Study On Assessment Of Rock Strength And In-situ Grouting Reinforcement Effect In Coal Mine Roadway By MWD Method

Real-time evaluation of the geological conditions of the surrounding rock in the roadway is important for the design of roadway support and disaster prevention.The design of roadway support under unclear geological conditions will cause the surrounding rock to deform and damage under the influence of long-term ground pressure,which has become a serious problem that plagues the safety of coal mines.Based on this,this study first theoretically analyzes the limitations of the current commonly used rock strength evaluation method(specific energy of drilling).Then,a new rock drillability index was constructed based on the dimensional analysis method.A new measurement while drilling test system was designed for the laboratory drilling tests.The reliability of the rock drillability index was verified by analyzing the test results.Moreover,based on the theory and laboratory test results,the method of discrete element numerical simulation was used to analyze the applicability of rock drillability index and drilling specific energy under different rock heterogeneity,rock strength and the drilling operating parameters.Finally,a new type of pressure-torsion integrated sensor was independently developed to measure the rock strength in the grouting area of the surrounding rock,and a method for quickly evaluating the effect of roadway grouting reinforcement based on the rock drillability index was proposed.The main research contents and conclusions are as follows:(1)Through the dimensional analysis method,an index that can describe the drillability of the rock is put forward.Then,this index was compared with the drilling specific energy,and the applicability of each index was discussed theoretically.In the laboratory drilling tests,this study has developed a new measurement while drilling test system(MWDTS)to carried out a series of drilling tests on cement mortar blocks with different strengths.Through these drilling tests,the operating parameters of drilling machine have been obtained to calculate the mathematical relationship between rock drillability index and drilling specific energy and the rock strength,which verifies the advantages and applicability of using rock drillability indexs to predict the rock strength.(2)The discrete element rock model with different strength and discreteness for cutting and pressing into the rock by PDC bit was established in the numerical simulation to study rock breaking mechanics.The simulation result reveals the change of rock drillability index and drilling specific energy with the rock strength,which verifies the results of the laboratory measurement while drilling tests.In addition,this study found that the rock drillability index and drilling specific energy can ignore the influence of rock heterogeneity to assess rock strength.(3)Aiming at the pneumatic bolt drilling machine,this study independently developed a pressure-torsion integrated sensor to carried out in-situ measurement while drilling tests in the grouting reinforcement area of coal mine roadway,which obtained the changing of the operating parameters of the pneumatic bolt drilling machine.Based on the rock drillability index,the strength of the drilled rock is determined,and a method for evaluating the effect of grouting reinforcement based on the strength of the rock while drilling is proposed.Based on the rock strength determined by the rock drillability index,this research proposes a method for evaluating the effect of grouting reinforcement based on the measurement while drilling method.There are 72 figures,15 tables and 120 references in dissertation.