Preliminary Study On The Failure Mechanism Of Loess Slope Under Action Of Cutting Coupled With Raining

With the rapid development of economy in the western region,geological disasters such as loess landslides have become more and more frequent,posing a serious threat to the safety of local people’s lives and property.Taking the "9 ·17" Baqiao landslide in Xi’an as the research background,through data analysis,field investigation,physics,mechanical test,physical model test,numerical simulation analysis and other methods,the "excavation-rainfall type" loess slope model was constructed,exploring the instability mechanism of loess slope excavation-rainfall coupling.The main research conclusions and understandings include:(1)The "9 17" Baqiao landslide in Xi’an is a serious disaster caused by the destruction of the loess slope instability.In addition to its special slope structure and loess composition the causes of the disaster include long-term slope foot excavation and atmospheric precipitation lasting for two weeks.The mechanism of the instability of excavation-rainfall coupling on loess slope is typical and representative.(2)Construct the loess slope model,Large landslide physical simulation test,Design three tests S-1(50cm for slope foot excavation),S-2(50cm+rain strength 68.3mm/h)and S-3(rain strength 68.3mm/h),The main test result is that①a 35cm appears at the front edge of excavation,Tavfissure 1～2mm wide,The slope body is basically stable;②sustained sustained rainfall to 38min,Local collapse begins at the front edge of the excavation,This phenomenon continued until 184min,And the slope body presents the destructive characteristics of gradual collapse from the leading edge to the trailing edge.Until 237min,the slope body slide up to 60cm;③for S-3 group,the same rainfall duration as S-2 group,slope erosion is serious,the slope foot formed mud flow,but the slope body did not slide.The test results show that the loess slope(slow slope)has a certain overall rainfall stability,and the superposition and coupling effect of the slope foot excavation and rainfall will induce the overall instability and disaster generation of the loess slope.(3)FLAC3D5.0 finite element numerical analysis shows①a significant increase at the slope foot for the S-1 group,the maximum displacement variable is 7.6 mm,the slope body stability coefficient 1.77 in a relatively stable state;②for the S-3 group,the shear strain increase at the slope foot is 1.2cm,the slope stability factor 1.23 and the slope body is in a relatively stable state;③for the S-2 group,the shear strain increase at the excavation surface is 2.8cm.The slope body stability coefficient is 0.91.Simsimulation results show that excavation-rainfall coupling is most unfavorable to the stability of loess slope.(4)The instability-disaster-causing mechanism of "tension-saturation-shear destruction" of the"excavation-rainfall type" loess slope is proposed.