Journal of Geotechnical and Geoenvironmental Engineering

Diving upon pullout of an installed anchor leads to an increase in embedment depth and, hence, capacity under operational loadings. It is particularly critical for dynamically installed anchors (DIAs) in calcareous sediments where the embedment depth is generally relatively shallow. This paper proposes a novel fish DIA featuring an elliptically shaped shaft, which reduces hydrodynamic drag resistance. Every cross section of the anchor shaft is elliptical, and the widest part is in the middle. The shaft is shaped to be thicker near the head to lower the mass centroid and increase its diving potential. The padeye is fitted perpendicularly to the wider part of the shaft, so that the maximum resistance area can be mobilized during pullout loading. The dynamic installation and monotonic pullout performance of the fish DIA in calcareous silt were assessed through a series of beam centrifuge tests at 133.3 times Earth’s gravity, varying the drop height (hence the impact velocity), reconsolidation period after installation and load inclination angle at the mudline. The anchor tip embedment depths of 1.02–1.42 times the anchor length lay in the range for OMNI-Max and torpedo DIAs in calcareous silt. A dimensionless embedment depth–based model, total energy–based models, and a conventional shear resistance model were found to be adequate for the prediction of embedment depths. The tracked anchor trajectory confirmed that the fish DIA dove under inclined mudline loading (${\theta }_0<45°$), as opposed to being pulled out for torpedo and OMNI-Max DIAs. The normalized vertical and horizontal holding capacities of the fish DIA were respectively 4.0 and 5.6 times those of a four-fin torpedo DIA.

To investigate the volumetric creep behavior of engineered sand containing nonplastic silt, a series of creep tests was performed under various stress conditions and initial void ratios. It was found that contractive or dilative volumetric creep behavior was determined by a specific combination of the void ratio ($e_c$) and the mean normal effective stress ($p_c^{\prime }$) at the beginning of creep. Based on the experimental results, the range for which no volumetric change occurs during creep was determined, and this group of specific combinations of $e_c$ and $p_c^{\prime }$ was defined as the zero-creep volume change zone (ZCVZ). The contractive or dilative volume change pattern during creep can be predicted by the positions of $e_c$ and $p_c^{\prime }$ relative to the ZCVZ on the $e-\log p^{\prime }$ plane. The creep mechanism of the observed volumetric behavior was explained by adopting the microscopic mechanisms of dislocation slip and the recovery process in the creep of metals.

The liquefaction resistance of postliquefaction sand is time-dependent and still largely unknown. In this paper, the time-dependent liquefaction resistance of a postliquefaction sand deposit is studied using 1-g shake table experimental modeling and piezocone penetration testing (CPTu). A uniform liquefiable sand deposit was air-pluviated and fully saturated in a large laminar shear box ($\mathrm{L}\times \mathrm{W}\times \mathrm{H}\text{:}2.29\times 2.13\times 1.83\mathrm{m}$). The sand deposit was subjected to a shaking event in the laminar shear box. Piezometers were embedded at different depths to capture the seismic response of liquefied sand. The measured excess pore pressures were used to verify the occurrence of liquefaction. A series of CPTu tests were conducted to measure the cone penetration resistance, friction resistance, and pore water pressure throughout the depth of the sand deposit prior to shaking and at different elapsed times following the shaking. To capture the sand aging effect after liquefaction, CPTu tests were done at different locations over a total elapsed time of 135 days. This research found that the cone penetration resistance of the sand deposit decreased significantly immediately after liquefaction compared with that before liquefaction. The cone penetration resistance of the postliquefaction sand deposit increased with time; a relationship between cone penetration resistance and time at different effective stresses is proposed. This research suggests that even a short period of time might have a significant effect on soil properties; aging time between earthquake and field tests cannot be neglected and should be documented for better data interpretation.

This technical note used the random finite-element method (RFEM) to investigate the influence of soil strength variability on the limit load of a shallow passive trapdoor embedded in cohesive soil. The mean undrained shear strength was held constant while the coefficient of variation and spatial correlation length were varied systematically. For trapdoors against soils with low values of the coefficient of variation, the mean limit load agreed well with the results from a uniform deterministic analysis. For higher values of the coefficient of variation, the mean limit load decreased. By interpreting the Monte Carlo simulations in a probabilistic context, the probability of failure was assessed as a function of the factor of safety based on the mean and the spatial variability of the soil. It was found, for example, that a factor of safety of 2.5 is required to avoid the probability of failure exceeding 5% for soils with strength variability within typical ranges.