Centrifuge investigation of the cyclic loading effect on the post-cyclic monotonic performance of a single-helix anchor in sand

Screw anchor application includes supporting structures subjected to cyclic loadings, as in the case of guyed towers. In the design of transmission line tower foundations in Brazil, most calculations are based on the limiting loading condition caused by an extreme environmental monotonic loading, and, therefore, the effects of cyclic loadings on the anchor response are disregarded. In this context, centrifuge tests were carried out to evaluate cyclic and post-cyclic responses of a single-helix anchor prototype in very dense sand. The centrifuge modelling used two single-helix anchor models (one instrumented with a load cell). A sequence of up to 2000 tensile loading cycles followed by a monotonic uplift loading was performed in each test. Noticeable displacement accumulation occurred in the first 10-500 cycles depending on the loading amplitude. In the postcyclic phase, some tests exhibited up to 9% of uplift capacity degradation although other tests exhibited up to 5% of capacity increase.