Whole life geotechnical design is an emerging philosophy in offshore geotechnical engineering to improve design outcomes by considering the whole life of imposed actions coupled with geotechnical properties that evolve with each action. Softening of normally consolidated clays from undrained cyclic loading intervened with consolidation has been shown to lead to hardening, manifested by evolving strength, stiffness, and coefficient of consolidation. This paper presents results from a set of stress-controlled direct simple shear (DSS) tests. The tests follow pre-failure episodic cyclic loading stress paths where each episode comprises a packet of undrained cycles of loads followed by full consolidation. The soil response under different numbers of cycles per loading packet and number of loading packets with intervening consolidation is investigated. The results from this study quantify the effect of the undrained cyclic loading history, for the same final number of cycles, on the evolution of the soil properties, to support the application of whole life geotechnical design in practice. Outcomes allow calibration of design curves that are traditionally used to capture softening, by introducing consolidation effects. This enables capturing the whole life softening and hardening processes, by extending the traditional contour diagram representation for undrained cyclic loading without consolidation to allow for consolidation periods.
The global offshore energy industry is going through a significant period of transition aiming to net zero greenhouse gas emissions in the coming few decades, where renewable energy is expected to be one of the fastest-growing energy sources globally in this domain (IEA, 2021). In line with the Paris agreement for climate neutral energy or energy with no greenhouse gas emissions in the coming 30 years, investments and technologies are needed to decarbonize the energy system. East Asia is responsible for 34% of the global energy-related emissions, where 53% reduction in carbon emissions is planned by 2050 through the transition towards renewable energies (IRENA, 2019). Asia's share of the global offshore market is expected to grow from 24 % in 2019 to 42% in 2025 (Reglobal, 2020). In addition, Europe is aiming to increase its offshore capacity from wind and other ocean energy (e.g., wave and tidal) to at least 340 GW by 2050, i.e., multiplying the capacity for offshore renewable energy by nearly 30 times (EC, 2020). In parallel, the UK is aiming to quadruple the amount of offshore wind generated to 40 GW by 2030 and to 100 GW or more by 2050 (CCC, 2020). Fig. 1 presents the global growth of the offshore wind market over the next decade where Asia is expected to double its share by 2030 although Europe is still expected to remain as the largest regional offshore wind market. The transition towards a clean decarbonized energy future is underway. To cope with the rapid development the world is witnessing, offshore industries are aiming for advancement of efficient offshore renewable energy structures through increasing the capacity and efficiency of designs.