Developing Failure Envelopes for Suction Caisson Foundations of Offshore Wind Turbines in Sand Using a Numerical Approach

The offshore wind industry is experiencing rapid growth worldwide, serving as an effective solution to counteract climate change induced by global warming. A fundamental component of this industry is offshore wind turbines, which play a pivotal role in converting wind energy into electricity, contributing to sustainable and clean energy. Today, modern foundations, such as suction caissons, play a very prominent role in reducing cost and installation time for offshore wind turbines. This article focuses on the bearing capacity analysis of caisson foundations utilized in offshore wind turbines situated in sandy soils under combined loading conditions. Additionally, the development of failure envelopes for these foundations is addressed. For this purpose, a novel numerical approach known as the "sequential swipe test" is employed to develop the failure envelopes. This method has been less commonly used in sandy soils so far. The failure envelopes are derived using a three-dimensional explicit elasto-plastic finite element method, taking into account the soil-foundation interaction. Then, the effects of dimensions and embedment ratios of the caisson foundations are investigated on the failure envelopes. The results reveal that as the embedment ratio increases from 0.5 to 1 and subsequently to 2, the normalized horizontal bearing capacity increases by 1.8 and 2.7 times, respectively. Similarly, for the normalized rotational bearing capacity, these values increase to 2 and 3.1, respectively. Afterward, analytical relationships for the development of failure envelopes are presented, offering accurate predictions of the bearing capacity of suction caisson foundations under combined loading conditions. Eventually, simplified algebraic expressions are proposed to enhance the efficiency and applicability of the introduced relationships in engineering problems and practical scenarios. These expressions quantify the parameters based on the embedment ratios of the caisson foundations, ranging from 0.5 to 2.