Research On The Failure Mechanism Of Fractured Rock Mass Using Discontinuous Deformation Analysis

With the rapid development of geotechnical engineering at home and abroad, investigating the stability of rock mass is more and more significant for engineering. Rock mass refers to one of the materials in the earth's crust, which is composed of intact rock material and discontinuity (e.g., joint or fracture). It's produced in a certain geological environment and experienced a series of geological constru ction movements. The mechanical properties of joints play a predominant role in determining its global stability, consequently, it has been a hot topic in the fields of geology and rock engineering fields. Although the processes and patterns of crack initiation, propagation and coalescence were widely studied, the failure mechanism and the anchored effect of fracture rock mass are not understood yet.In this thesis, some characteristics of fractured rock masses were studied on the basis of the modified discontinuous deformation analysis (DDA) method. Crack propagation patterns and stress-strain curves can also be obtained from the numerical simulation. In the meantime, correlation data analysis and laboratory test verification were applied to investigate and verify the aforementioned cases. The major work of this thesis is as follows:(1) The paper reviewed some of the basic concepts of the DDA method and t interpreted of DDA program's input parameters. In terms of numerical modeling, the data conversion from ANSYS to DDA was achieved using EXCEL table. Meanwhile, the calculation process was recorded by the software named "Screen Recorder".(2) The improved program of Discontinuous Deformation Analysis for Rock Failure (DDARF) was studied by theoretical and numerical trial and error analysis. Biaxial compression tests on specimens with single crack were carried out to simulate, which were compared with uniaxial compression experimental results. It is found that the crack initiation time was delayed in the biaxial compression case. Meanwhile, biaxial compression tests on specimens with double cracks were also simulated to investigate the effect of lateral pressure on the specimen through the crack initiation time, failure process, and the strength.(3) Numerical simulations of uniaxial compression test on specimens with double fractures with different dip,spacing and offset distance were done using DDARF program. The crack propagation process and stress-strain curves were studied to analyze the effect of crack geometric parameters.(4) The rock bolt element and material lines of DDA were applied to simulate the anchored effect of several types of specimens under compressive stress. Four kinds of specimens, including intact specimens, fractured specimens with one crack, fractured specimens anchored perpendicular to the crack and fractured specimens anchored perpendicular to the pressure, were carried out to simulate anchorage effect on mechanical properties of fractured specimens, which were also compared with laboratory test results. They agreed well with each other.(5) The DDARF program was also adopted to simulate an underground cavern after excavation considering two conditions with and without rock bolts. The failure process around the cavern and the displacements of key points in the surrounding rock mass were monitored and applied to investigate the stability. The numerical results show that the case of considering rock bolts has a very important role in controlling the stability of underground caverns.