Performance and consolidation-induced capacity improvements of dynamically installed anchors under sustained loading in clay
摘要
Anchors used in offshore floating systems may experience extreme loading events that cause significant movement and even failure. However, over the normal operating period dissipation of the excess pore pressure occurs, leading to a regain in soil strength and hence anchor capacity. The potential improvement in anchor stability due to the reconsolidation effect is often overlooked, especially in the design of dynamically installed anchors (DIAs). This paper considers the performance of a newly developed DIA under different sustained loading levels and the magnitude of this anchor capacity regain through a series of laboratory model tests, including self-weight consolidation and sustained loading tests. Test results show that the anchor capacity regain after installation is a hyperbolic function of self-weight consolidation time, and the uplift capacity increases by up to 51% compared with the unconsolidated capacity. The critical sustained loading level to avoid anchor failure is ~ 0.65Fu,m (Fu,m is the ultimate monotonic uplift capacity) under vertical loading and is ~ 0.80Fu,m for the anchor with flaps under 45° inclined loading. During sustained loading below these thresholds, the anchor capacity increases due to consolidation and hence improves the anchor stability. The maximum increase in post-sustained loading capacity relative to the monotonic capacity is 45%. Multi-amplitude sustained loading tests find that the extra capacity gain acquired in the small-amplitude sustained loading stage can be “banked” in the design, allowing the anchor to bear higher-level loads.