| Expansive soil has the characteristics of swell-shrinking,which will cause damage to the upper geotechnical structure of the expansive soil foundation under the influence of the environment.In recent years,Geosynthetic-Reinforced Pile-Suppoted(GRPS)embankments have been gradually used in high-speed railway crossing expansive soil regions.However,the current theoretical research and the working mechanism on GRPS is still not well studied.In this thesis,combined with the National Natural Science Foundation project“Investigation on the weakening and collapse mechanisms of soil arching in GeosytheticReinforced and Pile-Supported Embankment subjected to the swelling-shrinkage cyclic deformation of expansive soil foundation”,through preliminary project research,loaded swelling experiment,3D drying model test and numerical simulation to study the evolution of soil arching in Geosynthetic-Reinforced and Pile-Supported Embankment.The main research contest of this thesis includes the following aspects:(1)Through the loaded swelling experiment,obtained the swelling rate of two kinds of density soil with 16% water content.The parameters were provided for the following model test and numerical simulation.(2)A 3D drying model test of GRPS embankments subjected to the swelling of ground was carried out through a self-designed test platform.The settlement of foundation soil,the earth pressure,the stress of pile and the strains of geosynthetics in filling and loading stage were analyzed.Combined the load sharing between pile soil and the pile-soil stress ratio,the formation of the soil arching in filling and loading stage was confirmed,soil arching effect and membrane effect were quantitatively analyzed.Through the analysis of the soil pressure of the foundation,the earth pressure of the pile top and the displacement of the subsoil,it shows that the expansive soil swells after water injected into the model,the soil arching effect were weakened in this stage.In addition,the study shows that the large void ratio of expansive soil at the top of undergound collapses during the wetting.Soil arching effect strengthened again,and the enhanced soil arching effect was stronger than the fist time.(3)FLAC3D finite difference software was used to carry out numerical simulation research and parameter sensitivity analysis of GRPS enbankments subjected to the swelling of ground.The earth pressure of subsoil,the earth pressure of the pile top,the settlement of subsoil were analyzed in the filling stage,loading stage,and the wetting stage.Through the defined concept “soil arching degradation ratio”,the degradation ratio of soil arching was quantitatively analyzed.The results show that soil arching effect can be completely degenerated by the swelling of the bottom and middle subsoil.In addition,through the analysis of the parameter sensitivity of GRPS in expansive soil area with different pile spacing,it is confirmed that the smaller pile spacing has a better control effect on the settlement in the compression stage and the wetting stage.At the same time,the influence of different pile spacing and different foundation on soil arch height,load sharing between pile soil,and pilesoil stress ratio were discussed. |
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