考虑埋入长度效应的应变传感光纤-土体界面特性试验研究

摘要

The fiber optic sensing technique has been widely applied to geohazard monitoring and deformation measurement of geomaterials.This paper aims to understand the coupling mechanism between strain sensing optic fibers and the surrounding soil masses for interpreting the monitoring results.It examines the influence of fiber embedment length on the mechanical property of fiber-soil interface.There are insufficient investigations on the strain distribution and transfer mechanism along the sensing optic fiber during pullout process.Using the newly designed pullout devices,this paper evaluates the influence of four different embedment lengths of sensing optic fiber on the fiber-soil interfacial property.A mathematical model is used to fit the pullout curves.The results show that the effective pullout displacement and the maximum pullout force increase linearly with the increase of fiber embedment length.But the fiber-soil interfacial shear strength decreases with the increase of the embedment length.Furthermore,the Brillouin optical fiber time domain analysis (BOTDA)technology is used to measure the strain distribution along the sensing optical fiber during its gradual decoupling process from the soil mass.The distribution of fiber-soil interfacial shear stress is also calculated,which shows that the interface failure is highly progressive.These findings can provide reference for understanding the interaction mechanism between strain sensing fiber and surrounding soil,and promote the application of fiber optic sensing technique to geoengineering monitoring.%随着光纤传感技术越来越多地应用于地质灾害和岩土变形监测,理解应变传感光纤与周围岩土体之间的变形耦合机理成为监测结果分析中的重要一环.但是相关的研究较少,尤其是有关埋入长度对传感光纤-土体界面特性及应变传递过程的影响尚未得到充分的认识.本文通过拉拔试验,研究了不同埋入长度条件下纤-土界面的力学性质,并采用一个数学模型对拉拔曲线进行了预测.结果表明:该模型能较好地拟合拉拔力-拉拔位移曲线;有效拉拔位移和最大拉拔力均随着埋入长度的增加而线性增加;而传感光纤-土体界面抗剪强度则随着埋入长度的增加而降低.在此基础上,采用布里渊光时域分析技术(BOTDA)获取了传感光纤与土体界面逐渐脱离过程中光纤的应变分布情况,并计算了纤-土界面剪应力分布特征及其演化过程,结果进一步证实界面破坏有高度的渐进性.这些结果为掌握应变传感光纤与周围土体之间的协调变形机制提供了参考,为促进光纤传感技术应用于岩土变形监测打下了基础.