To obtain the analytical solution of cylindrical cavity unloading-contraction problem considering the effect of different degrees of intermediate principal stress

quantitative prediction of contraction and plastic deformation was conducted under a certain degree of unloading during cavity excavation. Based on the unified strength theory and by introducing the unloading factor and contraction coefficient

the dimensionless similarity solution of cylindrical cavity unloading-contraction was derived. Compared with the large strain solution without considering the influence of the intermediate principal stress

the effects of the influence coefficient of intermediate principal stress on the displacement and stress distribution of the borehole

and the effects of soil stiffness

cohesion

and friction angle on unloading-contraction were given. Results show that the larger the intermediate principal stress influence parameter b was

the smaller the borehole unloading-contraction effect was

and the essence was that the increase of b reduced the initial yield unloading pressure

delayed the appearance of the peripheral peak hoop stress

and helped to reduce the borehole wall plastic zone. The influence of b on the radial displacement and hoop stress of the borehole was not negligible

while the radial stress was less affected. Soil stiffness had a great influence on the relation between cavity unloading and contraction that the greater the stiffness was

the smaller the effect of b was. Based on the dimensionless unloading contraction solution of borehole

a more reasonable quantitative prediction of the radius variation of cavity at a specified unloading degree can be performed

which can be used in the practice of tunneling excavation and support

pile bearing capacity analysis after boring unloading

and stability analysis of well drilling.