OFDR光纤传感技术在十字岩柱暗挖法物理模型试验中的应用

Application of OFDR-based sensing technology in geo-mechanical model test on tunnel excavation using cross rock pillar method

现阶段岩土工程模型试验围岩变形监测多采用点式传感器,仅能获得部分测点的应变,而光纤传感作为一种迅速发展的分布式监测技术,能很好地解决这一问题。对于岩土工程室内试验,现有光纤传感技术无法满足试验对空间分辨精度的高要求。对一种新型光纤传感技术光频域反射技术(OFDR)的测量原理和优点进行介绍,并将其应用于浅埋超大断面圆形隧道十字岩柱开挖模型试验中,对整个模型不同断面进行水平向应变连续监测。根据试验结果,结合有限元分析,表明OFDR能准确记录试验过程中模型内部的应变变化,揭示围岩在十字岩柱开挖方法下的变形规律,反映十字岩柱对围岩的支撑作用,为今后隧道工程开挖提供参考。另外通过算法将应变结果转化为位移结果,并与多点位移计的监测结果进行对比分析,偏差在10%以内。结果表明,该技术可应用于岩土工程试验中的变形监测。

The point-type sensors are widely used for monitoring the surrounding rock detbrmatlon in geo-mechanical modelling tests, but they can only obtain the strains at a few measuring points. Fibre optic sensing, as one rapidly developing distributed monitoring technology, can resolve this problem, but it cannot yet meet the requirement of high spatial resolution. This paper introduces one new OFDR（optical frequency domain reflectometry）-based sensing technology, and applies it in the geo-mechanical test modelling the excavation of shallow buried large diameter circular tunnel using the cross rock pillar method to achieve the continuous monitoring on the horizontal strains ha different tunnel cross sections during excavation. Combined with the FEM analysis, the results show that the OFDR based sensing technology can accurately record the change of strain inside the geo-mechanical model during testing. It can reveal the deformation tendency of the surrounding rock when excavated using the cross rock pillar method, reflect the supporting effect of the cross rock pillar to the surround rock, and then guide the future tunnel excavation activities. The results are compared with the monitoring results obtained from the multipoint displacement meter after converting the strain-type results into the displacement-type results, and their deviations are within 10%. Generally, the OFDR-based sensing technology can be applied to the deformation monitoring in geo-mechanical modelling tests.