Research On Working Mechanism Of Composite Foundation With Concrete-cored DCM(CDCM) Pile Under Rigid Foundation

With the continuous improvement of the construction requirements for the bearing capacity and settlement of soft ground,various ground treatment technologies have continuously developed and emerged.The concrete-cored DCM pile(CDCM pile)is a composite pile formed by inserting the prefabricated concrete after the completion of the construction of the DCM pile.Combined with the characteristics of the high strength of the concrete pile and the great friction of the DCM pile,it can effectively improve the bearing capacity and reduce the settlement.However,the current research on the working mechanism of CDCM pile composite foundation has lagged behind engineering practice.The research on the working mechanism of CDCM pile composite foundation under rigid foundation has not only theoretical value,but also broad engineering application prospects.The interface friction characteristics between concrete-cored,DCM pile and soil is one of the key issues in the study of the working mechanism of the CDCM pile composite foundation.Previous studies have basically assumed that the interface friction is fully exerted,and the effect of the relative displacement of the interface has not been considered.In this paper,based on the previous studies,considering the interaction and deformation of concrete-cored,DCM pile and soil,an ideal elastic-plastic load transfer function based on the correlation between the friction and the relative displacement is established.According to the basic principle of load transfer method,the theoretical analysis method and iterative analysis method for working mechanism analysis of equal-core and short-core CDCM pile composite foundation under rigid foundation are proposed.Then,using the proposed method,the load transfer mechanism and deformation of CDCM pile composite foundation under the condition of equal-core and short-core are studied,and the influences of concrete-cored rate,core length ratio,area replacement ratio,load,soil around pile and pile-tip soils on the working behavior of composite foundation under rigid foundation are analyzed.The research results show that for the CDCM pile composite foundation under rigid foundation:(1)The friction at the interface has a direct effect on the load transfer of the CDCM pile composite foundation.When the depth is shallow,the degree of friction exertion at interface is smaller,while when the depth is deep,the degree of friction exertion at interface is significantly improved due to the development of the relative displacement at the interface.Compared with equal-core CDCM pile,the degree of friction exertion at the interface of short-core pile is more higher.(2)The concrete-cored bears most of the load,followed by the DCM pile and the soil around the pile.DCM pile also plays a role in transferring load between the concrete-cored and the soil around the pile.The load sharing ratio of concrete-cored can be increased with the increase of concrete-cored rate,but there is an optimal value.(3)For short-core CDCM pile,the stress of DCM pile at the bottom of concrete-cored produces 'sudden increase effect',which should be paid special attention in design and construction.