SEGREGATION TEST OF THE OFF-SHORE WIND TURBINE JACKET FOUNDATIONS MADE BY FREE FALL POURING

Abstract

One of the major concern of wind farm offshore is the type of wind turbine foundation to be installed. When it comes to talk about offshore installation of pre-piled fixed jacket foundations (3-4 legs), one of the most critical activities to be performed by the installer is the grouting operation. For currently wind turbines size, are being installed on the new wind farms developments, pre-piling jacket installation is a very extended alternative used and we could be talking about piles with easily 30m length and between 2-3 m diameter which are drilled into the seabed until only 4-5 m come out the seabed line. Once piles have been installed into the seabed it comes the time to proceed with jacket legs installation. For this operation, heavy lift vessel is spready used due to dimension and weight of these structures and once structure has been guide-lifted over the sea level it starts coming down into the sea until it´s fixed into the already installed piles. Next step is to grouting-secured together both structures (pile and jacket) pouring grout, throughout the already pre-installed grouting lines into the lower part of the jacket leg, along the ring around between jacket leg and piles border as well as the gap between the stabbing cone (being the sharp shaped ending up of the jacket leg) and the ground (we´re usually talking about mm distance). Due to complexity of the overall manoeuvre as well as required precision not only for the grout system but for the right parameters should be considered for pouring in order to ensure the grout correctly into the pile/jacket annulus without segregation or other undesirable effects occurring a mock-up test was carried out. The proposed and analysed method defines a protocol that could be used and repeated for others offshore windfarms that are planned to be installed in the future over pre-pilled foundations. Running a grout wall test based on protocol described on this paper prior to offshore grout operations will guarantee mix of grout and lub is in line with grouting foundations requirements, saving pumping grout time and therefore vessel stand by costs as well as money savings for grout exceeds, avoiding segregation problems could lead up to in worst case to foundations removal with massive vessel standby costs for reparation of the entire installation foundation operation.