Study On Shear Strength Characteristics Of Mud-sandstone Heterostructure In The Three Gorges Reservoir Area

After the completion of the Three Gorges Project as a project for people's livelihood,the geological environment of the reservoir area has become the focus of attention.Among the many strata,the Jurassic strata dominated by mud-sand interbedded rocks are the most widely distributed,and the interbedded rocks have steep neighbors.The characteristics of soft and hard are the main factors for slope instability.Based on the Barton strength criterion and 10 standard sections,combined with indoor direct shear test and numerical simulation of particle flow,the mud-sandstone heterogeneous structural surface specimens were studied in different experimental schemes.The lower shear strength characteristics and failure mechanism lead to the following conclusions:(1)Firstly,the sandstone indoor direct shear test was carried out,and the sandstone samples of the variable amplitude zone in the Three Gorges reservoir area were selected for the determination of the longitudinal and transverse wave velocity and density,and furtherly selected from the four groups of 16 typical sandstones with similar physical properties.The indoor direct shear test was carried out under four different normal stress conditions.The mudstone was combined with the existing reference data to obtain the indoor shear strength characteristics and macroscopic parameters of the sandstone and mudstone of the bank slope of the Three Gorges reservoir area.(2)Based on the 10 standard profiles proposed by Barton,a mud-sandstone PFC2 D numerical model was established.With reference to the obtained mudstone and sandstone macroscopic parameters in the laboratory test,the shear strength parameters of the 10 heterogeneous structural planes of the mud-sandstone under normal stress are obtained by the mesoscopic parameters calibration of the numerical model.Based on the Barton strength criterion,a hypothesis formula for the strength criterion of the mud-sandstone heterosexual structure under high and low stress conditions is proposed.By fitting and comparing with the shear strength obtained by numerical simulation test,the rationality and application of the hypothesis formula are verified.Sex.(3)From the numerical simulation of the shear stress-shear displacement curve,the same structural plane can be divided into two kinds in the different normal stress range: the normal stress is in the range of 5.0 MPa,and the yielding stage of the shear stress-shear displacement curve The boundary between the residual strength stage and the residual strength is not obvious;when the normal stress is greater than 5.0 MPa,the yield stage and residual strength stage of the curve become significantly longer.The shear strength of mudsandstone in low stress state(1.0-4.0 MPa),under the same normal stress condition,with the increase of the roughness coefficient of the structural plane,the increase of the undulation of the mud-sandstone structure surface will produce the "furrow effect".(4)The influence of normal stress and roughness coefficient on crack propagation position and crack penetration mode of mud-sandstone specimen failure process is analyzed,and the linear relationship between fracture number and normal stress is obtained.The heterogeneous structural plane is divided into three stages according to the transmission frequency during the loading to complete destruction process,which is the low frequency,high frequency and intermediate frequency stages;when the same structural surface roughness coefficient is the same,the increase of the normal stress will increase the three stages of sound.The frequency of the emission,the duration of the high frequency region will also become longer as the normal stress increases.