A new method to measure the deformation of SMW pile based on BOTDA
DING Yong1,3, WANG Ping2, HE Ning3, ZHAO Weibin3, WANG Guo-li3
(① Nanjing University of Science and Technology, Nanjing 210094, China )
(② China First Metallurgical Construction Co. LTD., Wuhan 430081, China)
(③ Nanjing Hydraulic Research Institute, Nanjing 210029, China)
Abstract: This paper presents a new method to measure the deformation of SMW pile. By using BOTDA distributed optical fiber sensing technology, transforming ordinary H-pile into a pile body having a self-sensing ability, so that it can automatically acquire structural health data like strain, bending moment, deflection etc. in the excavation process; through the force analysis of H-pile, putting forward a method of the pile bending moment continuous calculation which doesn’t need to determine the location of neutral face, and it can make temperature compensation. The technology once worked in a foundation pit, and as a successful application shows that it has good on-site adaptability, it can monitor the deformation of foundation pit in real time, moreover it has some advantages like distributed measurement, temperature self-compensation, etc., therefore it can be used widely as a new type of protective structure in foundation pit.
Key words: SMW pile; BOTDA; temperature compensation; strain; bending moment; deflection
0 引 言
SMW工法，具有构造简单、止水性能好、工期短、造价低、环境污染小等特点，目前已被广泛应用于各类基坑工程之中。但是，受到传统监测手段的限制，对SMW工法桩的实时变形监测还比较困难，目前工程上广泛采用的基于常规电测式传感器的人工采集数据的方法，有限的测点难以反映目标系统的整体情况，存在漏检的弊端，而且传感器使用寿命较短，存在长期的零点漂移问题，同时容易受到外界环境的各类不利因素（如温度、湿度变化及电磁干扰）的影响，往往无法保证监测数据的长期稳定性与准确性。
近年来兴起的BOTDA分布式光纤传感技术具有防水、抗腐蚀和耐久性长等特点，其传感元件体积小、重量轻，测量范围广，便于铺设安装，将其植入监测对象中不存在匹配的问题，对监测对象的性能和力学参数等影响较小[1]；光纤本身既是传感元件又是信号传输介质，可实现对监测对象的远程分布式监测[2-4]。因此，利用BOTDA技术对SMW工法桩进行实时变形
监测，可以有效的克服传统监测技术的不足，不失为常规基坑监测手段以外的有益补充。
