Study On The Cumulative Damage Mechanism And Stability Factors Of Soft And Hard Interbedded Slope Under Cyclic Shear

The induced earthquakes are in the state of “frequent-microseisms” since the impoundment of the Three Gorges Reservoir Area(TGRA).We realize that this external force affects the stability of the reservoir bank slope as the deepen of the investigate.The soft-hard interbedded slope,which locates in the TGRA,is a kind of slope with poor stability.Particularly,the following factors,i.e.,relative position of soft-hard layers,thickness and moisture content of soft layer,are the main reasons for the failure of soft-hard interbedded slope.How to consider these factors under the condition of frequent-microseisms is the focus of this paper.This paper is supported by NSFC(41972266,41372356).On the literature investigations,this shear tests of interbedded rock mass were first conducted,and the experimental data provide a basis for the improvement of the Nishihara model(NM).Subsequently,the meso degradation characteristics of rock mass discontinuities were obtained using the 2D Particle Flow Code discrete element method(2D PFC DEM).Finally,the slope stability under the condition of frequent-microseisms was explored using the 2D Universal Discrete Element Code(2D UDEC).The main study contents and investigations of this paper are as follows.(1)The im Pact of the thickness and moisture content of the soft layer on the shear strength,deformation characteristics and cumulative damage laws of rock mass were observed according to the shear tests.It can be explicity seen from the tests that the rock mass with thin soft layer shows the “strain-softening” characteristic under the cyclic shear action.(2)The shear tests of interbedded rock mass with second-order asperities were simulated using the 2D PFC DEM.The influence of water content and thickness of soft layer as well as the number of cycles on the cumulative damage laws of rock mass were investigated.The cumulative damage laws of rock mass,i.e.,the quantites,distribution patterns and development laws of meso-cracks,were gained.The numerical simulations also reveals The dynamic response characteristics such as the reduction of damping force and dynamic modulus were also found using the numerical simulations under cyclic shear.(3)The NM was improved to describe the deformation characteristics of rock mass under cyclic shear in this study.Based on test results and parameter sensitivity analysis,the rationality of the model was validated,and it can be easily found that this model can be used to describe the characteristics of “single-double inflection points” in the curves of shear cycles versus shear strain.(4)The deformation characteristics of interbedded rock slope with first-order asperities under the frequent-microseisms condition were simulated using the 2D UDEC.The im Pact of the thickness of soft layer and number of microseisms on the factor of safety(FOS)and failure modes of interbedded rock slope were studied,furthermore,the support suggestions were proposed for this kind of rock slopes.