Deep displacement monitoring and foundation base boundary reconstruction analysis of diaphragm wall based on ultra-weak FBG

Abstract The instability or destruction of diaphragm walls in underground engineering will cause significant economic losses and casualties. The distributed and high-precision monitoring of diaphragm wall deformation can provide reliable and detail data for disaster early-warning as well as economical design. However, recording continuous deformation of the diaphragm wall using traditional monitoring technologies remain challenging. Moreover, the basement movement of diaphragm wall is rarely considered in previous studies. In order to overcome the shortcomings of the current displacement monitoring methods and deal with the basement boundary issues, a new base boundary reconstruction (BR) was proposed and the ultra-weak Fiber Bragg grating (UWFBG) technology was adopted to monitor the displacement of the diaphragm wall. For validation, a laboratory test based on ultra-weak FBG was carried out and the feasibility of the BR method was demonstrated. Subsequently, the ultra-weak FBG and the BR method were applied to Shanghai metro line 18. The results showed that the monitoring technology and analysis method proposed in this paper can obtain detailed deformation information of the diaphragm wall in real-time, which not only provides an advanced monitoring method for the deep deformation of diaphragm wall, but also solves the deformation calculation issue with the base boundary condition changes involved.