Abstract
Joints between diaphragm wall panels are weak spots in wall construction. It is essential that potential leak sites are detected prior to excavation. In this study, a novel leak detection and monitoring system is presented that is based on fiber Bragg grating (FBG) sensing technology. A field study was performed in a deep excavation supported by diaphragm walls (in Hohhot, China) to validate the feasibility and effectiveness of the proposed method. Two schemes were trialed; one using pipes made of stainless steel, and one used a pipeless method. The results of the field study are presented and discussed. They show that potential leak sites in the wall joints could be determined prior to excavation using the proposed detection method. Stainless steel is a good material to use to make the detection tube because it can protect the FBG sensors and heating belts from damage and is more sensitive to water leakage. The field study provides good evidence for the feasibility of the new detection system. It also provides valuable experience for the field application of the system and has generated useful data to use in follow-up work.
Highlights
When the temperature of an fiber Bragg grating (FBG) sensor changes, there is a shift in the Bragg wavelength λB of the FBG [15,27,29,30]
A new leakage detection system for Diaphragm walls (D-walls) has been applied to a project site in Hohhot, China
The proposed detection system is based on FBG sensing technology
Summary
Diaphragm walls (D-walls) are commonly used in deep underground construction projects—e.g., deep basements for high-rise buildings, underground railway stations, underground parking garages, and other underground facilities that require deep excavations. They act as retaining walls to resist the lateral pressure acting on their backs and obstruct the flow of water, acting as a waterproof curtain to ensure that the deep excavations remain dry. Different methods have been applied on construction sites in order to improve the watertightness of the wall joints—e.g., installing rubber bands, metal sheets, or precast concrete elements as water-stops on the ends of the panels of the D-wall [2]. The construction procedures involved are complex and include trench excavation, refreshing of the bentonite suspension, lowering of steel reinforcement cages, installation of stop ends, and concreting
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