分布式光纤在基坑H型钢变形监测中的应用
文献综述
摘要：随着城市的建设和国家的发展，城市所能使用的面积正在逐渐减少，所以城市地下空间的开发利用正在成为各大城市解决土地稀缺的主要方向，其中应用最为广泛的莫过于基坑的发展。但是，基坑规模和开挖深度的增大使临时围护结构变形和稳定问题变得复杂和突出，这也成为研究人员日益关切的一个问题。为了确保基坑设计、施工的可靠性，除了在分析模型、计算方法、选用概率理论来尽量拟合实际情况以外，最重要是必须进行现场监测。SMW工法是利用专门的多轴搅拌机就地钻进切削土体，同时在钻头端部将水泥浆液注入土体，经充分搅拌混合后，再将H型钢(或其它芯材)插入搅拌桩体内，形成地下连续墙体，利用该墙体直接作为挡土和止水结构。基坑开挖过程中，水土压力和水平支撑轴力都作用在H型钢上，H型钢的受力变形状态直接反映了基坑的安全状况，只要从强度和位移这两个方面控制住H型钢的受力变形，就可以确保基坑不发生破坏，据此也可以对基坑的稳定性做出实时评价。针对H型钢在基坑过程中的变形问题，BOTDA 作为一种新型的分布式光纤传感监测技术，其分布式、高精度、实时性、长期性、远程控制等特点，正满足对 SMW 工法桩中的型钢进行长期监测的要求。利用 BOTDA 测量原理，可以测到光纤沿线任一点的布里渊散射频移，应用布里渊频移与应变的关系，便可得到光纤沿线任一点的应变，满足了对H型钢的变形监测。
关键词：SMW工法；分布式光纤；变形监测
Abstract: With the construction of cities and the development of the country, the area that can be used by cities is gradually decreasing, so the development and utilization of urban underground space is becoming the main direction to solve the shortage of land in all cities, among which the development of foundation pits is the most widely used. However, the increase of foundation pit scale and excavation depth has complicated and highlighted the deformation and stability of temporary enclosure structure, which has become a growing concern of researchers. In order to ensure the reliability of foundation pit design and construction, in addition to the analysis model, calculation method and probability theory to try to fit the actual situation, the most important thing must be on-site monitoring. SMW method USES a special multi-axis mixer to drill and cut the soil in place, and at the same time, the cement slurry is injected into the soil at the end of the drill bit. After full mixing and mixing, h-shaped steel (or other core material) is inserted into the body of the mixing pile to form an underground continuous wall, which is directly used as a soil and water retaining structure. The process of foundation pit excavation, soil and water pressure and horizontal supporting axial force effect on h-beam, h-beam deformation and stress of the directly reflects the safety of foundation pit, as long as the strength and displacement from the two aspects of the stress of the control of the h-beam deformation, can ensure that foundation pit without damage, accordingly can also make a real-time evaluation to the stability of the foundation pit. In view of the deformation problem of h-beam in foundation pit, BOTDA, as a new distributed fiber optic sensing and monitoring technology, has the characteristics of distributed, high-precision, real-time, long-term and remote control, which meets the requirements of long-term monitoring of section steel in SMW construction pile. Using the principle of BOTDA measurement, the brillouin dispersion rf shift at any point along the fiber can be measured, and the strain at any point along the fiber can be obtained by using the relationship between brillouin frequency shift and strain, which satisfies the deformation monitoring of h-beam.
Key words: SMW；Distributed fiber；Deformation monitoring
1前言
1.1国内外研究现状
现如今，国内外对于分布式光纤的应用都处于飞速发展的阶段，分布式光纤在很多重要的领域都可以应用。在国外，分布式光纤已经是处于比较成熟的阶段，在很多领域都发挥了弥足轻重的作用，如安全监测、温度检测等。我国虽然起步比较晚，但是发展极为迅速，到如今分布式光纤传感技术已经投入应用，在工程中带来更为便捷安全的使用效果。
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