Research On The Determination Methods And Anisotropic Characters Of Strength Of Jointed Rock Mass

Strength determination of of jointed rock mass has very important effect on the design, evaluation of stability and numerical calculation of rock mass engineering with a lot of joints. Simultaneously, it is also the most difficult and challenging problem during the research of rock mass engineering. Although many methods of strength study on the jointed rock mass including experimental evaluation, theory deduce, in-situ testing, similarity model testing and numerical simulating have been put forward at home and abroad, the strength of engineering rock mass cannot be exactly obtained due to sophisticated geology characters of rock mass.Based on the generalization of experimental strength determination methods of jointed rock mass, the author put forward the secondary strength reduction method resulting from "size effect reduction" and "joint reduction" for standard intact rock specimen in order to obtain the rock mass strength with different dimensions, and this improved method is successfully used to the practical rock mass engineering with in situ testing data and detailed geology informations.In addition, the author also propose a methodology of making the ideal geology model for rock mass structure, which includes three parameters of dominant joint sets, joint average spacing and joint equivalent connectivity. Numerical testing of PFC3D (three-dimensional Particle Flow Code) is employed for fitting the indoor testing results of intact rock and rock samples containing joints so that the mesoscopical parameter values of rock and joint can be obtained easily. Furthermore, the large rock samples including sevel joints are used to prove the reliable degree of mesoscopical parameters which have been obtained by the fitting means. The curves between stress and strain are regarded as the index of testing resusts in this paper. Finally, the "dummy numerical testing machine" based on mesoscopical parameters of rock and joints is be adopted as a effective tool to acquire the strength parameters of typical engineering rock mass from Huangshang tunnel and Jingchuan slope in China.Moreover, the anisotropic strength characters of jointed rock mass is analysed in detailed by means of a newly numerical testing method based on mesoscopic parameters of intact rock and joint. The specimens for numerical testing are divided into four kinds, namely, sample with single joint, sample with one set of joints, sample with two sets of joints and three sets of joints. And the testing conditions include the uniaxial compression and triaxial compression accompanying the different joint connectivity. The disadvantages in the theoretical and experimental analysis is found by the numerical study, furthermore, lots of valuable results is also obtained. The main conclusions are as follows.(1) The strength of jointed rock mass cannot be directly determined with single joint or one set of joints by the superposition theorem, at the meantime, the reduced strength due to increased joints or joint sets displays the anisotropic characters.(2) Expect for the geometrical distribution of joints, the anisotropic strength characters of jointed rock mass are not invariant, but variable with the confining pressure and separating states of joints.(3) Compared with the worst dip angle of single joint or joint set rock mass with through joint state under uniaxial compressive conditions, the worst dip angle of single joint or joint set rock mass is reduced because of different discontinuous states, and the anisotropic strength characters is similar to the rock mass with through joint or joint set under confining pressure.