Abstract
In the development of underground spaces, we found that the mechanical properties of rock mass often demonstrate strong nonlinear characteristics. Some new phenomena emerge in deep rock mass engineering. This includes zonal disintegration and rock burst. Zonal disintegration is very important in deep tunnels. In this paper, we start with the mechanical properties of deep rocks to understand the preconditions for zonal disintegration. Using the Failure Approach Index (FAI), the process of zonal disintegration can be modeled by FLAC (FISH language). Our results indicate that tensile failure in the Supporting Pressure Zone (SPZ) is a precondition for zonal disintegration. Various factors that affect the generation of zonal disintegration are studied. When the maximum stress is in the axial direction, zonal disintegration will be present in deep tunnels. The high axial stress is necessary for zonal disintegration. We will present a zonal disintegration simulation in one coal mine for comparison with the borehole teleview data. We suggest some measures to prevent the development of zonal disintegration.
Highlights
In this study, the zonal disintegration in the form of broken zone in the surrounding rock is not completely discontinuous. e rock mass fracture but not separation is considered to study the zonal rupture problem, so FLAC, which is usually used as a numerical simulation software for numerical analysis of continuous media, was chosen
Strain softening Mohr–Coulomb Model is appropriate for zonal disintegration simulation. e Failure Approach Index (FAI) can be used to represent the rock failure. e location and scope of nonfractured and fractured zones can be obtained from FAI
High axial stress is necessary for zonal disintegration generation. e precondition for zonal disintegration generation is that tensile failure happens in the Pressure Support Zone (PSZ) zone. e width of fractured zone caused by fast unloading is bigger than that of slow unloading
Summary
The zonal disintegration in the form of broken zone in the surrounding rock is not completely discontinuous. e rock mass fracture but not separation is considered to study the zonal rupture problem, so FLAC, which is usually used as a numerical simulation software for numerical analysis of continuous media, was chosen. E strain softening model in the software FLAC3D is based on Mohr-Coulomb with associated law of tensile flow and nonassociated law of shear flow. For strength criterion of zonal disintegration, we use the maximum tensile stress in the Mohr-Coulomb model of the software FLAC3D. When (σ1 + σ3)/2 ≤ σR, the YAI is shear yield criterion. From formula (12), the dangerous coefficient w is used to evaluate dangerous degree before stress reaches yield state. E failure degree is represented as 1 + FD after rock mass reaches yield state. When FAI is between 0 and 1, it represents that rock mass does not yield. When FAI equals 1.0, rock mass starts to yield into a plastic state. When FAI is more than 2.0, it represents that plastic shear strain has reached its limit. To display the location and scope of fracture zones, the elements with FAI bigger than 2.0 will be put into the “shear-break” group in the program and their stress state will be displayed on the nephogram
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