| The rock mass structural plane of coal measure strata is one of the main factors controlling the rock mass strength,which restricts the stability of the roof and floor of coal seam and surrounding rock of roadway.Therefore,it is of great significance to accurately grasp the distribution characteristics of coal measure rock mass structural plane for the correct evaluation of rock mass strength.Therefore,this paper takes coal measure fractured rock mass as the research object,analyzes the occurrence of fractures and builds a probability distribution model based on the field investigation of roadway rock mass structural plane.On this basis,Monte Carlo method is adopted to compile a random generation program of fracture network based on Matlab software and output the generated fracture network in dxf file format.The file format is invoked by FLAC3D5.0 numerical software to convert geometric model into numerical model.Establish different sizes of fracture network compression numerical simulation test,study the compression strength,modulus of elasticity with the scale of the fracture network and the rule of variation of confining pressure,it is concluded that coal rockmass mechanics properties of REV size,finally combining with indoor different scales fractured rock mass under uniaxial compression test results verify the accuracy of the numerical simulation.Through the full-text research,the following main results are obtained:(1)according to the huaibei Tuan sun ditch,five of the coal mine roadway rock fracture actual geology survey results,analysis of fracture occurrence,spacing and so on,studies have shown that the tendency,inclination of coal rock mass structure meet the normal distribution,and the crack spacing to satisfy negative exponential distribution,for subsequent randomly generated provides the probability distribution of fracture network.(2)Based on Monte Carlo method,a random fracture network generation program was developed using Matlab software.The program could select different size frames of fracture network,which laid a foundation for analyzing the relationship between mechanical properties and network scale.At the same time,according to the fracture network coordinates generated by the program,geometric data sets were established with the help of external software Auto CAD and FLAC3 D,and the numerical models of fracture network with different sizes were generated,which provided the model basis for the subsequent REV analysis of fractured rock mass.(3)A random fracture network of 20m×20m was established.Within this range,nine model sizes of different scales ranging from 0.04m×0.04 m to 19m×19m were selected,and six levels of confining pressures ranging from 0 to 5MPa were set.FLAC3 D was used to carry out compression tests of fracture networks of different scales under different confining pressures.In this paper,the change rate of the minimum difference between strength and elastic modulus obtained from the simulation of fracture networks with different sizes was used as the criterion to determine the REV size,so as to determine the REV size of strength and elastic modulus under each confining pressure condition.(4)According to the simulation results,it is concluded that the peak strength and elastic modulus of the stress-strain curve of the fracture network model have obvious size effect under different confining pressures.With the increase of the model size,the compressive strength and elastic modulus gradually decrease,and the decreasing rate gradually decreases and tends to be stable.It shows that the mechanical properties of coal measure fractured rock mass network have obvious REV characteristics.The simulation results show that the compressive strength REV size of the coal measure fractured rock mass is 16 m ×16m,which is unchanged with the confining pressure.The elastic modulus REV size is 13m×13m under 1MPa confining pressure,and remains unchanged under uniaxial and 2-5 mpa confining pressure,corresponding to 16m×16m REV size,which is consistent with the change law of compressive strength.(6)In order to analyze the fracture forms of fractured rock mass in the compressive yield state,the displacement variation cloud images in x and z directions of six study subareas ranging from 0.04m×0.04 m to 10m×10m were selected to obtain the same random fracture network model.At different scales,the fracture forms showed obvious differences.With the reduction of the model size,the fracture content in the model decreases,and the fracture form is controlled by the fracture distribution,showing that the displacement is concentrated at the fracture,and the model occurs shear slip along the fracture.However,the larger the model size,the more the number of cracks,the model failure presents the characteristics of homogeneous macroscopic,the fracture form is less affected by the structural plane,the overall compression shear failure.(7)Four random fracture network models with different sizes of150mm×150mm×150mm,100mm×100mm×100mm,70mm×70mm×70mm,and50mm×50mm×50mm were established on site,and uniaxial compression experiments were carried out.According to the experimental results of uniaxial compressive changes of different sizes,The uniaxial compression is shown to be consistent with the numerical simulation,which verifies the accuracy of the numerical model.Through the study of this paper,the fracture network of rock mass with different scales and FLAC3 D numerical grids generation technology,reveals the coal rock mass strength and deformation parameters changing with the model size,it is concluded that the REV size parameters,calculation model of coal rock mass fracture network and provide theoretical basis for determination of mechanical parameters.Figure [55] Table [23] Reference [80]... |
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