Investigation of Rebar Exposure Issues of Diaphragm Wall and Influencing Factors Analysis

The exposure of rebar in diaphragm wall was discovered after excavation in more than 20 subway stations, along the lines 1 to 4 in Suzhou, China. Such phenomena were investigated from strata formation, hydrogeological condition, construction techniques, adjacent surcharge load and other aspects. Based on field investigation, in situ testing and numerical simulation, the disturbance of trenching operations and the main factors that affect the stability of the diaphragm wall during the trenching process are analyzed comprehensively. The results show that the deformation behavior and stability of slurry trench walls are mainly influenced by strata characteristics, adjacent surcharge loading, formation of bentonite filter cake on trench walls, pressure of a confined aquifer, height of slurry filling and slurry density. The underground water pressure in the confined aquifer of silty soil layers is considered as one of the main controlling factors, which is verified by the subsequently dewatering and trenching tests. During the construction process, the deformation and stability of the trench walls can be improved by adjusting and controlling the crucial controlling factors. Further, relevant remedial measures as well as the preventive methods during the process of constructing diaphragm walls and subsequent soil excavation are addressed.