Bearing Behavior And Stability Analysis Of Pile Foundation For Bridge In Beads-shaped Caves

With the rapid development of infrastructure construction in China,more and more roads,bridges and other structures will inevitably go through karst area.Due to the complex geological conditions of the karst area,the development of the cave is affected by many factors,and engineering mechanics of cave is very unstable.Therefore,the pile foundation is usually the first choice in the karst area,The treatment of pile foundation in karst area includes the following methods:(1)Grouting reinforcement of the roof cracks.(2)The fill,replacement and mattress method can be used in shallow burial cave.(3)Crossing structure can be used to avoid the cave when the gap is not large.Due to the limitation of survey technology and the inevitable error,the location and geometry of cave can not be accurately predicted.Therefore,there will be situations when a pile penetrates through the cave or stands above the cave.In this paper,the theoretical and numerical calculation method are used to analyze the bearing characteristics and stability of the bridge pile foundation above bead-shaped caverns.The following researches are conducted.(1)The load transfer mechanism of pile-soil(rock)under the influence of beaded karst caves is studied by using the numerical simulation software,ABAQUS.The influence factors including pile length,pile diameter,thickness of sandstone strata,the friction angle and cohesion of the rock on the displacement field,stress field,percentage of pile end resistance and the failure rule of sandstone strata in karst caves are analyzed.(2)Accounting for the condition that the beaded karst caves is under the pile tip,the model of interaction between caves and pile is established.Furthermore,the maximum bending moment and stress of cave roof is calculated based on Reissner plate theory.The Hoek-Brown criterion is introduced to deducing the fomula of the safety thickness of punch,shear and bending capacities of cave roof.By using the numerical simulation program,the roof thickness of cave,cave span,roof friction angle,cohesion and geological strength index(GSI)are analyzed,which is the influence factors on the failure mode of the roof,roof stability,displacement and stress field,and development law of plastic zone.(3)In order to study the load transfer characteristics of the pile through continuous beaded caves,the soil-pile interaction model and load transmission function are set up in this passage based on the disturbed state concept(DSC),and the main parameters in the transfer function were analyzed,and the verification is conducted by the use of in-situ static load test of pile at the same time.(4)By combinating the load transmission function of soil-pile interaction model with the maximum deflection equation of roof based on the Reissner plate theory,the formula of the settlement of single pile in homogeneous foundation is established based on the load transfer method.The formula of settlement of single pile in stratified foundation is also established base theory above,which also takes the situations that the pile penetrates through the beaded caves and the pile tip lies above the beaded cave into account.(5)Finally,a practical engineering project is calculated and analyzed by the numerical analysis software to validate the rationality of the method.