Study On Seismic Performance Of Bridge Pier-Ground Soil System With Digging Well Foundation For Railway Bridges

Digging well foundation has been widely applied in railway bridges in China due to its simple and fast construction,less use of machinery.Construction speed,low cost and easy quality assurance are also its advantages compared with pile foundation.However,researches on seismic performance of bridge foundation at home and abroad are mainly focused on pile foundation.There are few researches on seismic performance of digging well foundation.Aiming at the problems existing in seismic design of digging well foundation,seismic performance of bridge pier-ground soil system with digging well foundation for railway bridges is studied based on model test,theoretical analysis and numerical simulation.The main research work are as follows:(1)The characteristics of seismic damage,model tests,static and dynamic seismic analysis models and research status of seismic analysis methods of railway bridges are summarized.The different provisions of seismic codes for foundation seismic design in various countries are compared.(2)The reduced model of railway pier supported by digging well foundation is made in the geotechnical model box,and its failure characteristics,bearing capacity,skeleton curve,hysteretic characteristics,energy dissipation capacity and stiffness degradation are studied by pseudo-static test.(3)Based on the pseudo-static test,the static nonlinear seismic analysis model of bridge pier-ground soil system with digging well foundation for railway bridges is studied.A modeling method for the soil-foundation interaction is proposed in accordance with the API specification,and a method for determining the resistance-displacement constitutive relation of soil around digging well foundation is proposed.The rationality of the model is verified by comparing the numerical analysis results with the model test.(4)Based on the proposed static nonlinear seismic analysis model of bridge pier-ground soil system with digging well foundation for railway bridges,the effects of depth to width ratio,lateral soil resistance,soil resistance of foundation side,soil resistance of foundation base and pier height on the failure mode,horizontal bearing capacity and plastic hinge mechanism of pier are systematically studied.(5)The reduction method of elastoplastic demand spectrum for subgrade yielding type and subgrade-pier mixed yielding type is researched.A method to establish elastoplastic demand spectrum considering soft deformation effect,kinematic effect and damping effect of foundation soil is proposed for the bridge piers with foundation soil yielding.The seismic performance evaluation index of bridge pier supported by the digging well foundation is proposed based on the latest research results at home and abroad.The capability spectrum method for seismic performance evaluation of railway pier is proposed,and the effectiveness of the method is verified by a specific example.(6)A dynamic nonlinear analysis model of bridge pier-ground soil system with digging well foundation for railway bridges under rare earthquakes is studied.A trilinear slip model which can simulate the separation slip effect between foundation and soil interface is proposed,and its applicability is discussed.The influence of soil nonlinearity on seismic response of bridge pier supported by the digging well is studied by an example.