Study on size effect of jointed rock mass and influencing factors of the REV size based on the SRM method

Based on the Yaojiayu tunnel of Binlai Expressway, the size effect of jointed rock mass and influencing factors of the representative elementary volume (REV) were studied. The point cloud image of jointed rock mass near the tunnel face was collected by 3D laser scanning technology. Through the Geology Plane software independently developed by Shandong University, the structural plane data were processed and obtained. According to the structural plane data, the discrete fracture network (DFN) was established. Based on the laboratory test results of rock samples in the tunnel site, the particles were embedded into DFN to construct the synthetic rock mass (SRM). The size effect and REV of the jointed rock mass were studied based on the uniaxial compressive strength (UCS) and Young's modulus obtained by uniaxial compression test simulations. It is concluded that the REV size of the jointed rock mass is 7 m x 7 m x 14 m, which provides the criterion and calculation parameters for simulating tunnel excavation in jointed rock mass by the continuous deformation calculation method. In order to study the influence of joint geometric parameters (trace length, spacing, and dip angle) on REV size, different multi-scale SRM models were established by changing the parameters of structural planes. It is observed that within a certain size range, the REV size is negatively correlated with the joint trace length and dip angle, while positively correlated with the joint spacing. And the size of REV is gradually stable with the increase of geometric parameters of joints. Based on the influence law of joint geometry parameters on REV, the REV size range of different engineering can be estimated approximately.