The breakage phenomenon has gained attention from geotechnical and mining engineers primarily due to its pivotal influence on the mechanical response of granular soils. Numerous researchers performed laboratory tests on crushable soils and incorporated the corresponding effects into numerical simulations. A systematic review of various studies is crucial for gaining insight into the current state of knowledge and for illuminating the required developments for upcoming research projects. The current state-of-the-art study summarizes both experimental evidence and numerical approaches, particularly focusing on discrete element simulations and constitutive models used to describe the behavior of crushable soils. The review begins by exploring particle breakage quantification, delving into experimental evidence to elucidate its influence on the mechanical behavior of granular soils, and examining the factors that affect the breakage phenomenon. In this context, the accuracy of various indices in estimating the extent of breakage has been assessed through ten series of experiments conducted on different crushable soils. Furthermore, alternative breakage indices are suggested for constitutive models to track the evolution of particle crushing under continuous shearing. Regarding numerical modeling, the review covers different approaches using the discrete element method (DEM) for simulating the behavior of crushable particulate media, discussing the advantages and disadvantages of each approach. Additionally, different families of constitutive models, including elastoplasticity, hypoplasticity, and thermodynamically based approaches, are analyzed. The performance of one model from each group is evaluated in simulating the response of Tacheng rockfill material under drained triaxial tests. Finally, new insights into the development of constitutive models and areas requiring further investigation utilizing DEM have been highlighted.

Changes in particle granulometry could lead to significant changes in a soil's behavior, making an understanding of micro-scale granulometry essential for practical applications. Changes in particle size, shape, and particle size distribution could result from a combination of applied normal and shearing stresses, which can in turn influence further response of the material. This study explored particle breakage during both compressive and shear loading under typical stresses. A deeper understanding of the phenomenon requires distinguishing broken and unbroken grains at the particle scale. Dynamic Image Analysis (DIA) was therefore employed to quantify changes in particle granulometry in two sands, a siliceous Ottawa sand and a calcareous sand known as Fiji Pink. Pre-sorted specimens having similar size, granulometry, and particle size distributions were tested using both oedometric and direct shear tests having the same aspect ratio, facilitating a direct comparison of the effects of shearing and compression on similar materials having different mineralogy. A breakage index was used for prognosis of particle breakage at key reference diameters. During oedometric tests, grain breakage was limited in both sands at stresses up to 1.2 MPa, but it increased significantly during direct shear tests. A conceptual model was proposed to explain the particle breakage mechanism during shear, at four key phase points representing (1) maximum compaction, (2) transition from compaction to dilative behavior, (3) maximum shear stress, and (4) peak test strain. In addition, a loading intensity framework was adopted to explain the relative roles of normal and shearing stresses on particle breakage. An increase of fines in soil during shearing was also observed and related to two sources: coarser grain abrasion and finer particle crushing. The vulnerability of grains with more anisotropic shapes was also observed. The loading intensity framework suggested that attrition of particle diameter could be divided into two phases, with a transitional critical loading intensity that appeared constant for each sand. For Ottawa sand, abrasion was the primary mechanism observed, causing a significant increase in Aspect Ratio (AR) and Sphericity (S) for finer grains. For Fiji sand, a transition from abrasion to attrition was noted, leading to limited sphericity decrease for the largest particles. Finer particles cushioning larger Fiji sand particles are more prone to breakage, resulting in increased AR and S. Finally, test results were used to propose a simple hyperbolic model to predict evolution of the particle size distribution during shear, for sands. The model was also verified using published data on grain evolution during shear of a different sand, not employed in its development.

A large-scale triaxial shear test was performed on a waste slag dam created from the accumulation of waste slag during the construction of a pumped-storage power station. By integrating previous experience, the particle breakage index was refined to study the relationship between particle breakage and the deformation strength characteristics of the soil-rock mixture under different dry densities and stress states. The results show that as the confining pressure increases, various dry densities enhance particle breakage, leading to a transition from initial dilatancy to shear shrinkage in the soil-rock mixture. This change results in a decrease in the nonlinear internal friction angle and a decrease in the shear strength. This research explores the shear failure mechanism caused by the breakage of soil-rock mixtures. Examination of the particle grade before and after shearing shows that the extent of particle breakage expands with higher confining pressure, especially within the 20 similar to 60 mm grain size range. The fractal dimension is calculated concurrently, showing a strong correlation with the breakage index. The concepts of the phase transition stress ratio and failure dilatancy ratio were applied to describe the deformation characteristics. Experimental results demonstrate that the influence of the phase transition stress ratio on the dilatancy becomes more significant with increased dry density, yet this effect diminishes with higher confining pressure. As the breakage index increases, the failure dilatancy rate decreases following a power function, resulting in a gradual reduction in the dilatancy phenomenon. Considering the substantial influence of clay particles on the cohesion of the soil-rock mixture and the negligible effect of breakage on fine particles, it is proposed that the cohesion remains unchanged for determining the friction parameter. With increasing breakage index, the internal friction angle decreases nonlinearly, weakening the shear strength. This analysis shows that the refined particle breakage index effectively captures the particle breakage characteristics of soil-rock mixtures, providing valuable insights into the deformation and strength characteristics of engineering structures affected by particle breakage.