Two different grab systems, suitable for wall thicknesses of 600 mm to 1,500 mm, are available for diaphragm wall excavation.
The grab is lowered into the panel and the soil is excavated in bites. Larger blocks or sections of rock can be excavated or displaced using modified grabs or heavy-duty chisels. Measuring systems can be installed to verify verticality.
On mechanical grabs, a cable system operates the jaws. Hydraulic grabs work with a hydraulic cylinder. They have very high closure forces and work with lower noise and less vibrations than mechanical grabs.