软土群桩原位足尺试验研究

Full scale in-situ static loading tests on pile groups in soft soils

软土地区群桩基础受力机理复杂,目前阶段国内外关于群桩的现场足尺试验比较缺乏。在南京市江宁区软土地基进行了9桩的钻孔灌注群桩的足尺试验,试验桩桩径为400 mm,桩长分为20,24 m。通过布设在桩身各控制断面主筋上的钢筋计测量桩身轴力,在群桩中不同基桩桩顶的压力盒测量桩顶荷载。对比分析了单桩和群桩的沉降特性、轴力特性、侧摩阻力特性以及群桩中各基桩的荷载分配规律,并将实测的桩顶反力和群桩效应系数与理论方法计算所得结果进行了比较,结果表明弹性理论计算所得的群桩中各基桩桩顶荷载差异比实测值大;考虑应力叠加的群桩效应系数的公式以及Converse-Labrre群桩效应公式与本次试验的实测数据比较吻合。

The bearing characteristics of pile groups in soft soils are complex. At present there are few full scale tests on in-situ pile groups at domestic and abroad. Full scale tests on bored pile groups are conducted to explore the performance of pile groups in soft soils in Jiangning District of Nanjing City. The pile diameter is 400 mm, and the pile length is 20 and 24 m. The loading tests are carried out on a single pile and pile groups with nine piles. Steel bar meters are fixed in the piles to measure the axial force. Pressure cells are placed at the top of the piles to get the accurate load on them. The data of the tests are listed to show the comparison of settlement, axial force, side resistance and load distribution of the single pile and pile groups. The measured values of counterforce of pile head and the effect coefficient of pile groups are compared with those calculated by different kinds of theoretical methods. The results show that the load distribution calculated by the elastic theory in the pile groups has larger difference compared with the measured value. The results of the formula for pile group effect coefficient considering stress superposition and the Converse-Labrre's formula for pile group effect coefficient agree well with the measured values.