武汉绿地中心大厦大直径嵌岩桩现场试验研究

武汉绿地中心大厦高636 m,基底平均压力达1500 k Pa,开展了桩径为1200 mm,有效桩长25.9~33.6 m,以较硬岩(微风化砂岩)和软岩(中—微风化泥岩)为桩端持力层共4组嵌岩桩承载力静载荷试验,并对桩身轴力与变形进行了量测。试验表明:4根试桩Q–s曲线皆为缓变型,极限承载力不小于45000 k N,对应工程桩桩顶标高沉降为9.7~10.8 mm,桩端沉降为2.4~2.8 mm,桩顶沉降的90%为桩身压缩量。软岩嵌岩桩与较硬岩嵌岩桩的侧摩阻力分布曲线及承载特性存在显著差异。四根试桩的端阻比介于45.3%~58.7%。软岩嵌岩桩的实测桩端阻力大于基岩单轴抗压强度,采用桩基规范方法计算将低估其实际承载力。本工程4根试桩均表现出较好的承载与变形控制能力,静载试验结果为本工程嵌岩桩设计提供了依据,同时为武汉地区大承载力嵌岩桩实践与理论研究提供了有益参考。

Field loading tests on large-diameter rock-socketed bored piles of Wuhan Greenland Center Tower

Wuhan Greenland Center Tower is 636 m high with the average pressure stress 1500 kPa on the bottom of foundation. The test piles with a diameter of 1200 mm and a length of about 55 m are applied to field full scale tests. Large tonnage load tests and measurements of axial force and deformation are carried out so that the status of load bearing and deformation capacity of socketed piles are obtained, and the test results are valuable to the study of the bearing capacity and load transfer mechanism of large-diameter socketed piles in Wuhan area. The results show that the load-settlement curves of the 4 piles are all mild ones, and their bearing capacities are larger than 45000 kPa. The settlements at engineering pile top are 9.7~10.82 mm, and those at pile tip are 2.35~2.83 mm. Side friction distribution and bearing characters of piles embeded in sand rocks are different from those of mudstone. The tip resistance ratios of the 4 piles are 45.3%~58.7%. The calculation method in China's technical code for building pile foundations underestimates the tip resistance of soft rock and very soft rock.