The Mechanism And Application Of Zonal Disintegration Of Rock Mass Around Deep Underground Workings

High stress, high temperature, joint crack and complicated environment are met in deep geology. The mechanical behaviors of deep rock mass are different from those of shallow rock mass. In deep rock mass engineering, the surrounding rock of deep workings is classified into fractured zone and non-fractured zone, which occur alternatively. The mechanism of the zonal disintegration should be expressed by using the special mechanical property of deep rock mass.In this paper, an approach to reveal the mechanism of zonal fracturing phenomenon is proposed and the strength criterion of deep rock mass is used. Two theory models and a numerical model are proposed and they can be suitable for different kinds of condition. The magnitude and size of the alternative occurrence of fractured zone and non-fractured zone can be determined by using the present method proposed by author. And it is observed from the numerical results that the size and quantity are dependent on excavation methods, strength of rock mass, size of deep workings, etc.Main research content in this paper is summarized as follows:â‘ The zonal fracture model of intact rock mass is established. It is assumed that the deep circular tunnel or spherical cavern is subjected to an in-situ far-field stress field, whose inner surface is subjected to an internal pressure which is changed during tunnel excavation. As a result, the tunnel excavation process is related to dynamic problem. The equation of motion expressed by displacement potential function is established, which describes the release of pre-existing stress upon excavation of the opening. The general solution of motion equations is obtained by using Laplace transform. The near-field stress redistribution and displacement field around the openings induced by excavation is obtained. Size and quantity of fractured zone and non-fractured zone are determined.â‘¡The zonal fracture model of crack-weakened rock mass is proposed. The size and quantity of fractured zone and non-fractured zone are controlled by cracks contained in rock masses. Zonal disintegration mechanism is mainly dependent on the strong interaction among cracks. The strong interaction among cracks is investigated by using the dislocation model, which is developed based on stress superposition principle and the Chebyshev expansion of the pseudo-traction. The nucleation, growth, interaction and coalescence of cracks were analyzed by using crack growth criterion. When cracks propagate and coalesce, failure of deep crack-weakened rock mass occurs, fractured zone is formed. Then, the influence of excavation time on size and quantity of fractured zone and non-fractured zone are given out.â‘¢The numerical model of deep crack-weakened rock mass is presented. The Finite Element Method was applied to simulate the zonal disintegration in deep workings. The random weak elements are treated as cracks within rock mass. The geological data and the mechanical parameters of rock mass around four diversion tunnels in Jinping Hydropower Station are from ECIDI. Size and quantity of fractured zone and non-fractured zone are determined. The influences of the mechanical parameter and the in-situ stress on the zonal fracture phenomenon are discussed.The mechanism of the zonal disintegration around deep workings is analyzed. The present method is helpful to understand the failure and deformation of the deep rock mass.