Physical modeling is an efficient method to simulate practical geotechnical problems and to provide insights into soil behavior. This study used geotechnical centrifuge models equipped with motorized pulling systems to pull coupons (thin metal plates) at constant speeds horizontally through clean, saturated sand models that were liquefied by cyclic loading. The model setup was aimed to mimic shearing mechanisms, large shear strains, and large strain rates observed in field-scale flow slides. In-flight cone penetration testing and bender element-based shear wave velocity measurements helped in characterizing soil state at coupon levels before liquefaction. In addition, a miniature pressure transducer was embedded in the coupon along its top horizontal surface to directly measure pore pressure response on the shear surface within the liquefied soil. In total, 11 coupon pulls were completed, with 6 of the 11 tests providing shear-induced pore pressure measurements at the coupon surface. Measured coupon pulling forces and pore pressure responses at shear-surface and free-field were interpreted to identify key behaviors. These key behaviors illustrated that relatively low coupon velocities were required to maintain liquefied conditions at the coupon surface. In addition, pulling force recovery during pore pressure dissipation appeared to be related to coupon velocity (i.e. strain rate).

In order to estimate accumulated excess pore pressures in the soil around a cyclically loaded (offshore) foundation structure, cyclic laboratory tests are required. In practice, the cyclic direct simple shear (DSS) test is often used. From numerous undrained tests (or alternatively tests under constant-volume condition) under varying stress conditions, contour diagrams can be derived, which characterize the soil's behavior under arbitrary cyclic loading conditions. Such contour diagrams can then be used as input for finite element models predicting the load-bearing behavior of foundation structures under undrained or partially drained cyclic loading. The paper deals with the general behavior of a poorly graded medium sand in cyclic DSS tests under undrained loading conditions. The main objective of the research was to investigate and parametrize the soil's behavior and to identify possible effects of sample preparation. Numerous tests with varying cyclic stress ratios (CSR) and mean stress ratios (MSR) have been conducted. Also the relative density of the sand was varied. A new set of equations for a relatively easy handable mathematical description of the resulting contour plots was developed and parametrized. In the original tests, the sand was poured into the testing frame and carefully compacted to the desired relative density by tamping. In offshore practice, a preconditioning of a soil sample is usually realised by cyclic preshearing with a certain CSR-value or additionally by preconsolidation under drained conditions. By that, a more realistic initial state of the soil shall be achieved. In order to investigate the effect of such a preconditioning on the resulting contour diagrams, additional tests were conducted in which preshearing and preconsolidation was applied and the results were compared to the test results without any preconditioning. The results clearly show a significant effect of preshearing and an even more pronounced effect of preconsolidation for the considered poorly graded medium sand.

The interface resistance during installation is crucial for the stability and safety of suction caisson in offshore geotechnical engineering, which is strongly affected by the penetration rate and soil-structure interface mechanical properties. This research conducts a series of clay-structure interface shear tests using modified direct simple shear device to fully study the mechanical behavior of clay-suction caisson interface. The effect of shear rate, over consolidation ratios (OCRs), interface boundary conditions, stress levels, and interface roughness were considered. Results show that as the OCR increases, the strength of both the clay and interface increase but show distinct patterns under constant volume (CV) and constant normal load (CNL) boundary condition. It was found that the interface strength is positively related to interface roughness and shear rate impact both the clay and corresponding interface strength. Under CNL conditions, the strength of normally consolidated (NC) clay decreases with rising shear rate, while the over consolidated (OC) clay demonstrate a opposite trend. In contrast, the effect of shear rate on interface behavior gets complicated owing to the combination of roughness, stress levels, and OCRs. Under CV conditions, the shear strength of clay and interface exhibits a logarithmic growth relationship with shear rates. The result of this work can provide a basis for interface resistance evaluation for suction caisson installation in clay.

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.

Plate anchors have become an attractive technology for anchoring offshore floating facilities such as floating renewable energy devices because they provide high holding capacity relative to their dry weight. This allows for the use of smaller anchors (relative to a driven or suction-installed pile), which provide cost savings on production, transport, and installation. Loads delivered to the anchor via mooring lines may increase pore water pressure in fine-grained soils. This excess pore pressure will dissipate with time, resulting in a local increase in the undrained shear strength of the soil surrounding the anchor, increasing the capacity. There may be opportunities to consider these capacity increases if the consolidation process occurs over time periods that are short relative to the lifetime of the facility. This paper considers the use of drainage channels in a plate to make the anchor permeable and quicken consolidation times. Experimental data generated from model-scale experiments conducted in a geotechnical centrifuge show (for the anchor design tested) that excess pore pressure just above the anchor dissipated almost an order of magnitude faster for a permeable anchor, and that after full consolidation, the permeable anchor capacity was higher. The latter finding was not anticipated and is believed to be due to changes in load distribution resulting from the rapid reduction in negative excess pore pressure underneath the permeable anchor.

In the context of offshore structure design, the consideration of earthquake and wave loadings is paramount due to their pivotal role as natural dynamic forces. These dynamic forces can induce vibrations in the pore water pressure, thereby precipitating seabed instability. However, the investigations of the earthquake-induced seabed behaviour are limited. Furthermore, contemporary studies on seismic seabed response often neglect the concurrent impact of ocean waves. Previous research predominantly relies on conventional mesh-based methods, such as the finite element method. To address the limitations inherent in such methods, such as computational time and mathematical complexity, this study employs a meshfree method based on the u - p approximation. The research assesses soil response under the Japan 311 earthquake and random wave loading in both time and frequency domains. Numerical findings indicate that earthquake-induced acceleration is notably amplified by the seabed foundation, particularly in the horizontal direction. The presence of wave loading significantly alters the development of pore pressure, yet it exerts no discernible impact on earthquake-induced acceleration in the seabed. Consequently, the contribution of random waves to seismic-induced seabed response analysis cannot be disregarded.