The “APE OctaKong” project revolutionized the way cofferdams could be driven at sea when it drove 120 piles at 72 foot in diameter to grade in 6 months. The “Tandem 200-6 Special” project revolutionized the way cell walls could be driven when it drove 240 single cell sheet walls at 37 foot wide. Now another revolution is taking place; Underwater soil compaction.
In between the two man-made islands for the Hong Kong Macao Bridge will be a 5,000m long tunnel. To build the tunnel they will use pre-made concrete sections that will be lowered onto the sea floor. Once all the tunnel sections have been lowered into place the water will be pumped out and a tunnel will be created. However, before the tunnel sections can be lowered down on the sea floor the ground must be hardened and flat. Traditional methods would required a large weight to be repeatedly dropped onto the gravel below until the ground is hardened to the required level, but when compacting soil at sea the accuracy of dropping a weight can be slow and tricky. Therefore, a method was created to use a 40 ton steel plate, that looks like a big clothing iron, connected to a single APE model 600 vibratory hammer. After the gravel is poured on the ocean floor the APE 600, using 550 tons of driving force, compacts the gravel to near perfect flatness. Much like ironing a wrinkled shirt, the sea floor is ironed out.
The only difference being that its down 50m underwater in complete darkness. With special sensors and GPS devices the APE 600′s location is known by operators of the ship above, even during continually changing currents. APE’s hammer are known to have underwater capabilities far superior to other vibratory hammer models in the market, but this job requires the hammer stay underwater for 4-5 days at a time at 50m deep working 24 hours a day. This would be the most rigorous underwater job ever done using APE equipment and the engineering limits of the APE 600 again would be tested, especially because the project will be 18 months long. After 1 month of operation the project has been a complete success. Today the 600 was pulled out of the water after it’s fourth 5 day dive and all indications show zero seawater entered the gearbox and all systems normal. We hope to see more contractors using this method in the future for underwater soil compaction jobs in the future. For more information of this project or information on underwater pile driving please feel free contact David White of APE China.