Study On The Supporting Design Theory For Expansive Soil Foundation Pit Based On Humidify Stress Field Theory

Under the influence of continuous rainfall and other wading conditions,some phenomena,such as the deformation of slope increasing progressively,the anchoring effect of supporting structure losing efficacy,the destruction of the whole slope,are more likely to happen in expansive soil foundation pit.In the engineering practice currently,the calculation method of strength parameters reduction was used to check the anchoring effect of supporting structure,which could cause the situation that the anchoring effect is insufficient or surplus.The determination of expansive force distribution and its role in the calculation of slope design,the calculation method for earth pressure of expansive soil under nonlimit state,are the two great difficulties of the design theory for expansive soil foundation pit slope.With the rapid development of urbanization in expansive soil distribution area,the problems of expansive soil foundation pit engineering loom large,the design theory considering the effect of expansion force for expansive soil foundation pit is the issue which should be settled at this stage.Geotechnical parameters recommended test methods for expansive soil were provided by studying and manufacturing relevant test apparatus in this thesis,and the fitting formulas for geotechnical parameters were established.The infiltration depth calculation model for expansive soil foundation pit was researched through the indoor model test and field model test and numerical calculation,and the infiltration depth calculation formulas in the region of the top and the surface of slope were established.Engineering practical expansive soil elastic-plastic constitutive model based on humidity stress field theory was put forward and implemented by the secondary development,which was applied to numerical calculation of expansive soil foundation pit.The distribution regularity of expansive force based on humidity stress field theory was established by analyzing the results of numerical calculation sequence comprehensive.Through the research on the stress Mohr circle under different displacement state,the calculation formulas of the value of shear strength under different displacement state were derived.The soil stress state behind the pile was analyzed by micro layer analysis method and Mohr-Coulomb strength theory,the potential slope sliding surface was searched and the formulas of the active and passive earth pressure of expansive soil under nonlimit state were derived via static equilibrium under the effect of the expansive force,in other words,the earth pressure calculation theory for expansive soil foundation pit was established.The engineering practical expansive soil elastic-plastic constitutive model and the theory of the active and passive earth pressure of expansive soil under nonlimit state proposed in this thesis were used for practical calculation by analysis of the soil foundation pit engineering in Chengdu,the calculated slope deformation curves were similar to the field test results,which verified the reasonable of the theory proposed in this thesis.In the meantime,the applicability of the earth pressure calculation theory proposed was also verified by comparing the theory with the field test results and the theory proposed by predecessors.In the end,the structure design parameters for flexible pile under the condition of different excavation depth in Chengdu expansive soil area were researched through the earth pressure calculation theory for expansive soil foundation pit,and the recommended values of the structure design parameters were as follows:Under the condition of different excavation depth 4.0m,the pile length 9.0m,the pile diameter 0.8m,the pile spacing 1.6m;Under the condition of different excavation depth 5.0m,the pile length 11.0m,the pile diameter 1.0m,the pile spacing 2.0m;Under the condition of different excavation depth 6.0m,the pile length 13.0m,the pile diameter 1.2m,the pile spacing 1.8m.Meanwhile,the influence of the supporting structure losing efficacy,the infiltration depth should be added to the recommended value of the pile length as safety stock.