上海地区成层土的单桩承载力研究

Bearing Capacity of Single Pile in Layered Soil in Shanghai Region

本文报道了上海地区由粘土和粉砂组成的不均匀地基中的打入桩和压入桩的研究工作。讨论了穿过上复砂质粉土进入粉砂层的单桩承载力，以及穿过粉砂层进入下卧软粘土的桩的情况。通过桩身轴力量测，发现粉砂层的极限端阻力σｕ及极限侧摩阻力平均值随进入粉砂层的深度呈线性增加，获得了σｕ及各自的临界深度的参考值；当桩端接近粉砂一粘土分界面时，桩可能会因冲穿粉砂层进入下卧粘土层而发生破坏，获得了σｕ及的临界厚度的参考值。由于粉砂层的剪缩性，使得同一桩端处的打入桩与用千斤顶逐步贯人的桩的承载力Ｐｕ、σｕ及值均有较大的差别。

In this paper driven and jacked piles in non-uniform ground consisting of clayey and silty soils in Shanghai region have been studied. The bearing capacity of single pile sunk through sandy silt and ending in underlying silty sand stratum is reported and the case of pile sunk through silty sand and ending in the underlying soft clay stratum is discussed as well.Through the monitoring of axial load of piles, it was found that both the ultimate end resistance and the average ultimate frictional resistance increase linearly with the embedded depth of pile in the silty sand layer, and the reference values of critical depths for and are given respectively. For the case of the pile tip approaching silty sand-clay interface,there is the possibility of failure due to the pile punching through silty sand,and the reference values of critical thickness for and are also reported.Owing to the reduction of volume of the rather loose silty sand layer, this property may be termed as the 'negative dilatancy'. It was found there has been much difference in ultimate values of pile capacity Pu, and for driven and jacked piles.