Experimental Analysis On Load-bearing Capacity And Optimization On Sparse Piles Composite Foundation With PTC

A new composite foundation with sparse pretensioned spun concrete buoyant piles has been applied to treating deep soft ground in expressway project. The PTC piles are slightness, the distance between the two piles are far off, and it has good load capacity even if single pile, in addition, unlike tradition composite foundation, there is a cap on the top of the pile in this new one, so the load-bearing performance and working mechanism are different from former, and more complicated. In this paper, the spot tests have been done in order to investigate load-bearing performance, and when the pile, the cap, and the soil are working at the same time, the rule of settlement of sparse piles composite foundation with PTC. Some useful information from test results are provided. There is a hysteresis on soil when loading, it puts up two phases on settlement. At the first phase, the piles are borne most part of the loading, and the soil is little. At the second phase, the soil be borne more and more loading but the loading that piles be borne is almost steadiness, at the end of this phase, the composite foundation is happened to destroyed. There are more loading have been impressed to the piles because of the cap on the top, and the negative settlement is approximate to zero. The loading on the surface of soil is near to uniformity in composite foundation. The capacity of load-bearing has been discounted as the soil around when loading and the function of cushion is feebleness. When loading the changes of load ratio and stress ratio has been embodied two phases too, they become little and little. At the end, Combine Mindlin method and Boussinesq method, the additional stress has been lay out, and the working mechanism are thoroughly analyzed of sparse piles composite foundation with PTC. A method to design and optimize on this composite foundation is provided, include of the size of cap on the top of pile, how to calculate the load on piles and soil, and the concise method with two step for calculating settlement.