Laboratory simulation test research on soil characteristics of foundation pit excavation considering the deflection of principal stress axis

Three-dimensional stress path of foundation pit excavation considering deflection of principal stress axis is deduced by numerical simulation. It is found that the direction of principal stress axis of soil mass in the pit varies greatly and that the soil mass on the side of the pit is approximate to the axial shear. On this basis, a series of undrained stress path tests were carried out with hollow cylinder torsion shear apparatus (HCA) to study the soil deformation characteristics during excavation of foundation pit. The test results show that with the increase of deflection angle of principal stress axis, the stress-strain curve develops faster and faster, the positive strain components and shear strain develop faster and the strain increases gradually during the excavation of foundation pit. As the distance from the center of the pit bottom increases in the horizontal direction, the development of strain becomes gentle and the final strain decreases gradually. The trend of stress-strain relation curve of soil mass on the side of pit is basically the same. The positive strain components and shear strain develop faster from the surface to the bottom of pit, and the strain at yield increases gradually.