带帽PTC单桩和复合地基承载特性试验研究

结合苏-沪高速公路疏桩复合地基处理工程，进行了自由带帽PTC管桩和双带帽PTC管桩复合地基的现场足尺试验研究。根据试验结果，研究了桩身-桩帽-桩间土的相互作用机理和承载特性，分析了桩帽、桩间土和桩端承载的滞后效应，以及桩帽、桩间土对桩身的消减作用。认为管桩复合地基的第1阶段桩身控制沉降，第2阶段土体控制沉降，探讨了桩帽-桩间土荷载分担比及应力比在不同沉降阶段的变化规律。最后，还提出了桩帽尺寸的设计方法以及取消碎石垫层的建议。

Experimental study on load-bearing characteristics for single PTC pile with cap and composite foundation with PTC (prestressed thin-wall concrete) piles

A series of field full scale tests on single PTC(prestressed thin-wall concrete) pile with cap and composite foundation with twin PTC piles with cap have been carried out to cater for the application of a new sparse piles composite foundation in Suzhou-Shanghai Expressway.Based on the data obtained from the tests,the interaction mechanism which is among the pile,the soil under the cap and the soil out of the area of the cap are studied;the load-bearing characteristics of the pile and the soil are elaborated one by one,and the effect that the soil lagging the pile in the development of load-bearing are analyzed,as well as the effect that the soil reducing the load-bearing capacity of the pile.The results indicate that there are two stages when settlement occurred,at the first stage the settlement is controlled by the pile and the next is by the soil.Finally,the changing rules of pile-soil load sharing ratio and stress ratio at the different settlement stages are discussed;the method of designing the dimension of the cap and proposal of eliding the cushion of the composite foundation are presented.