Rock Mass Characterization Research Articles

Numerical analysis on dynamic response and damage threshold characterization of deep rock mass under blasting excavation

The excessive destruction of surrounding rock in deep tunnel will change the original environmental state and destroy the natural ecological balance. Research on the dynamic response characteristics and damage thresholds of rock masses in deep environments plays a crucial role in determining the excavation range of blasted rock and establishing safety construction scheme. This study employs numerical simulation techniques to investigate the dynamic response characteristics of surrounding rock under different ground stress conditions. By introducing the dynamic ultimate tensile strength criterion, critical fracture stress threshold, and maximum damage radius of rock under coupled dynamic-static loading conditions are determined. The research shows that under uniaxial ground stress condition, increasing ground stress inhibits damage to the surrounding rock and the extension of cracks in the excavation area, while imposing restrictions on the attenuation rate of explosive stress. Under bidirectional equal ground stress condition, an increase in lateral pressure coefficient inhibits the development of damage zones along the excavation contour, yet enhances the extension of cracks in the maximum principal stress direction. Moreover, when lateral pressure coefficient becomes excessively large, the attenuation rate of explosive stress significantly increases. Based on the threshold values of peak particle velocity (PPV), the functional relationship is established to predict safety criteria for deep blasting excavation.

Comparative Study of Rock Mass Classification Systems: A Case Study of Nagdhunga-Naubisea Road Tunnel

Ground classification systems have been widely used to characterize the soil or rock mass for the analysis and design of underground structures. Deformation characteristics of rock mass around the underground excavation boundary varies according to types of rock and their properties, in situ stress condition and types of support used. Broadly used classification systems for underground structures are Rock Mass Rating (RMR) and Rock Quality Index (Q- Systems) but in-case of the Nagdhunga-Naubisea road tunnel Nippon Expressway Company Limited used NEXCO-System. Literally, the NEXCO classification is based on the velocity of elastic wave, geological condition, boring core condition, competence factor, stability of tunnel face and convergence. However, in-case of Nagdhunga-Naubisea road tunnel, grade point is computed using the similar parameters that are used in RMR- System and Q-System. This research focuses about comparison between ground classification from RMR, Q-system and NEXCO system. The geological descriptions obtained from project office at chainages (0+497 to 0+502), (0+508 to 0+513), (0+581.8 to 0+587.8) and (0+584.2 to 0+590.2) were used to correlate the relationship between RMR, Q-system and NEXCO system of rock mass classification systems. Results showed that from RMR, the ground classification is “poor” at all the chainages whereas from Q-system is “very poor” at chainage (0+508 to 0+513) and “poor” at other chainages. Similarly, from NEXCO- system it was found that “DII” at chainages (0+497 to 0+502) and (0+508 to 0+513) and CII for chainages (0+581.8 to 0+587.8) and (0+584.2 to 0+590.2). These results revealed that the ground classification from NEXCO as DII is similar to poor from RMR and poor or very poor from Q system where as CII from NEXCO is similar to poor from both RMR and Q system.

Improvements in Rock Mass Description for Stope Design by Geophysical and Geochemical Methods

Stope design is an important part of mine planning, and it aims to balance ore recovery, ore dilution, and production costs without compromising the safety aspects. This paper summarizes the main results from the research, which aims to introduce new techniques to describe the ore body and surrounding rock mass at the tunnel face prior to stope excavation. The research comprises a literature review and a survey among mining professionals to assess current stope design practices. The study identifies geotechnical data, software improvements, and integration of design into mine planning as the most critical areas for improvement. The empirical part of the study proposes new techniques for fast data acquisition. The laser-induced breakdown spectrometry (LIBS) technique is developed for measurements at the tunnel face and from core boxes to provide mineralogical and geometallurgical data. Ground-penetrating radar (GPR) studies are conducted to improve discontinuity characterization, and rapid photogrammetric methods are proposed for efficient tunnel geometry characterization. The techniques discussed in this paper already have many industrial applications. This study reveals their potential to be adopted and further developed to serve ore and rock mass characterization for stope design.

Study on the Anti-scouring and Energy Absorption Characteristics of Coupled Broken Coal Rock Mass and Packed STFs

Study on the Anti-scouring and Energy Absorption Characteristics of Coupled Broken Coal Rock Mass and Packed STFs

Experimental study on the influence of water-rock interaction on the time-varying characteristics of coal rock mass.

In order to study the influence of water-rock interaction on the mass time-varying characteristics of coal rocks, coal was selected as the research object and subjected to chemical immersion tests with different pH aqueous solutions for 12days. By experiment, the time-varying patterns of mass change fraction in coal samples, pH value in solution, and ions concentration of calcium and magnesium were obtained. Based on the gray correlation theory, the correlation degree between the mass change fraction and four influencing factors was analyzed. The gray prediction models for the mass time-varying characteristics of coal rocks have been established. The research shows that: (1) the influence waysanddegree of different pH aqueous solutions on the mass changes of coal rocks are different, (2) during the process of water-rock interaction, the change law of pH value, ions concentration of calcium and magnesium in solution are obvious, (3) the multiple regression modelscan be used to predict the mass change of coal rocks accurately under water-rock interaction.

Damage and failure characteristics of single fractured cyan sandstone subjected to freeze–thaw cycles under uniaxial compression

In order to explore the freeze–thaw (FT) damage characteristics of fractured rock masses, FT cycle tests and uniaxial compression tests were conducted on intact and pre-cracked cyan sandstone samples, respectively. The degradation laws of physical and mechanical properties of samples under FT cycle conditions were analyzed, and the FT damage mechanism and failure mechanism were explored accordingly. The results indicate that as the number of FT cycles (N) increases, the saturation weight change rate and porosity of the sample continue to increase, while the P-wave velocity continues to decrease. The closure stress, initiation stress, damage stress, and peak stress decrease linearly with increasing FT cycles, and increase linearly with increasing crack inclination angle (β). Moreover, as FT cycles increase, the geological strength index GSI decreases linearly, while the damage factor (D) increases linearly. A Hoek Brown strength degradation model for fractured rocks subjected to FT damage under uniaxial compression was obtained, and its high reliability was verified using test results. The FT damage of cyan sandstone is mainly dominated by the frost heave force inside the rock, and the degree of FT damage of fractured samples is much higher than that of intact ones. The concentration of frost heave force at the crack tip leading to cracking is the key to exacerbating the FT damage in fractured rock masses. However, the crack initiation mechanism is still controlled by β. Whenβ = 90°, it exhibits tensile initiation mode, and whenβ = 45°, it mainly exhibits shear initiation mode. Moreover, the fracture of the single crack sample conforms to the compression-shear fracture criterion. Taking the sample with pre-crack inclination angle of 45° as an example, the variation of KI and KII, and the relationship between them are discussed accordingly. The results of this paper are beneficial to clarify the influence of FT cycles on the mechanical properties of cyan sandstone, and can provide reference for the study of related issues.

Mechanical properties and failure mechanism of rock-like specimens with arc-shaped flaws under freeze–thaw cycles

To investigate the failure characteristics of jointed rock masses in cold regions after freeze–thaw (F-T) cycles, uniaxial compressive tests are conducted on rock-like specimens (a type of cement mortar) with prefabricated arc-shape flaws subjected to 0, 25, 50 and 100F-T cycles to determine their mechanical properties. Test results reveal that F-T cycles greatly affect the uniaxial compressive strengths (UCS) of the specimens, and the relationship between the peak strength and the number of freeze–thaw cycles is exponentially fitted. Notably, the initial 50 cycles have a more pronounced effect on UCS reduction compared to the subsequent 50 cycles, indicating that early F-T cycles are more detrimental to UCS. To further investigate the failure mechanism of the specimens, two-dimensional particle flow code (PFC2D) is utilized to simulate the F-T cycle process of the specimens. The mechanical properties and failure mechanism of specimens can be obtained after F-T cycles under uniaxial compression through numerical simulations. The findings indicate that F-T cycles can obviously deteriorate the ductility of the specimens, and to some extent, they also affect crack propagation during specimen failures. Through crack classification statistics and stress contour analysis of the simulated specimens, it reveals that different prefabricated flaw morphologies lead to distinct stress distributions, subsequently affecting crack propagation and specimen failure. It is also worth mentioning that the large curvature and inclination angle of the flaws may generate additional tensile and shear stress zones at the top of the flaw vault, which in turn may contribute to the development of crack propagation. The relevant experimental and numerical results are useful for investigating mechanical properties and failure mechanisms of rock masses in cold regions subjected to F-T cycles.

Determining Digital Representation and Representative Elementary Volume Size of Broken Rock Mass Using the Discrete Fracture Network–Discrete Element Method Coupling Technique

Obtaining the digital characterization and representative elementary volume (REV) of broken rock masses is an important foundation for simulating their mechanical properties and behavior. In this study, utilizing the broken surrounding rock of the main powerhouse at the Liyang pumped storage power station as an engineering background, a three-dimensional fracture network generation program is first developed based on the theories of discrete fracture network (DFN) and discrete element method (DEM). The program is then integrated with a distinct element modelling platform to generate equivalent rock mass models for broken rock masses based on the DFN–DEM coupling technique. Numerical compression tests are conducted on cylindrical rock specimens produced using the proposed modelling approach, aiming to determining the REV size of the target rock masses at the Liyang power station. A comparative validation is also performed to examine the REV result obtained from the proposed approach, which adopted a REV measuring scale index (RMSI) to determine the REV size. Results indicate that the organic integration of DFN simulation techniques and DEM platforms can effectively construct numerical models for actual broken rock masses, with structural surface distributions statistically similar to the real ones. The results also show that the REV size of the investigated rock masses determined by the cylindrical rock models is 5 m × 10 m, which aligns with the size determined by the cubic rock models, as the target cubes show the same height as the cylindrical specimens. This study provides a model and parameter basis for the numerical calculation of the mechanical behavior of broken rock mass.

Assigning resistivity values to rock quality designation indices using integrated unmanned aerial vehicle and 2D electrical resistivity tomography in granitic rock

Rock quality designation (RQD) is a standard technique in mining and geotechnical investigation for quantifying the quality and degree of jointing of the rock mass. However, the need for expeditious and inexpensive geotechnical site characterization is the prime motivation for modifying RQD. This research work integrates 2D Electrical Resistivity Tomography (2D ERT) and Unmanned Aerial Vehicle (UAV) conducted at Site 1 and Site 2. The UAV survey was performed to calculate RQD on the rock surface using volumetric Joint Counts (Jv) at Sites 1 and 2. A 2D ERT survey was conducted to obtain the corresponding subsurface resistivity values. Using k-nearest neighbours (k-NN), resistivity values were assigned to various RQD indices such as very poor rocks (<350 Ωm), poor rock (350–1150 Ωm), fair rock (1150–1850 Ωm), good rock (1850–2500 Ωm) and >2500 Ωm excellent rock. Based on the established correlation of RQD and resistivity, the subsurface rock mass quality at Site 1 was predominantly good and excellent rock, while at Site 2, poor rock was significantly reported. This research concluded that rock mass characterization using RQD is more rapid and inexpensive than the direct or indirect calculation of RQD. The combined 2D ERT and UAV deployed in this research study provide an environmentally non-destructive approach for slope stability assessment.

Modelling the probability of roof fall using digital tools

Information on rock mass characteristics, encompassing the overall quality of the rock masses and various geological parameters, is crucial in mining operations. This data guides the selection of mining techniques and the design of roof control methods to minimize the risk of flaking. However, the lithology of roof rocks is often so variable that predicting their behaviour, especially when disturbed by mining activities, is challenging. The study begins with a detailed review of existing literature on roof fall mechanisms and predictive modelling techniques. It was described the dataset used, which includes geological, environmental, and operational parameters collected from various mining sites. This article outlines a methodology for conducting detailed studies of the lithology of coal seam roof rocks in roadways and longwalls as mining progresses. According to the research, forecasting the extent of roof rock fall during the planning stage of mining operations can inform the implementation of appropriate countermeasures to minimize this phenomenon before exploitation begins, thereby significantly reducing ongoing mining costs. Block modelling and stratigraphic (mesh) modelling were employed to predict the volume of rockfall that could contaminate the ore in the analysed mining plot. In the future, this proposed methodology could be used to analyse the progression of roof falls, estimate the mass of falling roof rocks, and calibrate a system for continuous measurement of ore quality in mine workings.

A new empirical model for prediction of jumbo drills' penetration rate in underground mines based on the rock mass characteristics

A new empirical model for prediction of jumbo drills' penetration rate in underground mines based on the rock mass characteristics

Study on the Dynamic Response Characteristics of Surrounding Rock Mass of Underground Caverns under Blast load

Study on the Dynamic Response Characteristics of Surrounding Rock Mass of Underground Caverns under Blast load

Estimation of nonuniformity in characteristics of strong rock masses for radioactive waste disposal

Estimation of nonuniformity in characteristics of strong rock masses for radioactive waste disposal

DEM-based analysis of water inrush process of underground engineering face with intermittent joints in karst region

&#x0D; &#x0D; &#x0D; &#x0D; Water inrush disaster of karst tunnel often lead to significant economic losses and serious casualties, which is an urgent engineering roadblock to be solved in the construction of tunnel in karst area. In this paper, three-dimensional discrete element method considering fluid-solid coupling effect and structural characteristics of water-mud resistant rock mass is adopted to systematically study the evolution law of displacement field and seepage field of intermittent joint type water-mud resistant rock mass of tunnel face and its water inrush critical characteristics during the process of sequential excavation of karst tunnel close to the frontal high-pressure water-rich karst cavity. The results show that: With the tunnel face gradually approaching the front-concealed high-pressure water-rich karst cavity, the stability of water-mud resistant rock mass is increasingly affected by high-pressure karst water, and karst water pressure gradually becomes the main control factor. The closer the tunnel face is to the front-concealed high-pressure water-rich karst cavity, the greater the extrusion displacement of karst tunnel face and its increase amplitude, the higher damage degree of water-mud resistant rock mass of face. With the advance of tunnel excavation, the intermittent cracks in the water-mud resistant rock mass of face gradually connect and form a stable hydraulic connection. The flow velocity and seepage pressure of karst water rise significantly at the moment of overall instability of face and the formation of water inrush channel, showing obvious precursor characteristics. The research achievements provide a reference for early warning and prevention and control of water inrush disaster of karst tunnel face.&#x0D; &#x0D; &#x0D; &#x0D;

Mechanical properties of fracture-grouted prefabricated sandstone after thermal-acid coupling treatment: An experimental study

Grouting reinforcement is an efficient approach to increase the stability of engineered fractured rock masses that may be subjected to high temperatures and acidic groundwater in complex geological environments. To reveal the mechanical properties and failure characteristics of the grout-reinforced fractured rock masses under thermal-acid coupling conditions, prefabricated fractured red sandstone specimens with different inclination angles (IAs) were firstly grouted using a new high-strength fast anchoring agent (HSFAA). Then, the grout-reinforced specimens (GRSs) were then immersed in hydrochloric acid (HCl) solutions with different temperatures (varying from 25 to 300 °C). Finally, the macroscopic mechanical properties, microscopic morphology, and crack evolution characteristics of the GRSs after thermal and acid solution treatments were investigated by the uniaxial compression test, X-ray computed tomography (CT) and scanning electron microscopes (SEM). The results confirmed that the HSFAA featured with high fluidity, rapid setting, excellent early strength, and micro-expansion, was an ideal grouted reinforcement material for fractured rock masses. The compressive and tensile strengths of the HSFAA material at a 1-day curing were 2.01 and 1.64 times those of the ordinary Portland cement 42.5 (P.O 42.5), respectively. The fractured IA, thermal-acid coupling method and temperature affected the mass loss, strength parameters, and failure modes of the GRSs to different degrees. The thermal-acid coupling treatment affected the initiation location and extension direction of cracks within the GRSs. The increasing temperature led to the larger and more varied internal cracks, as well as the more complex 3D spatial morphology within the GRSs.

Retracted: Mechanical Characteristics and Permeability Characteristics of Dry-Hot Rock Mass

Retracted: Mechanical Characteristics and Permeability Characteristics of Dry-Hot Rock Mass

Study on the fault slip rule and the rockburst mechanism induced by mining the panel through fault

When mining near the fault can cause the fault to slip and release energy, resulting in rockburst and posing a significant safety risk to coal mine production. This paper proposes a numerical simulation method, based on FLAC3D numerical simulation, for calculating the dynamic response of fault slip below the impact of mining. The release patterns of energy from fault slip are compared between mining via the fault from the hanging wall and mining via the fault from the footwall. The dynamic response characteristics of coal and rock mass under the disturbance of fault slip induced dynamic loading are revealed. This research suggests that the fault slip seismic moment (M0) of the panel mined via the fault from footwall is substantially higher than from hanging wall. Moreover, the disturbance of the footwall panel mining via the fault leads to a more severe disturbance of the surrounding rock mass, resulting in a higher risk of rockburst. Plastic failure of the rock surrounded in the mining area under the strong dynamic loading of fault slip leads to a significant reduction in peak abutment stress, releasing tremendous energy. When the disturbance caused by fault slip dynamic load is relatively small, the maximum abutment stress increases, and the dynamic load increases the energy storage of surrounding rock. Based on energy theory, an energy criterion for the occurrence of fault slip type rockburst has been proposed. The results suggest that strong fault slip dynamic load has an obvious inducing effect on rockburst, and the stronger the dynamic load and greater static load of the rock, the more the manifestation of rockburst.

Rate-dependent constitutive modelling blasting crack initiation and propagation in rock masses

This study examines the fracture mechanism of cracks and the final blasting effects on defective rock masses under blasting loads. The failure processes of jointed rock with two prefabricated joints are investigated through numerical simulations using a two-dimensional finite element method. Subsequently, simulations are performed to analyze the blasting of granite specimens with various joint arrangements, focusing on the influence of front joint length, inclination angle, and blast hole distance on failure patterns, displacement, velocity, and stress at the joint ends. The numerical results provide a comprehensive summary of various typical failure modes near blast holes and joints for the first time. Specifically, the simulation successfully captures the characteristics of the ring crack zone, wing cracks, and main crack deflection affected by the front joint. Moreover, the results highlight the shielding effect of the front joint, which enhances damage in the medium between the borehole and the joint while exhibiting the opposite effect behind the joint in terms of stress wave propagation. Overall, this study offers objective insights into the mechanics and failure characteristics of jointed rock masses under blasting loads and serves as a valuable reference for the design and optimization of blasting operations.

Elastoplastic coupling analysis of surrounding rock-prestressed yielding anchor bolts/cables based on unified strength theory

A whole-process analytical theory for the coupled deformation of deep circular tunnel surrounding rock and prestressed yielding anchor bolt (cable) system is derived based on the unified strength theory and non-associated flow rule. This theory considers the strain softening characteristic of rock mass, the yielding reinforced characteristics of anchor bolt (cable), and the support timing. An analytical method is proposed to calculate the difference in displacement of anchor bolts (cables). This study highlights the importance of monitoring anchor bolts (cables) elongation rate in high-stress tunnels by integrating theoretical analysis with engineering practice. The displacement difference that occurs during the coordinated deformation of the bolts (cables) and the surrounding rock provides the support resistance. Therefore, the safety margin standard of elongation rate can be used to assess the integrity and effectiveness of the support structure during the real-time bolts (cables) action. The present study aims to validate the rationality of the analytical theory by conducting numerical simulations using ABAQUS software. Specifically, we focus on analyzing the ground response curves (GRC) underthe bolt (cable) support and the elongation rate of the bolt (cable). Various factors such as prestress, yielding amount, support timing, intermediate principal stress coefficient, radial/longitudinal spacing, and length are considered tocompare and analyze their effects on the GRC. The results showed that anchor bolts (cables) can significantly reduce the surrounding rock convergence. With prestressed bolt (cable) support, the GRC exhibits a stepwise drop, significantly and timely reducing the support force required for the surrounding rock equilibrium. After setting the yielding structure, the increase in anchor cable stress was limited, thereby slightly increasing the surrounding rock displacement. However, the anchor cable elongation rate significantly decreased, thereby greatly enhancing the support structure safety. The support timing affects the starting point of bolts (cables) function. The displacement control effect is more pronounced when support is provided earlier. However, this also leads to an increase in the elongation rate of the bolt (cable). The intermediate principal stress coefficient reflects the self-bearing capacity of the surrounding rock, and increasing this value can improve the deformation control performance of the surrounding rock under anchor bolt (cable) support as a whole and reduce the elongation rate through the coupled function of the surrounding rock–anchor bolt (cable) system. The spacing between anchor cables significantly impacts the convergence control of surrounding rock. Smaller spacing leads to better control of the surrounding rock deformation and lower stress of the anchor cables. As the length of the anchor cables increases, the elongation rate and stress of the anchor cables continuously decrease. However, the surrounding rock deformation exhibits an initially decreasing and increasing pattern. This paper presents a theoretical and computational approach to analyze the effect of prestressed yielding anchor bolt (cable) support and the safety of support structures in tunnel engineering. The findings of this study can serve as a valuable reference for the convergence analysis of circular tunnels in underground engineering.

Estimation of Fracture Size and Probability Density Function by Setting Scanlines in Rectangular Sampling Window

Abstract Rock masses are very important materials in geotechnical engineering. In engineering rock mass, fracture is the relatively weak part of mechanical strength in rock mass and is the most important factor controlling the deformation, damage, and permeability of rock mass. Therefore, investigating fractures is very important for characterizing rock mass. This paper proposed a new approach by using uniformly equidistant orthogonal scanlines. Within the study context, the solution formula of fracture size is derived by establishing the space intersection model of arbitrary fracture and scanline, rectangular window, and a rectangular box with a rectangular window. Then, fractures were randomly generated in a certain size cube and compared with the traditional Kulatilake trace length integral evaluation method. The study results have shown that the proposed method is more reasonable and accurate. Then, this method was applied to an adit of Songta Hydropower Station. Finally, a new fracture diameter probability density estimation method was proposed, the fracture diameter of the normal distribution was verified, and the parameters of the probability density function obtained by the scanlines method were in agreement with the initial set parameters. In summary, the proposed scanlines method can well estimate the mean value of the fracture diameter and the probability density function of the fracture size.