Quasi Static Test Research Of Concrete Pile-soil Interaction Based On Displacement

Compared with the traditional simply supported girder bridge,the upper structure and the lower structure of integral abutment bridges(IABS)connect as a whole,the cyclic loading under temperature or seismic load are mainly supported by abutment and the abutment pile foundation,etc.In foreign countries,H-steel piles are commonly used in integral bridges for their brilliant deformation capacity and seismic performance.However,the development history of IABS is relatively short in China,in addition,because of economy and engineers’ habits,concrete piles are choosed first for bridge engineering in China.However,further study need to be conducted to find out whether the concrete piles can be suitable for IABS under reciprocating load for their big stiffness and small deformation.In addition,P-y curve that based on large deformation is often used to calculate H-steel piles.For concrete piles,there is no design or calculation method about this kind of bridge piles in highway bridges or any other specifications of China.What’s more,the calculation methods which is given by the existing specification are commonly based on the design concept of linear elastic and small deformation,such as "C" method,"m" method and so on.However,it is hard for these calculation methods to meet the requirements of IABS which require for nonlinear and large deformation.As a result,the main work and research conclusions in this paper are shown as follows:(1)Quasi-static experiments of low cyclic repeated horizontal loading on concrete piles based on displacement are mainly designed and conducted.Test results show that main failure area of concrete piles are around embedded depth of 3.0 to 7.0 times pile diameter under low cyclic repeated horizontal loading.Meanwhile,section shape and reinforcement ratio have significant effect on cracks distribution of concrete piles,maximal bending moment and failure modes.With high ratio of reinforcement,concrete piles have larger elastic critical displacement,better deformation capacity and lower damage degree,as well as a better interaction with the soil.Results also show that concrete piles have a good ductility,hysteresis loops are almost shuttle shape,which illustrates that the piles have good anti-seismic performance and energy-dissipating capacity and can be applied to the IABS.(2)Experimental results illustrate that soil pressure around the pile increases with the increase of displacement load,until it reaches its ultimate passive soil pressure.The soil pressure around the pile is mainly distributed in the area around embedded depth of O.Oto 10.0times pile diameter.Within the scope,the rule of soil pressure around the pile is as follows:soil pressure is increasing rapidly from soil surface,then decline gradually.Soli pressure reaches a small negative value at a deep depth,however,negative soil pressure is small.Among then,the soil pressure is bigger in the shallow soil and the maximum value appears in the vicinity of 4.0 times of the pile diameter.(3)Depend on the tests results,pile displacement distribution and soil pressure calculating methods are presented,as well as a simplified calculating method of concrete pile-soil interaction.Results are compared with that of "m" and p-y method,which illustrate that "m" method overestimate the lateral bearing capacity of pile and load-displacement curve is not correct,while p-y method has accurate results when the displacement load is not large,however,the load-displacement curve doesn’t have a failure or descent stage,which means that p-y method overestimate the ductility and is partial unsafe.Also,it has large difference with the test results.In order to make up for the shortage,method presented in this paper can calculate pile internal force,displacement and soil pressure results accurately,which provides reference for related standards.