Mechanical Properties And Engineering Application Of Residual Soil Under Unloading Stress Path And Drying-Wetting Cycles

At present,most of the calculations of deformation,strength and stability of foundation pits are based on the stress-strain relationship of the load stress path test,and use the corresponding shear strength index as the calculation parameters.However,the soil in foundation pit is subjected to the unloading stress path.The residual soil is widely distributed in Fujian Province.It has constitutive property and water softening characteristics,and undergoes alternating dry and wet interaction under natural or artificial environment.Therefore,while analyzing the influence of the stress path on the soil,it is necessary to research the mechanical properties of the residual soil under the drying-wetting cycles.In this paper,the residual soil samples were taken from the pit side during excavation,and the triaxial shear tests under different stress state and stress path and drying-wetting action were carried out.According to the test results,the data normalization was analyzed,and the modified Duncan-Chang model and the method for determining the parameters were proposed considering the consolidation confining pressure and drying-wetting cycles.The MIDAS/GTS was used to simulate the deformation of foundation pit under different stress states,stress paths and drying-wetting conditions,and compared with the actual monitoring data.The results show that the modified Duncan-Chang model considering the radial unloading stress path and the drying-wetting cycles is the most consistent with the soil stress state of the actual residual soil foundation pit engineering.The main research work are presented as follows:1.Exploring the influence of consolidation mode,stress path and drying-wetting action on soil stress-strain relationship.Tests show that the KO consolidation specimen is stronger than the isotropic consolidation,and the initial tangential modulus is also increased.The strength and initial tangent modulus of the specimens under unloading stress path are lower than that under loading stress path.Furthermore,the strength of the specimen subjected to the drying-wetting action is less than that of the specimen that had not undergone drying-wetting action,and strength decreases rapidly after the first drying-wetting cycle;2.Organize the test data,and obtain the modified Duncan-Chang model parameters of the isotropic consolidation loading test,the KO consolidation unloading test and the three drying-wetting cycles unloading test respectively,then normalize the stress-strain equation considering the factors affecting the confining pressure and the number of drying-wetting cycles;3.Input the three constitutive parameters into MIDAS/GTS to simulate the foundation pit in Xiamen,compare the horizontal displacement of the pit side soil during the excavation and the deformation data of the actual foundation pit engineering,indicating the deformation data obtained by the constitutive model considered the unloading stress path and the drying-wetting cycle is the best one for predicting the horizontal displacement of the residual soil on the pit side.