桩基承载力多点动测法的理论与试验研究

Theoretical and experimental research on multi-point dynamic testing method for pile bearing capacity

桩基高应变试验与静载试验相比具有高效、快速和成本低的优势。提出并验证了一种新的高应变方法,即多点动测法,从理论和模型试验两方面研究单桩静、动载测试的承载力曲线差异及影响因素。基于非线性土阻力模型,首先建立高应变条件下的单桩离散质弹动力模型,推导自由落体重锤冲击力的解析表达,并给出动力响应的离散差分解法;利用多点动测法预测不同桩长的动载曲线,并与静载曲线、静动法预测结果做比较;在此基础上开展模型试验,探究同一模型桩静、动载承载力曲线的差异,验证多点动测法的可靠性。结果表明,多点动测法在桩长不大时预测的静载曲线较为准确,在桩长偏大时预测结果优于静动法;动、静承载曲线的差异与桩的波动效应有关,通过调整桩顶激振条件减弱波动效应,可提高多点动测法的预测准确性;构建的质弹动力模型能够考虑土体非线性,预测的动力响应与模型试验结果基本一致,能够同时适用于低、高应变下动力计算。研究成果对于桩基高应变测试方法、动力理论模型以及动静承载力曲线差异等研究具有一定的帮助。

Compared with static load test(SLT),high-strain dynamic test(HSDT)of pile foundation is more effective,rapid and less costly.A new HSDT method was proposed and verified,which is called the multi-point dynamic method(MPDM).The difference and influence factors of pile capacity curves between SLT and DLT were studied through theoretical analysis and model experiments in the presented paper.Based on the nonlinear soil resistance model,the dynamic discrete spring-mass model of single pile under high strain condition was established firstly;the analytical expression of impact force of free-fall hammer was derived and the discrete difference solution was given.The dynamic load curves under different pile lengths was calculated based on MPDM and compared with SLT results and results predicted by Statnamic method.On this basis,model experiments were conducted to explore the difference of dynamic and static capacity curves,and to verify the reliability of MPDM.The results have shown that the capacity curve predicted by MPDM was accurate for pile of short length;the prediction results was better than that of Statnamic method for long piles.The difference between the dynamic and static curves was related to the wave effect of pile,and the prediction accuracy of the multi-point dynamic measurement method can be improved by adjusting the excitation conditions at the pile top to attenuate the wave effect.The presented theoretical model,which can consider the soil nonlinearity,accurately predicted the dynamic response of model pile.And it is applicable for low stain and high strain dynamic load conditions.This research is helpful to study HSDT methods,dynamic theoretical model and the difference between dynamic and static capacity curves.