Research On Failure Mechanism And Stability Of Different Weathered Carbonaceous Shale Cutting Slope

Carbonaceous shale is a kind of soft rock that is widely distributed in Guangxi and southwestern regions of China.Because of its special physicochemical properties,carbonaceous shale is prone to weathering.For carbonaceous shale cutting slopes,slope weathering easily lead to deformation and destabilization,but for the differential weathering type of carbonaceous shale cutting slope,the difference in the degree of weathering cause the formation of particularity of the slope rock body and slope structure with different weathering resistance,resulting in the complex of such kind of deformation failure mode and the difficulty of stability evaluation.Therefore,it is necessary and highly practical to analyze the failure mechanism and stability of differential weathering carbonaceous shale slope.The main research results of this paper are as followed:(1)From the aspects of appearance,structure and mechanical properties of carbonaceous shale rock,an index system for weathering classification was established,the relationship between physical and mechanical indexes of carbonaceous shale and weathering grades was studied,and a classification standard of weathering grades was built,combining the analytical hierarchy process and fuzzy mathematics theory to evaluate of the weathering degree of the carbonaceous shale slope.The result shows that the carbonaceous shale rock slope has severe differential weathering.(2)Based on the water chemistry properties of carbonaceous shale,analyzing the disintegration resistance and mineral composition of different weathering carbonaceous shale,it is concluded that strong weathering carbonaceous shale are more likely to disintegrate in water,and proposed the conception that the "wedge cracking force" under the action of vertical cracks.Then the disintegration mechanism and failure modes of the differential weathering carbonaceous shale slope are analyzed.(3)Based on the orthogonal experimental design,selecting the representative stability factors:slope height,ratio of vertical distance from the slope to the top of the strong weathered rock,slope angle and strong weathered rock formation inclination.A total of 25 sets of slope numerical models were selected,using FLAC3D calculation software the slope safety factor was calculated to determine the stability of the slope;Finally,the order of sensitivity of various factors affecting the stability of the slope was obtained.(4)Taking the differential Weathered Carbonaceous Shale Slope at K21+450 as the research object,the stability of the slope with different excavation slope ratios and different excavation depths was simulated.The results show that the ratio of slope excavation is the most sensitive to the slope stability,the slower the slope,the greater the safety coefficient,and vice versa.Then combining the numerical analysis results excavate the slope in an optimal manner and analyze the deformation and stability of the slope after excavation.Finally selecting the method of prestressed anchor cables to reinforce the differential weathering carbonaceous shale slope.The results show that the reinforcement treatment method can effectively improve the slope stability and achieve the reinforcement effect.