Research On Dynamic Response Rules And Failure Mechanism Of Alternatively Distributed Soft And Hard Bedding Slopes Under Strong Earthquake

China is a country with frequent earthquake disasters,and personal casualties and economic damages caused by secondary geological disasters induced by earthquakes such as landslide,debris flow,collapse and rock falls are larger than the damages directly caused by earthquakes.On May 12,2008,Wenchuan earthquake induced countless secondary geological disasters,leading to disastrous destroy to epicentral regions and surrounding regions.Wide ranges of dynamic failures on steep bedding slopes were detected in the survey on secondary geological disasters induced by Wenchuan earthquake.Therefore,a lot of researchers have conducted researches on the failure mechanism and the dynamic response on steep bedding slopes under earthquake conditions,and abundant achievements have been obtained.However,no specific research on dynamic response rules or dynamic failure mechanism on extensive alternatively soft and hard steep bedding slopes in Wenchuan earthquake has been conducted.Therefore,by taking “May 12th” Wenchuan earthquake as the research background,based on field research on dynamic failure of alternatively soft and hard steep bedding slopes of Wenchuan earthquake region,this article establishes physical test models by taking the most representative slopes as research objectives.In addition,the centrifugal shaking test and the 3D discrete element numerical simulation method are adopted to analyze and discuss on the dynamic response characteristics and the failure mechanism of related type of slopes,with the following main works and achievements:(1)Based on field investigation on large numbers of dynamic failure cases of alternatively soft and hard steep bedding slopes induced in Wenchuan earthquake,dry slopes and water slopes are taken as representatives,to determine the similar constant and basic control flow of the model test by taking existing test conditions,general conditions of landslide engineering and similarity theory of centrifugal shaking table model test into consideration.The models of the two types of alternatively soft and hard steep bedding slopes are established in an abstract and generalized way,i.e.,alternatively soft and hard 60° slope structure(M1)and alternatively soft and hard 80° slope structure(M2),respectively.(2)The tests on ratios of hard rock and soft rock of the models are conducted,to determine the optimal similar materials and corresponding mixture ratios of the model tests,in which the ratio of hard rock is quartz sand: blanc fixe: cement: gypsum = 2:5:1:1,and that of soft rock is quartz sand: blanc fixe: gypsum=1:1:1.The seismic wave loading scheme is determined according to practical conditions and test design,to arrange for the test monitoring point and conduct optimization design with reasonable monitoring elements.(3)Under earthquake actions,the main deformation part of the alternatively soft and hard 60° slope model is the rock and earth mass within certain ranges of the whole slope surface,with the specific performance of the sliding down of the slide mass along with the soft layer under the horizontal earthquake action,showing smooth back wall on back edge;the rock and earth mass around the slop toe curves and uplifts;slippage is detected on the whole slope model,i.e.,bending sliding.The failure parts of the alternatively soft and hard 80° slope model are mainly detected close to slope toe and slop crest under the action of dynamic loading,with the performance of hierarchical sliding of the slope model under the action of the horizontal earthquake loading,with significant lower seat steep ridge and vertical tensile cracks on slope crest,turnover of the upper rock stratum to the free face,turnover and falling of rock mass on slope crest,significant bending,uplifting and fracture close to slope toe;the slippage-bending on bottom-turnover failure on top are observed in the whole slope model.(4)In the alternatively soft and hard 60° slope model,with the increase in elevation of the slope surface,there is a nonlinear increase in PGA amplification coefficient,with the most intensive dynamic response on slope crest.At the same time,in the alternatively soft and hard 80° slope model,with the increase in elevation of the slope surface,the PGA amplification coefficient an increase-decrease-increase trend,with the most intensive dynamic response on one third of the slope height and the slope shoulder.At the same time,at the same level,the accelerated velocity amplification coefficient changes larger when getting close to the slope surface due to less restriction on rock and earth mass when getting closer to the free face,leading to certain “surface trend effect”.(5)Based on the Hilbert-Huang transform and the marginal spectrum theory,the failure region in the alternatively soft and hard bedding slope under earthquake action involves in the rock and body mass within certain depth range;in addition,the horizontal influencing depth of the alternatively soft and hard 60° slope model is deeper than that of the alternatively soft and hard 80° slope model.(6)The two slope failure characteristics reflected from numerical simulation results and the test results of the centrifugal shaking table are basically the same.Therefore,the centrifugal shaking table test can be utilized to reveal the accelerated velocity dynamic response rules and the failure mechanism of the steep alternatively soft and hard bedding slopes under the action of earthquake loading.