Study On Stability And Field Monitoring Of Unsaturated Loess Multi-level Slope

With the implementation of the national western development strategy,the construction of high-speed railways in the northwest loess region has developed rapidly;Along the Zhongwei Lanzhou Railway,there are numerous ravines and large areas of earth and rock excavation,forming a large number of unsaturated loess multi-level slopes.These slopes are prone to instability due to their multiple stages and the unique mechanical properties of their own soil.In view of this,based on the unsaturated multistage loess slope project of Baiyin South Station of China Lanzhou Passenger Dedicated Railway,the stability study of unsaturated multistage loess slope is carried out in depth.Firstly,based on indoor soil tests,the physical and mechanical parameters of the soil are obtained.Through data mining and analysis of triaxial test data,the deformation mechanism of unsaturated loess multi-level slopes is revealed;Secondly,based on the Morgenstern Price limit equilibrium method,considering the influence of slope geometric parameters and matrix suction between blocks,a multi-stage stability calculation method for unsaturated loess slopes is established;Thirdly,establish a numerical analysis model to compare and analyze the stability of slopes under different working conditions;At the same time,sensitivity analysis was conducted on the factors affecting the stability of multi-level loess slopes using orthogonal experimental methods;Finally,in-depth and systematic research was conducted on the stability of unsaturated loess multi-level slopes through on-site monitoring.The research results can provide scientific basis for the stability evaluation of multi-level slopes in the northwest loess region.The main work and conclusions are as follows:(1)Through indoor geotechnical tests,the basic physical and mechanical parameters of loess were obtained.Data mining was used to analyze the results of triaxial tests,revealing the deformation mechanism of unsaturated loess multi-level slopes.The unsaturated loess multi-level slope formed a combination of confining pressure and matrix suction that was not conducive to soil stability,resulting in differences in deformation strength between the surface soil and deep soil of the slope,leading to slope instability.(2)Based on the Morgenstern Price limit equilibrium method,considering the influence of slope geometric parameters such as grade,slope height,slope ratio,platform width,and matrix suction on lateral stress,combined with the multi-level slope type equation and inter block stress equation,a stability calculation method for unsaturated loess multi-level slopes is established.(3)Simulate the deformation of unsaturated loess multi-level slopes under different working conditions using Plaxis 3D finite element software.Under natural conditions,the changes in horizontal displacement,plastic strain,and soil matrix suction of the most dangerous sliding surface of the slope were analyzed and compared with rainfall and earthquake conditions;Under rainfall conditions,the effects of different rainfall intensities,durations,and types on the horizontal displacement,plastic strain,and soil matrix suction of the slope were elucidated;Under earthquake conditions,the changes in slope displacement,velocity,and acceleration within 10 seconds of the earthquake were analyzed.(4)Introduce the main influencing factors of the stability of unsaturated loess multi-level slopes,select the soil parameters and geometric parameters of the slope as the research objects,and analyze the sensitivity of the influencing factors of slope stability through orthogonal experimental design method.According to the experimental results,it was found that the soil parameters of the slope have a greater impact on the stability of the slope compared to the geometric parameters of the slope.(5)Analyze the monitoring results of deep slope displacement measurement,soil pore water pressure,and Beidou navigation full phase shift on site.The monitoring results indicate that the variation of inclination displacement is influenced by the anchoring force,and the changes in pore water pressure and full phase displacement are closely related to the local hydrological climate.