Model Tests on Influence Factors on the Pullout Behavior of Suction Caisson in Stratified Soils

As offshore wind power constructions expand into deep waters, suction caissons have gradually become the preferred foundation. The controlled load of the suction caisson for the deep‐water wind turbine is the pullout load. A series of experimental tests have been conducted focusing on various factors influencing the pullout bearing capacity, including the stratified soil type, pullout rate, and loading frequency. Results indicated a significant impact of stratified soil types on the pullout bearing capacity. In the clay‐over‐sand stratified soil type, the pullout bearing capacities are found to be 425%, 155%, 283%, and 377% relative to those in pure sand, sandwich soil, sand‐over‐clay, and pure clay under monotonic pullout loadings. When the suction caissons are installed in stratified soils, increases in pullout rates are observed to enhance both the bearing capacity and the associated passive suction and displacement until the pullout bearing capacity is achieved. Low‐frequency cyclic loading induces greater accumulative displacement than high‐frequency cyclic loading. Mechanism of cyclic loading reducing the pullout capacity is detected by a Perspex model. Both pullout bearing capacity and passive suction are more substantially reduced after cyclic loading at high pullout rates. Considering the effect of stratified soil, modified equations are proposed to obtain the friction forces and reverse end bearing capacity. The research results are useful for further elucidating the mechanism of suction caisson in stratified soils to guide the engineering practice.