MC劲性复合桩在硬土层中应用的试验研究

Experimental study on the application of MC strength composite pile in the hard soil layer

结合MC劲性复合桩在硬土层中应用的工程实例,通过静载试验得出,MC劲性复合桩具有较大的竖向承载力优势。M桩取芯检测表明,软土层中成桩效果较好,较硬土层中成桩效果较差。基于此,认为在较硬土层中,桩侧阻由M桩承担,端阻由C桩承担。将动静对比分析得到的预制桩平均侧阻力和端阻力分别代入MC劲性复合桩中,计算极限承载力值介于2 886~3 335 kN之间,较常规桩竖向抗压承载优势明显。针对现行规范中MC劲性复合桩计算端阻力偏低,不适用硬地层的情况,提出了端阻力计算改进公式,侧阻力计算仍用原规范方法。改进后的方法在不影响侧阻计算的前提下,可以明显改善端阻力计算结果。限于各种原因,MC劲性复合桩静载试验没有得到极限承载力,通过高应变进行动静对比试验反推的结果,虽然符合端承摩擦桩的承载规律,端阻比例也在合理范围内,改进的方法虽然比规范方法更容易提高桩端阻力,但准确性和普适性还需进一步验证。

Combined with the engineering examples of the application of MC rigid composite pile in the hard soil layer,the advantages of MC rigid composite pile with a large vertical bearing capacity are obtained through the static load tests.The coring test of M pile shows that the effect of pile formation in soft soil layer is better than that in hard soil layer.It can be considered that in the hard soil layer,shaft resistance is provided by M pile and end resistance is borne by C pile.Substituting the average shaft resistance and end resistance of the precast piles obtained by the dynamic and static comparative analysis into the MC rigid composite piles,the calculated ultimate bearing capacity is between 2886 kN and 3335 kN,which has obvious advantages over conventional piles in vertical compressive bearing capacity.In view of the calculated end resistance of the MC pile is smaller than the measured value in the hard soil layer,an improved formula for the calculation of end resistance was proposed.The side resistance calculation still use the original specification method.The improved formula significantly improves the calculation accuracy of the end resistance without affecting the results of shaft resistance.Limited to various reasons,the ultimate bearing capacity of MC rigid composite piles has not been obtained through static load tests.The back-calculated results of dynamic and static comparison tests with high strain conform to the bearing law of end-bearing friction piles,and the end-resistance ratio is also within a reasonable range.Although the improved method is easier to increase the pile end resistance compared to the standard method,the accuracy and universality need to be further verified.