Study On Fracture Mechanism Of Brittle Rock Based On Moment Tensor Theory

Along with the National Strategy of One Belt and One Road putting forward,the infrastructure construction is a priority area which will be accelerated.Geotechnical engineering is a new technical system developed in the practice of infrastructure construction,and rock rupture is the main factor to induce major disasters in rock and soil.Therefore,it is very important to study the rock failure mechanism on the stability monitoring and disaster forecasting of infrastructure construction projects such as tunnels,slopes,railways and deep chambers etc.Based on the moment tensor theory method,this paper studied the fracture mechanism of intact rocks under the conditions of uni-axial and tri-axial compression test and the fracture mechanism of joint rock under the different condition of joint number,joint position and joint orientation.And then,the rock failure mechanism in the process of mine water inrush inoculation was analyzed using the micro-seismic data measured in Hebei Fanshan alunite mine.Afterwards,using laboratory test data of rock from Nickel Rim South in Sudbury,Canada,the correlations among rock mechanics parameters,seismic physical parameters and rock porosity were analyzed combining with rock physical and mechanical parameters model.The results of this study are as follows:(1)Using the laboratory test data of rock samples No.16,No.34,No.85,No.95 and No.108 from NR170143 borehoTe core of Nickel Rim South deposit located in Sudbury,Canada,a series of parameters models were created to analyze the relationship among rock mechanics parameters,seismic physical parameters and rock porosity.The relationship between axial stress and rock porosity was fitted to an experience formula.This empirical formula can be used as a judgment standard whether the loading pressure has reached the maximum value of rock compressive strength.It provided foreshadowing for the study of the rock fracture mechanism in subsequent chapters.(2)Using the methods of moment tensor inversion,T-k parameter representation method and fracture azimuth diagram,the failure mechanisms and its evolution law of intact rock simulated by Particle Flow Code under the conditions of uni-axial compression and tri-axial compression test were analyzed.The mesoscopic fracture parameters such as location,moment magnitude,moment tensor,fracture type,fracture azimuth,T-k parameter values and P-T parameter values of acoustic emission events produced in the failure process of intact rock were calculated.The study of these parameters is very helpful to understand the evolution law of the rock fracture mechanism of same type rock.It provides an important reference for predicting the failure trend of intact rock.(3)To reveal the influences of joint orientation,number and position on rock fracture mechanism,a large number of acoustic emission data produced in the rock failure process of crack breeding,development and breakthrough simulated and computed by Particle Flow Code.The mesoscopic fracture parameters such as location,moment tensor,fracture azimuth,fracture type,stress state and moment magnitude of acoustic emission events produced in the failure process of rocks with single joint and multiple joints were calculated based on the methods of moment tensor inversion,T-k parameter representation method and fracture azimuth diagram.It provides an important reference for predicting the failure trend of rocks with joints.(4)Based on the analysis method of moment tensor,the focal mechanism solutions were calculated using the microseismic events in the rock mass.The proportion and fracture azimuth of pure shear fracture composition were obtained to judge the detailed rock fracture types of microseismic events.Then,a group of rock fracture surfaces(potential water channels)were fitted using 3-D effect diagram of microseismic monitoring,of which the fracture azimuth of each fracture changes with spatial location.And then,the fracture process of rock mass in underground mine and the spatial location relationship between roadways and microseismic events in monitoring area were quantitative analyzed.The hazard area of rock mass fracture is confirmed ultimately.It provides an effective research method for the stability analysis of rock mass fracture hazard in underground mine.In this paper,the innovation points are achieved as follows:(1)A set of research methods based on the parameters models is created to analyze the correlation among rock mechanics parameters,seismic physical parameters and rock porosity.The relationship between rock porosity and the axial stress is summarized as the experience formula:?=a*e-b*p-c.(2)A method is created to research the fracture mechanism and evolution law of intact rocks and jointed rocks based on the theory of moment tensor.(3)An analytical method of rock mass stability in underground mine is put forward to calculate the fracture mechanisms of rock mass and their evolution law which is used to distinguish the fracture types and the fracture azimuths of micro-seismic events.The research methods and relevant conclusions in this paper can be used as new study techniques providing important reference for the stability monitoring and disaster forecasting of infrastructure construction projects such as tunnels,slopes,railways,deep caverns etc.