Sargassum is a type of seaweed that grows in the ocean, and forms large sheets that wash up on the beaches of the Caribbean. As it decomposes, it releases a highly unpleasant odor and a very corrosive gas. To control this, nets are installed just off the coast to contain them from moving inward.
When they are blocked, they generally die off and quickly sink to the bottom. There are times when large amounts of seaweed film arrive with currents, and the pressure is so great, that the anchors that are in place can be torn away. This is where Techno Metal Post’s helical pile technology comes in handy!
At the request of Alexis de Jaham, the head of the company ‘Filets DROM’, we are tasked with installing 10 P4-16N type helical piles in a test project, to replace the failed net anchors. On Thursday, January 19th, 2023, the team gathers at the ‘Commun du Cap-Est’ dock in Le François, at 8 am to begin the project.
We had a team of five people for the project: Alexis and Christophe, who managed the two inflatable boats that transported the barge and anchors; Matthieu, the diver; Louis-Felix, the helpful assistant; and myself (Pierre).
An aluminum barge that transported the EM1, the piles, two hexagonal extensions, some bolts, and a mallet, was towed by a fishing boat and two small inflatable boats. Once the barge arrived at the location, the team dropped 2 anchors at 15 meters (50 feet) deep, at each corner of the barge to secure it against the direction of the current. Once stabilized, the installation of piles began!
The piles need to be installed every 50 meters (164 feet), and each one is only between 1.5 and 2m in length (5-6.5 feet). Therefore, it is necessary to screw a hexagonal extension onto them. First step is to attach the extension to the pile. Two people need to be in the water to hold it in place, as the extension is aligned and placed in the center of the pile, to screw in a bolt and connect them. Once joined together, we can begin drilling, which is quick but delicate (around 1 minute). While drilling, the counter-torque, current and waves, moves and displaces the barge which makes the process more difficult.
A diver is underwater to warn me when the pile is drilled in deep enough (so the upper hole sits just above the sand). When the correct depth is reached, the first step is to disconnect the extension from the hydraulic machine. Without this step, the bolt at the bottom of the water is still under pressure, and very difficult to remove. Once the machine is detached from the extension and the helical pile, two men then hold the extension, while the diver removes the bolt underwater. Once the pile and the extension are separated, we lift the extension onto the barge and reattach it to the EM1.
Meanwhile, underwater, the diver attaches a shackle to the pile (which serves as a hook point for the net) and a buoy (marking the location of the pile to avoid losing it).
Once everyone is on board, we head to the next location and do it all over again.
The project started at 9 am and ended at 3 pm and was considered a great success!