THE MECHANISM OF THE ZONAL DISINTEGRATION PHENOMENON AROUND DEEP SPHERICAL TUNNELS

High stress, high temperature and complicated environment are encountered in deep geology. The mechanical behavior of the deep rock mass is different from that of shallow rock mass. In shallow rock mass engineering, the excavation-affected rock around tunnel contains a loose zone, a plastic zone and an elastic zone. In deep rock mass engineering, the surrounding rock mass around spherical tunnels is divided into fractured zone and non-fractured zone, which occurs alternatively. The mechanism of the zonal disintegration phenomenon around deep spherical tunnels is analyzed. The present model is helpful to understand the failure and deformation of the deep rock mass. The present theory model contains a spherical tunnel which is subjected to an in-situ far-field hydrostatic stress and a changing internal pressure during tunnel excavation. The dynamic problem can be expressed by displacement potential function and the general solution of motion equations can be obtained by using Laplace transform. The stress and displacement field around spherical opening are obtained. The fractured zone in the surrounding rock mass around deep spherical tunnel can be determined by using the deep rock mass strength criterion. Size and quantity of fractured zone and non-fractured zone in the surrounding rock mass around deep spherical tunnel are given. The stress field in the fractured zone is obtained based on the theory of deformation localization. The influencing factors of the zonal disintegration phenomenon include the mechanical properties, excavation method and the excavation velocity, etc.