This study conducts laboratory element tests to understand the dynamic response of gap-graded materials, mixtures of finer and coarser soil grains, that are used as a filter material in geo-hydro structures. Mixtures of coarse silica sand and three sizes of finer silica sands, having fine silica sand contents of 0%, 10%, 20%, 30%, 40%, 50% and 100%, have been tested to measure elastic wave properties. The results revealed that elastic wave velocities are influenced by void ratio and fine sand content, while the effect is greatly pronounced when a larger size ratio of gap-graded silica sand is concerned.
Triaxial monotonic compression experiments were conducted to study the influence of particle shape on the mechanical behaviours using four different shapes of glass beads. Meanwhile, elastic wave measurements were performed throughout the whole loading process. To ensure the particle shape is the only related factor that can affect the mechanical responses of granular materials, the initial packing densities were adjusted to give a similar relative density of around 100%. Stress responses and deformation characteristics of the tested granular materials are discussed, and then the variations of compression (P-) wave and shear (S-) wave velocities are analysed in this contribution.
Subsurface cavities potentially cause a catastrophic consequence, such as road cave-in. As a countermeasure, groundpenetrating radar method has been used to find subsurface cavities in shallow ground, whereas no established method is available to detect a cavity in deep ground. To understand micromechanics of wave propagation around a cavity, discrete element method (DEM) simulations were performed. The DEM analyses revealed that P-waves propagate faster along soil arching, whereas S-wave velocity is less sensitive to soil arching. Overall, both P- and S-wave velocities decreased due to loosening of soil where number of contacts per particle dropped in the vicinity of the cavity.
Suffusion is characterised as seepage induced loss of fine particles with no change in volume and an increase of hydraulic conductivity. The degree of migration of fine particles can affect both micro and macro structural behaviour of soil. This paper analyses the impacts of suffusion on the mechanical properties of widely graded volcanic soil with different relative densities in triaxial compression. It was observed that effects on the undrained mechanical behaviour of the soil were also dependent on the initial density of the specimen, with changes in the small strain stiffness, stress-strain relationship and soil dilatancy.
In this study, the seismic hazard was evaluated by focusing to the amplification characteristics of surface ground for the areas without ground and seismic data. In overseas, there are some areas having a high earthquake risk, but various data including ground survey results are not accumulated and ground risk is often not properly evaluated. The purpose of this study is to evaluate the amplification factor of surface ground in one of them, Yangon city where urban development is progressing recently. As the result, we established a method to evaluate the amplification factor by combining several estimation methods. This study can be considered useful to raise the awareness of earthquake risk assessment.
Underground spaces is thought to be exposed to less seismic impact than buildings constructed on the ground. Therefore, if the disadvantages against flood can be overcome, we can utilize the underground spaces as almighty shelter. When the new application of existing underground space to emergency shelter is considered, water inflow into large scale model should be carefully evaluated. In this report, fundamental theory of MPS method with polygon boundary is reviewed. A difficulty of modeling and its easy solution is proposed with a numerical example.
The 2018 Sulawesi earthquake caused massive ground flow in several areas in Palu city. In this study, the relationship between the input ground motion level and the behavior of surface soil in no flow area is evaluated by numerical approach. The ground was modeled with parameters as standard values on geological engineering or empirical relationship. As a result, there is no specific characteristic in the seismic behavior of the surface ground, and that the large-scale flow is caused by a combination of other causes in addition to the seismic behavior of the ground. In the future, plan to collect more data to elucidate the mechanism of large-scale flow.
Liquefaction of Pleistocene sand has been out of the scope of conventional liquefaction assessment, but it has been recently discussed more in practical field. This paper focuses on cementation, which is the main characteristic of Pleistocene sand, and consolidation and undrained cyclic loading were applied on artificially cemented specimens with measurement of shear wave velocity. As a result, the change in shear wave velocity during consolidation was less dependent on void ratio at non-cemented specimen than at cemented specimen. Increasing cementation content delayed the development of strain during undrained cyclic loading and resulted in transition to tougher failure mode.
Numerical simulations were carried out as a fundamental study on large strain liquefaction behavior based on the results of previous large-strain liquefaction tests up to γsa=60%. As a result, it was not possible to simulate the results of the previous large-strain liquefaction tests by using a parameter of initial φf. However, it was successful in simulating the large-strain behavior by using an observed φf after the strain localization in the experiments. Future issues include the development of a method to evaluate the continuous decrease in the φf due to accumulated cyclic shear strain during the liquefaction process, confirmation of the rate of decrease in the φf for various materials, and applicability of the method to two-dimensional FEM analysis.