Formation Mechanism And Stability Analysis Of A Loess Landslide Based On The Mechanical Properties Of Sliding Zone Soil

As the pace of China's western development is accelerating,the construction of multiple expresways in the Loess Plateau of northern Shaanxi needs to reconstruct the original slopes.The formation of cutting slopes at the foot of slopes has become a common phenomenon in the region,and it has resulted in Landslides,collapses,and other slope failures are occurring in an endless stream.This thesis explorates a landslide that occurred during the construction of a highway subgrade in Zhidan County.Based on the site investigation,this thesis took slide soil samples to conduct physical and mechanical tests on the indoor undisturbed and remolded soils,and studied the physical and mechanical properties of the sliding belt soils,then used the MIDAS NX finite element software to perform three-dimensional numerical simulations.Combined with indoor test results,summarized the formation mechanism of landslides,and finally used the theory of extenics to analyze landslide stability.The main results of the thesis are:(1)After summarizing and analyzing the engineering geology of landslides,take the slide soil samples after the landslides have undergone severe slides,and carry out physical tests to obtain parameters such as the water cut,dry density,liquid-plastic limit,and particle size grading,and perform direct shearing,triaxial test and ring shear tests yield relevant mechanical property parameters.The microstructure of the soil samples after shearing in the triaxial test was analyzed,and the development rules of the pores and cracks in the soil were obtained.The shear strength and parameters of the sliding belt soil were systematically analyzed by three mechanical tests,it is concluded that the sliding zone soil has strong mechanical properties at low moisture content,but its shear strength decreases sharply when the moisture content approaches saturation.(2)Three-dimensional numerical simulations were performed using the MIDAS NX finite element software.The results show that the landslide stability coefficient is less than 1 and is in an unstable state.The deformation of the slope body is mainly affected by the terrain,and the stability of the slope body is stable at a smooth terrain.,at the steep foot slope is low and the sliding displacement is large.In addition,the main landslide drives the east side landfill platform to a certain degree of displacement;the maximum shear strain appears in the sliding belt soil at the landslide shear outlet and runs along the sliding belt soil.It is a typical movement model of a traction landslide.(3)Combined the results of site surveys,indoor tests and numerical simulations,we believe that the factors affecting the stability of the landslide include structural surfaces,easy-slip formations,the role of water,and human engineering activities(the excavation of slopes foot).The excavation of the roadbed led to the foot of the slope in the air and partial revival of ancient landslide slopes.Pull cracks are generated at the rear edge and middle of the slope to facilitate infiltration of rainwater,and subsequent successive rainfalls lead to increasing signs of deformation of the landslide.The presence of the bottom Impermeable belt allows long-term storage of rainwater at the bottom of the soil,near the contact zone between the weak structural zone and the bedrock,the strength of the sliding zone soil decreases sharply,and eventually causes the slope of the slope foot to collapse and the slope of the trailing edge to expand and slide.(4)Adopted the theory of extenics to select 7 factors influencing the slope height,gradient,fissure development,moisture content of sliding zone,internal friction angle,cohesion and excavation amount of slope foot,and used entropy weight method to determine the weight of each factor.The comprehensive correlation degree of each index was calculated to determine the stability of the landslide.It was found that the landslide was in an unstable state during the peristaltic deformation stage.The stability of the landslide after the slide stopped was related to the excavation volume of the slope foot and the moisture content of the sliding belt soil.