一种新型复合桩(预灌混凝土)方案的技术经济研究——基于某桩基工程技术演变过程

Study on technical and economical mechanism of a new composite pile(pre-poured concrete)scheme——based on the evolution process of certain pile foundation engineering technique

桩基的施工特别是在有砂层的地基中成桩往往存在困难,首先是预制桩在穿透砂层时碰到困难,需要引孔才能解决此问题;但引孔却产生另一个次生问题即塌孔,尤其是在砂层比较厚的情况下,引孔所期望的目标很难实现。本文研究从打桩失败、引孔、护壁、塌孔及最后采用一种新型复合桩(预灌混凝土)的演变过程,有效解决了桩基承载力与达到有效桩长的问题。新型复合桩作为一项新技术,其抗压承载机理与常规采用的预应力管桩不同,为此开展相应的研究。通过现场试验和数值模拟试验,探索得出新型复合管桩的荷载传递规律与结果:新型复合桩有效防范塌孔现象的产生、承载力的提升值可达57.56%(超载推算值提高约100%)、节约成本约23.33%、沉降值只有PHC管桩的56.63%;新型复合桩是端承式摩擦桩,其受力机理中桩端阻力约占12%。案例的经验与理论可推广或借鉴用于其他类似工程问题的解决。

There are often difficulties in the construction of pile foundations,especially in foundations with sand layers.Firstly,prefabricated piles encounter difficulties when penetrating the sand layer,and the guide drilling is required to solve this problem;however,another secondary problem caused by the drilling is hole collapse,especially when the sand layer is relatively thick,and the desired goal of the drilling is difficult to achieve.This article studies the evolution processes of pile driving failure,guide drilling,wall protection,collapse,and finally the use of composite piles,effectively solving the problem of pile bearing capacity and achieving effective pile length.As a new technique,the compressive bearing mechanism of the new composite piles is different from that of conventional prestressed pipe piles,and corresponding study is carried out accordingly.Through the on-site tests and numerical simulation experiments,the load transfer law and results of composite pipe piles are explored:the new composite piles effectively prevent the occurrence of collapse,improve the bearing capacity by 57.56%(overload calculation increased by approximately 100%),save costs by about 23.33%,and the settlement value is only 56.63% of the PHC pile;the composite pile is an end bearing friction pile,with the pile end resistance accounting for about 12% of its stress mechanism.The experience and theory of the case can be generalized or referenced for solving other similar engineering problems.