基于BOTDR深基坑工程地下连续墙变形监测应用研究

Study on deformation monitoring of underground diaphragm wall based on deep foundation excavation with BOTDR

分布式光纤监测技术应用到基坑支护墙体的变形监测中可弥补传统监测方式实时性差、智能化程度低等缺点。本文介绍了基于BOTDR的光纤感测技术对基坑支护体系地下连续墙的变形监测的传感光缆布设方法、变形计算原理,并对计算过程中产生的误差进行分析。分析结果显示,误差大小与支护墙体的深度、变形大小成正比,与两测线间的距离呈反比。研发了新型高强度应变传感光缆并将其应用于苏州地铁车站的基坑开挖过程引起的支护墙体变形监测中。监测结果表明:三级钢支撑可有效控制变形,该围护结构设计可行,地下连续墙变形在合理范围内;光纤数据与测斜管数据对比基本一致,说明了该计算方法的可行性。研究成果表明该方法可大规模应用于基坑开挖引起的地下连续墙变形实时预警监测。

The application of distributed optical fiber monitoring technique to the deformation monitoring of foundation pit supporting walls can make up for the shortcomings of traditional monitoring methods such as poor real-time performance and low intelligence. This paper introduces the fiber optic sensing technique based on BOTDR to monitor the deformation of the underground diaphragm wall of the foundation pit support system, the sensor optical cable layout method, the deformation calculation principle and the errors generated in the calculation process are analyzed. The analysis results show that the values of the error are proportional to the depth and deformation of the supporting wall, and inversely proportional to the distance between the two survey lines. A new type of high-strength strain sensing optical cable is developed and applied to the deformation monitoring of the supporting wall caused by the excavation of the foundation pit of the Suzhou Metro station. The monitoring results show that the three-level steel supports can effectively control the deformation, the design of the retaining structure is feasible, and the deformation of the underground continuous wall is within a reasonable range;the comparison between the optical fiber data and the inclinometer data is basically consistent, which shows the feasibility of the calculation method. The study results show that this method can be applied to real-time early warning and monitoring of the diaphragm wall deformation caused by the excavation of foundation pit.