Study On The Deformation And Failure Mechanism Of Excavated Loess Slope In Yan’an

Excavation in loess slope is the major factor that result landslides in loess area. Study onthe trigger factors of landslides is the prerequisite and basic of landslide prevention. On thebasis of field investigation and data collection, deformation and failure mechanism of typicalexcavated loess slope will be research by laboratory tests, numerical analysis and kinematicssimulation. The result show that:1.On the basis of field investigation and data collection, the rule of excavated loess slopewas studied. There are four types of excavated induced loess landslide, excavated in the toe ofslope that induced ancientslide resurgence, cave-house induced landslide, built houses nearthe slope induced landslide and spoil of excavation induced landslide. In the first three ofthese types are more commonly.2.Select a typical slope in Huangling county as the sampling points. Then direct sheartest and triaxial compression test were done under different stress and water content usingundisturbed sample. The result show that the cohesion of soil reduce with the water contentincrease in both direct shear test and triaxial compression test, and the curve is an exponentialfunctions. But there is no correlativity between the internal friction and water content. Theinitial deformation modulus and secant modulus at strain of3%,6%,9%,12%,15%increaseswith confining pressure increasing, and E_i＞E_3%＞E_6%＞E_9%＞E_12%＞E_15%is satisfied exactly.There are three failure modes under triaxial stress: flerry, shear failure and swelling failure.Flerry occur when water content and confining pressure are low, and the Rupture surfaceconsistent with the maximum principal stress. Shear failure appear at medium water contentand medium confining pressure, the Rupture surface skewed with the maximum principalstress at the angle of45°+/2.There is swelling failure when water content and confiningpressure are high. There is no obvious shear and fracture surface in the sample except radialswelling and axial shortening. Overall, swelling failure is the main failure mode.3. Choose typical landslides （high and dangerous slopes） of excavated in the toe of slopethat induced ancientslide resurgence, cave-house induced landslide and built houses near theslope induced landslide. The change of stress and shear strength on sliding surface of eachlandslide during excavation were got through numerical analysis. Numerical simulationsshow that the excavation transformed stress distribution even the shear strength on slidingsurface. The shear stress gradually exceeds the shear strength on potential sliding surfaceduring excavation, and the stability factor reduced until slope destabilized. Kinematicssimulation of typical landslides dovetailed nicely with practical slope failure, and the failure of high and dangerous slopes were predicted.