The Settlement Mechanism Of Different Connection Between Pile And Raft And Its Application In Railway Subgrade

As a fast, safe, high-efficient and high-quality traffic form, the high-speed railway has become a common trend for many countries in development of passenger traffic. However, high-speed railway at the same places a more strict demand on the settlement of subgrade, especially post-construction settlement. Therefore, the settlement mechanism of different connection between pile and raft and its application in railway subgrade are researched in this paper. The major research work and achievements are as follows.1. A series of tests on conventional pile foundation and gapped pile foundation (with a gap between pile head and raft)were conducted. Through the analysis on continuous photos of colour sand layers and marked piles in the test, the settlement characteristic of gapped pile foundation was researched. Moreover, the penetration of pile toe and relative slip between pile and soil of the two kinds of foundations mentioned above were compared. Finally, the variation axial force and shaft friction of center pile was showed in this paper. The results show that gapped pile foundation can cause the soil among piles to deform in advance, enhance the interaction between soil and pile and reduction the relative slip between pile and soil and lead a more integral settlement of pile and soil of gapped pile foundation than that of conventional pile foundation.2. The in-situ monitoring data of the Beijing-Tianjin Rail Transport Project during early period was analyzed and the sections across DK84+050and DK84+150 were compared. Besides, the relation of settlement-time and settlement-depth and sharing of soil and pile were summarized.3. Through triaxial tests in laboratory the soil parameters of the project above were gained and the project was simulated by finite element software ABAQUS using modified Cambridge Model. The settlement at the time 20 year after the project in use was predicted. In addition, the development of the settlement of ground, pile and soil and pore pressure was analyzed.4. Based on the simulation of Section DK84+050, the application of gapped pile foundation in subgrade was researched and the comparison with practical project simulation was made. Furthermore, the development of the settlement of ground, the stress of soil and pile and dissipation of pore pressure was also studied. The conclusion is that the post-construction settlement of subgrade can be efficiently reduced by gapped pile foundation.