A Study On Stability Of Bridge Foundation Pile And Bearing Rock Strata In Karst Area

The formation of the karst cave makes the stress distribution of the surrounding rock mass in karst area,changes the mechanical characteristics of the rock mass,seriously affect the bearing capacity of rock strata,threat to the safety and stability of bridge pile foundation and brought a lot of difficulties to the site construction.Analyze and evaluate the stability of abutment and bearing rock strata in the karst region is very important for bridge design and construction.Based on an expressway bridge engineering of Baise to Jingxi in Guangxi,this paper discussed the bearing rock strata stability checking method,rock mechanics characteristics of bridge pile foundation and bearing rock strata,minimum safe thickness of the bearing rock strata,and so on.The main work includes the following aspects:1.A survey was carried out on a number of highway bridges in Guangxi,statistics and analyzes the structure form and disease characteristics of medium-small span bridges in karst area.The results showed that pile foundation is most widely used in karst area,light-weight structures are generally used for bridge superstructure,and foundation deformation damage is the main damage form of medium-small span bridges in karst area.2.The influence factors and unstable form of rock-socketed pile in the karst area are analyzed.Analysis method of stability for the bridge pile foundation and bearing rock strata are discussed.The formula for calculating the minimum safe thickness of the rock bearing stratum is obtained.A variety of mechanical models were used to carry out the anti-punching,anti-shearing and anti-bending analysis based on an engineering example,and comparison to the results of numerical calculation,it is found that the numerical results are more conservative than the analytical solution.3.Mechanical characteristics of bridge pile foundation and bearing rock strata were analyzed in the cave condition of different shape,size,location,upper load and the thickness of bearing rock strata by using the finite difference program FLAC3D.The influence law of cave for bridge pile foundation and bearing rock strata in different condition were discussed.By forming fitting function,the relationship between plie vertical displacement and the thickness of the rock bearing stratum in different upper loads were obtained.Finally,puts forward a method to confirm minimum safe thickness of the bearing rock strata by plastic zone and the vertical displacement of the pile.