| Restricted by terrain conditions,mountain road construction inevitably excavates or fills the slope,resulting in deformation and destruction of the slope.The landslide disaster has become one of the important factors restricting the construction of mountain roads,causing serious harm to the construction and operation of highways.The Tiechang landslide is located in the connection section of a Tiechang highway in a highway in Rongxian,Sichuan.The landslide is a creep-sliding ancient landslide that occurs in a gently inclined bedding slope.Since the ancient landslide was not fully disintegrated and destroyed,the accumulation body has good stratification,and the landform is strongly transformed in the later stage,the landslide is highly concealed,and it cannot be effectively identified during the survey stage.The height is 55.19m,and the supporting design is made with rock slope.However,when the construction was excavated to a depth of about 43m,the whole slope showed obvious tensile deformation,which led to the cracking of the original retaining structure,and the emergency treatment plan of back pressure at the foot of the slope had to be adopted to control the slope.Further deformation.Therefore,it is of great practical significance to study the deformation mechanism of the excavated slope in the developed section of the ancient landslide,evaluate the stability of the excavated slope,and prevent and control the design of this section of slope to ensure the safety of highway construction and operation.At the same time,the recognition of the basic characteristics of ancient landslides can provide a reference for the identification of similar ancient landslides.Based on the systematic investigation of engineering geological conditions and structural characteristics of the landslide body,this paper analyzes the genetic mechanism of the ancient landslide;based on the structural characteristics of the landslide body and the test results of the strength of the sliding zone soil,combined with the deformation characteristics of the excavated slope,the side The deformation mechanism of the slope and the numerical simulation method are used to simulate the deformation mechanism of the slope.The stability of the slope is evaluated by the limit equilibrium method and the finite element strength reduction method,and then the slope treatment engineering measures are proposed.The following recognition and research results have been achieved.(1)Based on the basic geological conditions in the study area and the basic characteristics of the landslide,the cause mechanism of the ancient landslide in Tiechang was analyzed.The formation of the Tiechang ancient landslide is mainly controlled by the gently inclined bedding slope structure,which is caused by creeping-cracking deformation and destruction of the weak interlayer along the bedding under the condition of heavy rainfall.The sliding distance of the landslide is relatively small,about 15m.The sliding body is not fully disintegrated and maintains good stratification.The scale of the landslide is about 3.4×10~6m~3.(2)The composition and physical and mechanical properties of the slip zone soil were tested.The mineral composition of slip zone soil is mainly clay mineral and quartz,the total amount of clay minerals accounts for about 61.2%,of which illite content is 42.8%,chlorite content is 15.9%,kaolinite content is 2.5%,slip zone soil It is mainly composed of hydrophilic materials;the physical characteristics of the slip zone soil have obvious changes relative to the slip body and bedrock.The moisture content of the slip zone soil is 22.19%,the dry density is 1.64g/cm~3,the specific gravity is 2.71g,the liquid The plastic value shows that the slip zone soil is soft plastic;the saturated shear strength of the slip zone soil is C=12.8KPa,?=7.6?,according to the shear strength value under different water content,it can be known that the strength of the slip zone soil is affected more big.(3)The structure of the ancient landslide,especially the material composition,structural characteristics and physical and mechanical properties of the sliding zone,is the geological basis for the deformation and destruction of the excavated slope in this section.Excavation and cutting slopes are the main factors that cause deformation and failure of slopes,and rainfall also plays an important role in slope deformation.Deformation and rupture characteristics show that when the cutting slope is excavated to expose the ancient landslide slip zone,the slope begins to deform,and the deformation continues to develop under the influence of rainfall.Its deformation failure mode is creep-pull along the ancient landslide slip zone Crack-shaped deformation.The deformation range has a good inheritance to ancient landslides.The cracks in the trailing edge are produced in a discontinuous arc shape.The length of a single crack is about 15m,the width is 3?50cm,and the bottom is10?40cm.There is obvious pull or shear misalignment.(4)Perform FLAC3D numerical simulation on the formation mechanism of the slope,and analyze the deformation and failure characteristics and the cause of instability of the slope.The results of FLAC3D numerical simulation show that during the excavation of the slope,the deformation and displacement of the slope body are mainly concentrated on the location of the excavation surface.After excavation to the bedrock surface,the overall displacement and deformation of the downhill slope in the natural state increase,and the slope Cracks appear.Under rainfall conditions,there is a significant displacement at the trailing edge of the slope body and the overall displacement of the landslide body is relatively large,it can be judged that the slope body has slipped.(5)The limit equilibrium method and the finite element strength reduction method are used to analyze the stability of the slope.The analysis shows that the stability coefficient of the slope under natural conditions is 1.045?1.1n4,which is in an unstable-basically stable state The stability coefficient of the slope after excavation under heavy rain conditions is 0.924?0.981,which is in an unstable state,in which the stability coefficient of the 2-2'profile in the natural state and the heavy rain state is the minimum,which is the most Unfavorable profile.The stability of the slope is greatly affected by rainfall,and the slope is unstable under rainfall conditions.(6)Take emergency measures for back pressure foot of the slope and carry out deformation monitoring after back pressure.Through monitoring and analysis,it can be seen that the slope is basically stable after back pressure.For later safety construction and highway operation Safety advises on the management of the slope.This paper proposes the use of"Dig out the soil according to a certain amount+anti-slide pile+slope protection+drainage interception"treatment measures for this slope. |
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