Recommended Junctions between Diaphragm Wall Panels for Deep Excavations-Paper

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The paper reviews methods for achieving watertight junctions between diaphragm wall panels in deep excavations. Panel joints are important primarily for waterproofing and excavation guidance, and their performance depends on construction quality, equipment, and verticality.<br /><br />The principal options are waterstop joints and milled joints. Waterstop joints use a temporary stop-end formwork carrying a sealing strip. Experience favors a single blade, typically 15–20 cm long: multiple blades can trap mud and debris, while longer blades may bend during concrete placement. Older stop-end tubes and grouting-tube approaches are generally discouraged. Waterstops are suitable for both grab and hydrofraise excavation and are especially recommended for deep structures under high water pressure.<br /><br />Milled joints are formed by cutting hardened concrete at the edges of primary panels. They provide effective watertightness but require a hydrofraise. Expansion joints can be combined with milling to improve sealing, particularly where low overhead clearance makes conventional stop ends impractical. This approach has so far been used under low-to-medium water head.<br /><br />Waterstops need not always extend to the wall toe. Their depth should be determined case by case, considering soil permeability, groundwater conditions, and risks such as increased leakage or loss of fines. They should generally extend at least to the final excavation level. Extending them deeper is possible but requires excellent verticality and careful management of installation risks.<br /><br />The paper estimates permeability at about 10⁻¹⁰ to 10⁻⁹ m/s for waterstop, milled, and milled-with-expansion joints, compared with about 10⁻⁸ m/s for dry joints and stop-end tubes. Overall, single-blade waterstops and milling are the most effective established solutions at depth, while increasingly deep projects demand highly skilled contractors and precise excavation control.

Keywords

diaphragm wall

deep excavation

watertight joints

waterstop joints

milled joints

panel joints

groundwater control

stop-end formwork

hydrofraise excavation

permeability