植入式光纤传感器在隧道结构中的边界效应研究

Study on boundary effect of embedded optical fiber sensor in tunnel structure

为探究植入式光纤传感器与隧道衬砌的应变传递的边界效应,分别从理论、试验和现场应用3个方面进行研究,并在实际工程中进行了验证。构建了光纤在混凝土衬砌中的应变传递模型,进行光纤应变传递机制分析,计算了光纤应变传递效率,并与数值计算结果对比,验证了力学计算模型的准确性。使用钢筋混凝土梁模拟隧道的混凝土衬砌,在其表面植入分布式光纤,进行了2组试验。对试验梁进行分级加载并使用BOFDA技术对光纤进行测试。试验结果表明:植入式光纤传感器存在边界效应,结构两端为光纤的低效率应变传递区,不能完全传递试验梁的应变;试验梁中部为光纤的高效率应变传递区,能够完全传递试验梁的应变。基于以上研究成果,在北京市新机场线地铁暗挖隧道CRD工法区间,采用植入式工艺在隧道衬砌内布设了分布式光纤传感器,进行了工程应用研究。监测结果表明,边界效应对工程监测结果影响很小,分布埋入式光纤布设工艺是可行的。该研究可为分布式光纤技术在地下工程结构监测中的应用提供参考。

To explore the boundary effect of the strain transmission between embedded optical fiber sensor and tunnel lining,the study was conducted from three aspects:theoretical,experimental studies and field applications.The results were verified in actual engineering.The strain transfer model of optical fiber in the concrete lining was constructed,and the mechanism of optical fiber strain transfer was analyzed.The strain transfer efficiency of optical fiber was then calculated and compared that with the numerical modeling results,which verified the accuracy of the mechanical calculation model.The concrete lining of tunnel was simulated with the reinforced concrete beams and distributed optical fibers were embedded on the surface of the concrete beams.Two groups of tests were carried out in this study.The test beams were loaded in stages and the optical fibers were tested by BOFDA technology.The test results show that the embedded fiber optic sensor has a boundary effect.The two ends of the beam structure are the low efficiency strain transmission area of the optical fibers,which cannot fully transfer the strain of the test beam.The middle part of the test beam is the high efficiency strain transfer area of the optical fibers,which can completely transfer the strain of the test beam.Based on the research results,the engineering application research was carried out.A distributed optical fiber sensor was installed in the tunnel lining in the CRD construction method section of the subway tunnel of the Beijing New Airport Line using the embedded fiber technology.The monitoring results show that the boundary effect has little influence on the monitoring results.The placement method of the distributed embedded optical fiber is feasible.This research can provide a reference for the application of distributed optical fiber technology in underground engineering structure monitoring.