Experimental Study On The Working Charactristic And The Unstable Failure Of The Concrete Pile Composite Ground

In recent years, a large number of high-speed railways and expressways were constructed. Along the way, there always have some areas with poor geological conditions. The composite ground is usually applied in the reinforcement treatment of soft ground. The theory and technology of composite ground under the flexible foundation often use the experience of the composite ground under the rigid foundation for reference. The stiffness of the foundation has a significantly important influence on the working mechanism of the composite ground. In this paper, we use methods of centrifuge test and numerical analysis to study the working characteristics and the causes of failure of concrete pile composite ground under the embankment. The composite ground in this paper is treated by concrete pile. The conclusions obtained are as follows:Firstly, by changing the parameters, the working mechanism of the composite ground is obtained. According to the results of centrifuge tests, it discovers that the pile and soil stress, the pile-soil stress ratio, the pile strain, the settlement of the composite ground, are affected by the pile spacing, the compression modulus, the upper load. The results indicate that there has a optimum pile spacing with other conditions same, which leads to the pile-soil stress ratio reaches maximum. The filling rate of embankment and the storage time also have important implications on the stability of the composite ground, and they should be designed based on the actual conditions.Secondly, according to the results of centrifuge tests, the failure modes of composite ground, and the causes of failure, are studied. Summarized the features and forms of the failure of composite ground. The failure forms of composite ground, under the embankment, are as follow, the pile punching failure, the local shear failure of toe of slope, the global slip-shear failure, the inclined deflection failure, and the layered shear failure. Through the analysis of failures, it discovers that the failure of the composite ground always includes various forms of failure, and the interactions among them results the failure of the whole ground. The failure modes in different parts, influenced by the pile spacing, the compression modulus, the upper load, are different. The failures gradually happened by the adjustment of gravel and the pile-soil interaction, caused by the failure of pile and soil.Thirdly, using the ABAQUS software establishs the non-linear3D-dimension coupling model of the concrete pile composite ground under the embankment. Considering the pile-soil interaction, the variation of the settlement deformation and lateral deformation of composite ground, and the distribution of pile stress, and the penetration of pile are researched. In addition, the failure modes and parts failed easily of the composite ground are discussed.