Stability Analysis And Control Of Jointed Rock Mass Based On DDARF Improvement Methods

With the continuous development and utilization of underground space, projects and scales of rock engineering are increasing rapidly, followed by the outstanding stability problems of surrounding rock. The key of stability evaluation in rock engineering is to find a suitable method to forecast and warn. Rock engineering is discontinuous, contains a lot of discontinuities, which largely control rock masses’ mechanical properties. So, for studying the stability of jointed rock mass, DDA (Discontinuous Deformation Analysis method) put forward by Dr. Gen-hua SHI is the most ideal choice. In order to reproduce and analyze the whole crack expansion process, DDARF (Discontinuous Deformation Analysis for Rock Failure) is taken as the main line, research involves the pretreatment improvement of numerical algorithm, as well as the secondary development of calculation method, supplemented by theoretical analysis and laboratory test. Results are applied to the stability analysis of underground engineering such as Yi’meng hydro-power station, Ba’di hydro-power station and so on. The main contents of this thesis contain the following aspects:(1) Coupled modeling program of DDARF and AutoCAD was established. Random joints network model was generated in the visual interface of AutoCAD by Monte-Carlo method, model built by this coupling module could be embedded into DDARF and converted into a data file, which would be applied to Yi’meng hydro-power station, the excavation sequence and anchorage scheme of caverns were optimized.(2) Diversified grid meshing method of DDARF was established. The numerical model could be divided into multiple sub-models according to research needs, each model was set different mesh density separately, at last, all sub-models were combined into the complete model. This method not only can satisfy the calculation accuracy of the research object, but also can control the total grid number of numerical calculation. Diversified grid meshing method of DDARF was applied to analyze the stability of surrounding rock mass in Ba’di hydro-power station and so on.(3) Elastic brittle properties of engineering rock mass is presented in most cases, based on which, elastic brittle constitutive model of DDARF was established. Maximum tensile stress criterion and Mohr-Coulomb criterion were used to judge blocks’ stress state. Elastic brittle constitutive model was applied to study cavern excavation in underground engineering, and compared with the original elastic constitutive model.(4) A new thinking about bolt support of DDARF was put forward. Assume that deformation of rock mass was caused mainly by discontinuities, and when a bolt passed through the discontinuity, a set of springs were added along the axial direction and the tangential direction of this bolt, which could simulate the bolt’s axial force and tangential force synchronously, and thus the full-column anchorage shearing bolt of DDARF was realized. An equivalent mode of increasing surrounding rock’s strength parameters was proposed, to simulate the supporting role of bolt in DDARF. At the same time, the judgment for drawing failure and slippage failure of bolts was implemented in DDARF, and compared with the laboratory tests.(5) DDARF mainly uses time step to control the end of calculation, it has great subjectivity. To overcome this disadvantage, displacement convergence criterion was established, and then, the automatic determine for calculation program’s termination in DDARF was realized. Relaxation factor’s influence on the convergence of DDARF was analyzed, and the reasonable scope of relaxation factor was obtained.(6) Crack expansion mechanism of jointed specimen was studied by laboratory test and DDARF, and the alignment is higher, which illustrates the simulation advantage of DDARF for crack expansion. Influence on crack expansion by joints’ angle, length and position was analyzed, and the sensitivity of joints’parameters on crack expansion of DDARF was studied. At the same time, crack expansion mechanism of surrounding rock for jointed cavern under excavation was studied, and the influence law of in-situ stress side pressure coefficient on crack expansion was summarized.(7) Methods of block theory to forecast and warn the key block in rock engineering were analyzed, and several kinds of software based on block theory were introduced simply. How to determine the key moments and the key parts in rock engineering by DDARF was studied, and then support it according to these special moments or parts, at the same time, supporting schemes were optimized.