynthetic-reinforced pile-supported (GRPS) embankment over soft soil, the methods used to calculate strains in geosynthetic reinforcement at a vertical stress were mostly developed based on a plane-strain or two-dimensional (2-D) condition or a strip between two pile caps. These 2-D-based methods cannot accurately predict the strain of geosynthetic reinforcement under a three-dimensional (3-D) condition. In this paper, a series of numerical models were established to compare the maximum strains and vertical deflections (also called sags) of geosynthetic reinforcement under the 2-D and 3-D conditions, considering the following influence factors: soil support, cap shape and pattern, and a cushion layer between cap and reinforcement. The numerical results show that the maximum strain in the geosynthetic reinforcement decreased with an increase of the modulus of subgrade reaction. The 2-D model underestimated the maximum strain and sag in the geosynthetic reinforcement as compared with the 3-D model. The cap shape and pattern had significant influences on the maximum strains in the geosynthetic reinforcements. An empirical method involving the geometric factors of cap shape and pattern, and the soil support was developed to convert the calculated strains of geosynthetic reinforcement in piled embankments under the 2-D condition to those under the 3-D condition and verified through a comparison with the results in the literature.

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.