Research On Ramming-reamed Pile Composite Foundation In The Improvement Of Foundations’ Settlement Properties Of Subway Station

ABSTRACT:The subway construction is an important content during the modernization construction in China. In the construction of subway station, the settlement has been the focal point of the study. In Beijing, the most basic structure of metro station uses the pile foundation right now. The use of pile foundation has better adaptability for different stratum, and the requirement of deformation and settlement can be met, but the length of the pile is generally longer which have leaded to the high cost all the long time and the bearing capacity of soil between piles has not been fully exploited. When the composite foundation is taken, the pile and soil bearing capacity will play sufficiently and reduce the pile layout, and the ramming-reamed pile is one of these piles. Ramming-reamed pile has high strength, stiffness, low-cost, short construction period, etc, which can improve the bearing capacity as well as control the ground deformation. The ramming-reamed pile not only can improve the bearing capacity of the foundation, but also is a good way to control the deformation of foundation.This paper makes an analysis about the load-bearing mechanism and settlement model of the ramming-reamed pile. With using the finite element method to establish the finite element model of subway station, this paper has done the analysis and comparison of pile foundation, ramming-reamed pile composite foundation and the joint action of them to meet the capacity requirements. The main results are as follows:1、Using pile foundation, the change of pile length is inversely related to the foundation settlement, which is proportional to the slab moment. And the change of pile length has a significant effect on the foundation and the slab moment.2、When using pile foundation, The change of pile diameter is proportional to the foundation and the slab moment, but the change is small.3、When using ramming-reamed pile composite foundation, the number of piles, length of pile, diameter of pile and the diameter of the head of the ramming-reamed pile is inversely related to the foundation settlement, and reducing the pile spacing, increasing the length of pile, diameter of pile and the diameter of the head of the ramming-reamed pile can all control the foundation settlement effectively. Concerning the effect of foundation settlement, the spacing is better than the length, diameter of pile and the diameter of the head. While the pile spacing is cut by a half, floor deformation will be reduced by50%with36%reduction of slab moment.4、With the use of ramming-reamed pile composite foundation the foundation settlement is much more even and all the change of these parameters has little effect on the slab moment.5、According to the characteristics of pile foundation and composite foundation of the station, the use of pile and ramming-reamed pile composite foundation together, which can control the foundation settlement. The bottom plate bending moment is smaller. Compared with pile foundation or composite foundation alone, the combination one has great advantage.6、Compared with pile foundation, the ramming-reamed pile has more advantage in construction technology and economic benefits. On the premise of meeting settlement need, the ramming-reamed pile can save the cost of22.8%-45.7%compared with pile foundation scheme of basic condition...