A significant amount of open-pit-mine broken sandstone (OMBS) is produced during open-pit mining. The mechanical strength of the loose sandstone is critical for ensuring dump slope stability and sustainable mine construction. This study investigates the modification of OMBS using artemisia sphaerocephala krasch (ASK) gum to enhance its engineering properties. Unconfined compressive strength, shear strength and permeability tests were conducted to quantitatively analyze the modification effect. And the stability was evaluated using FLAC3D simulation methods. The modification mechanism was characterized through SEM, FT-IR, XRD. The results demonstrated that the addition of 2 % ASK gum significantly improved OMBS mechanical performance and reduced permeability. Meanwhile, the failure mode of OMBS changed with the ASK gum content increasing. The simulation result indicated the stability of modified dump slope was better under the drying-wetting cycle. From the perspective of microstructure and chemical characteristics, the addition of ASK gum created new hydrogen bonds through intermolecular interactions with the hydrophilic groups between OMBS particles and formed a dense and stable structure through three reinforcement modes: surface encapsulation, pore filling, and bonding connection. This study provides a new idea for resource saving and environmentally friendly mining area development.

Discrete element modeling (DEM) is a useful tool for linking global responses of granular materials to underlying particle-level interactions. A DEM model capable of capturing realistic soil behavior must be calibrated to a reference dataset, typically consisting of laboratory experiments. Calibration of a DEM model often requires numerous simulations as contact parameters need to be iterated upon until the simulation results satisfactorily replicate the experimentally observed behaviors. This paper presents a sensitivity investigation that examines the effects of the contact parameters on the drained triaxial compression response of a poorly-graded sand. It then introduces a calibration procedure capable of providing contact parameters that satisfactorily reproduce the results of laboratory triaxial results in a few simulations. Results show that friction and rolling resistance coefficients jointly influence the mobilized peak and critical state friction angles, secant shear modulus, maximum dilation rate, total volumetric strain, and strain softening magnitude. These parameters also influence the mode of failure at contacts and the evolution of fabric anisotropy. The influence of mu r or mu on the triaxial response and particle-level interactions is coupled, becoming more profound as the other parameter is increased. Contact stiffness is shown to influence the shear modulus and volumetric change behavior independently of mu and mu r. An algorithm that estimates values for mu and mu r needed to reproduce experimental results is developed using triaxial response parameters from experimental datasets. The performance of the proposed calibration method is demonstrated for three natural sands showing that it provides appropriate calibrated parameters for poorly graded sands with different relative densities and confined with varying effective stress magnitudes.

Gravel-bearing sandstone reservoirs represent a significant type of reservoir in oil and gas exploration. Due to the difference of the spatial random distribution the content and the shape of the gravel particles, these reservoirs exhibit complex mechanical properties and failure modes. In this study, a numerical model of gravel-bearing sandstone was developed by using the Finite Element Method (FEM) and were verified by the actual indoor experimental data. The effect of the gravel particle sizes, gravel content, and gravel types on the compressive peak strength and microcrack evolution processes are further analyzed. The results reveal that cracks initiate within the sandstone matrix surrounding the gravel and propagate through the gravel with continued loading. The primary factors governing the stability of gravel-bearing sandstone are the gravel radius and content. The variation in gravel penetration rate is synchronized with the changes in peak strength. By embedding gravel particles of different shapes into the model, it is observed that the peak compressive strength of round gravel is comparable to that of elliptical gravel, with both exhibiting higher peak strengths than angular gravel. Regression models demonstrate that the tensile strength difference between the gravel and the sandstone matrix is a critical parameter influencing gravel penetration. Confining pressure has a relatively minor effect on the elastic modulus, while its impact on peak compressive strength is significantly more pronounced.

Effective erosion mitigation in the Pisha sandstone region is crucial for soil and water conservation in the Yellow River Basin, yet existing vegetation measures are inadequate in water-limited environments. This study examines the application of drought-tolerant biological soil crusts (biocrusts) for erosion control on sandstone slopes and evaluates their erosion-reducing effects under varying coverage and slope conditions through controlled artificial rainfall experiments. Key findings include: (1) biocrusts coverage demonstrated a linear relationship with initial runoff generation time and an exponential relationship with stable runoff generation time. On average, biocrusts delayed initial runoff generation by 396.32 % and extended stable runoff generation time by 153.93 %, thereby increasing the threshold for both initial and stable runoff generation on Pisha-sandstone surfaces. (2) biocrusts reduced runoff volume by an average of 23.89 %, enhanced infiltration volume by 69.19 %, decreased sediment yield by 64.24 %, and lowered the soil erosion modulus by 68.98 %. These results indicated significant promotion of water infiltration and reduction of water erosion. Both effects were positively influenced by coverage and negatively impacted by slope gradient. A critical slope angle of 15 degrees and a critical coverage of 60 % were identified. When the slope was gentle (S 15 degrees), the negative impact of slope predominated, diminishing the positive effect of biocrusts. Additionally, when coverage reached or exceeded 60 %, further increaseing in coverage accelerated the enhancement of infiltration and erosion reduction. Below this threshold, the rate of improvement gradually diminished with increasing coverage. (3) The structural equation model further elucidated that biocrusts mitigate erosion by enhancing the coverage, thereby reducing runoff velocity and modifying the runoff regime. This mechanism effectively dissipates runoff energy, leading to a decreased soil detachment rate and alleviation of soil erosion. Additionally, the relationship between runoff energy and soil detachment rate follows a power function curve, providing an effective method for predicting erosion in Pisha sandstone area. Consequently, biological soil crust technology shows considerable potential for preventing water erosion damage on Pisha sandstone slopes across various gradients.

This study investigates the mechanical properties and damage processes of cement-consolidated soils with Pisha sandstone geopolymer under impact loading using the Hopkinson lever impact test. The mechanical properties of cement-cured soils containing Pisha sandstone geopolymer were examined at various strain rates. The relationship between strain rate and strength of the geopolymer-cemented soil was established. As the strain rate increased, the coefficient of power increase for the Pisha sandstone geopolymer cement-cured soil initially rose before gradually stabilizing. The pore structure of the crushed specimens was analyzed using Mercury intrusion porosimetry. Based on the observed pore changes under impact loading, the pore intervals of the geopolymer-cemented soil were defined. A fitting model linking strain rate and porosity was developed. As strain rate increased, the porosity of the specimens first increased and then decreased, with larger internal pores gradually transforming into smaller ones. The highest porosity was observed at a strain rate of 64.67 s- 1. Crushing characteristics of the cement-cured soils under impact loading were determined through sieving statistics of the crushed particles. The average particle size of the fragments decreased as the strain rate increased. The fractal dimension initially decreased and then increased with the rise in strain rate, reaching its lowest value at a strain rate of 64.67 s- 1. Based on the dynamic mechanical properties, microscopic porosity, and fracture characteristics, the critical strain rate and damage form for cement-consolidated soils with Pisha sandstone geopolymer under impact loading were determined. This study offers valuable insights for the practical application of Pisha sandstone geopolymer cement-cured soils in engineering.

One of the main problems of carbonate sands is the fragile nature of particles and their susceptibility to breakage. Carbonate sands are affected by volumetric strain even at low stress levels, which is not the case with silicate sands. By defining a simple breakage model, the current study develops an elastoplastic critical state constitutive model that considers the impact of particle breakage on the mechanical behavior of carbonate sands. The particle breakage model depends on mean effective stress and critical breakage stress, which is assumed to correspond with the precompression pressure of soil in the oedometer test. In the proposed model, critical state line movement with the breakage parameter (alpha) considers the particle breakage effect. Based on the unified clay and sand model (CASM), a novel dynamic yield surface with a shape parameter affected by particle breaking has been created. Certain modifications are made to the modified Cam-Clay stress dilatancy to predict the behavior of carbonate sand. The current model has only ten parameters that simulate the carbonate sands' behavior even at high-stress levels without any breakage test. Experimental data with different soil densities, loading stress paths, and stress levels were compared with the model, and the results demonstrated satisfactory conformance.

Conventional plasticity assumes that a yield surface exists and the direction of plastic strain increment (DPSI) is uniquely dependent on the current stress state. Triaxial stress probing tests of yield and plastic flow of sand have been conducted using discrete-element modelling with polyhedral particles resembling the shapes of Toyoura sand. It is found that a yield surface does not exist, but a memory surface (MS) separating two types of distinct sand behaviour can be established. Within the MS, the DPSI is primarily controlled by the stress increment, and the magnitude of plastic strain increment is insensitive to the stress increment direction. When the stress state is on or outside the MS, a much larger plastic strain increment is observed if the stress increment points outside the MS, and the DPSI is dependent on both the current stress state and stress increment. The shape and size of the MS, which can be modelled by the SANISAND yield function, are dependent on the soil density and evolve with plastic strain.

Enhancing the structural stability of Pisha sandstone soil is an important measure to manage local soil erosion. However, Pisha sandstone soil is a challenging research hotspot because of its poor permeability, strong soil filtration effect, and inability to be effectively permeated by treatment solutions. In this study, by adjusting the soil water content to improve the spatial structure of the soil body and by conducting unconfined compressive strength and calcium ion conversion rate tests, we investigated the effect of spatial distribution differences in microbial-induced calcium carbonate deposition on the mechanical properties of Pisha sandstone-improved soil in terms of the amounts of clay dissolved and calcium carbonate produced. The results demonstrate that improving the soil particle structure promotes the uniform distribution of calcium carbonate crystals in the sand. After microbial-induced carbonate precipitation (MICP) treatment, the bacteria adsorbed onto the surface of the Pisha sandstone particles and formed dense calcium carbonate crystals at the contact points of the particles, which effectively enhanced the structural stability of the sand particles, thereby improving the mechanical properties of the microbial-cured soils. The failure mode of the specimen evolved from bottom shear failure to overall tensile failure. In addition, the release of structural water molecules in the clay minerals promoted the surface diffusion of calcium ions and accelerated the nucleation and crystal growth of the mineralization products. In general, the rational use of soil structural properties and the synergistic mineralization of MICP and clay minerals provide a new method for erosion control in Pisha sandstone areas.

Due to the development of plastic strains, the strain path within the meridian plane deviates from the reference line corresponding to elastic state. Similarly, under true triaxial stress conditions, the strain path within the deviatoric plane deviates from the reference line corresponding to the constant Lode angle. This deviation is attributed to the plastic shear strain associated with the Lode angle. To account for these phenomena, a novel three-dimensional elastoplastic constitutive model incorporating Lode angle is proposed to characterize the deformation behavior of sandstone. The yield and potential functions within this model incorporate parameters that vary with the plastic internal variable, enabling the evolution of the yield and plastic potential surfaces in both the meridian and deviatoric planes. The comparison between experimental data and the analytic solution derived from the constitutive model validates its reliability and accuracy. To examine the differences between yield surface and plastic potential surface, a comparison between the associated and non-associated flow rules is conducted. The results indicate that the associated flow rule tends to overestimate the dilatancy of sandstone. Furthermore, the role of Lode angle dependence in the potential function is explored, highlighting its importance in accurately describing the rock's deformation.

The deterioration of rock mass in the Three Gorges reservoir area results from the coupled damage effects of macro-micro cracks and dry-wet cycles, and the coupled damage progression can be characterized by energy release rate. In this study, a series of dry-wet cycle uniaxial compression tests was conducted on fractured sandstone, and a method was developed for calculating macro-micro damage (DR) and energy release rates (YR) of fractured sandstone subjected to dry-wet cycles by considering energy release rate, dry-wet damage and macro-micro damage. Therewith, the damage mechanisms and complex microcrack propagation patterns of rocks were investigated. Research indicates that sandstone degradation after a limited cycle count primarily exhibits exsolution of internal fillers, progressing to grain skeleton alteration and erosion with increased cycles. Compared with conventional methods, the DR and YR methodologies exhibit heightened sensitivity to microcrack closure during compaction and abrupt energy release at the point of failure. Based on DR and YR, the failure process of fractured sandstone can be classified into six stages: stress adjustment (I), microcracks equal closure (II), nonlinear slow closure (III), low-speed extension (IV), rapid extension (V), and macroscopic main fracture emergence (VI). The abrupt change in damage energy release rate during stage V may serve as a reliable precursor for inducing failure. The stage-based classification may enhance traditional methods by tracking damage progression and accurately identifying rock failure precursors. The findings are expected to provide a scientific basis for understanding damage mechanisms and enabling early warning of reservoir-bank slope failure. (c) 2025 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/ 4.0/).