The cyclic response in saturated sand is gaining increasing interest owing to the soil-structure interaction in seismic regions. The evolution of the pore water pressure in liquefiable soil can significantly reduce soil strength and impact the structural dynamic response. This paper proposes a semi-analytical solution for a cylindrical cavity subjected to cyclic loading in saturated sands, incorporating an anisotropic, non-associated SANISAND model. The problem is formulated as a set of first-order partial differential equations (PDEs) by combining geometric equations, equilibrium equations, stress-strain relationships and boundary conditions. Due to the non-self-similar nature of this problem, these PDEs are solved by the hybrid Eulerian-Lagrangian approach to determine the cyclic response of the cavity. Then finite-element simulations with a user-defined subroutine are performed to validate the proposed solution. Finally, parametric studies are presented with the focus on soil parameters and cyclic loading history. It is found that the cyclic responses of the cavity in saturated sands are sensitive to the initial void ratio, and the at-rest coefficient of earth pressure primarily affects the monotonic response but marginally affects the cyclic response. Cylindrical cavities are more likely to liquefy when the sands are compacted in a loose state and under lower displacement amplitudes. The proposed solution has potential use for future research on the cyclic response of the soil-structure interaction in geotechnical engineering.

Assessing foundation response to cyclic loading is vital when designing transport infrastructure, such as road pavements and rail tracks, as well as offshore, port, and tall tower structures. While detailed guidance is available on characterizing many soil types' cyclic behavior, relatively few studies have been reported on stiff, geologically aged, plastic clays. This paper addresses this gap in knowledge by reporting cyclic loading experiments on three natural stiff UK clays that were deposited and buried between the Jurassic Age and Eocene Epoch before geological unloading to their currently heavily over-consolidated states. High-quality samples taken at relatively shallow depths were reconsolidated to nominally in situ K0 stresses in triaxial and hollow cylinder apparatus before imposing cyclic loading. The completely stable, metastable, or unstable outcomes invoked by different levels of undrained cyclic loading are interpreted within a kinematic yielding framework that is compatible with monotonic control experiments' outcomes. The cyclic limits marking the onset of significant changes in permanent strain accumulation, pore pressure development, and stress-strain hysteresis demonstrate that the weathered Gault clay offers the lowest cyclic resistance. The experiments show that energy considerations provide a promising way of evaluating undrained pore pressure generation and stiffness degradation. They also provide a basis for developing cyclic constitutive models and analysis procedures for cyclic foundation design in stiff, high-OCR, plastic clay strata.

During previous medium intensity earthquakes, several cantilevered retaining structures shoring waterfront areas experienced large deformations or even collapsed. This was in contrary to the caisson type quay walls which performed better even during the very strong 1995 Kobe earthquake. Within this realm, recent studies have highlighted that saturated backfill adjacent to retaining structures may not fully liquefy and has a strong potential for shear-induced dilation mechanics owing to the presence of substantial static shear. However, despite these negative excess pore pressures and absence of a full liquefaction state in the backfill, cantilevered retaining walls may still experience large deformations. In this paper, a deformation mechanism is proposed for an embedded cantilever retaining wall supporting a submerged backfill made of Ottawa F-65 sand using a geotechnical centrifuge experiment. The dynamic response of the soil-structure system was measured, and the intra-cyclic mechanics were investigated. The entire earthquake duration of 20 s was divided into three different phases. In phase I (comprising of initial 6 s), the retaining wall experienced sliding deformations owing to its inertia with negligible soil straining at the backfill. Under the application of subsequent seismic pulses in phase II, large suction drops in excess pore pressures were observed during the translation of the retaining wall toward the backfill, which caused the negative excess pore pressure to exceed the hydrostatic value. However, the temporary release of the suction drops during the deformation of the wall toward the seaside resulted in significant softening as soil crosses the phase-transformation line. This ultimately resulted in significant plasticization of the backfill, and the wall initiated a rotation type deformation mechanism with a pivot point located near its base. Intra-cyclic observations revealed an increase in the magnitude of the phase transition in excess pore pressures, which contributed to the increased accumulated soil straining along the backfill. Owing to this, the wall experienced increasing rotations with the application of subsequent cycles in phase II (until 14 s) until the passive resistance in front of the wall was fully mobilized. However, a sudden catastrophic collapse of the wall could be avoided owing to the re-dilation mechanism, during which the soil again underwent a phase transformation and generated negative excess pore pressures on the completion of the wall translation toward the seaside. With the reduction in the amplitude of the applied cycles toward the end of shaking (phase III), the effective stress path in front of the wall moved away from the origin, and the mobilized passive stress reduced, which eventually resulted in the retaining wall achieving a stable state with no additional deformations. The proposed deformation mechanism highlights that a state of full liquefaction is not a necessary prerequisite for an embedded cantilever retaining wall to experience significant deformations, and an understanding of suction mechanics during excess pore pressure generation is critical.

This paper reports numerical simulation and field test research on the horizontal static and cyclic loading performance of a single pile reinforced by cement-soil. 3D numerical models of soil-cement soil-concrete pile with various reinforcement sizes were established in ABAQUS. By comparing the effects of different cement-soil reinforcement widths and depths on bearing capacity and bending moments, a reinforcement width of 3 times of the pile diameter and a reinforcement depth of 1/4 of embedded depth are the optimal design parameters. On this basis, unidirectional and bidirectional cyclic loading tests were conducted on reinforced and unreinforced piles with a length of 40 m and a diameter of 1.6 m, respectively. The test results indicate that the critical horizontal load of reinforced pile increased by 40%, and the peak bending moment decreased by approximately 14.5% compared to unreinforced pile. This enhancement is attributed to the cement-soil around the pile, which increases the soil resistance and limits the horizontal displacement of the pile head. The cyclic hysteresis curve of reinforced piles is fuller than that of unreinforced piles, exhibiting a larger hysteresis area and a 74.5% increase in the initial stiffness of the pile head. Additionally, the cement-soil surrounding the pile mitigates the effects of cyclic weakening and plastic accumulation under cyclic loading.