有孔管桩开孔应力集中系数试验研究

有孔管桩能够有效减轻静压沉桩挤土效应，加速超孔隙水压力的消散并降低其最大值，随着超孔隙水压力的加速消散，能够有效避免桩体上浮和偏移等不利情况，并能有效提高整体桩基的承载力和开挖基坑的稳定性。但桩身开孔将会引起管桩应力集中现象，并降低管桩极限承载力。为此，开展了有孔管桩应力集中现象和极限承载力模型试验，分析了桩身开孔所引起的应力集中系数和开孔对桩极限承载力的折减情况。通过试验研究，得出对称开孔桩型的整体承载力性能优于不对称开孔桩型，其中星状有孔管桩桩型的承载能力最好。试验成果为有孔管桩的设计和布孔选型提供了试验基础，并对其优化设计提供依据，对有孔管桩的推广应用有着积极的指导作用。

Experimental study of stress concentration factors of hollow pipe-piles

The hollow pipe-piles can effectively reduce soil squeezing effect during static pile driving, and accelerate the dissipation of excess pore water pressure, decreasing its maximum value. With accelerating the dissipation of excess pore water pressure, unfavorable situation including pile floating and skewing can be effectively avoided, while the bearing capacity of pile foundation as a whole and the stability of foundation pit can be raised. But the openings in the shaft of pipe-pile can certainly generate stress concentration and weaken the bearing capacity of the pipe-pile. Thus, a series of model tests on stress concentration and ultimate bearing capacity of the hollow pipe-pile is carried out. The stress concentration and the reduction of ultimate bearing capacity are analyzed. The testing results show that the performance of the piles with symmetrical opening holes is better than that with the asymmetric opening holes with regard to the bearing capacity, and the bearing capacity of the pipe-pile with hole opened in a radial direction is the highest among all types of piles. The above results can provide guidance for designing the hollow pipe-pile foundation and help promote their application.