Research on the multi-scale DFN-DEM equivalent modelling method for jointed rock masses and the collapse law of block structures

Abstract

The development scale, distribution characteristics and combination mode of structural planes in the construction of underground rock mass engineering projects are extremely uncertain. Determining how to fully consider the “real distribution” of conventional structural planes in response to the deformation and damage of surrounding rock while taking into account the exact influence of the “same type, weak scale” structure on the mechanical properties of rock masses is one of the current development directions of synthetic rock mass technology. In this paper, by comparing the theoretical formulas of self-similar grade sequence classification and verification through numerical simulation, the delineation standards for joint sizes of different scales were determined. Based on the representative elementary volume (REV) consideration of the equivalent continuum properties of jointed rock mass, a multi-scale DFN-DEM equivalent modeling method with joints of different sizes and block structures is proposed. Through the systematic analysis of joint combination models of different scales, the feasibility of this method for simulating rock masses with serial joints of different scales is verified by taking the Erlangshan Tunnel of the Linlin Expressway in Shandong Province, China, as the engineering background. The collapse block of the surrounding rock is analysed via mathematical statistics and analysis of shape, volume, quantity, etc., to reveal the spatial collapse distribution rules and response characteristics of block groups during tunnel construction. The following research results were obtained. 1) Fine joints mainly affect the mechanical properties and degree of fragmentation of the block group. The combination mode of large-scale joints directly affects the spatial collapse distribution of the block group. The occurrence characteristics of joints of different scales can be used to comprehensively determine the surrounding rock mass of the tunnel. 2) The larger the scale of the endowed joints, the larger the average volume of the collapsed blocks, and the statistics show a clear positive correlation law between the average volume of the collapsed blocks and the size of the joints.The research results provide a scientific basis for the prediction of dangerous rock collapse hazards, disaster identification, prevention and control during the construction of tunnels and underground projects in jointed rock mass areas and have important theoretical significance and engineering application value.