| Geosynthetic-reinforced pile-supported embankments(GRPS)is an efficient and economical method in dealing with large settlement of soft ground foundations,and has been widely employed into highway and railway construction.Soil arching effect is the main load-transfer mechanism of GRPS.Most studies mainly focus on the plane soil arching,but less attention was paid onto the spatial characteristics of the arching structure,such as the distribution of slippage plane within the embankment,the path of loading transfer,the effect of pile arrangement over deformation,and the coupling effect of the membrane-tension effect of geosynthetic and soil arching effect,etc.Therefore,the evolution of spatial soil arching was analyzed in this paper from micro-and-macro perspective based on discrete element method(DEM).The research of this paper are summarized as follows.(1)A series of two/three-dimensional DEM models were established based on laboratory model test.After validating the micro-parameters,the vertical stress distribution,force chains evolution,the maximum vertical displacement and deformation characteristics induced by 2D and 3D arching effects were analyzed and compared.Additional analyses were carried out to understand the influence of embankment height,pile clear spacing,friction coefficient and porosity on soil arching with respect to stress concentration ratio(SCR)and settlement along elevation at various sections.The numerical results indicated that a plane soil arch in a 2D embankment overestimates the degree of load transfer and underestimates the settlement at the crest and within the embankment along the elevation in a 3D embankment.A lower equal settlement plane can be found in a 2D embankment.Furthermore,an increase of fill height and friction angle,and a decrease of pile clear spacing and porosity can help improve the degree of reduction in load transfer and settlement in both 2D and 3D embankments.However,for partially mobilized soil arching in the 3D condition,the increase of fill height reduces the settlement of soils mainly in the portion above the square subsoil area,but has less influence over the portion above the rectangular subsoil area.(2)Considering the influence of pile arrangement over soil arching,we established the 3D DEM embankment models with caps in a triangular pattern,and compared the load and deformation response with embankments with caps in a square pattern.The numerical results indicated that embankments with caps in a triangular pattern have a larger load-transfer efficiency,smaller deformation,and a lower equal settlement plane(EPS).The height of EPS decreases first and then remains stable,with a critical embankment height ensuring no differential settlement at the crest being 2 times of pile clear spacing.Furthermore,porosity has a significant influence on deformation.Punching shear failure occurs in loose-state embankments with slip surface only above pile caps and large surface settlement.General shear failure occurs in medium dense/dense-state embankments with slip surfaces extending over pile caps and subsoil area.(3)The coupling result of soil arching effect and membrane-tensioned effect was also studied as the elevation of geosynthetic changes.The results indicated that the smallest deformation and the largest pile efficacy are found when geosynthetic is laid on the cap.The restriction of geosynthetic on embankment deformation and the load-transfer efficiency reduces with an increase of elevation of geosynthetic.What's more,the elevation of geosynthetic affects the embankment deformation mode and the distribution of vertical stress above subsoil,and thus affects the deformation and stress of geosynthetics.This paper made a further investigation over spatial soil arching from a macro-andmicro perspective,and the results provide a theoretical basis for engineering design and embankment construction. |
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