Mining Rock Mass Research Articles

Forecast of the geomechanical state of the rock mass in difficult mining and geological conditions based on in-situ test data

Forecast of the geomechanical state of the rock mass in difficult mining and geological conditions based on in-situ test data

Experimental Investigation on Rock Failure Characteristics of Large-Span Goafs Using Digital Image Correlation Analysis and Acoustic Emission Monitoring

Rockmass in deep mining is highly susceptible to large-scale collapses under high stress and blast-induced disturbances, leading to casualties and economic losses. To investigate the evolution characteristics of goaf instability and the types of seismic sources that induce instability, an experiment on goaf instability was designed under uniaxial compression conditions based on actual mining operations. The entire experimental process was monitored using digital image correlation analysis and acoustic emission monitoring. By calculating the digital speckle field on the surface of the rock specimen during the experiment, the evolution characteristics of the deformation and strain fields from the beginning of loading to complete failure were analyzed. The study explored the dynamic behavior of cracks from initiation to propagation and eventually inducing large-scale collapse. The results show that the instability process of the goaf begins with the formation of tensile cracks. As stress increases, shear cracks occur in the specimen, leading to macroscopic failure. Furthermore, based on the differences in overall microfracture types measured by RA-AF characteristic parameters during specimen failure, large amplitude acoustic emission events corresponding to the formation of dominant macroscopic cracks were selected, and the focal mechanisms of these events were inverted. The results indicate that shear failure sources are significantly more prevalent than tensile failure sources in acoustic emission events leading to goaf instability. These findings can provide useful guidance for the support design and the prevention and control of rockmass instability disasters.

Experimental investigation on the influence of weak interlayers on sandstone rockburst and associated microcracking mechanism

Weak interlayers (WI) are common in sedimentary rock masses in deep coal mines. The qualitative effect of the WI on rockbursts is widely acknowledged; however, its influence mechanism still needs further investigation. In the present study, true triaxial unloading rockburst tests of sandstone with WI and calcite veins (CV) were conducted to explore their influence mechanisms. To explore the impact of WI, the rockburst stress, failure modes, acoustic emission (AE) parameters (energy, entropy, and b-value), and spatial energy characteristics of AE events were analyzed. The influence of the area ratio of WI and their distribution patterns (centralization and dispersion) on rockburst were further investigated. The results indicate that the rockburst stress (peak of maximum principal stress) decreased by 4 % for every 1 % increase in the sandstone's dispersion WI area ratio (1.9%–9.3 %). Namely, rockburst is more likely to occur when there is appropriate WI distributed in the sandstone because WI exacerbates the microcrack activities and energy release. The CV will reduce the weakening effect of WI on rockburst stress and can enhance the rockburst intensity, especially in samples with dispersion WI. Moreover, the more considerable AE energy is released around CV for the sandstone with dispersion WI. The interface between WI and matrix is prone to rockburst for the sandstone with centralized WI because of the concentrated energy release. The results of this paper can provide a reference for the prevention and control of rockbursts in mine sedimentary rocks containing WI and CV.

Experimental study on dynamic response of hard rock blasting under in-situ stress

Deep mine rock mass is in high static stress and dynamic disturbance coupling conditions, its mechanical properties and failure mode is different from the shallow rock mass, which leads to low rock blasting efficiency and engineering geology hazards. In-depth research on the dynamic response of rock blasting under in-situ stress will help to optimize the blasting design, improve the blasting efficiency and safety of blasting operations, and provide theoretical support for rock blasting in deep mines. In this study, the blasting experiment was conducted on granite specimens under different biaxial static stress conditions. Meanwhile, the dynamic response of rock blasting was monitored, collected, and analyzed using a high-speed digital image correlation (DIC) measurement system, a strain wave acquisition system, and an acoustic emission (AE) system. The results show that small and medium pre-static loads inhibit blast crack propagation, at which time the cumulative AE hits from dynamic loads (CAECd) are more than those from pre-static loads (CAECs), but large pre-static loads promote crack propagation, at which time CAECs are more than CAECd. Secondly, as pre-static load increases, the specimen's maximum strain (εmax) decreases first and then increases, but as lateral pressure coefficient (K) increases, the εmax in the direction of lower static stress decreases gradually and the εmax in the direction of higher static stress remains constant. In addition, the confining pressure magnitude and K affect the area and shape of the failure zone of the specimen, as well as the size and propagation direction of the radial crack. Especially when the confining pressure is high, the specimen will undergo shear failure, and the smaller K is the more serious the shear failure. Finally, the failure criterion of rock under dynamic-static coupling conditions is proposed based on the energy index, and different failure types of rock are discussed.

Unraveling time-dependent roof stability dynamics in Iran's coal mines through laboratory-based rock displacement testing

Roof stability is a critical concern in coal mines, as the potential for roof collapse poses a significant risk to miners' safety and productivity. Roof stability is heavily influenced by the time-dependent properties of the rock mass above the workings. This study uses rock displacement testing to examine the effect of time-dependent properties on roof stability and resistance reduction in coal mines in Iran. The study employed laboratory-based rock displacement tests on samples collected from coal mines in Iran, subjected to varying stress levels over time, to simulate the gradual deterioration of rock mass strength in underground mining conditions. The samples were monitored for displacement under these conditions to quantify the reduction in roof resistance over time and assess its effect on roof stability. The study found that areas with high stress at equilibrium gradually fail with time, and the stress transfers from the failure zone into deeper solid rock. The results demonstrate that varying viscous parameters can lead to different relaxation behaviors and stress distribution. Furthermore, incorporating strength degradation into numerical simulation can capture the failure under creep conditions and improve the accuracy of predicting time-dependent roof failure. This research aims to enhance safety measures and reduce the risk of collapses by investigating the time-dependent properties of roof stability through rock displacement testing in Iran's coal mines. The study's innovative approach uses numerical simulation based on the viscoelastic-plastic model to simulate the time-dependent behavior of the rock and incorporate strength degradation into the simulation. The results provide valuable insights into the time-dependent behavior of rock mass in coal mines in Iran and contribute to developing strategies for improving roof stability and lessening the chance of roof collapses. The instantaneous elastic strain was 4.35 × 10–4, and creep simulation was activated to run for a time equivalent to 2 × 106 s.

Geo-mechanical classification of the Ighrem Aousser rock mass mining site of the Touissit Mining Company

Purpose. The paper aims to classify the rock mass of the Ighrem Aousser (I/A) mine and analyze its fracturing to determine the appropriate excavation supports. Methods. The study begins with a geo-mechanical classification of the mass using widely used methods: Rock Quality Designation (RQD), Rock Mass Rating (RMR), Q-Barton, and Geological Strength Index (GSI). Fracturing surveys were then conducted to identify the main fracture families using DIPS software. Finally, UNWEDGE software was used to measure the support systems. Findings. The study provides a comprehensive geological study, including field observations, core drilling analysis, and structural analysis with DIPS software. Results indicate that the I/A mine rock mass is highly fractured and altered, as confirmed by mechanical tests at the Mohammadia School of Engineers' laboratory and empirical classifications. Based on these findings, appropriate support systems were identified using UNWEDGE software. Originality. This study provides a detailed classification and structural analysis of the I/A rock mass to propose and measure excavation supports. Integrated approach not only advances understanding of rock mass behavior, but also ensures optimized safety, stability, and productivity of mining operations, setting a new standard in sustainable mining development. Practical implications. In the mining industry, classifying rock masses and designing excavation supports enhances safety, increases site productivity by reducing contamination and lowering mining costs.

Finite–Discrete Element Method Simulation Study on Development of Water-Conducting Fractures in Fault-Bearing Roof under Repeated Mining of Extra-Thick Coal Seams

The formation of water-conducting fractures in overlying strata caused by underground coal mining not only leads to roof water inrush disasters, but also water-conducting fractures penetrate the aquifer, resulting in the occurrence of a mine-water-inrush disaster and the loss of water resources. It destroys the sustainability of surface water and underground aquifers. This phenomenon is particularly significant in extra-thick coal seams and fault-bearing areas. Numerical simulation is an effective method to predict the failure range of mining overburden rock with low cost and high efficiency. The key to its accuracy lies in a reasonable constitutive model and simulation program. In this study, considering that the three parts of penetrating cracks, non-penetrating cracks, and intact rock blocks are often formed after rock failure, the contact state criterion and shear friction relationship of discrete rock blocks and the mixed fracture displacement–damage–load relationship are established, respectively. Combined with the Mohr–Coulomb criterion, the constitutive model of mining rock mass deformation–discrete block motion and interaction is formed. On this basis, according to the engineering geological conditions of Yushupo Coal Mine, a numerical model for the development of water-conducting cracks in the roof with faults under repeated mining of extra-thick coal seams is established. The results show the following: The constitutive relation of the continuous deformation–discrete block interaction of overlying strata and the corresponding finite element–discrete element FDEM numerical program and VUSDFLD multi-coal seam continuous mining subroutine can numerically realize the formation process of faults and water flowing fractures in overlying strata under continuous mining of extra-thick multi-coal seams. The toughness of sand mudstone is low, and the fracture will be further developed under the repeated disturbance of multi-thick coal seam mining. Finally, it is stabilized at 216–226 m, and the ratio of fracture height to mining thickness is 14.1. When the working face advances to the fault, the stress concentration occurs in the fault and its overlying rock, which leads to the local fracture of the roof rock mass and the formation of cracks. The fault group makes this phenomenon more obvious. The results have been preliminarily applied and tested in Ningwu mining area, which provides theoretical support for further development of roof water disaster control under the condition of an extra-thick coal seam and avoids the loss of water resources in surface water and underground aquifers.

Dynamic mechanical response and failure characteristics of coal and rock under saltwater immersion conditions

The stability of coal and rock masses in water-rich mines is affected by both mine water erosion and dynamic disturbances. Thus, it is necessary to study the dynamic mechanical response and failure characteristics of coal and rock under the combination of saltwater and a high strain rate. To this end, a split Hopkinson pressure bar device was employed to investigate the effects of impact velocity, water content, and immersion liquid on the dynamic mechanical behaviours of coal and rock. The results revealed that the weakening effect of saltwater on the dynamic mechanical properties of coal and rock is much greater than that of distilled water. With increasing moisture content, the dynamic compressive strength of the coal specimens decreases monotonically, while that of the rock shows a trend of first increasing and then decreasing. The failure process and destruction of coal and rock are comprehensively affected by both the external impact load and the physical and mechanical properties of the material. The degree of damage of the coal and rock specimens increases with increasing impact velocity and water content. Moreover, the influence of various factors on the impact fracture mechanism of coal and rock under saltwater immersion conditions was revealed. These findings are highly important for the design and maintenance of underground coal and rock building structures.

Pit Slope Configuration for Open Pit Mining – A Case Study

To achieve stable pit wall slopes, it is imperative to obtain a fair knowledge of the rock mass characterisation before designing the pit. Insufficient knowledge of the competency of the country rock could lead to using unsupported slope configuration in the design process which can consequently lead to slope failure. In this study, the geomechnical properties of the Bremen-Nkosuo concession are analysed using Bieniawski’s classification scheme to determine the Rock Mass Rating (RMR) for defining safe pit slope configuration of the Nkosuo pit. The findings show that the rockmass are best described as ‘fair’ for the two main lithologies existing at the concession. Subsequently, localised adjustment factors are applied to the calculated RMR to arrive at Mining Rock Mass Ratings (MRMR). These MRMR values are correlated with 50 m fixed stack height and 1.2 safety factor to determine optimum Bench Slack Angle (BSA) of 54° and 57° for host sedimentary and granitic rocks respectively. For individual benches, optimum slope design configurations were 10 m, 800, and 6.6 m respectively for bench height, bench face angle and catch berm for metasedimentary rocks. Likewise, that for granitic formation were 10 m bench height, 800 face angle and 6.0 m catch berm width. These configurations are in conformance with mineral and mining regulations of Ghana. Slope stability assessment was performed which included Slope Mass Rating (SMR), Kinematic and Limit equilibrium analysis. From the analysis, multi-bench scale slope instability occurrence was found to be rare but single-double scale could be possible at the western wall of the planned pit with probability of failure of about 0.4. Presplit and trim shots perimeter blasting techniques are recommended to maintain the integrity of the final pit walls at certain areas.

Effect of Directed Blasting on Geotechnology and Geomechanical Behavior of Rock Mass in Deep-Level Mining

Effect of Directed Blasting on Geotechnology and Geomechanical Behavior of Rock Mass in Deep-Level Mining

Study on precursor information and disaster mechanism of sudden change of seepage in mining rock mass

Abstract Changes in the stress field and seepage field of mining unloading are one of the important causes of deformation and destabilization of the rock body of the bottom slab. With the increase of mining intensity and depth, the disaster of water influx on the bottom plate under the dual action of mining unloading and pressurized water has become one of the main problems restricting the efficient and safe mining of coal. Based on the research background of confined water inrush from Ordovician limestone floor in North China Coalfield, the numerical analysis revealed that mining unloading concentrates stresses, increases deformation, and increases the plastic zone and permeability range. Based on laboratory acoustic emission and mechanical tests, it is found that the peak of acoustic emission ringing number can be one of the precursor information of limestone seepage mutation. This study reveals the evolution law of rock body deformation and permeability under the unloading path, and the research obtains the unloading seepage and water gushing disaster mechanism of the subgrade rock body.

Application of Bayesian method for mining-induced tremors: A case study of the Xinjulong coal mine in China

Mining-induced tremor is a dynamic phenomenon occurring during the fracturing or slipping of rock and coal mass in coal mines, and the tremor mechanism is one of the key problems in the field of rockburst. The Bayesian inversion method can more accurately analyse the source rupture type under the premise of considering waveform data and model errors. First, we added different noise levels to the waveform and determined filtering parameters based on the spectrum. The rationality of the Bayesian inversion was verified by observing the focal mechanism solution. Finally, a total of fourteen mining-induced tremors were selected, and the parameters of the moment tensor (MT), type of rupture, and fault plane solutions were obtained. The results demonstrate that (1) the tremor events in the roof are mainly tensile/shear failure, and compression failure mainly occurs in the coal seam. (2) Events on the floor are closely related to gob and mining activities. (3) The rupture form of the events near the tectonic region is more complex, and the fault plane solutions (strike, dip, and slip) were obtained by MT conversion. (4) The relation between rockbursts and mining-induced tremors is discussed by analysing events 1# and 14# that occurred in the Xinjulong coal mine. These research findings can provide a reference for the analysis of source parameters and rupture forms of mining-induced tremors.

Substantiation of the technological parameters of bucket-wheel excavator forward trench when mining titanium deposits

Purpose. To justify the parameters of the technological scheme of working out an advanced overburden bench by a bucket-wheel excavator, to reduce the cost of overburden work at Pit 7 of Vilnohirsk Mining and Metallurgical Plant. Methodology. Setting the parameters of the technological scheme of the bucket-wheel excavator was performed by the graphic-analytical method, which involves taking into account the technical characteristics of the mining machine, the physical and mechanical properties of the mining rocks and the stable slope angle of the advanced overburden bench. The substantiation of the effectiveness of application of the technological scheme with a forward trench was made by the technical and economic calculation of the specific costs on overburden works. Findings. The possibility of increasing the height of the overburden bench when using a technological scheme with a forward trench was evaluated. Reasonable parameters of the forward trench, in which the bucket-wheel excavator can develop a forward pit bench with a capacity of 40 m with a stable slope angle of 30°. This allows reducing the amount of mining haulage equipment and reducing overburden costs by up to 50 %. Originality. The minimum slope angle of the overburden slope at the maximum digging height of the ERShR-1600-40/7 excavator, which is equal to 40° at a slope height of 40 m, was established. The dependence of the resulting slope angle of on the re-excavation coefficient of the mining rock mass was established. This makes it possible to assert that when this angle is increased the re-excavation rate will decrease. It was established that at the applying technological scheme with a forward trench in the conditions of Vilnohirsk MMP, the coefficient of overburden re-excavation will be k = 0.09. Practical value. A technological scheme for the development of an advanced overburden bench by the bucket-wheel excavator with a forward trench allows increasing its developed bench height. This makes it possible to reduce the operational cost for overburden works by refuse from haulage mining system with dump trucks.

A new grouting cable without a core tube used for reinforcement of fractured rock mass

Grouting cable is a newly developed technology for the reinforcement of fractured rock mass in coal mines of China. It integrates the procedures of cable anchoring and grouting, thus simplifying the working procedure of roadway support. However, ordinary grouting cable products with a core tube have some significant defects, such as a narrow flow channel, difficulty in slurry diffusion and significant reduction of cable strength. To overcome these shortcomings of ordinary grouting cables, this paper proposes a new kind of grouting cable without a core tube. The ordinary plastic core tube is replaced by a steel core wrapped by several steel strands. The inner gap between the steel strands and steel core is used as the slurry flow channel. The optimised measures can significantly improve slurry diffusion and strength performance of the grouting cable. As a novel idea, several samples of the new grouting cable were produced. Lab testing and field application experiment indicated that slurry diffusion and strength performance of the new grouting cable had been significantly improved compared with ordinary ones.

Theoretical unloading fracture mechanism and stability analysis of the slope rock masses in open-pit mines

Instability of the rock slopes in open pit mines during the excavation unloading is an increasingly serious problem in the field of slope engineering. To explain the mechanical mechanism of slope unloading damage from a theoretical point of view, a simplified mechanical model of slope excavation based on the theory of fracture mechanics and the rock strength damage criterion is established. The damage process of the slope under excavation disturbance is dynamically analyzed by combining the interstructural characteristics of the slope. The solution equations for the extent of the plastic zone at the end of the crack of the excavated slope and its propagation length are derived. Calculation method of unloaded slope stability coefficient is proposed based on the mechanical model of crack propagation. The results show that (1) the stress intensity factor (SIF) at crack end in the slope under the action of unloading was larger than that under the original condition. (2) The range of the plastic zone at crack end in the slope rock mass can be attributed to the slope height, inverse logarithmic function to the slope angle, positive proportional function to the crack length, and the periodic fluctuation function of the crack angle. (3) The slope safety factor (SF) was found to be negatively related with the slope angle, slope height, crack angle, and the crack length unloading factor and positively related with the friction factor. Finally, the reasonableness of the theoretical derivation is verified by an engineering case study.

Analysis of unstable block by discrete element method during blasting excavation of fractured rock mass in underground mine

During the excavation process in fractured rock masses in underground mines, blasting excavation can cause dangerous block collapses on surrounding rock. The applicable blasting method can effectively reduce the damage of surrounding rock caused by blasting disturbance. In order to investigate the impact of blasting disturbances of dangerous blocks in fractured rock mass drift, this study focuses on the instability characteristics of dangerous blocks during the excavation process in a mine located in Jilin Province. Based on detailed detection of discontinuities characteristics in the study area, the damage effects of shaped charge hydraulic blasting and conventional blasting on surrounding rock structure are analyzed and compared by using equivalent static method. The 3DEC discrete element software was used to analyze the instability characteristics of surrounding rock dangerous blocks under these two different blasting methods. The results indicate that using shaped charge hydraulic blasting can effectively reduce the impact of blasting disturbances on the excavated rock mass and minimize dangerous block collapses during drift excavation.

Volumetric Structure of the Bachat Earthquake (Kuzbass) Aftershock Area and Stress State of Rock Mass under Open-Pit Mine

Abstract —The Bachat earthquake (M = 6.1) with the epicenter coordinates of 54.29° N, 86.17° E occurred on June, 18 2013 near the Bachatsky coal strip mine, is the world’s largest earthquake induced while mining solid minerals. More than 5000 aftershocks were registered and the spatial volumetric structure of the aftershock area was investigated. The Bachat coal field is located in the Salair zone of the Kuznetsk Depression and is represented by a brachysynclinal fold of a very complex structure characterized by the damage and fracturing behaviors of rocks. The main event is confined to the coal-mine pit wall, with the greatest density of aftershocks observed in its middle portion. In the cross section, aftershocks form a wide area with its deepened portion shifted towards the Kuznetsk Depression, while large faults bounding the depression dip down under the Salair Ridge. In the exposed pit wall, at a depth of 4 km, the activated area resembles a rhombus whose horizontal diagonal line runs across the entire length of the mine pit and decreases both in upward and downward directions. The area is seismically activated to a depth of 6 km, with more intense activation of rock mass observed within the 1–3 km depth interval. Results of the study of the mechanisms of aftershock sources revealed a disagreement between the stress state of rock mass of the Bachatsky open-pit coal mine modeled from the mechanisms of aftershocks, and the mainshock mechanism of the Bachat earthquake.

Research Review on Water Inrush Mechanism and Failure Criterion of Rock Mass in Deep Mines

Research Review on Water Inrush Mechanism and Failure Criterion of Rock Mass in Deep Mines

Numerical Simulation Research and Application of Support Design of Broken Rock Mass in Submarine Gold Mine

In order to solve the problem that the broken rock mass is easy to collapse and fall during the excavation of a submarine gold mine, two kinds of bolt-mesh-concreting combined support schemes are designed by means of field engineering geological investigation, indoor rock mechanics test, rock mass quality classification, and theoretical analysis. We use the numerical simulation for verification and carry out the field industrial test. The results show that the stability grade of broken surrounding rock is III–IV; both schemes can effectively control the deformation and failure of surrounding rock. Compared with the unsupported scheme, the maximum roof displacement in the scheme using roadway roof and sidewall support is reduced by 26.9%, the maximum thickness of the roof plastic zone is reduced by 58.2%, and the volume of the surrounding rock plastic zone is reduced by 26.32%. The bolt-mesh-shotcrete support has good control effect on the loose deformation of surrounding rock, which can effectively prevent the roof collapse and sidewall spalling of roadway. The field industrial test of support scheme meets the stability control requirements of broken rock mass in mines, and the application effect is obvious. The research results presented in this study provide valuable technical guidance and essential insights for the design of support systems in other similar mining projects, contributing to the effective control and stability of broken rock masses during excavation.

Rock mass classification method applying neural networks to minimize geomechanical characterization in underground Peruvian mines

This research aims to enhance the classification of the rock mass in underground mining, a common problem due to geological alterations that do not fit existing methods. Artificial neural networks are proposed as a solution, which use input/output data to learn and solve problems. The process involves gathering data on rock properties and training the neural networks to identify and classify various types of rock. Once trained, the neural networks can classify the rock mass in real-time during mine design and progression, adapting to different rock types with a low margin of error of 0.279% in determining the RMR index. This research overcomes the limitations of current classification methods, providing a more accurate and reliable solution for the classification of the rock mass in underground mining. In summary, artificial neural networks are utilized to improve the classification of rock mass in underground mining by adapting to geological changes and providing precise classification results.