Application Of Unsaturated Soil Pressure Theory In Supported Excavation In Yu County

The measured internal force and displacement for supporting structure of deep excavation are usually much smaller than those calculated with classic earth pressure theories.One of the important reasons is the matrix suction of unsaturated soil is not taken into account which reduces the shear force index.In this paper,a project is made in Yu County,Shanxi Province,the presumed loess soil-water characteristic curve is get based on the literature data.The curves obtained are compared with the database curves formed by 63 soil-water characteristic curve of loess to verify their correctness.The unsaturated soil theory is applied and the matric suction effect on shear strength of unsaturated soils is considered.Based on the technical specification for retaining and protection of building foundation excavations to calculate active and passive earth pressures,two methods of unsaturated soil treatment are compared and a check of design results is made.In order to verify the correctness of the theory and the universality of different construction methods,according to the load distribution on both sides of the river,two sections are selected to carry out the test of the bored piles and the Soil Mixing Wall(SMW)piles,respectively,and the displacement of the displacement control point is continuously monitored.It is found that the force and deformation of the supporting structure obtained by the shear strength of unsaturated soil is much smaller than that of the design by technical specification for retaining and protection of building foundation excavations,which is closer to the measured value.The influence of saturation changes in unsaturated soil to the supporting structure force and deformation is analysed,in the process of practical engineering analysis and consolidation,the internal relationship between the two methods of unsaturated soil treatment is found,we also strictly prove that the total cohesion method is equivalent to the Ning Lu suction stress method.The process of supporting structure design based on current specifications using the application of unsaturated soil shear strength values is proposed for reference.Based on the existence of soil slope on the upper side of the supported excavation in some test sections where the theoretical analysis and the actual displacement are different.The influence of the unsaturated slope on the soil pressure of the supporting structure is further analyzed.The modeling of the slope wall is analyzed.The maximum self-balancing width of the soil slope is compared with the estimation formula.Three theoretical conditions are proposed and the finite element simulation is carried out by using PLAXIS 3D.The comparison between the finite element simulation and the theoretical results verifies the theoretical correctness and proves the adoption of this.The theory can further reduce the internal force and displacement of the supporting structure.