Influence of cyclic movement on the hardening process of grout: case of offshore wind turbine installation

Abstract

The foundation of offshore wind turbines in a rocky seabed is a major technical challenge for engineers. To insure the stability of the wind turbine, the ring between the steel monopile and the seabed is filled with a grout. The objective of this research is to point out the influence of early age movements and deformational restraints on the performance of the grouted connections. Another objective is to evaluate the performance of different grout materials by means of several experimental tests. A first experimental campaign is performed to characterize the behavior of the grout during hardening and to define the stress induced by the restraint of the free deformations. In a second campaign, the behavior of the grout under cyclic displacements since casting is studied. A Temperature Stress Testing Machine (TSTM) has been used to simulate the influence of cyclic horizontal movements by applying cyclic displacements and loadings since casting on samples designed with different grout materials. A segregation device was used to simulate the effect of the waves in the vertical direction. The results of both campaigns are then used to evaluate the risk of damage caused by the movement of the waves during the hardening of the grout. From these newly developed experimental tools, new indicators were developed in order to compare the performance of different grouts under cyclic displacement since casting.