Characterization of Soft Clays and the Response of Soil Foundation Systems for Offshore Applications

The overwhelming bulk of our population, about 4 billion people, are concentrated along or near a coastline (within 250 miles). It is recognized that a mix of energy sources will be required to meet mainstream energy needs of this growing coastal population and bring about the benefits of a diversified energy portfolio. The oceans are teeming with energy, whether it be the more established offshore oil and gas fields or the newer renewable sources such as tidal, wave and offshore wind. This dissertation focused on contributing to the field of offshore geotechnics in two ways: first, to aid in offshore site characterization by developing a framework for correlating soil strength with geophysical measurements for shallow sediments; and second, to study the ultimate capacity of caisson foundations subjected to loads typically encountered in offshore wind tower installations in water depths up to 30 m. The research project describes a laboratory testing program of CKoU triaxial tests along with bender element measurements carried out at Texas A&M University for correlation of soil strength with stiffness. A new framework for correlating stiffness and strength is proposed, based on void ratio and over consolidation ratio (OCR). Although site specific correlations between soil strength and various geophysical measurements is required, the formulation provides a convenient way of estimating both absolute value and trends of behavior at different void ratios and OCRs. This experimental program also allows for the investigation of the small strain response of soils at shallow depths which was previously unstudied. The project also describes a centrifuge testing program carried out at Rensselaer Polytechnic Institute. Model caisson foundations with aspect ratios of two were subjected to combined vertical, horizontal and moment loads usually experienced by offshore wind turbine foundations. This dissertation focuses on the ultimate capacity of the pile response to lateral load, to ensure the foundation has sufficient strength in an extreme loading event