Rock Strength Parameters Research Articles

Appraisal of Different Artificial Intelligence Techniques for the Prediction of Marble Strength

Rock strength, specifically the uniaxial compressive strength (UCS), is a critical parameter mostly used in the effective and sustainable design of tunnels and other engineering structures. This parameter is determined using direct and indirect methods. The direct methods involve acquiring an NX core sample and using sophisticated laboratory procedures to determine UCS. However, the direct methods are time-consuming, expensive, and can yield uncertain results due to the presence of any flaws or discontinuities in the core sample. Therefore, most researchers prefer indirect methods for predicting rock strength. In this study, UCS was predicted using seven different artificial intelligence techniques: Artificial Neural Networks (ANNs), XG Boost Algorithm, Random Forest (RF), Support Vector Machine (SVM), Elastic Net (EN), Lasso, and Ridge models. The input variables used for rock strength prediction were moisture content (MC), P-waves, and rebound number (R). Four performance indicators were used to assess the efficacy of the models: coefficient of determination (R2), Root Mean Square Error (RMSE), Mean Square Error (MSE), and Mean Absolute Error (MAE). The results show that the ANN model had the best performance indicators, with values of 0.9995, 0.2634, 0.0694, and 0.1642 for R2, RMSE, MSE, and MAE, respectively. However, the XG Boost algorithm model performance was also excellent and comparable to the ANN model. Therefore, these two models were proposed for predicting UCS effectively. The outcomes of this research provide a theoretical foundation for field professionals in predicting the strength parameters of rock for the effective and sustainable design of engineering structures

Hybrid Fuzzy-Based Modeling of Shear Strength Parameters of Rocks Using Petrographic Properties

Hybrid Fuzzy-Based Modeling of Shear Strength Parameters of Rocks Using Petrographic Properties

Estimation of mechanics parameters of rock in consideration of confining pressure using monitoring while drilling data

During the drilling process, high-strength rock can lead to various issues such as drilling suppression, bit wear, and increased operational costs. To ensure safe and efficient drilling operations, it is crucial to accurately predict the strength parameters of the rock and recommend modifications to operational procedures. This paper proposes a low-cost and fast measurement method for predicting the strength parameters of rock in the field. To evaluate the effectiveness of this method, a drilling process monitoring experiment was conducted on sandstone, limestone, and granite. The experiment studied the effect of confining pressure on the response of cutting with an impregnated diamond bit. By analyzing the relationship between the thrust force, torque force, and penetration depth under different confining pressures, the researchers developed an analytical model for drilling that considers confining pressure, compressed crushed zone, and bit geometry. The results show that the confining pressure has a significant effect on the cutting response. As the confining pressure increases, the thrust force, torque force, and penetration depth at the cutting point also increase. Furthermore, a new measurement method was proposed to determine the strength parameters, such as cohesion, internal friction angle, and unconfined compressive strength. The estimated strength parameters for the three rock types using the drilling method were in good agreement with those of the standard laboratory test, with an error range of 10%. This method of estimating rock strength parameters is a practical tool for engineers. It can continuously and quickly obtain the drilling parameters of in-situ rocks.

Cutting energy characteristics for brittleness evaluation of rock using digital drilling method

The reliable evaluation of rock brittleness is essential in engineering geology for various applications, such as water conservancy, hydropower, transportation, energy exploration, and underground engineering development. This study proposes a new method for evaluating rock brittleness using a digital drilling approach. A cutting model was established to describe the relationship between the energy characteristics and mechanical parameters of the rock during the drilling process, accounting for the effects of friction and drilling fluid. Furthermore, a drilling-based index, the brittleness evaluation index (BEI), was developed to evaluate rock brittleness based on energy dissipation. We conducted drilling tests to investigate energy evolution, including cutting energy, friction energy, and liquid energy. The results indicated that cutting energy has a linear correlation with the strength parameters of rock, with a significant correlation coefficient. With increasing drilling depth, cutting energy and liquid energy exhibit a similar increasing trend, which initially remains constant and then increases linearly after a critical depth is reached. Friction energy rapidly increases with drilling depth at the beginning, and the growth rate decreases after reaching the critical point. Compared with the laboratory-determined brittleness index, our proposed method provides a reliable evaluation of rock brittleness. In summary, our study offers a practical approach to evaluating rock brittleness that could benefit various engineering applications.

Deep Learning for Intelligent Prediction of Rock Strength by Adopting Measurement While Drilling Data

Precise, rapid, and reliable prediction of rock strength parameters is of great significance for underground engineering. This paper presents a method for predicting rock strength parameters including the Poisson’s ratio (P), elastic modulus (E), and uniaxial compressive strength (UCS) based on computer drilling jumbo measurement while drilling (MWD) data. First, the distribution characteristics and correlation of MWD data are studied; second, a filtering method of MWD data is proposed, which reduces the influence of operational and mechanical factors; finally, an intelligent prediction model of rock mechanics parameters was established, 30 groups of test data were used for application, and the mean absolute percentage error (MAPE) of prediction results for P, E and UCS are 2.11%, 3.11%, and 2.9%, the determination coefficients (R2) are 0.4346, 0.8241, and 0.6616. Compared with the data before optimization, the accuracy of prediction results is improved significantly, it shows that the deep neural network model can accurately predict rock mass parameters.

Calculation of Risk Probability of Levee Landslide Based on Three-dimensional Lequilibrium Theory

Sliding instability is a common form of failure of embankments, and traditional dike safety evaluation often uses the safety factor value to judge whether it is safe or not. However, due to the uncertainty of the rock and soil characteristics of the embankment, the evaluation results of the safety factor method sometimes fail to reflect the reality, and it is reasonable to use the risk analysis of sliding instability considering these uncertainties. In this paper, the uncertainty of rock and soil strength parameters and the randomness of seepage field are considered, and the risk probability of sliding instability of the embankment is solved by relying on the reliability analysis method. In the reliability analysis, a three-dimensional bin method combining slope stability analysis and gradient optimization method of reliability analysis are proposed, which consider the safety performance, so that the stability evaluation is not too conservative, and the corresponding sliding risk probability can be obtained while obtaining reliable indicators. Finally, the calculation program is prepared for the proposed method, and the proposed method is verified to be reasonable and correct through the example.

A benchmark study of different numerical methods for predicting rock failure

Nowadays, with many available numerical methods developed in rock mechanics, researchers have always focused on the parameter calibration of the numerical model but ignored the predictive capability of these methods. A comparative study of nine commonly used numerical methods was performed for predicting rock failure through international cooperation organized by the Discontinuous Deformation Analysis (DDA) commission of the International Society for Rock Mechanics (ISRM). Two steps of numerical modelling were conducted including a calibration procedure from given experimental results and a numerical prediction for benchmark tests with these calibrated parameters for three types of rocks. Through the comparison between different numerical and experimental results, the inherent weaknesses and strengths of different numerical methods in terms of predicting rock failure were identified and analysed. The influence of human intervention in terms of parameter selection is even more significant than the choice of different numerical methods. Some potential factors (i.e., different boundary conditions, heterogeneity of rock material, strength parameters, particle packing, and failure criteria) that may occur in numerical and physical tests were further discussed. Through the comparison of different failure criteria, we found the selection of rock failure criterion might be the major factor that affected the predictive capability of numerical methods, and the nonlinear failure model (the Hoek–Brown criterion) showed the superiority in the prediction of rock fracturing subjected to complex stress conditions. This comparative work also enlightens the significance of a high-quality calibration process and the future advancement of rock failure criteria.

Study on influencing factors of slope stability and evolution law of safety factor in coal measure strata

Aiming at the influence factors and their action regulation of the slope stability in the coal measure strata of Beijing–Hong Kong & Macao Expressway, the influence characteristics of injection dip angle of rock stratum, thickness and strength parameters of the soft interlayer, slope height and size of slope angle on the slope safety factor are systematically studied by using the limit equilibrium method theory. The influence of slope height, thickness of weak interlayer and shear strength parameters on the stability of slope in coal measure strata with different dip angles is that the safety factor decreases first and then increases with the increase of strata dip angle. The minimum safety factor of slope under the action of each factor is near the strata dip angle of 30°, which indicates that the stability of slope in coal measure strata is poor when the dip angle of rock stratum is about 30°. With the increase of slope angle, the minimum safety factor decreases. However, when the slope angle is less than 40°, the slope is in a stable state and the dip angle of the strata do not affect the stability of the slope. Slopes with different slope angles have the minimum safety factor that is not affected by slope height. The difference between analytical solution and numerical solution is analyzed. The research provides a theoretical basis for the treatment of slopes in coal measure strata and has certain practical significance.

Numerical Investigation of the Formation of a Failure Cone during the Pullout of an Undercutting Anchor.

Previously published articles on anchors have mainly focused on determining the pullout force of the anchor (depending on the strength parameters of the concrete), the geometric parameters of the anchor head, and the effective anchor depth. The extent (volume) of the so-called failure cone has often addressed as a secondary matter, serving only to approximate the size of the zone of potential failure of the medium in which the anchor is installed. For the authors of these presented research results, from the perspective of evaluating the proposed stripping technology, an important aspect was the determination of the extent and volume of the stripping, as well as the determination of why the defragmentation of the cone of failure favors the removal of the stripping products. Therefore, it is reasonable to conduct research on the proposed topic. Thus far, the authors have shown that the ratio of the radius of the base of the destruction cone to the anchorage depth is significantly larger than in concrete (~1.5) and ranges from 3.9-4.2. The purpose of the presented research was to determine the influence of rock strength parameters on the mechanism of failure cone formation, including, in particular, the potential for defragmentation. The analysis was conducted with the finite element method (FEM) using the ABAQUS program. The scope of the analysis included two categories of rocks, i.e., those with low compressive strength (<100 MPa) and strong rocks (>100 MPa). Due to the limitations of the proposed stripping method, the analysis was conducted for an effective anchoring depth limited to 100 mm. It was shown that for anchorage depths <100 mm, for rocks with high compressive strength (above 100 MPa), there is a tendency to spontaneously generate radial cracks, leading to the fragmentation of the failure zone. The results of the numerical analysis were verified by field tests, yielding convergent results regarding the course of the de-fragmentation mechanism. In conclusion, it was found that in the case of gray sandstones, with strengths of 50-100 MPa, the uniform type of detachment (compact cone of detachment) dominates, but with a much larger radius of the base (a greater extent of detachment on the free surface).

Reliability Prediction of Tunnel Roof with a Nonlinear Failure Criterion

Based on the kinematics-based upper bound theorem and reliability theory, the stability of deep tunnel roofs in nonlinear Hoek-Brown media is investigated. The performance functions of rectangular and circular tunnels are proposed according to the roof collapse mode, respectively, with support pressure and pore water pressure being considered. With the proposed performance function of the rectangular tunnels, the first-order reliability method is utilized to perform reliability analysis. The rock strength parameters are regarded as random variables following the normal or lognormal distribution. To assess the validity of the obtained results, reliability indexes for different support pressure values are calculated and compared with solutions using the response surface method and Monte-Carlo simulation. The agreement shows that the first-order reliability method effectively evaluates the reliability index with the proposed performance function. Sensitivity analysis is performed to throw light on the significance of different random variables, and the impact of the variation coefficient on reliability indexes is discussed. For circular tunnels, MCS is utilized to evaluate the roof stability with the proposed performance function. The influences of the support pressure on the reliability index and the corresponding design points are investigated. The parametric study shows that the normal distribution of random variables has more influence on the failure probability than that of the lognormal distribution. However, the difference between the two distributions is small. σt is the major factor that influences the reliability index compared to the B and ru. The supporting pressure for circular tunnels is smaller than that of rectangular tunnels when a target reliability index of 2.5 (failure probability equals 0.62%) is given.

Fire-induced damage in tunnels: Thermo-mechanical modeling incorporating support system and geological conditions

The thermo-mechanical response of underground tunnels to fire loads is governed by interactions between the tunnel structure and the surrounding geological formation. Accordingly, for accurate prediction of damages in the tunnel structure subsequent to a fire event, it is critical to incorporate the state of the support system as well as in-situ conditions in the surrounding geology at the time of the fire event. Current tunnel-fire studies are mainly developed adopting beam-spring elements, thus disregarding the intricacies of the surrounding geological formation, its true constitutive behavior, as well as realistic tunnel-rock interactions. Another limitation in current tunnel-fire studies is assuming uniform temperature loads within the tunnel interface using time–temperature curves obtained from design codes, therefore ignoring the spatial nature of fire-induced temperatures along the tunnel interior. Temperature gradients can generate additional damage to the tunnel structure. This paper presents a comprehensive integrated numerical framework aimed to predict fire-induced damages in underground tunnels, incorporating four novel components: (i) detailed design of the tunnel support system and in-situ conditions; (ii) degradation of the original tunnel support system over the years due to presence of chloride and sulfates in nearby environment; (iii) thermal gradients generated along tunnel cross section due to real fire events; (iv) and thermo-mechanical interactions between the tunnel structure and the surrounding geological medium, incorporating thermal-induced strength degradation in the concrete and in the steel support elements following design standards from Eurocode. The numerical framework consists of fire simulation using computational fluid dynamics, and thermo-mechanical modeling of the tunnel response to fire. The proposed numerical framework has been utilized to simulate the Caldecott tunnel fire as the case study in this paper, and to evaluate the impacts from the in-situ stress regime and rock strength parameters on the thermo-mechanical behavior response of tunnel to fire events. Results provide a novel insight into the geomechanical response of horseshoe tunnels to fire. Findings reveal the critical zones prone to damage during a fire event to be highly governed by the in-situ stress field and the strength parameters of the surrounding geological strata.

Bearing capacity of foundations resting on rock masses subjected to Rayleigh waves

This study investigates the ultimate bearing capacity of shallow foundations resting on rock masses under earthquakes using upper-bound limit analysis. A modified pseudodynamic method (MPD) that considers the influence of Rayleigh waves is initially used to characterize the spatiotemporal variation in earthquake acceleration. The strength of rock masses is governed by the generalized Hoek‒Brown criterion and the plastic flow at failure is assumed to respect the associated flow rule. The generalized tangential technique is introduced to provide a linear approximation of the strength envelope for capturing the equivalent Mohr‒Coulomb strength parameters. The classic nonsymmetrical multi-block translational mechanism, which is capable of assessing a rock-foundation system under asymmetrical load, is reconstructed to portray the velocity discontinuity of the plastic failure region. Based upon the energy equilibrium theorem of the limit analysis, an analytical solution of seismic bearing capacity is derived and then formulated as a multivariate optimization problem. Comparisons show good agreement with the literature and validate the correctness and rationality of this work. Parametric study indicates that the seismic foundation capacity obtained by MPD tends to be conservative compared to the pseudostatic method with the same seismic coefficients, and that the period of a Rayleigh wave has only a slight effect on the bearing capacity. The failure region is more sensitive to the disturbance coefficient than it is to the other rock strength parameters.

A new method for determining muckpile fragmentation formed by blasting

Muckpile fragmentation formed by blasting depends on the specific charge factor, the discontinuities in the rock mass, and the rock strength. Determination of the discontinuity characteristics and rock strength is a long and difficult process. These two parameters are directly associated with the rock drilling speed. Therefore, it is the drilling speed of the machine used for the blast-hole, rather than the blasthole discontinuity characteristics and rock strength parameters, that is used in the prediction of muckpile fragmentation before blasting. Primarily, it has been suggested that the muckpile fragmentation values can be correctly determined by establishing correlations between the efficiency of the loader and muck pile fragmentation, since fragmentation is directly correlated with the former parameter. Subsequently, a correlation predicting the drilling speed of the drill machine was developed according to the discontinuity characteristics of the blasting surface and the rock strength. Finally, a correlation was developed predicting muckpile fragmentation according to the specific charge factor and the drilling speed of the drill machine The data was obtained by conducting blasting tests in two different limestone quarries.

Effects of Particle Size and Soil Bed on the Shear Strength of Materials in the Direct Shear Test

Generally, direct shear apparatus is used to determine the shear strength parameters of soil and rock for designing a geotechnical engineering structure. However, the size of the shearing box and the soil sample is key for evaluating the shear strength parameters of test materials, and also testing conditions in the laboratory are different from site conditions. This research aimed to focus experimentally on the effect of particle size and the property of subgrade materials that were necessary keys for installing apparatuses for the direct shear test. According to the experimental results based on a 5 x 5 cm shear box, an increase in average particle size and coefficient of curvature could provide higher shear strength in terms of internal friction angle of the sample, but not for the case of higher value of the uniformity coefficient. Using both 5 x 5 cm and 30 x 30 cm shear boxes, a large B/Dmax ratio is not the key for determining appropriate parameters when testing with samples that have a nearly uniform size. Samples varied in thickness of both the ballast and subgrade layers, were investigated and observed by a large shear box. It was found that good properties of subgrade materials affected the shear strength of ballast materials, and they provided underestimates of strength when the bottom of the shearing box was rigid. The modified parameter of ballast materials on the subgrade layer is suggested for obtaining strength parameters reflecting the ballasted track system.

Multi-scale deterioration of physical and mechanical properties of argillaceous siltstone under cyclic wetting-drying of Yangtze River water

Cyclic interactions between rocks and water have general significance and are particularly relevant to engineering failures and geohazards. A comprehensive investigation of the multi-scale deterioration effects and mechanisms of cyclic wetting-drying on rocks can contribute to better engineering applications, but the probabilistic characterization of rock mass properties under cyclic wetting-drying remains a problem due to the difficult-to-test parameters and limited data. Numerous experiments on rock samples of argillaceous siltstone subjected to cyclic wetting-drying of Yangtze River water demonstrate progressive alteration of rock properties on multiple scales, including changes in mineralogy, grain structure, computed tomography, microporosity, and complexity of micropores, with calcite and albite being the most active minerals. The uniaxial compression strength and indirect tensile strength decrease exponentially with the cyclic number, while the Young's modulus increases. Considering the probabilistic characteristics of the geological strength index, the probabilistic mechanical properties of rock mass of studied argillaceous siltstone are then estimated through the generalized Hoek-Brown criterion. The results indicate that the uniaxial compression strength and indirect tensile strength of rock mass both follow lognormal distributions, while the Young's modulus follows a skewed distribution. Long-term strength parameters of rock and rock mass can also be determined as they exhibit exponential trends with the cyclic number. During the cyclic wetting-drying process, the water-rock interactions produce progressive changes in mineral compositions, microstructures, and micropores; with the accumulation of variations of physical properties, defects grow and develop into weak zones, thus the mechanical properties of argillaceous siltstone are significantly weakened. Investigations of the wetting-drying effects on the geological strength index and probabilistic characteristics of rock sample properties are recommended to accurately evaluate rock mass properties affected by cyclic wetting-drying.

Water saturation effects on the mechanical characteristics and fracture evolution of sandstone containing pre-existing flaws

To comprehensively investigate the effect of water content on the crack propagation characteristics and fracture mechanism of jointed rock, uniaxial compression experiments were conducted on red sandstone specimens under different water content conditions and different bridge lengths. Acoustic emission (AE) techniques and digital image correlation (DIC) methods were applied to record the AE signals and deformation field of the specimens during the testing. The physical and mechanical properties, crack propagation characteristics and AE parameters of red sandstone under water–rock coupling were analysed. The results demonstrated that the water content and rock bridge length have conspicuous effects on the compressive strength, elastic modulus, temporal b value, P-wave velocity, and crack propagation model. The fracture initiates from the lowest pre-fabricated crack and the fracture mode gradually changes from shear to tensile fracture with the increase of the rock bridge length. Additionally, the micro-structure of the sandstone develops from a relatively dense pore cement structure to an irregular honeycomb structure. And the deterioration of the rock strength parameters could refer to the pore pressure generated by free water.

Study on the slope dynamic stability considering the progressive failure of the slip surface under earthquake

The strength of a rock-soil mass shows complex and obvious weakening characteristics under seismic dynamic load. The previous stability analysis methods of a seismic slope do not fully depict the attenuation law of geotechnical materials and cannot truly reflect the stable state of a slope under earthquake action. Based on the theoretical analysis of the progressive failure mechanism and the evolution law of a seismic slope, the adverse effect of progressive failure on slope stability is clarified. According to the progressive failure process of a slope under dynamic load, the strain-softening model and vibration deterioration model are introduced to represent the attenuation law of rock strength parameters, and a calculation method of seismic slope stability coupled with vibration disturbance and progressive failure is proposed. The method considers the strength parameter characteristics of a rock-soil mass in different stages and is combined with the vector sum method to obtain the time-history curve of the slope safety factor under earthquake action, which makes the evaluation result of slope stability more accurate and reliable. The numerical examples show that this method can effectively reflect the dynamic stability of seismic slopes, and solve the problem that the traditional calculation methods are difficult to characterize the strength attenuation characteristics of rock and soil mass. If these characteristics are not considered, the calculation results will be unsafe.

System reliability analysis of foundation stability of gravity dams considering anisotropic seepage and multiple sliding surfaces

PurposeFor gravity dams built on foundations with directional joint sets, the seepage in the foundation possesses anisotropic characteristics and may have adverse effects on the foundation stability. A methodology for system reliability analysis of gravity dam foundations considering anisotropic seepage and multiple sliding surfaces is proposed in this paper.Design/methodology/approachAnisotropic seepages in dam foundations are simulated using finite element method (FEM) with the equivalent continuum model (ECM), and their effect on dam foundation stability is involved by uplift pressures acting on the potential sliding surfaces. The system failure probability of the dam foundation is efficiently estimated using Monte Carlo method (MCM) combined with response surface method (RSM).FindingsThe case study shows that it is necessary to consider the possibly adverse effect of anisotropic seepage on foundation stability of gravity dams and the deterministic analysis of the foundation stability may be misleading. The system reliability analysis of the dam foundation is justified, as the uncertainties in shear strength parameters of the foundation rocks and joint sets as well as aperture, connectivity and spacing of the joint sets are quantified and the system effect of the multiple potential sliding surfaces on the foundation reliability is reasonably considered.Originality/value(1) A methodology is proposed for efficient system reliability analysis of foundation stability of gravity dams considering anisotropic seepage and multiple sliding surfaces (2) The influence of anisotropic seepage on the stability of gravity dam foundation is revealed (3) The influence of estimation errors of RSMs on the system reliability assessment of dam foundation is investigated.

Estimating strength parameters of Lower Gondwana coal measure rocks under dry and saturated conditions

Estimating strength parameters of Lower Gondwana coal measure rocks under dry and saturated conditions

Mineral Composition and Grain Size Effects on the Fracture and Acoustic Emission (AE) Characteristics of Rocks Under Compressive and Tensile Stress

The influence of rock mineral composition and mineral grain size on basic rock strength performance and AE characteristics have been studied, 13 different rocks microstructures are analyzed in an optical microscope thin section using petrographic image analysis, making it possible to determine the mineral composition and mineral texture characteristics of rocks. Then, the basic strength parameters of rock and AE signals generated during fracture propagation were obtained by UCT (uniaxial compression test) and BIT (Brazilian intension test). Finally, the relationship between basic strength parameters and AE characteristics of rock with mineral composition and grain size was analyzed. The results showed that different mineral constituents have significant effects on rock strength. The positive influence of plagioclase content on igneous strength was obtained. Sedimentary rocks strength increases initially and then decreases with the increase of plagioclase content. Besides, with the increase in quartz and K-feldspar content, the strength of the rock was weakened obviously. It is also found that the greater the dimensional deviation of mineral grain, the greater the strength of the rock. The strength of igneous rocks was inversely proportional to the mineral grain size, but there is no correlation between the sedimentary rocks strength and the mineral grain size. Furthermore, the tension–shear crack propagation of rock can effectively distinguish by judging that the data set of the AF–RA density graph was nearby the AF axis or RA axis and the peak frequency data sets of below 100 kHz or more than. Alterations in the rock nature are the main key reasons for the differences between AE hit rate, AE count rate, AE energy, and cumulative energy. The plagioclase content and grain size play a decisive role in AE signal characteristics and failure mode.