Centrifuge modelling of a helical anchor under different cyclic loading conditions in sand

Abstract

Helical foundations used in transmission towers, wind turbines, solar panel systems and other similar structures must exhibit adequate performance under cyclic loading. Although a number of studies on the cyclic behaviour of helical anchors has increased, the available observations are still incomplete in terms of providing conclusive recommendations for practical applicability. To address this need, cyclic and monotonic axial tensile load tests were conducted on a single-helix model anchor in very dense dry sand in a centrifuge. The cyclic tests were carried out with different load amplitudes and with the number of cycles varying between 1000 and 3000. After the cyclic tests, the post-cyclic tensile capacity was evaluated by way of monotonic loading tests. Two different displacement regimes were observed during cycling, with a noticeable development of cumulative permanent displacements in the first approximately 100 cycles. In most of the tests, a stable cyclic response and a slight reduction in the post-cyclic capacity were observed. Additionally, the effect of the cyclic loading sequence was evaluated by way of two additional tests in which the cyclic loading was applied with different amplitudes in different orders. The results indicated that the order of the cyclic sequences influences the displacement response and the losses in the post-cyclic capacity.