带帽有孔管桩复合地基承载力模型试验研究

有孔管桩能够有效地加速桩周土体超静孔隙水压力时空消散，减轻沉桩效应不利影响，但桩身开孔会削弱桩体承载力。为研究开孔管桩的承载力，对软土地基中无孔管桩和有孔管桩单桩及其相应的带帽单桩复合地基进行了静载荷试验，获得了各种管桩荷载-沉降曲线、沉降-时间对数曲线、桩身轴力的变化规律。研究结果表明：星状开孔的有孔管桩承载力和桩身轴力的折减率均最小；有孔管桩单桩及其带帽单桩复合地基的总沉降和沉降回弹率均小于无孔管桩；带帽有孔管桩复合地基承载力大于带帽无孔管桩复合地基的承载力；桩身开孔有利于桩周土体分担荷载，能减小土体含水量，降低复合地基总沉降，提高复合地基承载力；桩身开孔引起管桩损失的承载力，可以从带帽有孔管桩复合地基提高的承载力中得到弥补。

Experimental study on bearing capacity of composite foundation of pipe-pile with holes and cap

The pipe-pile with holes can effectively accelerate the time-space dissipation of excess pore water pressure in the soil around the pile, and reduce the negative effects of sinking-piles. However, the bearing capacity of piles is weakened by opening holes on the pile wall. In order to investigate the reduction of bearing capacity of pipe-piles due to the holes, static tests of single piles and composite foundations of a single pile with a cap were conducted on a pipe-pile without holes and three kinds of pipe-piles with holes in a soft soil foundation. The load-settlement curves, the settlement-log time curves, and axial force of all piles were obtained and their variations with different parameters were investigated. The results show that the reduction of the bearing capacity and the axial force are the least for the pipe-piles with radially-distributed holes. The total settlement and its rebound rate of pipe-piles with holes are smaller than its counterpart without holes for both single-pile tests and the tests of composite foundations of a single pile with a cap. The bearing capacity of composite foundations of pipe-piles with holes and a cap is greater than that of the corresponding composite foundation of a pipe-pile with a cap and without holes. The test results demonstrate that because of the holes, the load taken by the surrounding soil is increased, while the water content of the soil and the total settlement of the composite foundation are both reduced, thereby improving the bearing capacity of the composite foundation. The partial loss of the bearing capacity of pipe piles due to the holes can be made up by the increase of the bearing capacity of the composite foundation using such pipe-piles.