Whole-life geotechnical design accounts for the evolution of geotechnical properties due to the actions imparted on the infrastructure during the design life to improve design outcomes. In fine-grained soils, geotechnical properties evolve as a result of cyclic softening from excess pore pressure generation under undrained cyclic loading, and hardening during subsequent dissipation. Traditionally geotechnical design has focused on reduced strength and stiffness from softening, overlooking beneficial effects of hardening leading to increases in strength and stiffness. This paper presents a surrogate model that can capture the evolution of geotechnical properties of normally and lightly over consolidated clays through episodes of undrained pre-failure cyclic loading with intervening consolidation, validated against laboratory element test results. The surrogate model is shown to capture the essential elements of the whole-life soil-structure interaction, which include: (i) the excess pore pressure generated during undrained cyclic loading and the associated soil softening; (ii) the reduction in void ratio caused by the dissipation of excess pore pressured during the consolidation process; and (iii) the evolution of undrained shear strength and stiffness through these processes. The surrogate model allows rapid estimation of evolving soil properties in design, enabling automated optimization of geotechnical design calculations (such as required size of foundations or anchors), and use in probabilistic analyses such as Monte Carlo approaches, to quantify the influence of uncertainty in loading history and geotechnical parameters on system reliability.

The dynamic stability of offshore foundations in the marine environment is one of the major technical challenges. Millions of loading cycles from waves and winds act on the foundations and seabed in their entire service life. The mixing of adjacent soil layers due to naturally occurring sediment or the construction process raises more difficulties in the design. Previous studies have focused on the dynamic constitutive relations of idealized clean sand or clay under cyclic loading, while the cyclic characteristics of sand-clay mixtures are still unclear. In this study, the dynamic responses of sand-clay mixtures under a large number of shear cycles were investigated through 25 constant-volume cyclic direct simple shear tests on sand-clay mixtures with sand contents of 0 %, 25 %, 50 %, and 75 %. The results indicate that high sand contents and high cyclic stress ratios accelerate the reduction of effective stress in sand-clay mixtures, resulting in a more rapid increase in shear strain. As the sand content increases from 0 % to 75 %, the normalized shear modulus decreases by 35.9 % at a shear strain of 1 %. In contrast, the normalized dynamic shear strength is reduced from between 0.490 and 0.525 to between 0.181 and 0.325 after over 5000 loading cycles.

The paper studies the effect of soil strength and stiffness degradation on the undrained cyclic performance of offshore foundations in low-plasticity cohesive soil using 3D finite element modelling. Cyclic triaxial tests on reconstituted kaolin are conducted at the ETH Zurich laboratory, providing insights into key parameters affecting the degradation process. A simplified soil constitutive model accounting for cyclic degradation is developed and encoded in Abaqus via a user subroutine. The model is calibrated against experimental results and validated with published centrifuge model tests of monopiles under cyclic lateral loading. It is subsequently used to evaluate the performance of suction caisson foundations with different aspect ratios (L/D = 0.5 and 2) under short-term cyclic and seismic loading. Due to its ductile resistance mechanism, the L/D = 0.5 caisson exhibits superior perfor-mance under vertical cyclic loading in fast-degrading soil. Under inclined cyclic loading, the slower degradation rate of the L/D = 2 caisson governs response, reversing the trend. Under seismic shaking, the degradation-induced resistance imbalance amplifies the irrecoverable settlements produced by kinematic shearing at the caisson sidewalls. For the fast-degrading soil examined, degradation is shown to increase settlements by up to 50%.

Vibratory penetration was successfully used to install 120 integral thin-walled steel cylinders 22 m in diameter in the Hong Kong-Zhuhai-Macao Bridge. However, the eight-hammer group was found overpowered at the western island and underpowered at the eastern site due to insufficient understanding of the mechanisms of vibratory piling. In this study, energy analysis was conducted to reveal the energy characteristics of vibratory penetration, including the periodical energy superposition along the cylinder shaft, the continuous energy consumption in the soil, and the dynamic equilibrium of the total energy. The influences of vibratory soil resistance and loading frequency on the energy distributions have been thoroughly discussed. In contrast to the notion that larger input energy leads to a faster penetration, it is revealed that the vibratory penetration velocity positively correlates to the energy stored in the cylinder, the ratio of kinetic to strain energy, and the characteristic frequencies of the soil-pile system. The actual output power of the vibratory motors is influenced by the vibratory force, the ultimate soil resistance, and the soil mobilization degree. The vibration frequency is optimized as 31.1 Hz for Cylinder E9 and 15 Hz for Cylinder W36 to ensure efficiency and safety.