Study On The Formation Mechanism Of Deep-steated Crack Of The Right Bank Slope In The Yebatan Hydropower Station

Since the Deep-steated cracks have been revealed in the dam site of hydropower stations in 1980,the cause of formation has been widely concerned by the engineering and academic circles.At present,there is no consensus on this issue.It is of great practical significance and theoretical value to reveal the mechanism of Deep-steated crack and fracture for the investigation,design,construction and operation of hydropower stations.The paper based on the typical Deep-steated crack as the research object in right bank of Yebatan Hydropower Station,and detailed survey data in the field,combined with laboratory test results,using the seismic wave CT technology,revealing the fracture development distribution and deformation and failure characteristics of Deep-steated crack;.According to the features of fracture in Deep-steated crack set up geological mechanics model and carry out the experiment of physical simulation,the analysis the relaotion between area of stress concentration and fault under unloading conditions.Based on the 3DEC discrete element software build 3D model and numerical simulation experiment,analyses the rule of the stress concentration and release Within the rock of cutting by parallel structure plane under the process of incised valley.Contrast above experiment and Deep-steated crack at the scene further discuss the cause of the fault controlling deformation of deep fracture.The main research results are as follows:(1)The deformation of the Deep-steated crack of the right bank is mainly developed in the high elevation,with the decrease of the height,the quantity decreases rapidly.In the horizontal direction,the width of the fracture zone is 80-150 m,the depth of the deformation zone is 4~55m.In the horizontal direction,the deformation of deep fracture is good,and the correlation is poor in the longitudinal direction.(2)The dominant direction of Deep-steated crack and fracture is NW,which is close to or parallel to the river.The dominant direction of the structural plane of the right bank is NWW and NE.According to the measured data,the deformation and fracture of the right bank belong to Faul Controlled Deep-steated crack,and its development and failure characteristics are controlled by the fault.On the right side of the structure,the "X" conjugate system is shown,and the direction of the principal stress direction of the tectonic stress plane is N60 ~80° E,which is in agreement with the measured results.(3)Under the unloading state,the accumulated residual strain can be released rapidly,and a large number of tensile stress concentration zones are formed in the special rock mass.The rule is: the tensile stress mainly concentrated area between parallel faults,and reached the maximum at the ends of the fault,in the intersection of multiple fault zone,the stress concentration increased,while the tensile stress concentration zone often banded development process.The distribution law of the development is consistent with the distribution of Deep-steated crack and rupture in space.(4)From the angle of stress accumulation and dispersion,the formation process of Deep-steated crack can be divided into two stages,the strain energy accumulation and strain energy release phase.The formation region of Deep-steated crack shows strong energy to concentration and release feature,is the result of mutual transformation of Compressive stress concentration and tensile stress concentration in geological process.(5)The set of Deep-steated cracks on the right bank of the Yebatan Hydropower Station is the result of difference of unloading rebound,which suffers high stress slope condition and special structure rock combination,with the slope stress strongly released in canyon formation process,and superimposed special unloading method,under the controlled of two parallel and intersecting faults.