珊瑚礁灰岩层后压浆桩增强效应作用机制

Enhanced mechanism of post-grouting pile in coral-reef limestone formations

珊瑚礁灰岩层中桩基承载特性的研究是岩土工程的热点问题。基于某跨海大桥工程开展的珊瑚礁灰岩层中桩端后压浆桩现场静载荷试验,对比分析了压浆前后的实测结果,研究了桩端后压浆的预压作用对桩阻力的影响,并在桩端后压浆试验结果分析的基础上,进一步研究了后压浆桩增强效应作用机制。结果表明,桩端后压浆技术可应用于珊瑚礁灰岩地层中,能有效地提高桩基承载力和减小沉降量;钻孔取芯试验明确了压力浆液在桩端以下一定范围内的分布情况,并证实了压力浆液对珊瑚礁灰岩的孔隙有充填作用;桩端压浆后,在桩端未能消散的压力产生负摩阻力,使负摩阻力在竖向荷载作用下提前发挥,并增大了压浆桩的侧阻力。此外,桩端后压浆的预压作用提高了桩端阻力,并减小了桩端位移,改善了桩基的承载性状。

The investigation on the bearing behavior of pile foundation in coral-reef limestone formation is a hot issue in the geotechnical engineering. Based on the field static loading test of tip post-grouting pile in coral reef limestone formations in the project of a cross-sea bridge, this work analyzed the test results of the trial pile before and after grouting, and the influences of the preloading effect of post-grouting at the pile tip on the pile resistance. The mechanism of improvement for the grouted pile was further studied by the analysis of test results of post-grouting at the pile tip. The results show that the post-grouting technique can be applied to the coral-reef limestone formations, which can effectively improve the bearing capacity of pile foundation and decrease the settlement. Coring test reveals the distribution of pressurized grout, and verifies that the pore of coral-reef limestone is filled by the pressurized grout. The negative side friction is mobilized before application of vertical load because of the negative side friction arising from grout pressure after tip grouting. Thus, the side friction of grouted pile increases. Additionally, the preloading effect of post-grouting at the pile tip enhances the tip resistance and reduces the tip displacement. Consequently, the bearing behavior of pile foundation is improved by post-grouting at the pile tip.