Parameter Estimation Of Rock Mass Structure Surface And Stability Analysis On High And Steep Rock Slopes In Deep Valleys

The mechanical behavior about the slope rock mass strongly depends on the geometric and mechanical properties of discontinuous structural planes,so the existence of discontinuities is the most critical factor leading to the failure and instability of rock slope.Therefore,in order to better explore the geometric and mechanical properties of rock mass structural planes,so as to carry out reasonable research on the stability of rock slope,this article is based on the Huangzang Temple Water Control Project in Qilian County,Qinghai Province,using 3D laser scanning technology and the corresponding 3D roughness characterization method,the engineering large-scale rock mass structural surface roughness research was carried out,and the shear strength of the rock mass structural surface was reasonably estimated.Then,through the statistical analysis of the rock mass structural characteristics of the engineering slope,a complex rock mass structural slope model conforming to the statistical characteristics is constructed.Finally,the discrete element software 3DEC is used to analyze the stability of the slope model of the right bank abutment of Huangzang Temple which combined with the strength reduction method of the rock mass structural plane.The main research results are as follows:（1）Discrete element fracture network slope model on the combination of bonded block model and discrete fracture network（BBM-DFN）is proposed,which combines the randomness of the block distribution characteristics of the bonded block model（BBM）with the regularity of the statistical distribution of the discrete fracture network model（DFN）.（2）Based on the 3D laser scanning point cloud data of rock discontinuities and the Grasselli 3D roughness characterization method,the multi-scale influence law of the location of window sampling center on the 3D roughness of engineering large-scale rock discontinuities is studied.The results show that the size effect of three-dimensional roughness of structural plane is different due to different sampling center positions,and there is a minimum effective sampling size for the feature sampling center.For example,the effective sampling size of structural plane for the feature sampling center in this paper is 1550 mm*1550 mm;the different positions of the sampling center of the window lead to different three-dimensional roughness values of the same size structural plane in the same shear direction,and the roughness difference decreases with the increase of the sampling window size;the three-dimensional roughness values of structural planes in different analysis directions are different,so the three-dimensional roughness of structural plane is anisotropic.For the minimum three-dimensional roughness value of structural plane,the location of sampling center has little influence on its existence range.Moreover,the minimum roughness value of structural plane of large-scale rock mass studied in this paper has an angle range of 110°to 130°.（3）Based on Cottrell’s revised and improved Grasselli shear strength theory,combined with the three-dimensional roughness value of the characteristic sampling surface and the rock mechanics index obtained by the design unit based on the indoor rock mechanics experiment,comprehensively estimated the shear strength parameters about the rock mass structural plane of the right bank abutment slope of Huangzang Temple.Finally,the estimated shear strength parameters of rock mass discontinuities were compared with the shear strength parameter values of rock mass discontinuities obtained by the design unit based on the field test results,which verified the rationality of the shear strength estimation method and evaluation parameters of rock mass discontinuities.（4）Based on the statistical analysis of the complex rock mass structural slope model of the right abutment slope of Huangzangsi,a discrete element fracture network slope model with BBM-DFN combined with each other in accordance was constructed.Finally,based on the strength reduction method of rock mass structural planes,the 3DEC discrete element software is used to analyze the stability of the slope on the right bank abutment of Huangzang Temple under different working conditions.It can be seen that the stability of the slope is mainly controlled by the combination of fault fs₀₁and fault fp_04-6,and the stability coefficients of the slope under different working conditions are as follows:the stability coefficient of the natural right bank abutment slope is 1.13;the stability coefficient of the slope on the right bank abutment is 1.19 when the excavation is above 2631m without support;the stability coefficient of the slope on the right bank dam abutment is obviously less than1 when completely excavated and without support,so under the condition of unreduced strength,the slope is extremely unstable and has serious deformation damage;the stability coefficient of the slope on the right bank abutment is 1.25 when fully excavated and supported.