Study On The Development Characteristics And Formation Mechanism Of Stacked Landslide In The Mountainous Areas Of Southern Shaanxi

Accumulated layer landslides are widely distributed in China.In recent years,accumulated layer landslides have occurred frequently,causing huge losses.There are a large number of accumulated layer landslides with expansive soil in the mountainous areas of southern Shaanxi.The development characteristics and formation mechanism are very complicated,which brings great difficulties to the treatment of this landslide.The development characteristics of the accumulated layer landslides are summarized in the mountainous areas of southern Shaanxi to provide a reference for the actual treatment of landslide.Then,according to the similar principle,the indoor landslide model test is designed to study the formation mechanism of accumulated layer landslides with expansive soil.The main conclusions are as follows:(1)Through a large number of investigation reports and related data,the development characteristics of accumulated layer landslides in the mountainous areas of southern Shaanxi are summarized.Most of the accumulated layer landslides are distributed in the ablated mid-mountain and low-mountain areas.The terrain slopes are basically between 10° and 40°,and most of the landslides are developed on sunny slopes.The rainfall in this area mainly concentrates in summer and autumn.In space it is characterized by that the western part more than the eastern and the southern part more than the northern.The deformation characteristics of the accumulated layer landslides in the mountainous areas of southern Shaanxi are hydrophilicity,shallowness,progressive traction and seasonality.(2)Based on the similarity theory,the indoor landslide model with inclination angles of 25° and 40° were designed.The landslide's formation mechanism under the three conditions of rainfall intensity,dry-wet cycle effect and bottom unloading is studied.Combined the single-valued condition and the dimensional homogeneous theorem of the similar third theorem,the similarity ratio of each parameters is derived and applied to the indoor landslide model test considering the relevant parameters.(3)Under different rainfall intensity conditions,the landslides deformation with different dip angles will increase with the increase of rainfall intensity,and the two landslides deformation are larger at the foot and slope,and the top slope deformation is small.The landslide models with 25°and 40° angle have the largest deformation in the middle of the landslide,and the deformation values are 28.9mm and 20.2mm respectively.During the rainfall infiltration process,the self-weight of the landslide body increases,and the seepage force will be gathering in the weak part of the landslide.Under the action of its own gravity,the landside will slide along the weak side of the landslide causing the landslide to be unstable.(4)Under the conditions of dry and wet circulation,the 25° landslide model and the 40° landslide model experienced a first dry and wet cycle,and the deformation in the middle landslide increased by 27.1 mm and 29.7 mm,respectively.After the second cycle,the deformation in the middle landslide only increased by 3.4mm and 9.8mm.The increase of the deformation of the slope foot and the slope top is generally the same as that of the middle landslide.This indicates that the influence of the wet and dry cycle on the landslide mainly occurs in the first circulation.The circulation effect will cause many cracks on the surface of the expansive soil landslide.Under the continuous action of rainfall,rainwater will infiltrate into the landslide body along the crack,resulting in the formation of through cracks inside the soil,which will reduce the strength of the soil and induce the formation of landslides.(5)Under the condition of bottom unloading,the final deformation of the slope foot,the slope middle and the slope top under 25° and 40° landslide model is relatively close,and the difference is no more than 20 mm,which indicates that the landslides with two different inclinations have a relatively overall deformation.Due to the excavation of the slope foot,the stress in the landslide changes sharply,the stress is redistributed,and the high-steep airfront surface is formed.The soil slides down and generates tensile stress,which causes arc-shaped cracks in the middle and trailing edges of the landslide,eventually leading to landslides instability.