Study On Identification And Stability Of Dangerous Rock Mass Of High-steep Hillslope At The Taoziping Tunnel Exit

With the main lines of communication extending to the mountains,the stability of rock mass has become one of the key issues in geological engineering research.In this paper,the high and steep slope at the Taoziping tunnel exit in the Dujiangyan City to Siguniang Mountain Railway(hereinafter referred to as Du-Si Railway)is taken as the research object,using the UAV photogrametry technology to identify and investigate the dangerous rock mass on the slope.Analysing the stability of the dangerous rock mass and the slope,and simulating the motion characteristics of rockfall after collapse.Combined with the field situation and simulation results,the prevention and control suggestions of rockfall are put forward.The main research results of this paper are as follows:1.The UAV photogrammetry technology is used to establish the real landscape 3D model and digital surface model(DSM)of the slope.In the real landscape 3D model,15 single dangerous rock masses and 3 complex dangerous rock masses are identified based on the identification characteristics of dangerous rock masses.In the model,the geometric dimension of dangerous rock masses,trace length and aperture of structural plane are measured directly.At the same time,based on the plane fitting principle and spatial geometric relations,the occurrence calculation program of the structural plane was compiled in MATLAB,and 218 structural planes were counted.2.Combined with the analysis of the field investigation results,the dangerous rock mass of the slope is mainly distributed at the top of the slope and the middle and lower part of the slope near the side of the debris flow ditch.Under the geological tectonic function,river erosion,weathering and human engineering activities,the development and evolution stages of dangerous rock mass can be divided into three stages: the formation and extension of cracks,the formation of dangerous rock mass by tensile fracture failure,and the collapse of instability dangerous rock mass.3.The stability of single dangerous rock mass is analyzed by static analytical calculation method.The results show that under natural condition,there are three unstable dangerous rock mass and four under-stable dangerous rock mass.Under rainstorm condition,there are seven unstable dangerous rock masses and three under-stable dangerous rock masses.Under earthquake condition,there are eight unstable dangerous rock masses and three understable dangerous rock masses.The stability of complex dangerous rock mass is analyzed by stereographic projection method.The results show that S1,S2 and S3 are unstable in the natural state and have the risk of plane-sliding failure and wedge-sliding failure,which is consistent with the field investigation results.4.The slope has three groups of preferred structural planes J1,J2 and J3 by clustering method.The probability distribution models of trace length and inclination Angle of the three groups of preferred structural planes are obtained by statistical analysis,and the 2D random structural planes network is generated by the MATLAB software.The structure plane network is imported into the UDEC to establish the complex joint slope model,and the slope stability was calculated under natural condition,rainstorm condition and earthquake condition respectively.The simulation results show that the slope is in a stable state under natural condition,and only part of rock mass with tension at the top of the slope is prone to tensile failure.Under rainstorm condition,the stability of slope is decreased to some extent,but it is still in a stable state.In addition to the rock mass with tension at the top of the slope,some rock mass at the middle and upper part of the slope is prone to slippage failure.Under earthquake condition,the slope is in an unstable state,which is prone to shear failure and tensile failure,the maximum total displacement of rock mass is36.78 cm.At the same time,some rock mass on the slope appears projectile collapse.5.The rockfall motion characteristics of single dangerous rock mass are simulated by ROCFALL.The simulation results show that W1,W5,W7,W8,W11 and W15 may threaten the safety of railway line.The rockfall motion characteristics of complex dangerous rock mass are simulated by Rocky For3 D,and the dominant path of rockfall is predicted based on the reach probability and the spatial occurrence probability.the motion simulation results and the classification results of rockfall hazard shows that: S1 is classified as high danger-extremely high danger to the railway line;S2 is classified as low danger to the railway line.S3 is not a direct threat to the railway line security but a large amount of rock blocks accumulates in shangmujiangping Gully from S3,which provides the material source for debris flow.