Rock Mass Characterization Research Articles

Quantifying uncertainty in rock mass properties: Implications for GSI, RMi, and RMR assessments

Probability-based empirical methods were employed as an alternative approach to predicting uncertainties associated with rock mass properties. The focus was on developing probabilistic spreadsheets to forecast rock mass classification indexes. Histograms were constructed to describe the best distribution in predicting rock mass properties. The developed models also offer utility in predicting the impact of discontinuities within the rock mass on rock strength and rock mass classification systems. Statistical analyses identified volumetric joint count, joint spacing, joint frequency, and rock strength as the most influential parameters. Moreover, the statistical analysis revealed varying degrees of correlation among different rock mass properties. While some properties demonstrated significant correlations suitable for modelling, others did not align well with any correlation model. The results highlight the need for a comprehensive approach to rock mass characterization, considering multiple factors beyond volumetric joint count. Geological complexities, including tectonic activity and weathering processes, may obscure direct correlations. These results emphasize the importance of empirical modelling and detailed site investigations for accurate assessment of rock mass quality and stability in the Himalaya.

Probabilistic evaluation method for the stability of large underground cavern considering the uncertainty of rock mass mechanical parameters: A case study of Baihetan underground powerhouse project

For deep large underground cavern projects under complex geological conditions, the determination of rock mass mechanical parameters and stability analysis is fraught with a great deal of uncertainty. This paper proposes a set of methods for estimating rock mass mechanical parameters and probabilistic stability assessment suitable for construction characteristics of large underground caverns. On the one hand, according to the Hoek-Brown criterion and Monte Carlo simulation, a dynamic estimation method for rock mass mechanical parameters is proposed by using Rock Mass Rating (RMR), the uniaxial compressive strength (UCS) of intact rock, and the material constant (mb) as input parameters. On the other hand, considering the uncertainty of rock mass mechanical parameters, a probabilistic evaluation method applicable to the unloading response characteristics of rock mass (including displacement and fracturing zones) around the large cavern is put forward, combining the point estimation method and numerical simulation. The proposed methods were applied to an underground powerhouse, with an excavation span of 34 m and height of 88.7 m, at the Baihetan hydropower station in the southwest of China. Based on extensive field investigations and tests, the probability distributions of key rock mass mechanical parameters were obtained. Furthermore, the high sensitivity of input parameters in the H-B criterion for estimating rock mass mechanical parameters were revealed. Through dynamic simulation, the probability distributions of the displacement and fracturing zones in surrounding rock during the layer-by-layer excavation of the cavern were presented. Comprehensive on-site tests showed that the simulated results were in basic agreement with the actual unloading response behavior during the cavern excavation, validating the correctness and applicability of the proposed methods. The study provides a relatively comprehensive approach for estimating rock mass mechanical parameters and stability evaluation in similar underground engineering projects, and also has guiding significance for predicting and preventing engineering rock mass hazards.

Study on fragmentation characteristics of rock mass in bench blasting with different coupling media

Study on fragmentation characteristics of rock mass in bench blasting with different coupling media

Frost heaving and crack initiation characteristics of tunnel rock mass in cold regions under low-temperature degradation

Frost heaving and crack initiation characteristics of tunnel rock mass in cold regions under low-temperature degradation

Experimental and numerical analysis of Brazilian splitting mechanical properties and failure mechanism for composite discs

The properties of structural planes and the strength of rock matrix significantly influence the splitting characteristics of composite rock masses. To investigate the effects of structural plane and differences in matrix strength on the mechanical behavior and failure characteristics of composite jointed rock bodies, composite jointed disc specimens with varying structural plane roughness and matrix combinations were prepared. These specimens were then subjected to Brazilian split tests under different loading angles ranging from 0° to 90°. Results indicate that the failure mode of the specimens is determined by the angle of the structural plane. As the structural plane angle increases, the failure mode transitions from structural plane failure to combination failure and finally back to structural plane failure. Increased roughness of the structural plane reduces the extent of structural plane failure, while matrix strength has no significant impact on the failure mode. The failure load of the specimens increases with increasing structural plane angle, roughness, and matrix strength. The influence of structural plane roughness and matrix strength on the mechanical properties of the specimens grows with increasing structural plane angle. Increases in structural plane roughness and matrix strength significantly enhance the strain energy and dissipated energy of the disc model. Finally, an analysis of the stress state on the structural planes is combined with an exploration of the failure mechanisms of the specimens.

Utilizing Deep Learning for the Automated Extraction of Rock Mass Features from Point Clouds

Utilizing Deep Learning for the Automated Extraction of Rock Mass Features from Point Clouds

A new approach for 3D structure characterization of rock mass using an improved elliptical discrete fracture network model

Fracture structures in rock masses profoundly affect the stability of deep rock engineering, whereas conventional methods utilizing local surface fracture data on rock mass and disk models are limited in characterizing complex three-dimensional (3D) fractures. This raises two critical inquiries: How to enhance the comprehensiveness of fracture parameter collected on-site? And how to improve the accuracy of 3D fracture reconstruction? Hence, we proposed an approach for characterizing 3D fractures of rock mass by optimizing on-site acquisition techniques and discrete fracture network model. By integrating unmanned aerial vehicle (UAV) and borehole TV imaging techniques, we extracted comprehensive fracture parameters (e.g., trace length, orientation, and spacing) from the surface to the interior of the engineered rock mass. Leveraging the capability of the non-similar elliptical discrete fracture network model to more accurately represent fracture shapes, we introduced a dual-parameter correction method that integrates rotation angle and volume density adjustments into Monte Carlo simulation, resulting in an improved comprehensive parameter elliptical discrete fracture network (CPE-DFN) model. This model exhibited a substantial improvement in accuracy compared to previous disk models, achieving enhancements ranging from 11.2% to 24.9%. Finally, we validated the applicability and precision of this new method for 3D fracture characterization using comprehensive fracture data collected from a deep tunnel in western Sichuan, China, with an error of less than 8%. This work holds potential applications in investigating preferential flow paths as well as evaluating rock mass integrity and fractured zones in rock masses.

Investigate on the mechanical properties and microscopic three-dimensional morphology of rock failure surfaces under different stress states

The macro and micro morphology of rock failure surfaces play crucial roles in determining the rock mechanical and seepage properties. The morphology of unloaded deep rock failure surfaces exhibits significant variability and complexity. Surface roughness is closely linked to both shear strength and crack seepage behavior. Understanding these morphology parameters is vital for comprehending the mechanical behavior and seepage characteristics of rock masses. In this study, three-dimensional optical scanning technology was employed to analyze the micromorphological properties of limestone and sandstone failure surfaces under varying stress conditions. Line and surface roughness characteristics of different rock failure surfaces were then determined. Our findings reveal a critical confining pressure value (12 MPa) that influences the damage features of Ordovician limestone failure surfaces. With increasing confining pressure, pore depth and crack formation connecting the pores also increase. Beyond the critical confining pressure, the mesoscopic roughness of the failure surface decreases, and the range of interval-distributed pore roughness diminishes. Additionally, we conducted a detailed investigation into the water conductivity properties of rocks under different stress states using Barton's joint roughness coefficient (JRC) index and rock fractal theory. The roughness features of rock failure surfaces were classified into three categories based on mesoscopic pore and crack undulation forms: straight, wavy, and jagged. We also observed significant confining pressure effects on limestone and sandstone, which exceeding the critical confining pressure led to increased water conductivity in both rocks, albeit through different mechanisms. While sandstone exhibits fissures running across it, limestone shows shear abrasion holes. Beyond the critical confining pressure, the rock failure surface becomes smoother, leading to decreased water flow blocking capacity. The fractal dimension of Ordovician limestone increases significantly under critical confining pressure, leading to a more complex mesoscopic crack extension route.

The mechanism of low strain rate and moderate principal stress effects in triaxial prestressed marble under lateral impulsive load

Stress waves have a significant impact on the strength and deformation characteristics of deep rock masses at a certain distance from the epicenter or explosion source. In order to study the dynamic responses of deep-buried marble under the disturbance condition, the true triaxial compression test (TTC), the true triaxial disturbed compression test with lateral impulsive load (TTDC) and the synchronous acoustic emission monitoring on the marble were respectively conducted to simulate the influencing process of the seismic wave. The test results show that under lateral impulsive load, a ‘short-range plateau’ phenomenon occurs in the stress-strain curves of the marble samples. With the increase of intermediate principal stress σ2, the ‘short-range plateau’ of ε2 and ε3 curves gradually shrinks and even disappears, and the anisotropy of sample deformation becomes more obvious. The σ2 significantly affects the microfracture activity and the evolution of energy inside the samples under the impulsive load in the whole process of true triaxial disturbed compression. The lateral impulsive load weakens the marble strength which shows an obvious low strain-rate disturbance effect. The marble samples under the impulsive load have a high sensitivity to axial load and are liable to form local brittle fracture. This fracture induced by local stress concentration and strain energy release becomes more pronounced when the axial load is further applied to the samples. By contrast, the impulsive load in σ2 direction has a protective effect on limiting the lateral deformation of the samples and improving its axial deformation capacity, which greatly changes the action mechanism of σ2 on the sample lateral deformation. The variation of marble mechanical properties under lateral impulsive load is the result of the interaction between the low strain-rate disturbance and the intermediate principal stress effect.

Dynamic stress characterization and instability risk identification using multisource acoustic signals in cut-and-fill stopes

The quantitative characterization of rock mass and stress changes induced by mining activities is crucial for structural stability monitoring and disaster early warning. This paper investigates the time–space–intensity distribution of microseismic sources during the pillar-free large-area continuous extraction. Furthermore, it explores a method involving collaborative evolution patterns of the velocity field and spatial b-value to identify stress and structural changes at the panel stope. Results show that anomalous zones in wave velocities and b-values form at the intersections of extraction drifts, strike drifts, cross drifts, and connection roadways influenced by mining activities, as well as in footwall ore-rock contacts, often accompanied by the nucleation of microseismic events. The synergistic use of wave velocity fields and spatial b-value models reveals the relationship between stress migration behavior and stope structure changes due to mining disturbances. The velocity field primarily reflects macroscopic changes in the structure and stress distribution, while spatial b-values further explain stress gradients in specific areas. Additionally, we have advanced the identification of an instability disaster at the connection roadway and cross drift intersection based on increases in wave velocity and abnormal changes in b-value. This paper demonstrates the potential of risk identification using the proposed method, providing insights into predicting geotechnical engineering disasters in complex stress environments.

A Critical Discussion on the Use of Discrete Fracture Network Models in Rock Engineering Practice: Why Rock Mass Characterisation Methods can Benefit from Considering Fracture Connectivity

A Critical Discussion on the Use of Discrete Fracture Network Models in Rock Engineering Practice: Why Rock Mass Characterisation Methods can Benefit from Considering Fracture Connectivity

Rock Mass Characterization and Slope Stability Analysis Inlet Portal of Jragung Dam Diversion Tunnel, Indonesia

Abstract Slope stability is a serious problem that academics are still looking into in terms of human safety, equipment, and structures along the slope. Failure on slopes happens for a variety of reasons, including rock physical and mechanical properties, discontinuity factors, slope geometry, and external variables like as rainfall and seismic activity. The research location was conducted on the Jragung dam diversion tunnel, administratively located in Candirejo village, Pringapus sub-district, Semarang, Central Java Province. The purpose of this study was to use an empirical and numerical method to investigate the impact of rock mass categorisation on slope stability. The RMR (Rock mass rating) method is used to characterize rock mass, and the SMR (Slope mass rating) method is used to measure slope stability. The numerical slope stability analyses were carried out with the help of Phase2 (Rocscience, Inc.). The results showed that the slope at the intake portal was class IV (poor), and that it was unstable utilizing the SMR technique. According to numerical research, the basic design cut slopes with a 51° inclination were found to be unstable even after strengthening. It was suggested that the slope geometry and support measures be adjusted even more. Modified cut slopes were found to be stable after the slope inclinations were changed from 51° to 27° and shotcrete and rock bolt reinforcement were added.

Mehaničko ponašanje stijenske mase pri ispitivanju smicanja simuliranih materijala

In this paper, the influence of joint distribution on the deformation and strength characteristics of rock mass is studied through direct shear tests of five typical distribution types of simulated materials including two joints. The spatial distribution pattern of joints determines the deformation and failure process and the final shape of rock mass, which is mainly manifested as lap failure between joints. By comparing the 25 stress-strain curves obtained from the test, the stress-strain curves are classified into five types. With the increase of the normal stress, the composite shear type gradually transforms to the shear type, and the shear type gradually transforms to the yield type. The joint distribution pattern has a great influence on the shear strength and the maximum difference is 64 %.

A new method to automatically identify and characterize rock mass discontinuities using a smartphone: Experiences from a slope and a tunnel

Smartphones equipped with high-resolution lenses and advanced photo processing capabilities have evolved into versatile, multifunctional devices. This paper introduces a novel method for extracting and analyzing rock mass discontinuities using smartphones, encompassing smartphone photography, ground control point selection, point cloud reconstruction, and discontinuity set identification and analysis. The method was validated through a slope case study in Bayi District, Linzhi city, Tibet, China, under natural light and a tunnel case study in Northwest China under artificial light, and the results agreed well with traditional compass measurements. Notably, the method proved efficient, reducing the measurement time to 15 min compared to 1.5 h with a geological compass in Case 1. Significant insights were gained regarding the impact of photo quantity and shooting distance on point cloud accuracy, along with the influence of lighting in tunnel environments, thus offering valuable guidance for fieldwork. Moreover, the potential of this smartphone-based method was confirmed through comparative analysis with laser scanner data. In summary, rock mass measurements using smartphones are validated as simple, efficient, and practical approaches for geological studies.

Estimation of rock core indices for development of underground infrastructure using non-invasive geophysical methods

Rock mass characterization offers the basis of the stability criterion for the planning and advancement of civil engineering projects. Rock core index (RCI) is one of the key geotechnical parameters adopted in rock mechanics and rock engineering. RCI provides risk assessment regarding the success criteria of engineering design. Consequently, an accurate estimate of such parameters is a challenging task in the context of credibility, budget, and time. However, the traditional estimation of geomechanical parameters needs lots of drilling tests at some selected points. The point-scale data often cause more ambiguity and less authenticity in engineering design. Besides, the conventional approaches are invasive, uneconomical, and laborious and cannot investigate the complete project site. We offer an indirect technique for the estimate of RCI using empirical relationships between drilling and geophysical data, which addresses the drawbacks of the conventional methods. Geophysical techniques offer the subsurface volumetric data and are faster, more affordable, and easier to use. In this study, we employ a non-invasive CSAMT (controlled-source audio-frequency magnetotellurics) method for the first time to quickly assess 2D and 3D RCI models. The suggested approach assesses the intricate geological subsurface at a depth of 1 km in order to produce a more precise and complete image of the quality of the rock mass across a wide area. These findings are crucial for improving our understanding of the intricate geological conditions, estimating the likelihood of failure early on, and supporting the safe, stable, and cost-effective construction of deep underground engineering structures. In regions where there is a deficiency of mechanical drilling data, our approach decreases the gaps between an appropriate geotechnical model and insufficient data, yields more objective indices, and serves as a guide for more correct engineering structure design.

Study on deformation and failure characteristics of oblique-cut locked rock slope under rainfall conditions

Based on the disaster-pregnant environment and development characteristics of landslide disasters in the western region of Henan Province, a generalized model was established by taking the “oblique-cut” locking rock slope in the layered rock slope as the research object. The numerical simulation method was used to analyze the deformation and failure mechanism and stability influence law of the oblique-cut locking rock slope in western Henan under rainfall conditions. The results show that the inclination angle of the weak interlayer directly affects the deformation and failure characteristics of the slope rock mass. With the increase of the geometric parameters of the slope and the inclination angle of the weak interlayer, the failure mechanism is manifested as the slip shear failure along the level at the foot of the slope → the slip shear failure along the level at the foot of the slope (the sliding surface moves upward) → the shear failure in the middle of the slope surface → the slip shear failure along the level at the foot of the slope (the sliding surface moves downward) → the uplift shear failure at the lower edge of the rock layer. When the dip angle of the weak interlayer is constant, the slope stability decreases gradually with the increase in slope gradient and slope height, and the geometric factors of the slope control the overall change trend of the slope stability coefficient. When the slope is greater than 55° and the slope height is greater than 55 m, the shear stress of the slope locking section exceeds its shear strength, and the probability of landslide instability is greatly increased.

Numerical research on disastrous mechanism of seepage instability of karst collapse column considering variable mass effect

In order to reveal the disastrous mechanism of seepage instability of karst collapse column considering variable mass effect, a variable mass fluid–solid coupling mechanical model of water inrush is established, by considering the random distribution characteristics of a collapse column. Taking Qianjin coal mine as the research background, based on the Weibull distribution theory, the heterogeneous distribution characteristics of rock mass is described, and COMSOL Multiphysics numerical simulation software is employed to simulate the seepage characteristics and inrush water changes in collapse columns under different conditions of homogeneity, water pressure, and initial porosity. The research results show that the greater the homogeneity is, the more water conduction channels are formed, and the porosity increases accordingly, when considering the influence of different homogeneity on the seepage characteristics of broken rock mass, which eventually leads to water inrush accidents and a sharp increase in water inflow. Besides, when studying the seepage evolution law of different water pressures on a broken rock mass, an elevation of water pressure dramatically increases the porosity and seepage rate of the water. Over time, the broken rock particles gradually migrate and the fine particles are transported and eroded by the water flow, resulting in changes in the seepage characteristics and the formation of potential water diversion channels. Finally, when taking into account the effect of different initial porosity on the fractured rock mass seepage characteristics, the greater the original porosity is, the higher the seepage velocity is, and the particle migration increases the permeability. This leads to a more pronounced conductive water passage formation, which reveals the disastrous mechanism of seepage instability of karst collapse column considering variable mass effect.

Dynamic response characteristics and damage calculation method of fractured rock mass under blasting disturbance

The mechanical responses and damage characteristics of fractured rock masses under dynamic loads play a significant role in ensuring the safety of blasting operations. The study employs dynamic finite element method (FEM) to simulate blasting in fractured rock masses, revealing the propagation features of blasting stress waves, the evolution of effective stress and the mechanism of damage evolution around the borehole. Based on the Weibull distribution, a rock damage model was established, which yielded the stress-strain relationship and damage equation for rocks under uniaxial impact. The parameters of the damage equation were fitted through numerical SHPB tests. The results indicate that in the direction of higher initial stress, the stress wave propagates faster, and the development of damage surfaces is more pronounced. In cylindrical charge blasting, the maximum blasting stress occurs in the middle section of the borehole, with limited influence from the charge on the bottom of the hole. Within a range of approximately 2 to 3 times the borehole diameter, the surrounding rock sustains complete damage. While within a range of about 4 to 5 times the borehole diameter, the degree of damage to the surrounding rock decreases rapidly, and beyond this range, the damage to the surrounding rock gradually diminishes.

Enhanced Rock Slope Stability Analysis: Integrating the Partial Factor Method into the Limit Equilibrium Method

Rock slope stability is crucial for sustainable design. Especially concerning natural or artificial rock-cut slopes. The stability of these slopes depends largely on features of rock mass, particularly discontinuities. Failure modes are determined by these features and are evaluated using kinematics analysis with stereographic projections. Various methods exist for analyzing rock slopes, including the limit equilibrium method (LEM), which assesses stability based on a factor of safety (FS). Conversely, the partial factor method (PFM), predominantly used in Europe, offers a more reliable and probabilistic approach, incorporating uncertainty factors. Although Eurocode, which employs the PFM, is widely utilized, it faces disputes and undergoes updates based on ISRM recommendations. The partial factor method is considered more conservative than the limit equilibrium method due to its comprehensive probabilistic approach. The choice between methods depends on project requirements, data availability, and expertise. This study compares the limit equilibrium and partial factor methods for rock slope analysis, concluding that the partial factor method is more conservative and sustainable for long-term stability assessment. Whereas, the traditional method is often used for short-term assessments.

Rock characterization, UAV photogrammetry and use of algorithms of machine learning as tools in mapping discontinuities and characterizing rock masses in Acoculco Caldera Complex

The use of UAV represents a very useful tool for rock mass characterization, particularly in large, unsafe, and not accessible areas characterized by a complex geometry. This investigation was mainly focused on mapping discontinuities and characterizing rock masses using UAV photogrammetry, machine learning, including different algorithms, and intact rock laboratory analyses, respectively. To this aim different outcrops from those described as a part of the basement of the Acoculco Caldera Complex, composed by a series of folded limestones were selected. The results indicate that geomechanical and physical properties, together with outcrop information are very important to assign suitable properties to large rock units. In turn, the great number of plots of discontinuity orientation extracted from the 3D point cloud data by the used of our code written in python language allowed to easily identify the presence of a total of seven discontinuity sets, some of them related to the bedding sequence and some others related to shear and tensile stress due to folding.