Infrastructure damage attributed to strain-softening of clayey soils has been documented in many case histories involving seismic loading. For critical infrastructure projects, potential deformations due to seismic loading are increasingly being analyzed using numerical modeling approaches, such as nonlinear deformation analyses. These analyses rely on material models which can represent the aspects of soil behavior important to the problem being analyzed. This study examines the ability of the effective stress-based PM4Silt constitutive model to represent cyclic-softening in single element direct simple shear simulations and field scale simulations of the Fourth Avenue landslide. Guidance is provided regarding calibration of PM4Silt and the sensitivity of the solution to the input parameters is explored. The results using PM4Silt are then compared to a total stress-based constitutive model to understand how differences in constitutive model complexity affect the results at both the element scale and field scale. Mesh dependency of the solution using both models is explored with and without regularization approaches. PM4Silt is shown to reproduce the deformations observed at the Fourth Avenue Landslide. Effective stress-based constitutive models are found to be more appropriate than total stress-based models when element level response or a more complete estimation of deformations patterns, both inside and outside the failure mass, is required. Total stress-based models are found to be adequate if the user is primarily interested in whether failure will occur. Mesh dependency is observed in the PM4Silt model, but these effects are reduced by using a displacement-based calibration procedure.

The influence of water on the structure's dynamic response can be simulated by using added mass, which is generally derived for a cantilever fixed on a rigid base. However, because the embedded pile portion cannot fully restrain the extended part, the base of the extended pile may not be fixed, and the conventional added mass may be inappropriate. Therefore, this study conducts several analyses by using COMSOL finite element software to confirm the suitability of theoretical (rigid-base) hydrodynamic added mass in the flexible base condition. Comparing hydrodynamic added mass values between theoretical and numerical results reveals that errors primarily concentrated around peak values rather than uniformly across frequencies and that the peak error under the flexible-base condition occurs at a lower frequency. After evaluating the response envelope in time domain analyses with actual seismic data, it is confirmed that the hydrodynamic added mass model is generally reliable.

In this study, the Discrete Element Method (DEM) is employed to simulate earthquake-induced rockfalls by assigning displacement information to the slope. Under earthquake conditions, rockfall experiences two modes in the earthquakes, referred to as the rolling & sliding mode and the jumping mode. The categorization of these two modes is judged by the occurrence of jumping. Additionally, this study investigates the effects of the two parameters of the earthquake wave, frequency and amplitude, on rockfall movements by using three rock shapes in different roundness with assuming a sinusoidal earthquake wave. The findings reveal that the high frequency tends to facilitate a transition of rockfalls from the rolling & sliding mode to the jumping mode. With a comparison between the two modes in earthquake motion, it is found that the jumping mode has a significant effect on rockfall movements because for the rolling & sliding mode, the ratio of rockfall movements under earthquake and non-earthquake is in a range of 0.78~1.44 while for the jumping mode, it is in a range of 0.76~5.88. Finally, the 2016 Kumamoto earthquake is employed to have an evaluation of rockfalls with consideration of earthquake motion and material property variation.

In geotechnical design, it is often assumed that soil deforms in either a fully drained or undrained manner. However, in complex scenarios, evaluating a partially drained condition where volumetric changes and pore water pressures coexist becomes essential for a conservative design. Evidence from centrifuge tests in offshore systems suggests that drainage conditions are key to identify a critical design condition and to explain the deformation levels observed in liquefiable sites. This study investigates the effect of partial drainage conditions on the mechanical behavior of liquefiable sands using 3D DEM simulations. A set of virtual sand specimens is created by isotopically compressing representative samples of Toyoura sand with a specific interparticle friction value. The mechanical response of partially drained assemblies is simulated by applying a controlled volumetric strain condition to the DEM sample. The fully drained response is used to develop the strain control in the partially drained simulations. The coordination number and the deviatoric fabric are tracked along the stress path to examine the effect of drainage around the instability onset. Results indicate that partially drained shearing induces a controlled reduction in mean stresses and a contraction of the specimen in the early stages of shearing. Similar micromechanical features are observed between the partially drained and fully drained tests.

Initial static shear history has been shown to be a critical factor in the liquefaction behaviour of sand. This paper presents a comprehensive study of liquefaction behaviour of Toyoura sand under initial static shear by conducting multi direction dynamic cyclic simple shear(MDDCSS) tests and numerical simulations based on the discrete element method(DEM). These two methods are complementary to each other. The test results showed that the observed types of failure could be distinguished into flow liquefaction, cyclic mobility and residual deformation accumulation, and the types of failure are related to the initial relative density, initial static shear and cyclic shear stress amplitude. The typical failure mode of loose sand is flow liquefaction, while the medium-dense and dense sand are cyclic mobility and residual deformation accumulation. The effect of initial static shear will reduce the dynamic strength of Toyoura sand and have different effect on sand with different initial relative density. The dynamic strength of loose and medium-dense sand decreases with the increase of initial static shear. The dynamic strength of dense sand decreases first and then increases with the increase of initial static shear. In addition, for loose and medium-dense sand, the liquefaction resistance when the initial static shear is perpendicular to cyclic shear stress is greater than that in parallel. For dense sand, when the initial static shear ratio is less than 0.2, the liquefaction resistance when the initial static shear is perpendicular to cyclic shear stress is greater than that in parallel. Otherwise, the liquefaction resistance under the initial static shear perpendicular to the cyclic shear stress is less than that under parallel.

A novel graphical calibration technique for UBCSAND model parameters is presented and compared to: (1) a numerical approach based on minimization of residuals; and (2) an informed trial-and-error approach based on a rigorous analytical integration. Errors in the numerical integration of the model are identified and minimised by comparing the analytical solution against results from an Euler integration. Variations in the calibrated parameters are discussed for drained monotonic triaxial loading considering different types of aggregates.