At Beitan in Baoshan district STEC is excavating a tunnel boring machine shaft. Because of the 30m depth of the tunnel floor and the challenges of ground water at that depth, the client has chosen for wet excavation as the only viable option.

A diver is suited up to go down and identify and clear debris from the floor of the trench so that the cutter dredger pump can work uninterrupted.

The diver has collected big pieces of concrete from the floor of the pit, working at a water depth of 30 meters. A clean floor ensures the cutter doesn’t catch in steel rebar waste or breaks its teeth on rocks.

The pump is fitted with a double cutter head assisted by water jetting. The BELL-200 can pump up 800 m3 of mixture per hour, of which 30% solids. The main challenge is to move the pump expediently at 30m depth so that it can get to the soil and create a high soil mixture content.

The wet excavation is done with a BELL 200 pump, powered by a ICE 400 hydraulic power pack. As divers go down into the pit this is an important safety precaution not to work with electric equipment.

The BELL 200 is fitted with a double cutter head that cuts up the clay and because of its counter directional cutting direction can stay positioned in place when lifted by crane.

The cutter pump is attached to 30m long pipes, the lifting head above the water line is approximately 10 meters.

The mixture is separated by this unit manufactured by Bauer. The soil is trucked out, the water is circulated back so it can transport more soil out of the trench.

Remember to always clear the lines with water before switching off, otherwise the pipes may get clogged with the soil mixture and you’ll need to take the pipes apart to clear the blockage!