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Evaluation of Design Methods for Shallow Foundations
Published in Chong Tang, Kok-Kwang Phoon, Model Uncertainties in Foundation Design, 2021
In offshore geotechnical engineering, shallow foundations also become an economic and sometimes the only practical solution as an alternative to pile foundations (Randolph and Gourvenec 2011). Historically, offshore shallow foundations either comprised large concrete gravity bases supporting large, fixed substructures or steel mudmats used as temporary support for piled jackets. Recently, offshore shallow foundations have become more diverse, including concrete or steel bucket foundations, as shown in Figure 4.1. Spudcans are a type of temporary shallow foundation used for mobile drilling rigs (commonly called jack-ups) that are presented separately in Chapter 5. Because of the increasing demand for oil and gas worldwide, design practice in offshore geotechnical engineering grew out of onshore practice, but two application areas tended to diverge over the last thirty years, driven partly by the scale of offshore foundation elements (that are typically much larger than those used onshore) and partly by fundamental differences in construction (or installation) techniques (e.g. Randolph et al. 2005; Houlsby 2016). Compared to onshore shallow foundations, offshore shallow foundations are usually required to withstand much larger horizontal loads and overturning moments. In the design of offshore shallow foundations, more attention is placed on the capacity in which the cyclic loading effect is critical (Andersen 2009, 2015).
Soil response
Published in White David, Cassidy Mark, Offshore Geotechnical Engineering, 2017
The significant feature of offshore geotechnical engineering is that offshore structures are subjected to severe wave and storm loads. Therefore, cyclic behaviour of soils supporting offshore structures is of the utmost importance to offshore geotechnical engineers. To design for repeated loading, it is necessary to account for the significantly different behaviour of soils loaded under cyclic or repeated stresses. Cyclic loading generates excess pore pressures, reducing effective stresses in the seabed and causing average and cyclic shear strains to develop with continued cycling, ultimately leading to a loss of shear strength or stiffness of the seabed sediments. No all-embracing constitutive model has been developed to date that captures all the key characteristics of soil response under cyclic loading and for practical purposes it is necessary to make use of simple approaches for estimating the cyclic behaviour of soils, relying on laboratory testing in order to determine the necessary soil parameters.
Modeling of large deformation problem considering spatially variable soils in offshore engineering
Published in Marine Georesources & Geotechnology, 2021
Jinhui Li, Wuzhang Luo, Yinghui Tian, Yuan Wang, Mark Jason Cassidy
Large deformation problems are common in offshore geotechnical engineering, such as penetration of penetrometers, installation of foundations (e.g., jack-up spudcan foundations, suction caissons, anchors) and even subsea landslides. This is further complicated due to the spatial variability of seabed soils, which is due to a combination of geologic, environmental and physical-chemical process (Dasaka and Zhang 2012; Ching and Phoon 2013). Very limited knowledge is known about the coupling of these two aspects, though each individual problem has been addressed by quite a few studies.