Rock Strength Research Articles

Shallow Foundation Load Testing on Natural Florida Limestone: Single Rock Layer and Rock-Over-Sand Subsurface

This article presents three shallow foundation load tests under various layer conditions (single rock layer and rock-over-sand subsurface), rock strengths, and limestone formations. Rock coring with laboratory triaxial testing, standard penetration tests (SPT), seismic shear tests, and measuring while drilling (MWD) tests were performed to identify the representative mass bulk dry unit weight (γ<sub>dt</sub>) and the spatial variability of γ<sub>dt</sub>. The geometric mean and median γ<sub>dt</sub>, together with seismic shear results, were used to characterize rock strength and stiffness. Each footing test was sized at 1.07–1.83 m to fit the 12.20 m load frame (8.01 MN capacity) using laboratory-assessed bilinear strength envelopes of the rock. Predicted bearing capacities with Florida bearing capacity equations provided reasonable estimates for three load tests. Mean and differential settlement, including spatial variability for a single footing on a heterogeneous rock layer, were captured with the Fenton and Griffiths method. For the settlement prediction of rock-over-sand subsurface, a parametric study was conducted for typical footing size, rock thickness, and mass properties with the finite element method (FEM), and a Winkler approach with a stress-dependent weighted harmonic mean modulus (E<sub>eq</sub>). The proposed method achieved good agreement with the FEM results and was validated with load tests.

Rock strength and stress dependence of local flow-path connectivity within faults or fractures: a preliminary overview of virtual and in-situ hydraulic tests

Abstract Global flow path connectivity along faults or fractures depends on the degree of local flow path connectivity within each fault or fracture and is a key control of groundwater flow and solute transport. However, the mechanical controls on spatial variations in local flow path connectivity within individual faults or fractures are poorly understood. Local flow path connectivity is quantifiable by the laboratory-scale flow dimensions (n lab) within individual faults or fractures, with a lower n lab indicating lower local flow path connectivity. Virtual hydraulic tests were performed on modeled individual fractures to derive a relationship between n lab and a mappable indicator, the ductility index (DI), defined by the mean stress, groundwater pressure, and rock tensile strength. The derived relationship was verified with data obtained from in-situ hydraulic tests of natural faults in rocks with low matrix permeability, poor swelling capacity, and few fracture mineral fillings, also incorporating the effect of linkage among faults in the field. The test results demonstrated that local flow path connectivity within faults or fractures can be high (n lab > 1.5) when DI < 2 but is generally low (n lab < 1.5) when DI > 2, depending on the level of effective-normal-stress-dependent (DI-dependent) fracture-normal displacement. This relationship between n lab and DI is valid even when the value of DI is varied, or the faults are sheared. These findings can be used to help map spatial variations in local flow path connectivity within faults or fractures from limited borehole data.

A comparative study of hybrid adaptive neuro-fuzzy inference systems to predict the unconfined compressive strength of rocks

The accurate prediction of unconfined compressive strength (UCS) in rock samples is critical for the successful planning, design, and implementation of mining and civil engineering projects. UCS is crucial in assessing the stability and durability of rock masses, which directly influences the safety, efficiency, and cost-effectiveness of construction and excavation operations. Here’s a refined version of your text for enhanced clarity and flow: in this part, the execution of the proposed model was compared for both single and hybrid configurations. Hybrid models included support vector regression (SVR) combined with the Seahorse Optimizer (SVSH) and SVR combined with the COOT optimization algorithm (SVCO). For training, 70% of the UCS dataset was utilized, while the remaining 30% was equally divided between testing (15%) and validation (15%). For the model evaluation, several metrics were considered in this work, including the R2, RMSE, WAPE, MAE, and RAE, which ensure fairness in the analysis. The closer the R2 value comes to 1, the better the performance. The error metrics should be close to 0 for better accuracy. From Table 2, one can observe that the result of the standalone SVR model gave an RMSE of 6.213 during training and 9.454 during testing, hence showing poor performance. However, the inclusion of optimization algorithms significantly improved the performance of the SVR framework. Among the hybrid models, the SVSH model had the best performance, with an R2 value of 0.998 and an RMSE of 1.261 during training. The SVCO model performed moderately, with an R2 value of 0.988 during training.

Knowledge-Based Machine learning for Real-Time rock strength testing while Drilling: Bridging Simulation and Reality

Knowledge-Based Machine learning for Real-Time rock strength testing while Drilling: Bridging Simulation and Reality

Simulation of the enclosing rock displacements around the development mine workings

Purpose is to develop and substantiate a mathematical model for forecasting of rock displacements around the development mine workings and optimization of techniques for their reinforcement. Methods. A comprehensive approach has been applied including numerical simulation; theoretical analysis; and experiments. Special attention has been paid to rock displacements based upon stress-strain state of the rock mass. The developed KMS-Ш software was used for the calculation helping model displacements and analyze the obtained data. Findings. Recommendations have been proposed to decrease a rock dilatancy coefficient achieved through correction of support parameters; mine working geometry; and control of rock deformation rate. It has been demonstrated that rock bolting use lowers significantly the intensity of the displacements. It has been identified that a decline in rock strength results in the increased failure zones; at the same time, the improved plastic properties minimize elastic energy accumulation reducing the displacement probability of the opposite crack surfaces. Originality. An algorithm has been developed forecasting displacements of the mine working peripheries taking into consideration the mining, geological, and engineering factors. A mathematical model has been represented to identify both elastic and non-elastic deformations in a border zone. The dependencies between border rock mass displacements, mine working depth, and rock strength have been defined. Practical implications. Determination of optimum parameters of rock strengthening helps minimize failure zones; better stability of mine workings; and reduce the possibility of dangerous geomechanical phenomena. Use of the proposed model makes it possible to improve mining efficiency owing to more accurate forecasting of displacements.

Study of the relationship between uniaxial compressive strength and the point load index test in rocks from the bank in Seybaplaya Campeche Mexico

The present research focuses on analyzing the uniaxial compressive strength of rocks and its relationship with point load index testing. It is important to note that Seybaplaya, located in Campeche Mexico, is recognized for its fishing, industrial and commercial activities and where a rock bench is located from which samples were obtained to carry out the study. As a result, equations were developed that allow predicting the simple uniaxial compressive strength based on the values obtained from the point load index test. It is relevant to highlight that these relationships are valid only for rocks with lithological characteristics similar to those used in this study. The analysis results and conclusions demonstrate the linearity of the relationships between the simple uniaxial compressive strength and the point load index test.

Study of the relationship between uniaxial compressive strength and the indirect tensile test (BTS) in rocks from the bank in Seybaplaya Campeche Mexico

The present research focuses on analyzing the uniaxial compressive strength of rocks and its relationship with the indirect tensile test (the Brazilian method). It is important to note that Seybaplaya, located in Campeche, Mexico, is known for its fishing, industrial and commercial activities, and is home to a rock bank from which samples were obtained for this study. As a result, an equation was developed that allows predicting the simple uniaxial compressive strength from the values obtained in the indirect tensile test. It should be noted that this relationship is valid only for rocks with similar lithological characteristics of the samples analyzed. The results of the analysis and conclusions show the linearity of the relationship between the simple uniaxial compression resistance and the indirect tensile test.

Rate of Penetration Prediction for Large Diameter Offshore Drilling for Windfarm Structures

It is essential to shift towards sustainable energy in a world with increased awareness of global warming and climate change. There is an anticipated increase in offshore wind farms in the upcoming years. There is a need to explore new locations in tougher soil conditions for the wind farm developments as the sweet spots or technically easy spots have been taken. The rock strength must be overcome in the new locations of concern. Due to pile buckling the conventional pile driving technique becomes an undesirable solution. An alternative method that can complete wind farm infrastructure efficiently in challenging soil and rocks is drilling. In addition, there are some regions where pile driving becomes unviable due to the rules associated with maximum noise levels. The cost of the project increases significantly in the case of the use of noise mitigation measurements. Again, drilling can be considered as an alternative solution, because as a result, the noise generated during installation decreases significantly. The important role in the total drilling process is the drilling phase itself, and it can easily be equal to more than half of the total pile installation time. It is necessary to have a very decent prediction of the drilling rate for the installation of a large number of foundation piles, especially since it is important to have this information during the tender phase of a project. The currently available drilling rate models are based on empirical evidence and tend to be specific to certain drilling methods in each type of rock. This study aims to better predict the drilling rate which will be applicable for different amounts of large-diameter drilling for various rock and soil types. Significant importance will be given to the analysis of conventional top-hole drilling performance. Investigation of top hole and deep hole drilling bit design will be conducted and its applicability to soil drilling for windfarm installation will be tested.

Experimental Study on the Damage Evolution Mechanism of Siltstone by Water Content and Confining Pressure

ABSTRACTProlonged exposure of deep coal mines to erosion from groundwater results in a gradual accumulation of rock mass damage, which can lead to geological hazards such as deformation and instability. These challenges significantly impact the safe operation of deep coal mines. To understand the mechanisms behind siltstone damage progression related to water content and confining pressure, this study explores the influence of these factors on the deformation and damage evolution of siltstone, employing a combination of rock mechanics testing, numerical simulation, and CT scanning techniques. Results demonstrate that increasing water content reduces the compressive strength of rock, leading to more complex failure modes. In contrast, higher confining pressure strengthens the compressive capacity, thereby suppressing the formation and growth of transverse cracks under compression. Using Avizo software, a three‐dimensional model of siltstone was developed to visualize the distribution of fractures in a three‐dimensional field. In the MATLAB platform, a box dimension algorithm based on three‐dimensional digital volume imaging was developed, employing box dimension theory and digital image storage methods. Fractal analysis reveals that the fractal dimension of internal fractures in loaded samples increases linearly with water content, indicating more extensive fracture development and greater specimen damage. Applying the box dimension from three‐dimensional digital volume images as a metric facilitates characterizing the damage evolution in siltstone under different water content conditions. This approach provides a new means to quantitatively evaluate the growth and complexity of internal fractures in siltstone, offering insights into rock damage progression under varying moisture conditions.

Justification of Progressive Parameters of The Sides of Copper Ore Quarries

A methodological approach to the justification of steep (progressive) sides of copper ore quarries is presented on the basis of complex geomechanical studies of rocks directly in the instrument arrays using cores obtained from specially drilled engineering-geological wells to determine the size of structural blocks, the quality index of the array and the structural attenuation coefficient and parallel laboratory study of the strength and physical properties of rocks. The assessment of the stability of the sides of the quarry by various calculation methods made it possible to verify their reliability and good convergence. Rather steep (progressive) parameters of the sides of the quarry are recommended, at their height of 300 m, their angles of inclination range from 46° to 52° with a coefficient of stability ranging from 1.19 to 1.37. The implementation of geotechnological studies based on rating classifications allows us to obtain reliable strength characteristics of rocks necessary for numerical modeling of geomechanical processes. The stability of the sides of the quarry was assessed by various calculation methods, which made it possible to verify their reliability and good convergence of numerical- analytical and rating calculation systems, which are carried out using special programs.

Prediction Rock Strength Properties for Southern Iraqi Field. Application of Petrophysical and Mechanical Properties Relationship, Using Wireline Log Data

Rock Strength Properties (Internal Friction Angle

A study on the effect of crack orientations, crack types and SHPB characteristics on the failure behaviour of pre-cracked sandstone rock specimens

The present study aims to understand the experimental and numerical behavior of intact and pre-cracked fine-grained sandstone specimens under indirect dynamic tensile loading conditions. The dynamic experimental analyses are carried out using the split Hopkinson pressure bar (SHPB) device to determine the tensile strength of sandstone rock. In addition to the dynamic tests, the physical, petrological, and mechanical tests under static loading of the sandstone rock are also studied. Thereafter, a three-dimensional (3D) finite element (FE) numerical model is developed, and a strain rate-dependent modified Drucker Prager constitutive model is used to validate the numerical model with the indirect dynamic tensile experimental test results. The validated parameters are then used to determine the behavior of pre-cracked sandstone specimens through numerical simulations. Two sets of numerical models with diametral cracks and cross-sectional cracks are introduced into the intact rock specimens. The orientation of the crack is changed from 0° to 90° and the numerical analyses are performed for 0°, 30°, 45°, 60°, 75° and 90° crack orientations with respect to the loading axis of the bars in the SHPB setup. Along with crack orientations, the loading rate is changed with varying gas gun pressures for the two sets of numerical models. The stress-strain responses are retrieved from the center and tip of the pre-crack introduced in the sandstone specimen. A comparative analysis is conducted for the responses obtained at the center and tip of the diametral and cross-sectional cracks and the results are stated herein.

Research on rock strength prediction model based on machine learning algorithm

The compressive strength of rocks is one of its mechanical characteristics. It has been a difficult problem to predict rock compressive strength conveniently and efficiently, and to solve the limitations of traditional rock compressive strength tests such as high cost, long time consumption, and reliability assurance. In this study, a data set containing 1774 groups of rock compressive strength test data was constructed through file retrieval, including 9 input parameters: rock type, temperature, confining pressure, dimension of specimen, shape of specimen, and experimental method. Eight supervised learning algorithms were used to learn the rock compressive strength test data, and eight rock compressive strength prediction models considering multiple factors were established to obtain a better method of predicting rock compressive strength. By selecting different features, the optimal feature combination for predicting rock compressive strength was obtained, and the optimal parameters for different models were obtained through the Sparrow Search Algorithm (SSA). Finally, four regression evaluation indicators, including mean absolute error (MAE), root mean square error (RMSE), mean absolute percentage error (MAPE), and coefficient of determination (R2), were used to evaluate the predictive performance of the established regression models. The results showed that the best-trained model had a MAPE as low as 3.61%, MAE as low as 9.19 MPa, and R2 as high as 0.995. It is noteworthy that AdaBoost was found to be the best model for predicting rock compressive strength. This study presents a significant advancement in the field by demonstrating the effectiveness of machine learning algorithms in this context, which have not been extensively applied to rock compressive strength predictions. The findings suggest that these models can offer substantial improvements over traditional methods, not only in accuracy but also in operational efficiency. This research is important for geotechnical engineering, as accurate rock strength predictions are critical for the design and stability assessments of construction projects, ultimately contributing to safer and more cost-effective engineering solutions.

Analysis of natural and technological factors of changes in exogeodynamic conditions of mine No. 2 of the Stebnytsky potassium deposit as a consequence of self-rehabilitation flooding

The Stebnytsy deposit of potash salts is located in the foothills of the Ukrainian Carpathians. The engineering-geological and hydrogeological conditions of the field’s operation due to the development of a thick layers of loose and water-soluble rocks are difficult of loose and water-soluble rocks are complex and therefore sensitive to mining-technological influences, extraction of rocks, deformation of the surface, hydrographic network, activation of the interaction of surface and groundwater. The most threatening situation was at mine No. 2, where in 1978, due to too intensive blasting, violation of waterproof layers, loosening and increase of water permeability, reduction of rock strength, an emergency breakthrough of super-saline waters occurred in the spent chambers of the first horizon. The total inflow of brines during the years of existence of the flow here constantly increased and reached up to 1700 m³/day, in 2002, the outflow of suprasaline waters developed in 22 points and acquired an irreversibly negative character, suffusion-diffusion processes began to develop actively. During the operation of the mine, ore extraction was carried out for a long time without laying out spent cavities, as a result of which more than 15 million m³ of unlined cavities were formed at the mine, the deformations of which disturbed the geodynamic regime of the salt-bearing massif with the subsequent development of sedimentary and karst-failure processes. In 2004, a comprehensive project for the conservation of mine No. 2 and the reclamation of disturbed lands was approved in order to restore the ecological balance in this area. Mine conservation works were carried out behind the design schedule, which led to the failure of the main provisions of the project and increased the danger due to the expansion of existing karst cavities and the formation of new ones. It can be argued that the works on the conservation of mine No. 2, including: preparation of brines, feeding them to underground mine workings, laying of chambers, etc., were carried out in a timely and incomplete manner, which does not ensure the cessation of negative consequences for the natural environment and ecological safety. The results of our research can be used in the future in the development of projects for the conservation or liquidation of salt mines.

Numerical Simulation of Uplift Behavior of a Rock-Socketed Pier Anchored by Inclined Anchors in Rock Masses

The rock-socketed pier anchored by inclined anchors (RPIA) is a new type of foundation developed by combining a rock-socketed pier and inclined anchors. Current research on RPIA is relatively limited, and the impact of design parameters on its bearing performance remains unclear. To investigate the uplift-bearing performance of RPIA, a finite-element model that considers the nonlinear properties of materials and multidirectional interactions was developed and verified. Based on this model, numerical simulations were performed on twenty-five RPIA that were designed using the L25 orthogonal array proposed by the Taguchi method, and the uplift load–displacement curve for each RPIA was obtained. Based on the interpretation of the elastic limit, uplift resistance, initial stiffness, and the ductility index for each simulated RPIA, the sensitivity of each factor was examined by analyzing the signal-to-noise ratio and variance. The results indicated that rock strength and pier diameter were the main factors determining the uplift performance of the RPIAs, while the angle of inclined anchors is the most influential factor affecting the ductility of RPIA. The primary role of the inclined anchor is to reduce the extraction of the pier after failure of the side resistance between the pier and rock mass, thus significantly enhancing the ductility of the uplift-loaded RPIA. The addition of reinforcements around the connection joints of the pier and anchors may prevent concrete failure and to fully execute the role of inclined anchors.

The Practicality of Quality Assessment Metrics for Millimetre‐Scale Digital Image Correlation Speckle Patterns

ABSTRACTDigital image correlation (DIC), often used in multidisciplinary applications by nonexperts, relies heavily on the quality of a speckle pattern for accurate deformation tracking. Numerous metrics have been developed to assess speckle pattern quality and guide decision‐making in DIC postprocessing. This investigation considered the applicability of these metrics in the selection of an optimal speckling method for two‐dimensional DIC strain measurements, using the standard Brazilian tensile strength rock mechanics laboratory test as a case study. Four speckle patterning methods—spray paint, airbrush, stamp and laser engraving—were optimized to produce patterns of good visual quality for this specific DIC setup. Twenty specimens, five for each method, were prepared, and their speckle patterns were analysed using 10 published metrics. Each pattern was also deformed numerically to quantify the associated systematic and random errors. Overall, none of the 10 metrics demonstrated substantial agreement with the numerical experiment errors due to their failure to account for the confounding influence of pattern characteristics. Consequently, these tools are limited in their usefulness to evaluate the accuracy and reproducibility of speckle patterns with similar characteristics. Numerical simulation of pattern deformation is recommended as the most accurate resource for nonexpert DIC users to assess reproducibility and select optimal patterning methods in practical applications.

Analyzing Pillar Strength and Behavior using Wolfram Mathematica code: Effects of Cracks, Size and Discretization

The stability of fractured rock masses and the modeling of underground mining pillars necessitate a comprehensive understanding of behavioral models and mechanical properties. This study employs the Wolfram Mathematica code to investigate mining pillar reliability, specifically focusing on elucidating the influence of scale and shape on pillar strength. Drawing inspiration from methodologies in the existing literature, our approach is based on the Mohr-Coulomb theory and Griffiths's random field of rock strength. This study highlights the significance of shape, where pillar strength exhibits exponential growth with increasing width-to-height ratios. Beyond a critical value, strength surges, especially under elevated confining stress. Additionally, a critical mesh size significantly affects the weakest pillar behavior. Our results confirm the 'size effect,' wherein strength generally decreases with increasing pillar volume. Thus, strength decreases with rising volume until a threshold. Particularly noteworthy is the phenomenon observed in the presence of cracks; initially, an increase in mesh size leads to a decline in strength, corresponding to an increase in the number of cracks. However, this decline stabilizes beyond a critical mesh size, after which strength experiences a resurgence echoing behavior seen in the homogeneous case. In this paper, the reproduction of the scale effect by an algorithm based on the Mathematica code was made to allow a probabilistic study to be carried out because of the random existence of discontinuities in nature – another hand to carry out stochastic modeling of fractures and its influence on the rock mass strength.

The Use of Conversion Factor and Strength Ratio in the Estimating of Basaltic Rocks Strength and Investigation of Their Changes with the Concrete Curing Time

The Use of Conversion Factor and Strength Ratio in the Estimating of Basaltic Rocks Strength and Investigation of Their Changes with the Concrete Curing Time

Deformation mechanisms and geometries of superposed fault zones in dolostones

Understanding how heterogeneous rock volumes deform is crucial in structural geology, and several studies have addressed this issue by focusing on the impact that the mechanical stratigraphy of a layered stratigraphic sequence has on deformation. However, mechanical layering can also develop subparallel to fault surfaces within the upper crust, and how these anisotropies affect subsequent deformation has been much less explored. This work addresses this aspect by structurally and mechanically characterizing superposed fault zones developed in Triassic dolostones that crop out in the fold-and-thrust belt of the southern Apennines. We investigate how layering associated with an early, reservoir-scale, normal fault zone (F1), inherited from Upper Triassic−Lower Jurassic pre-orogenic extension, influenced the deformation mechanisms and the geometry of younger strike-slip faults (F2) that formed at an angle to it in the early Pliocene in association with out-of-sequence tectonics during the Apennine orogeny. We combined field surveys and laboratory analyses using a multiscalar and multimethodological approach. Meso- and microstructural observations and geomechanical, laboratory, and in situ tests were employed to describe fault rock attributes. We found that the architecture of the F1 normal fault primarily consists of four tens-of-meters-thick, subparallel fault rock units. They have a cataclastic core, and are bounded in the hanging wall by cemented micromosaic breccia, and in the footwall by high-strain and low-strain fault rocks. The younger F2 strike-slip faults developed alternatively as either cataclastic shear bands or compaction bands and occur in either localized or anastomosing geometries. By combining data, we demonstrate that the particle size distribution, porosity, and rock strength of the fault rock units related to older normal faults are the main controls on the deformation mechanisms (i.e., cataclasis versus compaction) and geometry (i.e., localized anastomosed) of the subsequent strike-slip faults. Our study highlights that preexisting highly porous fault rocks favor the development of compaction deformation bands. Conversely, low rock strength facilitates the formation of discrete and diffuse slip surfaces. These results can have significant implications for assessing fluid flow in multifaulted dolomite reservoirs.

A Direct Measurement Method for the Uniaxial Tensile Strength of Rock

A universally applicable direct tension test method is proposed in this paper based on the concept of “compression-to-tension”. Using this method, one or two typical rocks were selected for each of the three types of rocks. The testing results of the direct tension method proposed were compared with the internationally recommended Brazilian splitting method to validate the feasibility of the direct tension method. Results showed that the tensile strengths of six typical rocks were consistent using the direct tensile test method proposed in this study and the Brazilian splitting method recommended internationally. The direct tensile strength deviation coefficient (Cv) of the six types of rocks was less than 0.1, indicating very small variability. In this study, the deviation coefficient (Cv) of the axial displacement corresponding to the tensile strength in both the direct tensile and indirect tensile tests was also less than 0.1, reflecting minimal variability. This shows the consistency of the two tensile test results to a certain extent, and also shows that the direct tensile test method is feasible to determine the tensile strength of rock.