The clamshell grab (also called clamshell bucket) consists of two shell-shaped jaws that are opened and closed hydraulically or by cable. In the open position, it is lowered onto the material; the shells close and enclose the load. Unlike a bucket, the grab is suitable for vertical excavation (e.g., shaft sinking) and underwater dredging.
Applications: Shaft excavation, pile cap exposure, slurry wall excavation, waterway maintenance, port dredging, and material handling (bulk materials, scrap, biomass). Cable excavators equipped with clamshell grabs (duty-cycle cranes) are widely used in specialized deep foundation work and ports. Hydraulic excavators use grabs for canal cleaning and trench excavation.
Gripping force depends on closing cylinder volume and hydraulic pressure. Different shell designs are adapted for various materials: closed shells (for fine material, sealing), perforated shells (drainage), and toothed shells (for scrap and biomass). Manufacturers: Arden Equipment, Kinshofer, MBI, and Nemag (port material handling).