强风化岩层大直径后压浆嵌岩桩承载性状试验研究

Experimental study on bearing behavior of large-diameter post-grouted rock-socketed pile in strongly weathered rock formations

为研究组合后压浆对强风化岩层大直径嵌岩桩承载性状的影响,对深圳地区超高层建筑的2根直径为2800 mm的嵌岩灌注桩进行了大吨位静载试验,对比分析了高水平荷载作用下未压浆桩与组合后压浆桩的承载、变形特性与荷载传递规律,将得到的试验数据与现行规范及地勘报告中的推荐值进行对比,并在统计分析的基础上给出了强风化岩层的大直径后压浆桩侧摩阻力与端阻力增强系数,并验证了增强系数取值的合理性与可靠性。结果表明:与未压浆桩相比,组合后压浆桩侧摩阻力与桩端阻力均大幅度提高,且对桩基荷载传递特性产生显著影响,使得强风化岩层中组合后压浆桩表现出更高的承载与变形控制能力;在极限荷载作用下,未压浆桩与组合后压浆桩均表现为端承摩擦型桩,即组合后压浆不改变大直径嵌岩桩的承载性状。此外,采用现行规范中的增强系数计算将低估压浆桩的实际承载力,而由试验得到的强风化岩层侧摩阻力、端阻力增强系数取值范围分别为2.49~3.05、2.24~2.43,以此计算后压浆桩的承载力更为合理可行。

To study the influence of combined post-grouting on the bearing behavior of large-diameter rock-socketed piles in strongly weathered rock formations,large-tonnage static load tests were conducted on two rock-socketed cast-in-place piles with a diameter of 2800 mm in super high-rise buildings in Shenzhen.The load-bearing characteristics,deformation characteristics,and load transfer mechanism of ungrouted piles and combined post-grouted piles under high-level loads were compared and analyzed.The obtained test data were compared with the current specifications and recommended values in the geological survey report.On the basis of statistical analysis,the improvement coefficients of side resistance and base resistance of large-diameter post-grouted piles in strongly weathered rock strata were given.Finally,its rationality and reliability were verified.The results indicate that the side resistance and base resistance of combined post-grouted piles are substantially improved compared with those of ungrouted piles,and the load transfer characteristics of the rock-socketed pile are significantly affected by combined post-grouting,yielding higher load-bearing and deformation control capabilities of the combined post-grouted pile in strongly weathered rock formations.Under the ultimate load,both the ungrouted pile and the combined post-grouted pile are end-bearing friction piles,while the combined post-grouting cannot change the bearing behavior of the large-diameter rock-socketed pile.In addition,the calculation method in Chinese technical code for building pile foundations underestimates the actual side resistance of large-diameter rock-socketed piles,and the value ranges of improvement coefficient of side resistance and base resistance of strongly weathered rock formations are 2.49-3.05 and 2.24-2.43,respectively,which is more reasonable and feasible.