Visible Study On Evolution Law Of Soil Arching Effect Of Pile-supported Embankment Subjected To Wetting And Drying Of Expansive Soil Foundation

Expansive soil has the characteristics of water expansion and water loss shrinkage.As a typical high-speed railway subgrade structure,the pile-supported embankment is widely used in soft soil and moderately compressible soil areas.But for the pile-supported embankment in the expansive soil area,the expansion and contraction deformation of the foundation will change the form of the existing soil arch in the subgrade,resulting in the degradation of the soil arch effect.However,the current research on soil arching effect focuses on the formation process of soil arching.There are few theoretical studies considering the influence of expansion and contraction deformation of expansive soil foundation on soil arching effect of pile-supported subgrade,and there is still a lack of in-depth understanding of the evolution law of soil arching effect.Based on the National Natural Science Foundation of China project "Study on the degradation and failure mechanism of soil arching effect of high-speed rail pile network structure subgrade under the action of expansion and contraction cycle of expansive soil foundation",this paper carried out basic physical and mechanical tests of Maitreya expansive soil,indoor plane strain model test,and numerical simulation.The evolution law of soil arching effect of pile-supported roadbed caused by expansion and contraction deformation of expansive soil foundation is studied.The main research contents include the following aspects:(1)Through a series of basic physical property tests,the basic physical property indexes of Maitreya undisturbed expansive soil,including particle gradation,specific surface area and cation exchange capacity,were determined.The soil-water characteristic test,shrinkage test,expansion test under load and direct shear test were carried out,and the soilwater characteristic curve,expansion and contraction characteristics and shear strength were obtained.Based on the loaded expansion test results,the expansion prediction curves of the Maitreya undisturbed expansive soil under different stress levels were obtained.(2)The model test of soil arching effect of pile-supported subgrade under the action of expansion and contraction deformation of expansive soil foundation was carried out with a model test device designed and processed by ourselves,considering the subgrade load,subgrade filling height,differential settlement,and foundation expansion between piles The influence of factors on the formation and degradation of soil arch effect,combined with the pile-soil stress ratio,embankment load transfer efficiency,soil arch rate and other indicators,the strength of soil arch was evaluated.It is found that the displacement patterns of soil arch during the formation and degradation process are similar: a triangular subsidence(uplift)area is formed first,and then the height of the triangular area gradually increases,and finally penetrates the model and spreads outward in an inverted trapezoid shape.Among them,the subgrade filling height helps to increase the degree and speed of soil arching effect,but it also increases the decay speed when soil arching is degraded.The subgrade load weakens the strength of the soil arch.The smaller the differential settlement when the soil arch is formed,the faster the degradation speed is when the soil arch is degraded.(3)The PFC2 D discrete element software is used to carry out the numerical simulation research and parameter sensitivity analysis of the pilesupported roadbed under the action of the expansive soil foundation.The change law of soil pressure and particle displacement during the formation and degradation of soil arch was studied,and the effects of different pile spacings,different subgrade filling heights,and different subgrade loads on load transfer efficiency and contact force chain were discussed.