Study On Stability Of Loess Slope Under The Coupling Effect Of Rainfall And Earthquake

In China,loess area with an earthquake intensity above?degree reaches 335,100square kilometers,and geological hazards caused by various types of loess landslides are very serious.Moisture content increased and shear strength reduced of the loess slope were caused continued rainfall within a week before Min County-Zhang County Ms6.6 earthquake.It is a typical example of the earthquake triggered a lot of loess landslides induced by the coupling effect of rainfall and earthquake.In order to study the failure mechanism of loess slopes under the coupling effect of rainfall and earthquake,the safe avoidance distance of loess landslides.Conducted direct shear test of loess,X-Ray test and CT test,Q₃loess moisture content have important influence on shear strength parameters,and microstructure characteristics and the deformation mechanism is revealed when the loess sample was damped.Based on the failure mechanism of loess slope composed of rigid block and plastic body,the upper bound solution are obtained,and the block limit analysis method is proposed.A model consisting of a plane?straight line?and a curved surface?curve?was proposed,and the mechanical equations of the loess slope sliding block were established,and the solutions of the critical acceleration coefficient of slope failure and the displacement of block are given.A large-scale shaking table test was carried out for the proposed model of loess slope,the failure model and displacement of the loess slope under the coupling effect of rainfall and earthquake were verified.The cause of the sliding block and sliding track of the loess slope is revealed,and the sliding displacement value for judging the failure of the loess slope is given.The main content of the paper are as follows:1.The shear strength of the loess were determined to use direct shear test.Main chemical components and the percentage of each chemical component were calculated in the sample.The images with 500 and 1000 magnifications were scanned,and results showed that the Q₃loess was mainly granular structure by X-Ray test.The soil sample was scanned by CT test when the sample was before and after damped.The scanned layers were studied to use Matlab software.The total pore area,maximum pore area,and maximum center-of-mass were examined in the scanned layer.The Q₃loess moisture content have important influence on shear strength parameters,and microstructure characteristics and the deformation mechanism is revealed when the loess sample was damped.2.Based on the limit analysis upper bound method,a new model of slope failure has been proposed which was consisted of plastic shear zone and rigid block zone.The stability ratio of slope was obtained in different height ratio on slope.The slope failure of four cases were examined:?I?natural state.?II?earthquake effect.?III?rainfall effect.?IV?coupling effect of rainfall and earthquake.The present stability ratios were compared to the previous results,which showed the superiority of the mechanism and rationality of the analysis,and the block limit analysis method is proposed.3.Based on block sliding displacement method and types of loess landslide.A muti-blocks failure mechanism of loess slope was proposed which was consisted of plastic shear zone and rigid block zone.According to Newton's second law,the mechanical equation of the sliding block was established,and the solution of the critical acceleration coefficient and sliding displacement was obtained through integration.As k?t?is greater than k_c,the loess slope begins to deform and slide.The sliding block is large,k?t?has little effect u,and vice versa.As k?t?increases,u also increases.With the increase of the sliding time,the displacement of the larger block is larger.The larger?,the smaller u,and the larger the sliding block,the faster the displacement decreases.?is different,and u changes greatly.The dynamic shear strength during the sliding of the block can be obtained according to the dynamic safety factor.4.A slope model was made to use the similarity ratio based on a real slope which is in new direct,Lanzhou city.The test of loess slope model was adopted results of the infiltration test which rainfall intensity was 15 mm/h and total rainfall was 50 mm.The Sine wave,Wenchuan wave and Min County wave were adopted,added up to 15operating conditions and each time was about 15 s in the test,the XTDIC displacement test system were installed in the slope model.The results shows that the loess slope emerged the acceleration amplification effect appears,and its maximum value is about 2.6,which gives the Q₃loess liquefaction criterion under earthquake.The displacement in the x,y,z and absolute?u_x,u_y,u_zand u_a?were measured under 600 gal,700 gal,800 gal,976 gal and 1300 gal in the 50 s.The results showed that slope emerged the acceleration magnified effect.u_aoccurred as loaded to 700 gal,and u_maxwere 138 mm on the 1300 gal.The coupling effect of rainfall and earthquake,loess liquefaction are induced the final slip distances of loess slope.The change of u_yis the main reason for the curve trajectory of the sliding blocks,and?u of different measuring points is the reason for the formation of the sliding blocks.The loess slope would occurred failure when sliding displacement equal to 3.63 cm.The research can provide a theoretical basis for loess slope design and treatment.