The use of helical anchors has been increasing in recent years; however, the current understanding of its behaviour does not allow for reliable estimates of uplift capacity and load–displacement response. The need for improvement of the design methods has motivated the present study, which investigates the effect of installation on the helical anchor response in very dense sand. This work is divided into three parts. The first part describes the results of centrifuge model tests and microtomographic analysis performed to examine the uplift response of a single-helix anchor and the soil disturbance caused by the installation process. The aim of these tests was to define appropriate hypotheses for the numerical prediction of helical anchor performance. In the second part, the load–displacement curve of a tested helical anchor was numerically simulated with the finite difference software FLAC3D, considering the installation effect observed experimentally. In the third part of the paper, the adjusted numerical model was used in a parametric analysis to provide some guidelines for the design of helical anchors in dense sand. Additionally, from the results of the numerical investigation and experimental observations, two different approaches are presented for improving the accuracy of analytical predictions of helical anchor capacity. Both suggested methods showed good agreement with centrifuge and field testing data.

Centrifuge modelling is an advantageous technique to simulate the behaviour of helical anchors in sand. The uplift capacity of a single-helix anchor is the sum of the helix bearing resistance plus the shaft resistance; therefore, recommendations to avoid the grain-size effect of previous model tests on plate anchors and on regular piles appear to be reasonable for helical anchor model tests. However, there are two important differences between centrifuge models of plate anchors and helical anchors: the ratio of the helical plate to the shaft diameter and the plate installation procedure. Consequently, the shaft friction and the plate bearing resistance of helical anchors can be affected by the scaling effect in a different manner. To clarify this uncertainty, this study was proposed to investigate the grain-size effect on the results of uplift capacity of helical anchor models in sand. Anchor models with different scales were tested to simulate the same prototype in very dense dry sand in a centrifuge. These experiments have shown that no scale effect was found for models with the ratio of the effective helical radius to the average grain size >58. The findings obtained here could guide future centrifuge model studies on helical anchors.

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.