The long-term disposal of high-level radioactive waste (HLW) in deep geological repositories requires the reliable performance of engineered barrier systems (EBS). Compacted bentonite, widely used for its high swelling capacity, low permeability, and self-sealing properties, plays a critical role in these barriers. However, understanding the complex coupled thermo-hydro-mechanical (THM) behavior governing water infiltration dynamics remains a significant challenge, especially when gap spaces (or technological voids) are present. This study investigates water infiltration dynamics in bentonite-based EBS using a novel laboratory-scale experimental setup. Time-lapse photography was employed to monitor the evolution of hydration and swelling under thermal gradients and varying gap sizes, simulating repository conditions. The experimental program was designed to compare the effects of two gap sizes on infiltration rates, swelling behavior, and desiccation cracking. Results demonstrated that larger void spaces accommodated greater swelling, leading to lower dry density and higher permeability, while smaller gaps restricted desiccation cracking due to mechanical constraints. The correlation between pixel intensity and water content allowed the derivation of a linear calibration model, enabling real-time, non-destructive estimation of moisture distribution in bentonite. Findings in this study highlight the interplay between gap size, water infiltration, and thermal effects, emphasizing the need for optimized EBS designs to balance mechanical integrity and hydraulic performance. It is anticipated that the insights provided by this study contribute to the refinement of predictive models and advancing the safe and effective containment of HLW over geological timescales.

This paper investigates the impact dynamics of pile-soil interactions, focusing on the mechanisms of kinetic energy dissipation within these systems during vehicular impacts. The study aimed to quantitatively evaluate the force-displacement and energy-displacement responses of piles embedded in crushed limestone material through dynamic bogie testing. A three-dimensional, large-deformation, nonlinear finite element model was developed to enhance the analysis. The computational model integrated a damage-based, elastoviscoplastic soil model with an elastoplastic steel pile model, incorporating strain rate effects. A continuum, damage-based element-erosion algorithm is also employed to accurately simulate large soil deformations, representing a significant advancement in simulation capabilities. The proposed model was validated against physical impact test data, demonstrating a strong correlation with measured force-displacement and energy-displacement results. This model was subsequently utilized to investigate the effects of impact velocity and soil strength on the energy dissipation capacity of pile-soil systems during lateral vehicular impacts. Additionally, this study critically examined the limitations of conventional simulation methods, such as the Updated Lagrangian Finite Element Method (UL-FEM), in capturing the dynamic pile-soil interactions and large soil deformations involved in laterally-impacted pile-soil systems. The research provided fundamental insights into the mechanics of dynamic soil-structure interactions under impact loading, contributing significantly to the geotechnical design and analysis of soil-embedded vehicle barrier systems.

Soil-embedded vehicle barriers, such as W-beam guardrail systems, play a pivotal role in transportation safety, mitigating the risks associated with vehicular collisions with roadside hazards. The efficacy of these barriers greatly depends on the pile-soil system's kinetic energy dissipation capability during vehicular impacts. However, a comprehensive understanding of how soil strength, embedment depth, and impact velocity collectively govern the dynamic behavior of the pile-soil system remains a gap in current research. This study explores the dynamics of lateral impacts on piles embedded in various granular soils. The process of dynamic lateral impact and interaction between the pile and the soil was modeled using the Updated Lagrangian Finite Element Method (UL-FEM). A damage-based element erosion algorithm was incorporated into the model to accommodate severe mesh distortions and element entanglements of the soil material brought by the pile impact. Validation against well-documented large-scale physical impact tests ascertained the model's fidelity. Our findings elucidate the significant differences in resistive forces between piles in strong versus weak granular soils - notably, the former exhibited resistive forces roughly double their weaker counterparts under equivalent embedment depths and varied impact velocities. Intriguingly, a stiff pile in weak soil necessitates nearly double the embedment depth to match the energy dissipation of its strong-soil counterpart. Furthermore, the study discerned consistent depth of rotation point ranges for piles embedded in distinct soil strengths, regardless of embedment depth and impact velocity.