Study On The Calculation And Application Of The Persistent Ratio In Jointed Rock

In rock mass, the specific rock structure formed by the intersection of various discontinuities determines engineering mechanical properties of rock mass. The network simulation method based on Monte Carlo principle is a reliable way to study IV, V class rock discontinuities which are widely distributed but difficult to accurately locate. Through statistical analysis and network simulation of measured rock discontinuities data, we can obtain a network image of discontinuities which has the same statistical characteristics with the field measuring results on a computer. On this basis, the rock persistent ratio of different shear directions can be obtained by analyzing the combination failure modes of discontinuities and rock bridges in different directions. The calculation results of rock persistent ratio reflect the connectivity rate of rock mass in all directions, usually the persistent ratio only rate as an indicator of a macro qualitative analysis, the application of this index is still room for further development. In the field of slope stability analysis, the traditional method of analysis does not consider the discontinuous characteristic, if the persistent ratio was introduced in slope stability analysis to consider the anisotropic of rock, then this defect can be effectively compensated. It is contemplated that if the persistent ratio was used to modify shear strength parameters of rock mass in the process of searching the critical slip surface, the critical failure mode considered the anisotropy of rock mass can be obtained. This paper carried out research in the following areas:The basic principles and methods of discontinuities’ statistical analysis, network simulation and the calculation of persistent ratio are reviewed. Measured discontinuities data of Songta and other hydropower stations are analyzed, and the distribution characteristics of discontinuities are studied. At the same time, by using the case of two sets of discontinuities and taking the method with fixed shearing end points, the relationship between the persistent ratio and shear band under various conditions are analyzed.In addition, the calculation result of the persistent ratio under different sizes and different normal stress conditions are studied.The running problem of the discontinuities’statistics program under Windows platform is solved, statistical grouping and geometric parameters’statistical work of the discontinuities is simplified. Using VBA program, the function of data checking and file format conversion are added, some other flaws of the statistical program are fixed. The network simulation program is improved, the function of outputting simulating network diagrams in AutoCAD format file is added, which provides the basis of simulated results’ further application.The feasible approach of applying the calculation result of discontinuities’network Simulation and the persistent ratio to Sarma method is proposed. By introducing the persistent ratio, reduction is made on the strength parameters of slides’ side and bottom in searching process, and the method considered the anisotropy mechanical properties of rock is successfully achieved. The slope stability verified calculation results of an example, Manwan and three Gorges Dam hydropower station are all in line with the actual site conditions.