Tensile strength is one of the most important characteristics of rock masses that could govern the stability of rock structures. Due to difficulties in its direct measurements, indirect methods such as the Brazilian test have been developed to assess the tensile strength of laboratory-scale rock material. This study considers the effect of loading contact angle on the indirect tensile strength of rock-like disks by adopting experimental and discrete element methods. Several experimental specimens made of synthetic materials were examined under diametrical loading, and consequently, a numerical model using PFC3D was calibrated accordingly. Then, the impacts of the loading contact angle (θ) on the tensile strength, failure pattern, and contact force chain were investigated in detail. The results indicated that as θ increases from 0°, suggested by ASTM, to 90°, the tensile state is dominated at the specimen center, whereas for angles greater than 90°, the dominant stress state changed to compression. Also, while σxx (tensile stress) at the center of the disk did not change for θ below 40°, the σyy (compressive stress) and σzz (out-of-plan normal stress) increased after θ =30°. The analysis of developed cracks suggested that when θ is lower than 30°, the percentage of tensile and shear cracks were constant (80% and 20%, respectively). As the loading contact angle increased, tensile cracks decreased, whereas the other increased. By analyzing the failed specimens, three categories of crack patterns and two categories of contact force chains were identified.

In part II of this study, a second method for the prediction of the crack initiation stress was sug-gested. The new technique is based on an elementary mathematical calculus theory. Particularly, the one that supports that the points where the second derivative of a function is equal to zero can be considered as possible inflection points of the function. The proposed Second Derivative meth-od fulfilled all the necessary criteria, that were mentioned in part I, so that it can further advance the research field. The method was applied to ten rock specimens, specifically eight marbles and two vesicular basalts, that were subjected to uniaxial compressive tests. The predicted crack initi-ation stresses from the new method were compared with those obtained from the established techniques of the existing literature. The new method had very close results with all other utilized methods for the marbles, thus meaning that the proposed Second Derivative technique can accu-rately and consistently determine the onset of stable crack growth for that rock type. On the con-trary, the new method displayed a poor correlation with the other techniques for the two basalts, hence indicating that further tests need to be conducted in the future for that rock type.

The Vajont Landslide, one of the most catastrophic events in history, has been extensively studied for over 60 years. Navigating the extensive Vajont literature presents challenges due to the volume of information, persistent questions, ongoing controversies, and even unreliable information. This review offers a novel synthesis by identifying the most influential hypotheses through the lens of updated geomorphological reconstructions, evolving interpretations of the sliding surface, and conflicting assumptions. It highlights how certain long-held assumptions may have led to biased conclusions, presents a concise dataset of key geotechnical parameters, and stresses the need for future analyses that integrate rainfall and reservoir effects over time, account for possible progressive strength degradation, and revisit slope stability under more realistic boundary conditions. By clarifying closed questions and spotlighting persistent uncertainties, this paper aims to guide future research and reframe understanding of the Vajont landslide.

In part I of this study, the great practical importance of the onset of stable crack growth was out-lined, since several researchers have supported that it can serve as a more realistic estimation of the in-situ spalling strength of the rock mass, in comparison with the more frequently used uniaxi-al compressive strength. Moreover, a short review was also provided regarding the empirical techniques that have been proposed in the last six decades for the prediction of the crack initiation stress. The main criticism of each method was also mentioned. Subsequently, a new method was proposed, based on the Trapezoid Rule, an elementary calculus approximation technique. The lat-ter technique possesses a strong and robust physical explanation, easy application, and complete objectiveness. The Trapezoid Rule method was applied to ten rock specimens, eight marbles and two vesicular basalts, that were subjected to uniaxial compressive tests. The results of the newly suggested method were compared to those obtained using the established methods of the existing literature. Ultimately, it displayed exceptionally close results with all other methods for the ten specimens, thus indicating that it can accurately and consistently predict the crack initiation stress for the two rock types.

In this paper, the geometry of borehole forced by two-dimensional stress was studied based on classical rock mechanics. The relation between horizontal principal stress and geometrical parameters of deformed circular borehole was established. The new prediction model of horizontal stress was deduced based on the above quantitative relation. Additionally, the stress computation was realized based on elliptical parameters of borehole. Subsequently, the feasibility and scientificity of the calculation method of horizontal principal stress were further confirmed via an experiment of borehole deformation based on borehole deformation. The feasibility and applicability of the method were verified based on actual drilling data in Xinjiang Province. The results demonstrated that the geometric shape of circular borehole after deformation was elliptical under the action of planar two-dimensional stress, and the horizontal principal stress could be expressed by the elliptic geometric parameters after deformation. The shape structure of the circular borehole under the action of non-uniform horizontal principal stress was elliptical, and the horizontal principal stress calculated using the parameters of the elliptical shape structure was directly proportional to the loading load. Larger the borehole diameter, smaller was the error of the method. The results provide new insights for in-situ measurement and inversion of deep horizontal in-situ stress.

Abstract The integration of artificial intelligence (AI) into blasting operations has demonstrated significant improvements in precision, safety, and operational efficiency. By leveraging AI algorithms to optimize blast design, monitor field conditions, and analyze fragmentation data, more informed decision-making is achieved. In small-scale mining, safe and efficient blasting practices are critical to protecting workers, maximizing resource extraction, and minimizing environmental impacts. This study first reviews the applications, advantages, and limitations of various AI techniques used in predicting blast performance and environmental effects, with specific attention to the overlooked impact of multicollinearity and the absence of explicit mathematical expressions in many soft computing models. In the experimental section, an imperialist competitive algorithm (ICA)-optimized artificial neural network (ANN) model is developed to predict the percentage of oversized material produced by small-scale blasting. Field data, including blast parameters and rock strength, were collected from a dolomite quarry in Akoko, Edo State, Nigeria. Fragmentation analysis was conducted using WipFrag 4.0 software across 48 blast rounds, using the primary crusher gape as the decision threshold. Input parameter selection was guided by multicollinearity analysis to ensure robust modeling. Evaluation metrics such as root-mean-square error (RMSE), correlation coefficient (R²), mean absolute percentage error (MAPE), variance accounted for (VAF), Nash–Sutcliffe efficiency (NSE), and performance index (PI) confirmed that the ICA-ANN model significantly outperformed the standard ANN. While the conventional ANN model underestimated oversize by 14.7%, the ICA-ANN achieved a lower prediction error of 2.7%. The proposed model offers a practical and accurate tool for predicting oversized fragmentation in small-scale rock engineering scenarios, contributing to improved blasting efficiency and sustainability in the mining sector.

Creep is a time-dependent plastic deformation that occurs in materials subjected to sustained underground stresses. This phenomenon is particularly significant in rocksalt, where understanding its behavior is critical due to its direct impact on mining operations and the long-term stability of underground structures. This study investigates the creep behavior of rocksalt from the Khewra Mine, located in Pakistan, through a combination of laboratory testing and numerical analysis. Triaxial creep tests were conducted on selected samples from the Khewra Salt Mine, and the resulting data were incorporated into a numerical model. Due to limited resources, certain parameters were assumed based on data from the Asse Mine in Germany. A symmetrical single-pillar model was developed in FLAC3D to simulate the mechanical response, using dilatancy and failure strength criteria to evaluate the pillar's utilization factor. The simulation results indicate the early formation of micro-fractures throughout the pillar, while macro-fractures gradually develop along its outer boundary over time. Zones between 3.4 and 4.1 meters from the center show significantly high tensile stresses, suggesting potential instability and risk of failure at the pillar's edges. These findings highlight the need for a more comprehensive investigation of the mechanical properties and creep behavior of Khewra rocksalt to ensure safe and sustainable mining practices.

Heterogeneity of natural rock mass differs from most other engineering materials. Although the heterogeneity, such as macroscopic fracture, potentially contributes to the deformability of rock mass, evidence for macroscopic heterogeneity from field studies has been circumstantial. We present the results of field drilling energy experiment on the rock mass of tuff, limestone and marble types that shows the evidence for the rock mass deformability from macroscopic heterogeneity caused by fracture, reflecting borehole macroscopic heterogeneity associated with drill energy. The experimental results show that the macroscopic heterogeneity is expected to vary linearly with the fracture frequency, and depends on rock types and drilling energy. The contributions of macroscopic heterogeneity for deformability of rock mass have undergone a leading role.

Friction coefficient, as a parameter of mechanical state, plays a crucial role in the shear failure of rocks in the field of Earth sciences. This paper investigates the frictional characteristics and anisotropy of rock by analyzing the coefficient of variation of the friction coefficient (f) and the anisotropy index of rock friction coefficients Af. Rotational friction tests were conducted using cylindrical granite against square samples of granite, sandstone, and andesite in three directions to analyze the relationship between the friction coefficient and various drilling parameters. This study reveals the variations in the friction coefficient and notable changes in the friction coefficient’s anisotropy. The results indicate a correlation between the alignment of turning points during the frictional stage and the rock strength. During the experiment, the friction coefficient undergoes cyclic variation before gradually stabilizing. The anisotropy of rotational friction follows the order: granite > andesite > sandstone, suggesting that the higher rock strength corresponds to greater frictional anisotropy. The rotational friction control coefficient C is derived and linked to the rotational friction stage. The duration of effective contact between rock surfaces and directional cutting efficiency are the primary factors contributing to anisotropy. The results offer practical implications for drilling design and seismic risk assessment in anisotropic rock formations.

The utilization of blasting has been prevalent in mining and civil engineering domains due to its cost-effectiveness and affordability as a method for fracturing rock. The achievement of an ideal blast results in the most effective fragmentation while ensuring safety, cost-effectiveness, and environmental sustainability. In developing blast efficiency model, this study considered uniaxial compressive strength (UCS), spacing, hole depth, stemming length, point load index, powder factor, charge weight and burden. The model was trained by artificial neural network (ANN) and linear multivariate regression (LMVR) using 85 production datasets. After training four-layer ANN architecture 8-4-1 was found to be optimum. The prediction accurateness of two developed models was analysed using mean square error (MSE), performance index (PI), variance accounted for (VAF), root mean square error (RMSE), and co-efficient of determination (R2). The obtained values of performance parameters reveals ANN model to be more accurate as compared to the LMVR model. The ANN and LMVR model have R2 value of 90.9% and 56.3%. The optimized model was employed to achieve the optimal blast design for high strength granite to enhance blast efficiency. The test data result was utilized to optimize the blast parameters, including spacing, stemming length, burden, charge length, and charge. The values chosen for these parameters were 1.8 m, 1.8 m, 1.5 m, 157.17 kg, and 1.35 kg/m3, respectively, based on the optimum model.