Abstract:

The tunnel of the southern side of Suai Passage in Shantou constructed by open cut method is located in sea cofferdam area. The special characteristics of uppersoft lowerhard strata of the cofferdam cause great difficult for slurry protection of the trench wall and trenching of the underground diaphragm wall. The trench cutting technology of “soil clawed by trench cutting machine + impact drill” is adopted at the early stage of trench cutting of underground diaphragm wall; the hydraulic claw bucket is adopted for the trench cutting in mucky soil, sandy soil and fully weathered rock; and the compact drill is adopted for hole drilling and correcting in strongly weathered rock, moderately weathered rock and slightly weathered rock. It takes more than 20 days to complete a single trench section, and the longest time is up to 40 days, which severely affects the construction schedule. The construction efficiency of underground diaphragm wall has been remarkably improved by modifying drill bit of rotary drill, core drilling of strongly weathered and moderately weathered rock and adopting trench cutting machine, compact hammer and rotary drill. Through comparing and selecting of trench cutting scheme, design optimizing of inrock wall thickness, boulder breaking and bedrock treating, the foundation pit is completed successfully, which accumulates construction experience for underground diaphragm wall in uppersoft lowerhard strata.

Key words: underground diaphragm wall, uppersoft lowerhard strata, trench cutting technology, boulder, bedrock