Abstract: In order to investigate whether the stability of the underground diaphragm wall is affected by the grip strength of reinforced concrete wrapped by slurry, this paper takes the Deep Drainage Pipeline System of Suzhou River project as the background. The pull-out destructive tests were carried out based on the self-developed high-power central pull-out test device and the bottom-up mud replacement method by using large-size specimens and the same concrete and slurry ratios as the actual project. The bonding characteristics of the interface between steel, glass fibre reinforcement and concrete were analysed to reveal the effect of casting method, bond length and main reinforcement material on the bond strength under two casting environments. The results show that: (1) There is no significant difference on the concrete compressive strength of specimens cast in normal environment and in slurry, and the mean difference on the concrete compressive strength of specimens cast in the two different environments is within 3%. (2) For both steel and glass fibre reinforcement, the load-displacement curves differed between the normal environment and the mud-soaked environment; it can be divided into elastic deformation phase, plastic deformation phase and broken phase. (3) The grip force after mud immersion is less than that under normal casting conditions. As the bond length increases, the influence of mud on the grip force at the reinforcement-concrete interface gradually becomes greater, and the influence of mud on the grip force at the glass fibre reinforcement-concrete interface gradually decreases. The average bond strength after slurry immersion was significantly reduced by 19.2% for steel and 44.5% for glass fibre reinforcement. The slip values after the effect of mud immersion were less than those under normal conditions. (4) The forms of cracks produced on the specimen surfaces were classified as radial cracks, circular cracks and falling-offs of the surrounding specimens, and the formation of cracks was mainly concentrated in the normal pouring environment.

Key words: reinforced concrete, central pull-out test, underground diaphragm walls, glass ?bre reinforcement, bond strength