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The minimum and maximum void ratios (emin and emax, respectively) of soils are intrinsic soil properties related to their particle size distribution (PSD) and particle shape. Different attempts have been made to predict these reference void ratios for cohesionless soils through the involved particle morphology. However, these predictive models do not handle flaky and elongated particles. Besides, these kinds of models just consider the particle shape throughout a two-dimensional analysis. In this current study, experimental work has been carried out on particles with five different geological and morphological properties and nine different gradations. The particle shape effect involves glass beads, rounded, angular, flaky, and elongated particles to expand both the range of particle sphericity and roundness. A wide range of particle sizes, including uniformly distributed, widely distributed, and upward concave graded soils were chosen. Particle sphericity and roundness were measured by micro CT images and image processing. Furthermore, a comprehensive database was gathered based on past experimental results from the literature. This database was used to derive the predictive equations for determining emin,emax, and the void ratio range (emax-emin), considering sphericity, roundness, and uniformity coefficient. The developed new formulas show good agreement with the current and past experimental results.

Transporting finer fractions inside the soil skeleton or the erosion of base soils within the filter are the two main challenges for earthen hydraulic structures, their foundations, and filter design. Soil particle morphology could influence pore size distribution and transport of fine grains; however, there is not sufficient knowledge on the effect of grain shape on internal erosion. Some experiments designed and conducted in the present study to evaluate the suffusion potential of aggregates with various shapes and different gradations. Particles with six types of grain morphologies and five gradations were collected, and 26 tests were performed. Furthermore, using 3D image processing and visual comparison, particle shape assessed in terms of three features, including sphericity, roundness, and roughness. Results indicated that particle shape influences flow rate, washed-out fine grains in permeameter wall, vertical strain, and mass loss. An increase in the sphericity and roundness causes an increase in the loss of fine grains, pipe in cell sidewall, and vertical strain. Concerning the particle regularity as an indicator of grain morphology, it was demonstrated that the grains with lower regularity are more resistant to suffusion, and thus the resistance to suffusion would decrease with particle regularity. Spherical glass bead and rounded/ medium sphericity specimens were more prone to suffusion at an equivalent or even lower hydraulic gradient than the soil samples with angular/low sphericity grains.Graphic abstract

An innovative method for modeling a complicated geotechnical problem combining the coarse and fine zones is to use the hybrid methods. The granular zone of a geotechnical system can be modeled by the discrete element method (DEM) and the fine zone by continuum-based methods. The advantage of this approach is the use of the capabilities of both methods. In the present research, by combining DEM and finite difference method (FDM), a 2D numerical laboratory framework is constructed. Simulation of a vertically loaded stone column installed in clay was chosen to examine the capabilities of the present approach. The contrast between the stone column aggregates, which usually consist of crushed stone with distinct behavior, and the host medium, which is clay with continuum behavior, makes the stone column suitable for this kind of coupled simulation. The coupled numerical model is validated by comparing the load–settlement response of the numerical model and the reported experimental results. Afterward, the failure mechanism of the stone column is evaluated. The column bulging was captured properly, and it was found that in addition to the bulging, the contraction occurs at the upper portion of the column. It was also found that at the early stages of loading, the compaction occurs in the column. However, at later stages of loading, the bulging will happen. Furthermore, the results showed that bulging decreases the internal stresses of the column. All of these achievements were obtained by micro and macro investigations. The obtained results indicate that the coupled DEM–FDM method is a robust approach to simulate the behavior of some geotechnical problems.

This paper presents a comprehensive evaluation of the performance of Rigid Inclusion (RI) columns through the application of the Composite Modulus Calculation (CMC) methodology, addressing both short-term mechanical behavior and long-term settlement trends. The investigation is based on a real-world infrastructure project situated along the southern coast of Iran, involving the construction of large-scale storage tanks on geotechnically problematic soils. In the short-term analysis, a three-dimensional numerical model was developed and calibrated using the results of a full-scale static load test conducted on a single RI column. The close agreement between measured and simulated responses substantiates the accuracy of the adopted numerical approach. Subsequently, long-term performance was assessed via systematic interpretation of settlement monitoring data, analyzed within the CMC framework to capture the time-dependent behavior of the ground-structure system. Results indicate a pronounced mitigation of vertical deformations following ground improvement. Specifically, center settlements were reduced from an initial estimated value of approximately 42.3 cm to 17.9 cm, while peripheral settlements declined from 36.7 cm to 18.1 cm. These reductions signify the effectiveness of RI columns in enhancing vertical load distribution and controlling excessive settlements. Moreover, the utilization of RIs with varying embedment depths successfully minimized differential settlement across the tank footprint, maintaining total and differential displacements within permissible engineering thresholds. A hydrostatic loading test, spanning 133 days and achieving a maximum water elevation of 18 m, served as a validation benchmark. The recorded settlement profiles exhibited strong correlation with numerical predictions, reinforcing the robustness and conservative nature of the modeling strategy. The findings underscore the practical applicability and reliability of the CMC approach in large-scale geotechnical design scenarios involving extensive RI networks. The method offers a computationally efficient yet accurate alternative to fully discretized modeling techniques, particularly in cases demanding high-volume parametric analyses and performance-based design assessments.

Soil engineering properties can be improved employing different methods. Among them is mixing soil with tire derived additives (TDA). TDAs generally increase some parameters of mixture such as damping ratio, permeability, ductility and also in some cases shear strength. Various properties of TDAs from mechanical properties to their geometry can affect the mixture behavior. In this paper using the YADE platform, simulations of triaxial tests on sand tire mixtures are presented. To take compressibility into consideration, each rubber crumb particle is made of several spheres connected elastically to each other. For sand particle generation the clump technique was employed. Shapes of both sand and rubber particles are inspired from real grains. As properties of sand and rubber are different, especially Young modulus, rubber sand interaction is considered as soft rigid contact. Therefor harmonic average and arithmetic average was used to compute contact Young modulus (and then stiffness). The model was validated by comparison of results of triaxial tests simulation on pure rubber sample with literature ones which both exhibited linear stress-strain curve. Then triaxial tests with different sand to rubber ratio were simulated to see whether harmonic average or arithmetic average gives the best match to literature. The results show shear strength reduces by decreasing of sand to rubber ratio. This is the same as what is reported in literature.

Combination of the continuum-based numerical methods and the discrete element method (DEM) could be a powerful way of simulating complex problems. This approach benefits from the capabilities of both methods. The main feature of the discrete element method is that the soil grains are considered as individual particles without need to impose any behaviour law in modelling the medium. The limitation of this method is, however, its high computational demand. In continuum based methods, on the other hand, it is impossible to trace micro scale phenomena. According to these facts, combining continuum and discrete methods is an optimal way in approaching geotechnical problems which deal with granular soils. In this approach, the coarse grain zone (medium) is modelled using DEM and the surrounding media are modelled using the continuum methods. Stone columns that are widely used for improving and/or increasing the strength of weak soils could be modelled using this type of coupled simulation. The Coarse aggregates present in the stone column make it appropriate for the coupled modelling. In this paper, the ordinary and encased stone columns have been simulated by combining 2D DEM and finite difference method (FDM). Clump technique was employed to achieve the interlocking of aggregate particles in DEM, and the surrounding cohesive soil was modelled using FDM. The obtained results were validated by the reported experimental results in the literature, indicating that the coupled DEM-FDM method is a robust way to simulate stone columns.

A transformed approach has been made to predict the impression of inclusion geogrid on the reinforced soil’s bearing capacity underneath the strip foundation. The influence of the friction factor of the tensile strength of the reinforcement element performs a significant purpose in estimating the tolerance of the strengthened soil. Analytical study and experimental tests have been performed to validate the proposed empirical approach. This study analyzed certain parameters that influence the efficiency of the strip footing placed on reinforced soil, such as effects of two geogrid layers, the efficacy of geogrid embedment depths, the distance between geogrid layers, the tensile strength of geogrid, the contact surface friction angle, and shear stress distribution along the interactions at the soil–geogrid interface. Consequently, a simple new equation was proposed to modify the reinforced soil’s increased bearing capacity, then a comparative study was executed by the analytical method of literature. Finally, the calculations confirmed a good agreement between laboratory and analytical results such that the error rate was less than 2%. It was found that the value of strain-induced at the midpoint of geogrid decreases with depth, and their magnitude is constant at a 0.5B embedment depth. The impact of geogrid with length ratio (L/B = 5–7) on the strain values has similar behavior, but it is a significant effect of shorter geogrid length layers.

This study focuses on numerical modelling of rockfill material with the discrete element method (DEM). This method was used due to the special features of rockfill material, such as intense particle breakage and high contracting behaviour, which are inherently due to large particle size. Because the DEM models the interaction of separate elements, it is capable of modelling discrete structures of granular materials and particle breakage. The model used in this study uses PFC 2D and considers breakable clumps. To validate the presented model for rockfill material, numerical single crushing tests and triaxial tests on the Purulia dam’s material were simulated. Due to the size-dependant crushing strength being involved in the breakage criterion, and also considering particle confinement, size-dependant and stress level-dependant behaviour was successfully simulated on modelled rockfill material. The variation of the sample’s particle grading from before the biaxial tests and after shear failure occurred was reported. The obtained results demonstrate the accuracy of the adopted model and the model’s capability for considering a rockfill material’s strength, deformation and crushing behaviour.

Mixing sand or soil with small pieces of tire is common practice in civil engineering applications. Although the properties of the soil are changed, it is environmentally friendly and sometimes economical. Nevertheless, the mechanical behavior of such mixtures is still not fully understood and more numerical investigations are required. This paper presents a novel approach for the modeling of sand–tire mixtures based on the discrete element method. The sand grains are represented by rigid agglomerates whereas the tire grains are represented by deformable agglomerates. The approach considers both grain shape and deformability. The micromechanical parameters of the contact law are calibrated based on experimental results from the literature. The effects of tire content and confining pressure on the stress–strain response are investigated in detail by performing numerical triaxial compression tests. The main results indicate that both strength and stiffness of the samples decrease with increasing tire content. A tire contact of 40% is identified as the boundary between rubber-like and sand-like behavior.

Pore geometrical models are widely used to study transport in porous media, permeability, internal stability, and filter compatibility. Transport of fine grains through the voids between the skeleton of the coarser fraction is mainly controlled by the pore throats or constriction sizes. This study compares various constriction size distribution criteria and capillary tube models, which elucidate the limitations of the Kovacs capillary tube model, and this model is explained and developed. The new proposed threshold boundaries ( d 0 = 2 . 3 d 85 f and d 0 = 2 . 8 d 85 f ) categorized soil samples as internally stable, transient zone, or unstable. The model also incorporates the precise shape coefficient of particles. This improved model was validated based on a database from the literature, as well as performing 10 new experimental tests on two ideal gradation curves that identified the threshold boundary of Kenney and Lau criteria. This proposed model, which is dependent on grading, porosity, and grain shape, provides accurate predictions using a precise shape factor. This finding may enhance our knowledge about transport in porous media and contribute toward internal stability assessing for practical applications.