Study On Model Test Of Jointed Rock Mass Characteristics And Representative Elementary Volume(REV)

The nature of the rock material is very complex because of its special formation process. Generally, affected by complicated geological processes, the structural features and mechanical properties of rock mass in nature is complex with the structural planes of different sizes and the diverse nature inside. This Paper studied on the strength and deformation properties of jointed rock mass by the both model test and numerical simulation. The REV (Representative Elementary Volume) of rock mass is an important concept of continuum mechanics. REV is a scale that is the minimum scale when the rock mechanical properties can be treated as equivalent continuous, The main contents are as follows:(1) Studied the strength and deformation characteristics of jointed rock mass by the laboratory model test. The main research objects are three kinds of specimens, namely intact specimens, jointed specimens and anchored-jointed specimens. ComPared with intact specimen, jointed specimen is a specimen with three prefabricated joints with different certain angles, and anchored-jointed specimen is a specimen with reservable anchor holes joints and bolt which is anchored to the anchor holes after the specimen reaches a certain strength. The joints is prefabricated with3angles (the angle between joints and the the horizontal plane) of30degree,45degree,60degree. Carried out the uniaxial compression tests on those specimens. The main contents and conclusions in laboratery test are as follows:1) tested different mixing-proportion mortar specimens’uniaxial compressive strengths and splitting tensile strengths; defined a mixing-proportion that make(makes) the mortar specimen’s physical and mechanical Parameters accord with a fixed similar ratio comPared to the real rock mass; choose aluminium alloy bar as the similar rock bolt based on the similar ratio.2) tested three types of specimens’uniaxial compressive strengths and splitting tensile strengths; analyzed the joints’weakening effects and rock bolts’ strengthening effects on the specimens’ mechanical properties; The Results showed that with the joint angle increased, the weakening effects of jointed rock mass is more obvious. At this point, the rock bolts’ strengthening effects on the specimens have become more significant.There is a significant imPact on the failure modes of rock mass by the joint and the anchorage. (2) It’s summarized the research results of the previous, briefly introduced that the present numerical method of research in jointed rock masses,the characteristics of equivalent continuum approach, and the principle of equivalent strength approach. Besides It’s summarized that the present methods of research in REV of jointed rock masses which focuses on the ideas and procedures of the numerical method.(3) With the hydropower station of the DaGang mountain as the engineering background, we determined the size of REV and the equivalent mechanical Parameters of the object rock mass by numerical simulation method. We get the yield curve of the rock mass which meets the REV size by the numerical loading test. The results showed that the yield curve of the rock did meet the exponential function.(4) Quasi-three-dimensional calculation model of the DaGangShan Hydropower cavern was established. And two types of calculation Parameters were adopted. One is the corrected Parameter calculated by Parameter inversion using statistical characteristics of geological Parameters of rock mass (provided by the design unit) and the displacement data based on field monitoring. Another calculation scheme is to obtain the REV size of different rock zone and rock equivalent Parameters and strength yield function consider random joints, by the way of the numerical simulation. Simulated the excavation of the caverns of the engineering calculations by using the two Parameters. Studied on the displacement of key points in the calculation results and taking into account the fracture fissures’opening displacement of surrounding rock, corrected the calculating displacement by using the empirical formula developed by the precedent scholars of Shandong University. The results showed that the corrected displacements of the key points coincide well with the monnitoring displacement. It proved that the calculation scheme based on the REV to study the equivalent Paramerers of rock mass and the yiele fuction to simulate is more convenient and realistic. Again, when we treated the rock mass as an equivalent continuum material in a numerical calculation, the opening displacement of the surrounding rock fractures can not be ignored.