Monitoring of wind turbine soil foundations improved by rigid columns
Elisabeth Haza-Rozier1, Gratien Vinceslas1, Alain Le Kouby
2, Olivier Crochemore3, Delphine Jacqueline1
1CEREMA Normandie Centre, Rouen, France, 2IFSTTAR, Paris, France, 3Futuren, Paris, France
Within the the French National Research Project SOLCYP (Pile under cyclic cyclic loading), the foundations of a wind turbine were instrumented. The foundation principle is such that wind turbine is fixed to a rigid slab lying on a granular layer that allows stress distribution on in situ subgrade improved by 84 rigid columns.
Sensors were placed on wind turbine edge essentially, in areas supporting highest stresses variations. Vertical displacements and total stress sensors at the head of columns, on the granular layer under the slab and on soil were measured. Moreover, vibrating wire extensometers are positioned in two columns in order to measure load distribution. The behaviour of the structure has been monitored since excavation stage, till machine construction, and then during service working of the turbine wind until now.
Working platform induced an important confinement of columns’heads. Pressures are concentred on edge, displacement are still small.
The effect of wind speed on load distribution has been shown to be significant. Additional wind turbine foundations monitoring are still required in different types of soils.
Some of the objectives of the foundation monitoring were to get the ratio load applied / bearing capacity of the column and the type of load cycles that were applied to the rigid columns during wind turbine foundation service life.