Strength Characteristics Of Slip Soil And Stability Of Huangnibazi Landslide In Li County,Sichuan

The geological conditions in the western mountainous areas are complex,landslide disasters occur frequently,disaster losses are serious,and disaster prevention and mitigation work has a long way to go.The Huangnibazi landslide occurred on August 9,2017 in Li County,Sichuan Province.After the landslide is unstable,the accumulation body continues to slide for more than three months,after which the deceleration begins to creep slowly,posing a serious threat to the residents and traffic safety at the leading edge of the slope.The reason why the landslide slides for a long time is not only affected by the topography and rainfall,but also the strength characteristics and variation law of the slip soil.Therefore,it is necessary to find out the strength characteristics and stability of the landslide slip soil,and it is of great significance for guiding disaster prevention and mitigation.Through more than one year of investigation and monitoring,the microstructure of the slip soil,mineral composition and hydration reaction test,direct shear test,ring shear test and triaxial creep test,numerical model analysis and calculation work,this paper analyzes the geological characteristics and deformation mechanism of landslide,and studies the mechanical properties,shear strength and creep properties of the slip soil,and calculates and analyzes the seepage field and stability of the landslide.The following research results were obtained:（1）The Huangnibazi landslide belongs to a large-composite-medium-speed-soil landslide.The landslide volume is 1.2 million m³ and the maximum slip distance is174m.The landslide movement process is divided into constant speed stage,acceleration stage,deceleration stage and peristaltic stage.The landslide is divided into main sliding,secondary sliding,traction,accumulation and extrusion deformation zones in space,and the deformation failure mode changes with spatial evolution.The landslide has the characteristics of long sliding time,short slip path and step-by-step destruction.The induced factors are mainly rainfall.The comprehensive analysis considers that straight terrain,complex failure modes and special slip zone properties are the reasons for the long-term slow movement of the landslide.（2）The physical properties of the slip soil are quite special.Sliding soil silt and clay content in more than 38%,the content of clay mineral is 57.29%,the mineral is mostly flaky,and the particles are rearranged along the shear plane after shearing;During the saturated water process,some of the detrital minerals in the slip soil will be converted into clay minerals,and the soluble minerals will dissolve,resulting in the change of the microstructure of the slip soil,the plasma concentrations of K⁺、Na⁺、Ca²⁺、SO₄^2-、HCO₃^-and Cl^-all showed a logarithmic growth trend.（3）The direct shear test of the slip soil show that the undisturbed soil has a strong original structure,and the shear strength of the undisturbed and remolded soil decreases rapidly with the increase of water content,and it decreases significantly faster and then slower with the soaking time.The decline of shear strength of undisturbed soil is much larger than that of remolded soil.The decrease of cohesive force is greater than the internal friction angle.The shear strength of slip soil decreases sharply during the stage of 18.1²4.6%.The immersion in water for48h⁷2h is the turning interval of the slip soil and the transition range of each ion solubility from rapid to slow change.The agglomeration of cohesion is attributed to the interaction of water and soil such as mineral dissolution and ion exchange,which changes the microstructure of the slip soil.The internal friction angle is attenuated due to the conversion of the detrital mineral portion to a clay mineral having a smaller internal friction angle during the soil-water reaction and the water lubrication reduces the frictional resistance between particles.（4）The ring shear test shows that shear stress-displacement curve fluctuates greatly when the shear rate is large,and it needs more deformation to reach the steady state.With the increase of shear rate,the peak strength and residual strength of the slip soil increase,and the increase of residual strength is related to the high clay content of the slip soil;The peak cohesive force,peak internal friction angle and comprehensive internal friction angle of the slip soil can be fitted to shear rate to a good logarithmic relationship.（5）The triaxial creep test show that the creep process of the sliding soil includes the transient elastoplastic deformation,the decay creep and the steady creep stage,and the softening of the soil caused by the structural transformation plays a leading role in the creep;The deformation rate and deformation value of the slip soil are positively correlated with the axial stress value;Long-term strength of the slip soil:c=16.4 kPa,?=14.34^?,compared with the peak strength parameters,decreased by 43.8%and 28.9%,respectively,which has shown that the effect of time effect on cohesion is greater than the internal friction angle,while the decrease in internal friction angle indicates that the continuous adjustment of particle position is significant.（6）The simulation analysis shows that the stability coefficient of the natural state landslide is 1.018,which is in an unstable state.Under the condition of 20mm/d rainfall,the stability of the landslide will decrease rapidly and become unstable.