The discrete element method (DEM) has emerged as an essential computational tool in geotechnical engineering for the simulation of granular materials, offering significant advantages over traditional continuum-based methods such as the finite element method (FEM) and the finite difference method (FDM). The DEM’s ability to model particle-level interactions, including contact forces, rotations, and particle breakage, allows for a more precise understanding of granular media behavior under various loading conditions. However, accurate DEM simulations require meticulous calibration of input parameters, such as particle density, stiffness, and friction, to effectively replicate real-world behavior. This study proposes a simplified calibration procedure, intended to be conducted prior to any granular material flow DEM modeling, based on three fundamental physical tests: bulk density, surface friction, and angle of repose. The ability of these tests, conducted on dry quartz sand, to accurately determine DEM micromechanical parameters, was validated through numerical simulation of cylinder tests with varying height-to-radius ratios. The results demonstrated that this calibration approach effectively reduced computational complexity while maintaining high accuracy, with validation errors of 0% to 12%. This research underscores the efficacy of simplified DEM calibration methods in enhancing the predictive reliability of simulations, particularly for sand modeling in geotechnical applications.

Dynamic compaction (DC) is vastly utilized to improve the strength characteristics of the soils. To predict the soil deformations derived from the DC operations, usually numerical simulation analysis is applied. For the conduction of such simulations, several numerical approaches with different elemental formulations can be used. From the perspective of finite element analysis (FEA), there are four main formulations including the Lagrangian, Arbitrary Lagrangian-Eulerian (ALE), Coupled Lagrangian-Eulerian (CEL), and Smoothed Particle Hydrodynamic (SPH). In this research, a comparative study has been conducted to evaluate the computational efficiency of those four approaches in the prediction of soil large deformations during the DC operations. To do this, for a DC operation executed in a road embankment construction project in China, the real field data was compared to the results obtained from the numerical simulations via the ABAQUS program. The findings demonstrate that of all those approaches, the Lagrangian approach delivers the minimum accuracy of the predicted results, albeit with the least running time. In contrast, the ALE formulation predicted closer estimations of soil deformations although it was found to be less time-efficient. Interestingly, the CEL and SPH approaches predicted the soil deformations with the maximum degree of accuracy whereas they were not as time-efficient as the Lagrangian approach. To address this issue, a hybrid model of Lagrangian and SPH formulations was constituted to satisfy the maximum accuracy with the minimum running time. Such a hybrid model is highly applicable for the accurate prediction of soil large deformations during the DC operations.

Missile impacts on underground structures pose significant safety concerns, necessitating thorough investigation to enhance the resilience and safety of such infrastructures. This study aims to evaluate the effects of missile impacts on underground structures by comparing the impact of rigid and deformable impactors using advanced simulation techniques. The simulation of 3D models of impact scenarios on underground structure was carried out using ANSYS/LSDYNA software. The simulations focused on assessing the differences in damage caused by rigid and deformable impactors. Due to the symmetry of the geometry and loading, a quarter of the model was simulated to reduce calculation time. Various material models were employed, including MAT_RHT for rock, MAT_CSCM_CONCRETE for concrete, and MAT_PLASTIC_KINEMATIC for rebars and impactors. Different contact algorithms and boundary conditions were applied to replicate real-world scenarios accurately. Our analysis revealed that employing a deformable impactor significantly reduces the damage to both the ground and the tunnel lining compared to a rigid impactor. Specifically, the velocities observed for rigid and deformable impactors were 91.8 and 65.7 m/s, respectively. Validation of the numerical model was achieved through comparison with experimental data on RC beams subjected to impact, demonstrating the model’s reliability in predicting impact responses. Our findings underscore the critical influence of impactor material behaviour on damage outcomes. The results advocate for the consideration of nonrigid materials in impact assessments for stiff structures, contributing to enhanced safety protocols and design strategies for underground infrastructure.

The direct shear test is a fundamental method in geotechnical engineering that provides crucial soil shear strength parameters, including cohesion (c) and the angle of internal friction (ϕ). These parameters play a pivotal role in structural design, slope stability assessment, and soil stability evaluation. However, achieving a uniform normal stress distribution within the shear box remains a challenging task, which can result in inaccuracies in test results. This study investigates the impact of shear box shape, specifically comparing circular and square configurations, on the outcomes of the direct shear test. The findings reveal that the choice of lower or upper box movement has a minimal effect on test results. Moreover, circular boxes demonstrate superior normal stress distribution, leading to reduced variations in comparison to square boxes. Wall friction effects lead to lower shear capacity measurements, with circular boxes yielding higher shear levels when contrasted with square boxes. Additionally, the soil along the sides and corners of the specimen experiences diminished shear stress due to reduced normal stress. This research contributes significantly to our comprehension of how shear box shape influences the determination of shear strength parameters in direct shear tests, ultimately enhancing the reliability of geotechnical engineering assessments.

The uncracked semi-circular bend (SCB) test has recently gained attention as a simple and material-efficient method for determining the tensile strength of brittle geomaterials. However, as reported in the literature and confirmed by our experiments, localized damage at the roller supports remains a critical limitation that may compromise measurement accuracy and test validity. This study addresses this limitation through experimental testing on red and gray sandstone, complemented by numerical simulations to provide deeper insight into stress distribution and fracture mechanisms in the SCB test. Experimental results showed that six out of twelve specimens experienced local damage, ranging from slight crushing and surficial cracking at the base roller zones in red sandstone to rock chipping in gray sandstone. The stiffer sandstone exhibited more severe local damage due to its limited deformability. These damages were attributed to minor geometric imperfections introduced during sample preparation. Nevertheless, all tests yielded valid tensile strength values, with SCB results showing good agreement with Brazilian test outcomes and demonstrating significantly lower coefficients of variation. Finite element simulations confirmed that crack initiation consistently occurred at the middle of the flat edge under pure tensile stress, indicating a mode I fracture mechanism. Numerical analyses further revealed pronounced stress concentrations, particularly compressive stresses, at the roller contact zones, induced by the specimen’s low span-to-depth ratio, which increased the fracture load required for failure.