Estimation of horizontal bearing capacity of mat foundation on structured and over-consolidated clays under cyclic wave loads

Abstract

Bottom-supported platform with mat foundations is considered as a cost-effective option for offshore wind power installations due to its rapid installation and extraction period. However, the contact interface between mat foundation and soft seabed may undergo softening due to cyclic wave loads in operation, leading to bearing capacity losses especially in horizontal direction. In this study, the behavior of mat foundation on clay seabed under cyclic wave loads is investigated and the weakening effect on bearing capacity is presented. A unified elastoplastic constitutive model is adopted to consider the soil structure and over-consolidation in natural clay. Responses of excess pore water pressure, effective stress and horizontal bearing capacity for clays with various degrees of clay structures and over-consolidation ratios (OCR) are studied. Effects of wave frequencies and amplitudes on weakening effect of the interface are presented and discussed. Results indicate that the degrees of weakening effects of the normalized horizontal bearing capacity decrease with the increase of the degree of clays structure and OCR value. The clays structure is not easily damaged under the action of cyclic wave loads. The clay's over-consolidation state can be easily dissipated and transformed into normally consolidated clays under the action of wave loads with frequency equal to 0.4/s. The horizontal bearing capacity is basically consistent with the evolution tendency of the vertical effective stress at the interface of mat foundation and clay seabed, and it can be considered that the weakening effect of the horizontal bearing capacity is controlled by the interface.