Study On Mechanical Properties Of Surrounding Rock Of Tectonically Deformed Coal And Simulation Of Deformation And Failure Under Multi-stage Reaming

Tectonically deformed coal is a kind of coal whose internal structure changes under the action of structure.There are many micro fissures in the coal,the network of structural plane is complex and has the characteristics of loose structure and low mechanical strength.In recent years,attention has been paid to the development of coalbed methane in tectonically deformed coal,so it is of great significance to further study the mechanical properties of tectonically deformed coal and the deformation and failure problems on the meso scale.However,it is difficult to directly test the basic mechanical properties of tectonically deformed coal in the actual operation process due to the limitations of in-situ testing,sampling difficulties and indoor test instrument conditions.In addition,it is difficult to realize the real-time monitoring of the fracture and deformation of the tectonically deformed coal under different test conditions,which limit the study of the deformation and failure mechanism of the tectonically deformed coal on the meso scale.However,the numerical simulation is more efficient and intuitive,which can study the tectonically deformed coal from the micro scale.In this paper,based on the discrete element method and synthetic rock mass method,a cross mesh DFN model is proposed and programmed to construct SRM model of tectonically deformed coal.The mechanical numerical simulation test of SRM model is carried out to study and analyze the strength,deformation,fracture development and failure mode of tectonically deformed coal,and summarize the corresponding mechanism and conclusion.In addition,SRM model of tectonically deformed coal is applied to the numerical simulation test of multi-stage reaming in horizontal well to study and analyze the deformation and failure mechanism of surrounding rock of tectonically deformed coal in multi-stage reaming.The main progress and conclusions of this paper are as follows:(1)By collecting tectonically deformed coal samples,observing and analyzing the macro structural form of tectonically deformed coal,according to the flaky or scaly structure of the collected samples,a cross network DFN model is proposed.(2)The synthetic rock mass method is selected as the numerical modeling method of tectonically deformed coal,and the SRM model of tectonically deformed coal is completed.The indoor uniaxial test and triaxial test were selected as the meso parameter calibration test to determine the micromechanical parameters required by the SRM model.(3)The program is compiled to carry out the uniaxial compression and triaxial compression numerical simulation tests of the structural coal with SRM model and BPM model,and the deformation and failure law of tectonically deformed coal are obtained.The results show that both structural plane and confining pressure can affect the mechanical properties of tectonically deformed coal.The structural plane network in tectonically deformed coal can significantly reduce the mechanical strength of coal body,and confining pressure can improve the mechanical strength of tectonically deformed coal.With the increase of confining pressure,the influence of structural plane becomes weaker and weaker,and the failure of tectonically deformed coal changes from brittle failure to plastic failure.(4)Based on SRM model,the numerical model of coal multi-stage reaming is constructed,and the brick assembly technology is used to quickly generate the required size of the numerical model.Through the numerical simulation of multi-stage reaming of tectonically deformed coal,the failure and deformation mechanism of the surrounding rock of tectonically deformed coal in the process of multi-stage reaming is obtained.With the development of hole enlargement,the surrounding rock of tectonically deformed coal changes from shear failure to tensile failure.There are 68 figures,9 tables and 103 references in this paper.