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In this study, a full-scale high-speed railway embankment model was established for assessment of the tensile force of the geogrid embedded in the sand cushion. Water bags were distributed around pile caps to create a model of the subsoil. The settlement of the subsoil was determined by the vertical deformation of the water bags. The tensile force of the geogrid, induced by the spreading force of the embankment, and caused by the vertical loads applied to the geogrid, were separately measured by two types of optical fiber sensing approaches, i.e., the pulse-prepump–Brillouin optical time domain analysis (PPP–BOTDA) and fiber Bragg grating (FBG) sensors. After the completion of the construction of the embankment, the measured tensile force of the geogrid, caused by the spreading force, is about 12% of that calculated by using the BS8006 standard. During the process of subsoil consolidation, the soil arching in the embankment fully develops as the subsoil settlement increases. At the ultimate limit state, the largest tensile force of the geogrid caused by the vertical loads occurs at the edge of the pile cap, which is about 34% of that calculated by using BS8006. As a design method, BS8006 calculates the tensile force of the geogrid at the ultimate limit state, and the experimental results reveal that the computational procedure specified in BS8006 is safe for determination of the tensile force of the geogrid. [ABSTRACT FROM AUTHOR]

Soil arching is a common phenomenon in pile-supported, geosynthetic-reinforced or unreinforced embankments resting on soft soil. Although the system behavior under static loading is well known (soil arching and bearing effects in geosynthetic reinforcement), the bearing behavior under dynamic loading is not yet fully understood and cannot be predicted. In this paper, the properties of soil arching under dynamic load have been investigated by performing numerical studies using the FEM and model tests. Embankments with different heights under dynamic load have been investigated. The behavior of soil arching under dynamic load can be classified into two types: for the model test without a geogrid and subsoil, the soil arching collapsed under dynamic load when the ratio of the height of the embankment to the diameter of the hole is less than 3, whereas the soil arching will not collapse under dynamic load when the ratio of the height of the embankment to the diameter of the hole is greater than 3. In numerical analysis, because of the existence of the geogrid, the value of the ratio of the height of the embankment to the center-to-center pile distance ensuring the stability of soil arching under dynamic load was 1.4, which is less than the value acquired in model tests, and it indicates that the existence of a geogrid and subsoil can improve the stability of soil arching under dynamic load. [ABSTRACT FROM AUTHOR]

Piled embankment provides an economic and effective solution to the problem of constructing embankment over soft soil, in which the soil arching plays a significant role in load transformation. However, most of current lines of research for piled embankments are focusing on the soil arching under static loading, and the behavior of soil arching under traffic loading needs to be investigated. This paper investigates the response of soil arching in the piled embankment (without the geosynthetic reinforcement) under dynamic loading using finite element method (FEM). The influence of the vehicle speeds, the numbers of the traffic load cycles, and the embankment fill friction angle for a given geometry ( s = 2.5 m, h = 3.5 m, a = 1 m) is also carried out. It shows that the traffic loading has a significant effect on the behavior of the piled embankment, especially for the settlement of embankment, while the embankment fill friction angle has negligible effect on that. The maximum passive earth pressure coefficient for the embankment under traffic loading is about 30 % larger than that under static loading and occurred at the height between the outer and inner radii of the hemisphere arch. Significant effects are found in vehicle speeds and numbers of the traffic load cycles on the settlement of the embankment just above the subsoil, while with limited influence on the vertical and horizontal stress and earth pressure coefficients. [ABSTRACT FROM AUTHOR]

Full-scale tests were performed on embankments with a beam foundation supported by floating and end-bearing piles. An analytical model based on the soil arching mechanism appeared to be able to predict accurately the vertical load transferred to a group of beams at a small center-to-center distance. However, when the distance between the beams was too wide or the embankment was too low to mobilize soil arching, the vertical load transferred to a beam could be predicted accurately with a model based on the punching shear mechanism. Greater embankment loads could be transferred to a piled beam through soil arching than could be transferred through punching shear. Beams in a piled embankment should be placed sufficiently close to each other to allow application of the soil arching model for design. Embankment loads could be transferred to both floating and end-bearing piles. Although load-transfer behavior was similar, the settlement of floating piles was significantly larger than the settlement of end-bearing piles. Settlement in a piled embankment could be reduced considerably by the application of end-bearing piles with a group of beams at a small center-to-center distance. [ABSTRACT FROM AUTHOR]

Abstract: It is an economic way to use the piled embankment for the construction of embankment over soft soil. The combination of piles and reinforcement can effectively reduce the differential settlement at the surface of embankment. The paper presents a simplified model for analysis of an embankment of granular fill on soft ground supported by reinforcement and piles. This model is based on consideration of the arching effect in granular material proposed by Hewlett & Randolph. The vertical equilibrium of the unit body at the center of pile caps immediately below the reinforcement is established. The refinements of the model are that the failure mechanisms of the arch both at the crown and at the pile cap were considered, three-dimensional situation was taken into account for reinforced piled embankment, calculation of the vertical stress carried by the subsoil due to arching effect and reinforcement for multi-layered soil was proposed. Using the simplified model, the influence of embankment height, one-dimensional compression modulus of subsoil, tensile stiffness of reinforcement on stress reduction ratio (SRR) and tensile force of reinforcement is investigated. It is found that the model can be used to assess the relative contribution of the reinforcement and subsoil. The results show that subsoil gives a major contribution to overall vertical equilibrium, while the reinforcement gives obvious contribution at relatively large settlement. The inclusion of the reinforcement can reduce the vertical stress acting on the subsoil. The simplified model is then evaluated by three case studies. The results of this model show good consistence with these cases. [Copyright &y& Elsevier]

Abstract: Reinforcing compressible soils by rigid inclusions is a method to reduce and homogenize settlements under many types of structures. A granular mattress, set between the structure and the group of inclusions, transfers by arching effects a part of loadings to the piles embedded in rigid substrate. A geosynthetic can be added between the heads of the rigid inclusions and the granular mattress. In addition to the arching effect, a membrane effect happens caused by the stretching of the geosynthetic sheet. An experimental mobile tray device, especially designed to test this reinforcement technique in centrifuge at 20g, consists in simulating the settlement of the soft soil located between the inclusions. An initial pretension can be applied to the geosynthetic. A parametric study of the load transfer mechanisms in the mattress is conducted with three different thicknesses of granular mattress, two different rigid inclusions networks and different initial pretensions in the geosynthetic. The efficacy of the load transfer and the settlements at the surface of the granular mattress are studied and discussed. With and without geosynthetic reinforcement, load transfer mechanisms are better for thicker load transfer mattresses and for higher mesh densities. The improvement made by a geosynthetic reinforcement is clearly shown trough both load transfer and differential settlement reduction. [Copyright &y& Elsevier]

Abstract: The stability analysis of a piled embankment under seismic loading is considered, with a special emphasis on the optimization of the reinforcement layout by splitting the initial group of vertical piles into two symmetrically inclined arrays of parallel inclusions. The bidirectionally-reinforced soil thus obtained is appropriately described, at the macroscopic scale, by a three-phase model, conceived as an extension of the two-phase model previously developed for unidirectionally-reinforced soils. The model is implemented in a finite element formulation and related numerical code, which is used for simulating the behavior of the piled embankment up to failure. The results of these simulations, which favourably compare with upper bound yield design calculations, clearly indicate that the seismic resistance of the embankment can be considerably increased from symmetrically inclining the piles, even without taking the potential benefits of their flexural resistance into account. [Copyright &y& Elsevier]

This paper presents a probabilistic analysis of a geosynthetics-reinforced and pile-supported (GRPS) embankment by using reliability, sensitivity and uncertainty propagation techniques. Compared to the traditional deterministic evaluation methods, the analyses performed in this work allow designers to rationally consider the uncertainties of material properties and quantify their influences on the embankment performance. Additionally, complementary information/results could be obtained which enables an informed design decision for engineers. This feature is further enhanced in the paper by proposing a new analysis procedure in which four carefully selected probabilistic techniques are combined with an efficient deterministic model. The contribution of the proposed procedure lies in providing a variety of valuable results (e.g., failure probability and sensitivity index) related to the GRPS embankment performance but with a limited computational time. An application of the procedure is presented in the paper. The obtained results revealed that the studied GRPS embankments have relatively low failure probabilities considering a usual traffic loading but could be risky under extreme loading conditions. Based on the sensitivity analysis, all the random parameters are ranked according to their quantified importance. Some discussions are also provided, trying to link the procedure with practical designs and to explain the uncertainty modeling with more details. [ABSTRACT FROM AUTHOR]

• Subsoil provides a substantial support and reduces the reinforcement tension. • Design guideline CUR226 and standard EBGEO agree well with the numerical results. • 3D Numerical discrete analysis and comparison with analytical models. Three-dimensional numerical analyses using the discrete element method are conducted to investigate several fundamental aspects related to soil-structure interaction and mobilization mechanisms in the geosynthetic-reinforced and pile-supported embankments. The contributions of the soil arching, tensioned membrane effect, friction interaction, subsoil support, and punching failure are investigated. The results indicated that the inclusion of the geosynthetic enhances the stress transfer from the subsoil to piles due to the tensioned membrane action, and the stress distribution is more uniform as compared to piled embankment without geosynthetic. However, the tension distribution in geosynthetic is not uniform and the maximum tension occurs near the pile edge. Numerical results also proved that the subsoil provides substantial support and reduces the reinforcement tension while shear stresses are mobilized along the upper and lower sides of soil-geosynthetic interfaces. These mechanisms should be considered in theoretical models to produce a more realistic approach. Finally, ten available design methods are reviewed and compared to the numerical results to assess the performance of analytical models. The results showed that the design method of Pham, CUR 226 design guideline, and EBGEO design standard agree well with the numerical results and are generally better than the results of all other methods. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]