Geotechnics, Volume 4, Issue 3 (September 2024) – 4 articles

In this study, the effects of the grain size and gradation of riprap, the overtopping flow depth, and the downstream slope of the embankment on the scouring and deposition characteristics at the downstream toe of the embankment were investigated. For the experiment, three different downstream slopes (1:2, 1:3, and 1:4), three different overflow depths (1, 2, and 3 cm), and three different sizes of riprap particles (d₅₀ of 16.41 mm, 8.48 mm, and 3.39 mm, herein referred to as coarse gravel, medium gravel, and granule, respectively) were used in the laboratory. The experimental results demonstrated that the scour depth and deposition height increased with increasing energy head for each downstream slope condition. Among the three particle sizes, coarse gravel shows the lowest scour depth and the highest deposition height. For the 1:2 slope, the coarse gravel particle size was 62% and 75% less resistant to scouring than the medium gravel and granule particles, respectively. For the 1:3 slope case, this was 31% and 46%, and for the 1:4 slope case, this was 39% and 49% less than the medium gravel and granule size particles, respectively. Full article

This study presents a microscale framework for investigating the seismic stability of bridge-pier structures using the discrete element method (DEM), with a focus on rocking isolation mechanisms. The piers and the deck are modeled as rigid blocks that follow rigid body dynamics. The rigid block is modeled as a collection of glued particles with geometrical arrangement and physical properties that mimic an actual block. To facilitate numerical contact points between the base of the block and the flat base wall, smaller particle sizes were introduced at the base of the block. A Hertz contact model was employed to model the interaction between contacting entities for better estimation of the contact constitutive parameters. Validation was performed using well-documented experimental data featuring the free-rocking of a granite stone block as well as existing analytical techniques. DEM simulations were performed on single blocks as well as on a bridge deck-pier system subjected to dynamic and seismic loadings. The study shows the effectiveness of rocking isolation through a comparative analysis of acceleration and angular velocity under varying seismic intensities, with acceleration reduction up to 70% for piers and 60% for the deck in a high-intensity scenario, affirming the potential of rocking isolation as a viable seismic mitigation strategy. The study monitors the structural response, contact mechanics, and energy dissipation of the pier–deck system. The application of the DEM model advances the analysis of bridge pier and deck interactions under seismic loads, providing new insights into the detailed behavior of rocking bridge piers and their potential for seismic isolation. Full article

Artificial ground freezing (AGF) has emerged as a prominent treatment method due to its ability to mechanically strengthen the soil while reducing its permeability. However, its implementation has raised concerns about its impact, particularly with respect to frost heave and subsequent thaw-induced displacements. These soil movements can cause subsidence and pose a significant threat to the integrity of surface structures. Overburden pressure plays a crucial role in AGF and determines the amount of heave generated. This paper presents an analysis of the existing literature about soil freezing and thawing. The aim is to offer an understanding of these processes, specifically with regard to their application in AGF. This paper explains the behavior of soil during freezing, with particular emphasis on the influence of overburden pressure. It also investigates frozen soils’ thawing and freeze–thaw (FT) cycles’ long-term effects on soil properties. AGF offers improved soil strength and reduced water permeability, enhancing construction project stability. However, the interplay between the temperature, soil composition, and initial ground conditions during freezing is complex. This thermo-hydro-chemo-mechanical process strengthens the soil and reduces its permeability, but it can also induce frost heave due to water expansion and ice lens formation. Overburden pressure from the overlying soil limits ice lens growth. FT cycles significantly impact soil properties. In fine-grained soils, FT cycles can lead to over-consolidation, while rapid thawing can generate high pore pressures and compromise stability. Importantly, FT acts as a weathering mechanism, influencing soil properties at both the microscopic and macroscopic scales. These cycles can loosen over-consolidated soil, densify normally consolidated soil, and increase overall hydraulic conductivity due to structural changes. They can also weaken the soil’s structure and deteriorate its mechanical performance. Full article

In precedent years mostly, though rarely nowadays, shear deformable structures were constructed across the globe. Also, the soil is deformed as a shear cantilever, which means that the shear forces and stresses are more prominent than the respective normal forces and stresses; thus, the dynamic soil–structure interaction of shear deformable bodies is an important aspect to be researched. In this article, the dynamic soil–structure interaction of shear deformable structures is investigated through nonlinear finite element modelling. The goal of this work is to enlighten the qualitative response of both soil and structures, as well as the differences between the sole structure and the soil–structure system. The Athens 1999 earthquake accelerogram is used, which is considered as a palm load (which means a load that is not periodic like the Ricker wavelets), in order to enlighten the importance of the investigation of palm loading. It is demonstrated that the total displacements of the soil–structure system are larger than the case of the sole structure, as expected when taking into account the dynamic soil–structure interaction. However, the residual displacements of the top are larger when a moderate soil thickness is assumed. Moreover, the output acceleration functions over time, comparing the same buildings as the sole building and as the soil-building system, have the same time function, but they are amplified with a constant value. As a consequence, the critical time of the maximum energy flux that is transmitted to the building is not dependent on the dynamic soil–structure interaction. Full article