Abstract:

At the background of zonal disintegration was found in the model test, the strain field of the circular tunnel was studied by using the classical Fenner formula. The discontinuity of the radial strain and the concentration of elastic deformation energy were found at the ultimate balance boundary. The formation of the circular crack which is concentric to the opening is the rupture and separation between the ultimate balance zone and the elastic zone caused by the discontinuity of the strain field. Zonal disintegration is the result of ultimate balance zone expanding to deeper rock mass after the separation. The analysis results explain the non-monotonic under changing laws of the strain and displacement in surrounding rock mass with the distance to the cavity increasing; and the formula of radius of the fractured zones was got and it showed that there exist the equal ratio relations between the radiuses. The value of it was corresponding to the geostress state and the parameter of the surrounding rocks. Taking the parameters in the model test into the formula, it obtained that n =1.1. It matches well with the shape character of the fractured zones in the disassembled model after test.

Key words: zonal disintegration, mechanism analysis, discontinuity of radical strain, concentration of deformation energy