Considering the stress deflection of foundation pit unloading soft soil study on deformation characteristics

Abstract

The deflection of the main stress caused by the unloading of the foundation pit is bound to change the stress state of the surrounding soil and produce deformation. By analyzing the stress state of the surrounding soil after the foundation pit excavation and introducing the stress ratio vector, the soil constitutive model considering the stress deflection is derived. The constitutive model shows that: After excavation and unloading of foundation pit, the strain of surrounding soil is not only affected by the change of stress, but also closely related to the deflection of principal stress axis, and then the influence of different azimuth on the deformation characteristics of unloading soil is discussed by static shear test with different azimuth of principal stress axis. The test results show that: When the azimuth Angle of the principal stress is between 0° and 45°, the shear strength of the soil sample decreases with the increase, and the strain increases with the increase. At 45°∼75°, the shear strength of soil samples increases with the increase, and the strain decreases with the increase. The variation of the deformation modulus of the soil samples under different azimuths of the principal stress is like a “scoop” curve, which is mainly the reflection of the anisotropy of the soil, and shows strong anisotropy at 0°∼15°. By normalizing the stress-strain relationship curves of soil under different azimuth of principal stress, it is found that the strain of soil is not only related to stress, but also affected by the change of principal stress direction. The experimental results are in good agreement with the constitutive model proposed in this paper.