Research On Vertically Bearing Behavior And Reliability Analysis Of Concrete-cored DCM Pile

Concrete-cored DCM pile provides a new way to treat soft soil. The new type of pile is consisted of concrete core pile and cemented-soil encircling the core pile. Bearing behaviors of concrete-cored DCM pile under vertical load are studies by ways of model tests, field tests and elastic-plastic FEM analysis. The reliability of bearing capacity of concrete-cored DCM pile is analyzed in this dissertation.The major achievements in the dissertation are obtained as follows:1. Study on load transfer property of concrete-cored DCM pile. Experimental research and FEM analysis are conducted to investigate load transfer character between the concrete core and the cemented-soil. The result of model test indicated that the cohesive strength of the two parts displays liner relationship with the unconfined compressive strength fcu, and the ultimate skin friction between the two parts is approximately 0.213 times that of fcu. The field tests get bigger result because of the lateral compression of the earth. The calculated result of FEM indicates that the frictional load transferred to the cemented-soil distributed to the soil surrounding the pile completely at the same length.2. Experimental study on bearing behavior of concrete-cored DCM pile. According to the load transfer mechanism of concrete-cored DCM pile, a new method, the sectioning and summarizing method, is developed to estimate the bearing capacity of the pile. The pile is divided into two parts: the upper part comprising the concrete core pile and the lower part of pure cemented-soil. The bearing capacities of the two parts are estimated separately according to different principles, and the bearing capacity of the entire pile is the summation of the two parts. The frictional resistance of the upper part isβs times that of bored and cast-in-place pile, in which the coefficientβs can be determined by the compression rigidity of the pile or the extent of the soil being compacted.3. Theoretical research on bearing behavior of concrete-cored DCM pile.The sectioning and recursion method is developed. The entire pile is divided into several parts in response to variations of soil stratums or diversities of load transfer functions. The load (Q) and settlement (s) relation of each part can be obtained using this method. Parametric analysis is conducted and suggestions are proposed for the optimization of the pile.4. JC method is utilized to estimate the bearing capacity reliability of concrete-cored DCM pile in Tianjin City. The analysis result indicates that the reliability index of concrete-cored DCM pile is 2.232, which is a little smaller than the precast concrete pile and cast-in-place pile.