Deep and Extra Deep Diaphragm Walls in Shanghai - Increasing Demand for Infrastructure in Megacities Drives the Requirement of Increasing Depth for Diaphragm Walls-Paper

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Shanghai’s rapid urban growth and expanding subway, flood-control, sewage, and skyscraper projects are driving demand for increasingly deep diaphragm walls. The paper reviews Shanghai projects ranging from 58.5 m to experimental panels at 150 m and explains how trench cutters enable construction at these depths.<br /><br />Trench cutters use rotating wheels to break up soil and rock, which is mixed with bentonite slurry and pumped to a plant for cleaning. Different wheel and tooth configurations suit varying ground conditions, including rock strengths up to 250 MPa. Compared with hydraulic grabs, cutters are better suited to dense or hard layers, deep excavation, and strict verticality requirements. The Overlap Cutter Joint (OCJ) system also allows deep wall construction without a practical depth limitation.<br /><br />Project examples show the progression from early cutter use at the 58.5 m World Expo substation to 72 m metro walls, 75.5 m walls at Xuhui Center, and a 105 m shaft at Yunlingxi. Three 150 m test panels were successfully completed in 2018, with maximum vertical deviation below 15 cm against a 1/1000 alignment requirement. The trials demonstrated the feasibility of ultra-deep diaphragm walls in Shanghai’s alternating layers of clay and sand.<br /><br />Construction requires careful management of trench stability and alignment. Soft upper soils often need improvement; slurry must be desanded before alignment checks; and deep panels can take several days to excavate. Long reinforcement cages, rapid concrete delivery, heavy lifting equipment, and urban logistics add further demands.<br /><br />The authors expect deep and ultra-deep walls to become more common, with projects exceeding 100 m increasingly necessary. Trench cutter technology offers high productivity, low noise and vibration, accurate excavation, and adaptability to confined urban sites, making it well suited to the infrastructure needs of megacities.

Keywords

Shanghai

diaphragm walls

trench cutters

deep excavation

bentonite slurry

urban infrastructure

subway projects

flood control

Overlap Cutter Joint

verticality control