Study On The Collapse Characteristics And Distribution Law Of The North Bank Of Jing River In Pingliang City

Collapse is one of the most common geological disasters in western China.Loess collapse mainly happens in the Loess Plateau area.Because of its relatively small size,the damage of it is often neglected.Though,the loess collapse is widely developed in the Loess Plateau area,and it plays a significant role to the loess slope stability and evolution.Taking the north bank of Jing river of Pingliang City as the target area,the paper investigates the distribution and development law and evolustion progress of the collapse hazards in this erea,as well as the critical damage conditions of the tensile crack-falling collapse.First,this paper investigates the collapse hazards in the north bank of Jing river in Pingliang City,and classifies the collapse according to its material composition and failure mode.The distribution characters of collapse are influenced by the landform and stratum.The loess collapses are relatively fewer and mainly distributed on the loess platform and on high and steep slope at both sides of the gully of the investigation area.Compared with the loess collapses,the loess-bedrock collapses are relatively larger,and distributed in the gully mouth where the bedrock is exposed.Then the factors of the collapse are analyzed.The main factors of collapse include terrain and physiognomy,lithology of stratum,structure of slopes,water,weathering,human engineering activities,root split effect and splitting wedge effect.The paper analyzes the influence of each factor on the collapse,and researches the evolution process of the collapse.Finally,the paper analyzes the critical damage conditions of the tension crack-type collapse.The failure mode is cantilever and tension crack-type collapse.It's because the bottom mudstone is weathered and forms cavities,and then cantilevers are formed at the cavity upside.With the increasing weathering and denudation of mudstone at the bottom,the cantilever grows to a certain length,and then the gravity of the bedrock and the overburden material acted on the root of the cantilever will be greater than the tensile strength of the bedrock.By this time,the bedrock will grows tension cracks.When the cracks grow continuously,the bedrock and loess will finally collapse together.Based on the material mechanics and elasto-plastic mechanics,this paper sums up the mechanics model,deduces the equation of critical length of cantilever,analyzes and contrasts the results of the material mechanics and elasto-plastic mechanics,and verifies the two theories according to the numerical calculation and the actual investigation.