Research Of Large Diameter Concrete Pile Composite Foundation And Raft Foundation Force Characteristic On Soft Rock Site

According to the characteristics of geological conditions in Chengdu area, China Southwest Geotechnical Investigation & Design Institute put forward the concept of large diameter plain concrete pile composite foundation. Large diameter concrete pile diameter is usually between 800-1200mm, greater than ordinary plain concrete pile diameter. The operation is convenient, the replacement rate is high, can play a more effective role of the foundation soil, also can improve the overall stiffness of the composite foundation, reduce the settlement of foundation. In this paper, combined with the variable rigidity design, through on-site monitoring and ABAQUS finite element numerical simulation analysis of the calculated results provide the basis for considering the upper structure raft foundation and composite foundation under the action of the collaborative optimization design. The main conclusions of this paper are as follows:(1) Large diameter concrete pile side there has been negative friction, and exists in the pile opposition of 0-2.5m, about 2 times to the pile diameter;(2) The structure of column raft reinforced stress concentration in the medium, the core tube at low level, the steel stress distribution and upper structure constraints are closely related. Between the two columns will appear inflection point, namely the raft between two column on the "arch" effect;(3) A linear correlation between the thickness of raft foundation and raft and the basic integral moment;(4) Compared to the uniform pile composite foundation, "strong inside and weak outside" variable stiffness pile composite foundation can reduce the bending moment of the raft foundation and cost effective size. There is a range of reasonable pile spacing ratio and pile length ratio of the bending moment of the raft foundation level decreased significantly, while the maximum saving costs and materials.(5) The results of current design methods do not meet the actual engineering, which causes conservative design, resulting in higher engineering costs;(6) To provide a reference to the current specification of the optimization design method of direction, preliminary analysis of interaction between pile cloth design, according to the settlement and distribution of internal force, take corresponding measures to optimize the analysis, finally obtained the optimal solution iteratively.