上海软土地基超长打入PHC桩工程性状研究

Behavior of long PHC piles driven in Shanghai soft clay

通过对上海软土地基中64～77m的超长打入PHC桩打桩过程中锤击数、土塞高度随深度变化的跟踪监测及土塞的标准贯入试验和竖向荷载下的静载试验,探讨了超长PHC桩在上海软土地基中的贯入度与土层的关系,分析了打入承压水层中对土塞闭塞效应的影响以及桩的竖向承载力性状。这对软土地基中的超长PHC桩的设计、施工和深入研究具有重要指导作用。

The prestressed high strength concrete pipe(PHC) piles of 64～77 m are driven into Shanghai soft clay. The bearing capacity of open-end piles are affected by the degree of soil plugging. There are no reports about the effect of soil plugging and bearing capacity of long slender pile. Based on the results of field tests, the records of driven piles and the results of static load tests with the PHC piles are presented. The records of driven pile show that the blow counts per meter and the length of soil plug vary with the depth of piles in ground. Especially, when piles are driven into fine sandy artesian aquifer, the length of soil plug increases rapidly with the depth of piles driven in ground. A month later after the completion of pile installation, some soil plugs are destroyed under high artesian head. According to the SPT tests in soil plugs, the influence of artesian aquifer on the stability of soil plug is discussed. The vertical load tests are performed posteriorly to the SPT tests of soil plugs. Furthermore, the effect of the soil plug is discussed with respect to their contribution to the bearing capacity of long PHC piles.