An improved numerical manifold method for investigation of fracturing expan- sion and squeezing deformation of surrounding rock mass in deep coal roadway

It is known that the fracturing expansion and squeezing deformation of the surrounding rock mass in the deep coal roadways is a continuum-discontinuum progressive failure evolution process which involves the pre-peak dilatancy damage and post-peak fracture expansion of rocks. However,this process cannot be well described and quantified by either traditional theoretical models,analytical solutions or laboratory experiments. Hence,it is essential to develop a numerical approach for the modelling of fracturing expansion in surrounding rock mass during deep coal roadway excavation. The numerical manifold method is a continuum-discontinuum coupling approach which has been widely adopted in the numerical simulations of geotechnical engineering. The most innovative feature of numerical manifold method is its two cover systems,which helps to solve both continuous and discontinuous problems flexibly and effectively in a unified framework. Besides,the interactions ( including squeezing,slipping and debonding) among discontinuous in- terfaces as well as large deformation (including translation and rotation) can be easily captured using the contact algo- rithm of numerical manifold method. In this study,a new modelling approach for the investigation of fracturing expan- sion and large squeezing deformation of surrounding rock mass in deep coal roadways is developed based on the origi- nal NMM approach. The main research work done is as follows:① A Voronoi tessellation technique is embedded into the original numerical manifold method to generate random polygonal loops,based on which an interface contact model considering the cohesion and tensile strength of discontinuities is developed accounting for the fracturing criterion of the rock mass;② An explicit integration version of numerical manifold method is developed,and the aforementioned Voronoi tessellation technique and interface contact model are embedded;③ Based on the above modifications,a road- way excavation modelling approach combining core softening and eliminating technique is developed for the simulation of unloading and spatial supporting effects during roadway digging;④ With the newly developed excavation modelling approach,the progressive failure process of the surrounding rock mass during a deep coal roadway excavation is simu- lated and the fracture evolution process as well as the formation mechanism of the excavation damaged zone (EDZ) is explored in details. Simulation results show that the continuum-discontinuum progressive failure evolution process which involves the pre-peak dilatancy damage,complex crack propagation and post-peak fracture expanding of rocks can be captured by the modified NMM approach. In addition,the fracturing expansion characteristics,convergence dis- placement and EDZ distribution of the surrounding rock mass is well predicted.