上海地区静钻根植桩承载特性现场试验研究

静钻根植桩是一种绿色环保的新型桩基，具有低噪声、无挤土、少排泥等优势，可应用于高层建筑、桥梁等工程中。基于现场抗压和抗拔静载试验及桩身内力测试，分析了上海地区静钻根植桩的竖向承载变形特性以及桩身轴力和侧摩阻力分布。研究结果表明：静钻根植桩在上海典型地层条件下具有较好的适用性，抗压试桩和抗拔试桩的承载力均大于规范估算值，采用目前的承载力计算方法有一定的安全储备；抗压试桩在加载初期，桩身轴力可以直接传递到桩端，在极限荷载下桩端（扩大头）承载力约占总荷载的25%；静钻根植桩极限侧摩阻力主要与土的特性和埋深有关，上部土层（埋深30m以上）接近规范建议的预制桩侧摩阻力上限值，下部土层（埋深30m以下）较规范建议的预制桩侧阻上限高约14%~28%。

Field study on bearing characteristics of pre-bored precast pile with enlarged base in Shanghai

The pre-bored precast pile with enlarged base (PPEB pile) is an innovative type of environmentally friendly pile foundation. It has the advantages of low noise, no squeezing of the soil, less mud discharge and so on. It is used in high-rise buildings, bridges and other engineering fields. Based on the compression tests, uplift static load tests and pile internal force tests, the vertical load-deformation characteristics, distributions of axial force and shaft resistance of PPEB piles in Shanghai area were analysed. The test results show that the PPEB pile has good applicability in typical stratum of Shanghai. The bearing capacities of the piles from the compression tests and the uplift tests are both higher than the estimated values based on the technical code, so the calculation methods of bearing capacities of PPEB piles in the current design code provide sufficient safety reserve. The axial force in the piles can be directly transmitted to the pile toe at the initial stage of compression tests, and the toe resistance is about 25% of the total load (under the ultimate conditions). The ultimate shaft resistance of PPEB piles is mainly affected by the soil properties and burying depth. The ultimate shaft resistance in the upper soil layers (buried depth is above 30m) is close to the upper limit value of shaft resistance of precast piles, while the shaft resistance in the lower soil layers (buried depth is below 30m) is about 14%-28% higher than the upper limit of precast piles recommended in the technical code.