Two different grab systems (mechanical and hydraulic), suitable for wall thicknesses of 600 to 1,500mm, are available for trench excavation.
The grab is lowered into the trench and the soil is discontinuously transported. Larger blocks or sections of rock are punched through, excavated or displaced using modified grabs or heavy-duty chisels. Measuring systems can be installed to verify verticality.
On mechanical grabs, a rope and pulley system operates the jaws. To increase the closure force, the closing cable is reeved five to six times. Hydraulic grabs work with a hydraulic cylinder. They have very high closure forces and work with lower noise and less vibrations than mechanical grabs.