Bearing behaviour of shallow foundations for wind energy converters on sandy soils under cyclic eccentric loads

ABSTRACT For wind energy converters (WECs), the behaviour under cyclic loading is critical to the operation and lifetime, especially because the cyclic load is associated with eccentricity. In various geotechnical design standards, the eccentricity of shallow foundation for WECs is supposed to be limited. In the German geotechnical design standards, it is specifically required that no gapping shall occur under quasi-static eccentric load. This verification is often decisive in practical design and leads to potential over-dimensioning. The one possible favourable effect of limiting the gapping of WECs on non-cohesive subsoils is to limit the accumulation of permanent rotation under cyclic loads indirectly. In this article, the experimental results of cyclic rotation accumulation of shallow foundation on non-cohesive subsoils from literatures and own medium scale tests are discussed. It is shown that the gapping has no direct influence on the rotation accumulation rate, instead it is the load magnitude relative to the bearing capacity of foundation that is decisive to the cyclic rotation accumulation behaviour. Based on these observations, the verification ‘no gapping under quasi-static eccentric load case’ seems dispensable in the design of WEC shallow foundations on non-cohesive subsoils.