| The Western Sichuan area is located in the transitional part of the Qinghai Tibet Plateau and the Sichuan basin in the region.It is the most important abrupt change belt in China.The terrain is steep and the terrain is undulating,the erosion is intense,the strata and geological structure are complex,the neotectonic movement is strong,and the seismic activity is frequent.Geological hazards are widely distributed and often have the characteristics of serious danger,great harm and quick disaster,which threaten the safety of life and property.Every year,a great deal of manpower,material and financial resources have been put into operation,and the control works have been carried out for these geological disasters,especially since the earthquake.In order to effectively control geological hazards in mountainous areas in the future,it is necessary to make a careful summary of the experience and lessons of geological hazard prevention and control.This paper reviews the background of regional geological environment in Western Sichuan and analyses the characteristics of complex geological environment in this area.Through remote sensing interpretation and field review,the spatial distribution of landslides,collapses,debris flows and other geological hazards in this area are revealed.The structural integrity and engineering effects of landslides,debris flows and collapses are summarized and evaluated after completion of three representative prevention and control projects.Failure engineering is classified and failure reasons are analyzed.On this basis,representative engineering cases are selected to deeply analyze the failure process of prevention and control engineering,and the failure mechanism of control engineering is analyzed by mechanical calculation and numerical simulation.This paper focuses on the failure process and failure mechanism of complex geological environment evaluation and disaster prevention and control engineering in Western Sichuan,and the effect evaluation of control engineering.The main progresses and conclusions of this paper are as follows:(1)Comprehensive collection of geological environment data in Western Sichuan,including engineering geological data such as stratigraphic lithology,topographic and geomorphological data,meteorological data such as temperature and rainfall data,neotectonic movement and activity characteristics of fault tectonic belts.On this basis,the regional geological environment in Western Sichuan is systematically analyzed.According to the characteristics of tectonic movement in the region,the study area is divided into five major regional tectonic units,namely the Kang Dian SN direction structural belt,the Mt.Qian front thrust belt,the Western Sichuan foreland basin,the fresh water fault zone and the arc arc structural belt,and the Kang Dian SN tectonic belt and the Xian Shui River fault zone are selected to study their movement,dynamic characteristics and activity.The strong supergene transformation since Cenozoic laid a foundation for the occurrence of geological hazards such as collapse,slip and flow in the area.Coupling of endogenetic and extromotive forces result in that most of the areas in the area are high-risk areas of geological hazards.(2)Taking the geological hazard prevention and control projects of major cities and towns and rivers in the region as the research object,the integrity,damage and engineering mission of 154 engineering structures after the completion of major control projects in the region were analyzed by means of remote sensing,structural data collection and field investigation,and the engineering effect was evaluated.The study reveals that more than 90% of the harnessing projects in Western Sichuan have the purpose of disaster prevention and mitigation,which is manifested in that the landslide supporting projects ensure the safety of urban and major infrastructures,and the debris flow sand-retaining projects keep the solid sources in ditches to the greatest extent.Although part of the reservoir is full or close to the full reservoir,they can still exert the function of preventing and controlling collapse actively and passively.It protects the normal passage of trunk roads such as G213 and threatens the safety of residential areas and towns.(3)To sort out the landslide prevention and control projects that have failed or partially damaged in Western Sichuan,and comprehensively analyze the characteristics of the failure of landslide,collapse and debris flow control projects.This paper summarizes and analyses the failure modes of landslide supporting projects.Taking Wupo Village landslide in Badi,a typical slope break area in Western Sichuan,as a representative case,it qualitatively analyses the failure process of landform evolution,deposit formation,slope structure and formation of weak interlayer,which is caused by insufficient embedding capacity of rock mass with weak interlayer under accumulation body,and then uses numerical value.The failure process of the control project is simulated and analyzed.This kind of slope structure is representative in Western Sichuan.The failure mechanism analysis of support of Wupo village landslide in Badi provides a reference for the objective understanding and effective treatment of this kind of landslide.(4)Taking the representative debris flow disasters in Western Sichuan as the research object,the classification of control measures,the effectiveness of control measures,the safety and effectiveness of prevention and control projects,the level of prevention and control projects,the construction period and other indicators are comprehensively analyzed,and the failure types of control projects are summarized and classified.Firstly,the failure of debris flow control project is more common because of the serious underestimation of material sources and the inadequate estimation of extreme climate after the great earthquake,which leads to the low design strength;secondly,the overturning instability of the protective embankment foundation after the erosion due to the acceleration of flow velocity after the collapse of the slope or flood section.Taking Yanglinggou Debris Flow Project as a representative case,the carrying capacity of the project is calculated respectively for its normal flow and bursting flow under natural conditions,and for its bursting flow under reinforcing dam body conditions.Finally,the key parameters of this kind of debris flow disaster are calculated and optimized,which can provide some reference for the treatment of this kind of debris flow disaster.(5)The failure of passive network,which is frequently used in collapse prevention and control measures,is analyzed.The main reasons for its instability are small block size estimation of dangerous rock,inadequate estimation of the scale of dangerous rock,and only single passive network blocking measures are adopted in the prevention and control scheme which should take both active and passive measures into account.Further analysis reveals that part of the passive network project is due to emergency needs,and there is no systematic study of the characteristics of dangerous rock mass,which leads to a large proportion of the damage caused by lagging instability of the seismic cracked slope.The passive network set up in the emergency protection course of Minjiang G213 line after the earthquake is more damaged,and the measures such as shed cave and rock retaining wall have achieved good results in the later period. |
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