基于光纤传感技术的泥岩地基动力打入桩施工效应现场试验

Field test of construction effect of dynamic driven pile in mudstone foundation based on fiber optic sensing technology

为探讨泥岩地基动力打入桩的施工效应与承载力异常问题,基于低温敏光纤应变传感器联合桩端全截面轮辐压力传感器实时监测打桩过程中桩身应力及桩端阻力,明确打桩过程中试桩内力和桩端阻力随贯入深度的变化规律;通过竖向抗压静载荷试验与高应变动测分析各试桩的承载特性;利用打桩锤击数和锤重分析锤击能对动力打入桩沉桩效应的影响,借助打桩前后桩边标准贯入试验锤击数随桩长的分布,揭示动力打桩对桩周泥岩强度的影响机制。结果表明:沉桩过程中不同测试传感器得到的桩端阻力时程曲线变化规律较为一致,静载试验获得的试桩极限承载力比高应变动测得到的结果偏高,试桩均表现出端承型桩的特性;重锤打桩桩身应变变化幅度明显较大,打桩能量与试桩的竖向承载力有关,高能量打桩导致泥岩结构损伤加重,会降低动力打入桩的承载力;打桩后桩周泥岩的标贯试验锤击数与打桩前相比明显减小,宏观上表明动力打桩对桩周泥岩结构造成不同程度的损伤,可以认为泥岩结构损伤是动力打入桩承载力降低的主要原因之一。

In order to discuss the construction effect and bearing capacity abnormality of dynamic driven pile in mudstone foundation,the stress and end resistance of pile were monitored based on low temperature sensitive fiber optic strain sensor and full section spoke pressure sensor of pile end.The variation of internal force and end resistance of test pile with penetration depth was clarified.The bearing characteristics of each test pile were analyzed by vertical compressive static load and high strain variation measurement.The influence of hammer energy on the driving effect of prefabricated piles was studied by using hammer number and hammer weight.The influence mechanism of dynamic pile driving on the strength of mudstone around pile was revealed by means of the distribution of hammer number of standard penetration test of pile edge before and after pile driving.The test results show that the time-history curve of the end resistance measured by different sensors is consistent during the pile driving process.The ultimate bearing capacity of test pile obtained from static load test is higher than that obtained from variable test,and all test piles show the characteristics of end bearing pile.The strain variation range of heavy hammer driving pile is obviously larger,and the pile driving energy is related to the vertical bearing capacity of pile.High energy driving pile will lead to aggravated damage of mudstone structure and reduce the bearing capacity of driven pile.Compared with before pile driving,the hammer number of mudstone around pile after pile driving decreases obviously,which indicates that dynamic pile driving causes damage to mudstone structure around pile to different degrees in macro view.It can be considered that mudstone structure damage is one of the main reasons for the reduction of dynamic drive pile bearing capacity.