后压浆桩增强效应作用机制及荷载沉降关系研究

基于台州湾大桥及接线工程开展的6个标段场地10根大直径超长钻孔灌注桩现场静载荷试验结果,分析后压浆桩的荷载传递特性,并在后压浆桩增强效应作用机制的基础上,采用双曲线函数的荷载传递模型,给出了后压浆桩荷载沉降关系的计算方法,并确定了不同土层桩侧和桩端增强系数,最后通过工程实例验证了该方法的合理性。结果表明,桩端压浆对桩端土体产生预压作用,使桩端阻力在竖向荷载作用下提前发挥,改善了桩端阻力与桩侧阻力发挥的异步性和不协调性;后压浆桩是在浆液对桩端土的加固、桩端压浆的预压作用、压浆形成桩底扩大头及浆液上返对桩侧加固四方面因素共同作用下显著增强桩端阻力和桩侧阻力,而忽略浆泡半径的影响或不考虑浆液上返段的作用都不能很好的预测压浆桩的极限承载力。

Enhanced mechanism and load-settlement relationship of post-grouting piles

Based on the results of ten in-situ pile load tests of Taizhou Bay Bridge and its connecting projects in six different sites, the load transfer characteristics of grouted piles are analyzed. The hyperbolic load transfer function is used to calculate the load-settlement relationship of the grouted piles on the basis of the mechanism of strengthening effect. The improvement coefficients for side friction and tip resistance in different soil deposits are determined to account for the effect of grouting. Finally, case history is cited to demonstrate the validity of the method. The results indicate that the tip resistance of the grouted piles is mobilized before application of vertical load because of the preloading effect of soil beneath pile tip arising from tip grouting. Thus, the strain incompatibility between the tip resistance and the side friction of pile is improved. Moreover, the tip resistance and side friction of grouted piles will be significantly enhanced under the combined action of ground improvement of the soil beneath pile tip, preloading effect, enlarged tip area and the upward grout penetration along the pile side due to tip pressure grouting. However, ignoring the influence of grout bulb radius or grout climbing height may lead to an undesirable bearing capacity of the grouted piles.