Rock Instability Research Articles

Geochemical and mineralogical analysis of low-grade metamorphic rocks and their response to shallow landslide occurrence in Central Nepal

BackgroundThe weathering intensity and geochemical properties of a rock contribute to shallow landslide occurrences. This study aims to establish the role of rock weathering in shallow slope instability in low-grade metamorphic rocks of the Lesser Himalaya region of central Nepal. The rocks of the Kuncha Formation, which consist of phyllites, metasandstones, and gritty phyllites are characterized by the formation of shallow landslides. Field characterization of the rock mass within the landslide body, along with petrographic observations, clay mineral analysis, and major bulk geochemistry were adopted to establish a relationship between rock weathering and landslide occurrence.ResultsThe landslides distributed within the Kuncha Formation in the study area are debris-related slides and falls, rock falls, and complex slides. Microscopic petrographic observation of rock from the landslide area revealed well-developed microcracks and intergranular microfractures within the weathered samples, which suggests extensive disintegration and physical alteration. Kinematic analysis of the landslide slope revealed that discontinuities and bedding planes also affected the failure of the slope. The occurrence of neo-formed clay minerals and the conversion of biotite-muscovite to vermiculite, kaolinite, and mixed-layer clays indicate chemical weathering. The CIA ranges between 71 and 80 for the rock samples and between 72 and 84 for the soil samples, signifying moderate to extreme weathering effects. The higher values of PIA and CIW reveal K-feldspar and plagioclase alteration to clay minerals by weathering and alteration. CIA-LOI plots reveal significant relationships corresponding to weathering effects.ConclusionThe transition of rock from a fresh to a moderately weathered state and the development of clay minerals and major discontinuities played a crucial role in shallow landslide occurrence. The weakened physical properties of the rock mass due to weathering coupled with unfavorable joints and fracture conditions have led to instability of the hillslopes in the study area. It was observed that one of the driving factors that drives slopes to erosion and landslides is weathering. The dominant occurrence of landslides in the weathered rock domain within the study area validates the occurrence of landslides and weathering interconnections.

Investigating infrared Radiation, Energy, and fracture evolution features of dry and wet coal under cyclic loading

The continuous mining activities at the working face cause periodic disturbances to the surrounding coal rock mass. Investigating the response characteristics of surface infrared radiation temperature, energy evolution features, and fracture development patterns in coal rock under cyclic loading and unloading is crucial for enhancing our understanding of the mechanisms of damage, degradation, and instability in rocks associated with mining operations. In this research work, we conducted infrared radiation observation experiments on both dry and wet coal samples subjected to uniaxial cyclic loading and unloading. Furthermore, we carried out a thorough analysis of the resulting temperature variations, energy changes, and fracture evolution patterns. It was found that the average infrared radiation temperature (AIRT) generally increases during the loading phase and decreases during the unloading phase, with the variance of successive minus infrared image temperature (VSMIT) exhibiting a sharp change just prior to failure. Energy analysis indicates that dissipated energy during the pore compaction and elastic deformation stages is minimal, while in the plastic deformation stage, the proportion of dissipated energy to total energy increases, displaying a “concave” upward trend. Additionally, fitting results show that the AIRT follows a single exponential decay relationship with dissipated energy, with wet coal exhibiting a greater decay coefficient, highlighting that moisture accelerates the rate of temperature decline. The Particle Flow Code (PFC) simulation results further demonstrate that the number of cracks in dry coal samples significantly exceeds that in wet coal samples, showing a single exponential relationship between the number of fractures and dissipated energy, which indicates that the development of fractures in dry coal rock occurs at a faster rate with increasing dissipated energy compared to wet coal rock.

Research on the Support Technology for Deep Large-Section Refuge Chambers in Broken Surrounding Rock in a Roadway

The phenomenon of peripheral rock instability is more common in crushed bedrock roadways, and the fundamental reason for this lies in the significantly different characteristics of its peripheral rock stress field. Taking the newly dug belt inclined shaft of PingDingShan TianAn Coal Co., Ltd. No. 6 Mine as the engineering background, a mechanical model of a broken perimeter rock roadway was established by using classical rock mechanics theory. Stress distribution around the roadway of the broken perimeter rock medium was systematically analyzed, and radial and tangential stress formulas of the broken perimeter rock were deduced. Through the formula calculation, it was deduced that there was a stress drop in the intact surrounding rock outside the disturbed zone, and the radial stress of the intact surrounding rock in its deep part was relatively increased, while the tangential stress was relatively decreased. The existence of crushed surrounding rock increased the minimum principal stress and decreased the maximum principal stress of the unfractured surrounding rock, which proves that a well-maintained disturbed zone can play a lining role. Thus, a “U-shaped steel + inverted arch + bottom arch linkage beam + floor bolt compensation” support program was proposed. This joint support program easily forms a closed support structure, which is more effective in controlling the deformation of tunnel perimeter rock. The support structure can effectively resist the deformation of the surrounding rock and enhance bottom drum resistance. Through numerical simulation, it was concluded that the horizontal displacement of the two gangs was reduced by 70%, and the displacement of the top and bottom plates was reduced by 77% after optimization of the support, which effectively controlled the stability of the broken surrounding rock.

Acoustic and thermal response characteristics and failure mode of gas-bearing coal–rock composite structure under loading

Exploring the characteristics of the instability and failure processes of gas-bearing coal and rock is crucial for monitoring and predicting mine gas accidents. Thus, a real gas environment was simulated based on a self-developed gas–solid coupling infrared observation system. The acoustic–thermal response characteristics and failure mode of the gas-bearing coal–rock composite structure were studied. The results showed the following: (1) From the plastic stage, the average infrared radiation temperature of the coal increased significantly. The variances of differential infrared temperature (VDIRT) of the combination and coal started to mutate approximately 30 s before the peak, and the b value of the combination began to fluctuate frequently, while the VDIRT of rock remained approximately 2.128 × 10−4 throughout the process. (2) When stress was about to peak, a clear temperature boundary formed between coal and rock. Acoustic emissions with high energy were mainly concentrated at the interface and inside the coal. (3) The early plastic stage was dominated by high-frequency, low-amplitude events. In the post-peak stage and late plastic stage, the proportion of events with 80–90 dB amplitude rose, and there was a significant increase in low-frequency, high-amplitude events. (4) As the loading proceeded, the density and area gradually increased and tended to move toward the shear crack region. The distribution range of the rise time/amplitude expanded from 0–12 ms/V at the beginning of the loading to the range of 0–60 ms/V in the post-peak stage.

Assessment of the influence of natural thermal cycles on dolomitic limestone rock columns: A 10-year monitoring study

Rock instabilities hazards can lead to major risks. Even if different external factors such as precipitation, seismic activity or freezing, are known to trigger rockfalls, it is more and more assumed that thermal cycling has a role in rock mass deformation, displacement and, moreover cracking initiation or propagation. Here we present 10 years monitoring of a 50-meter-high dolomitic cliff, located above an important highway in the south of France to support this thinking. Local rock surface temperature and joint apertures were recorded on eleven sensors. Their evolution is studied separately and together to characterise the influence of temperature variation on joint apertures. During small time periods, a reversible and proportional behaviour is observed, that can be attributed to thermoelasticity, but over the whole period, a significant drift in displacements is measured, meaning that at least a viscoplastic or fatigue behaviour should be considered.

Analysis of progressive collapse disaster and its anchoring effectiveness in jointed rock tunnel

AbstractThe complexity and variability of the structural distribution and combination characteristics of jointed rock masses make the response mechanism of tunnel rock collapse different, and there is a lack of systematic research on the existing perimeter rock instability mode and bolt support scheme. Based on numerical simulations of the block system structure of a nodular rock mass, the existing theory of bolt support is compared and analyzed to explore the scope of their respective applications. Combined with the spatial and temporal transport law of block instability, a new batch instability model of jointed rock tunnels is proposed, which reveals the progressive collapse catastrophe evolution mechanism of a collapsed interlocking block system after the instability of the key blocks and elucidates the coupling mechanism between the bolts and the block system structure as well as their anchoring effectiveness. Finally, for the actual tunnel project, the instability batches of the surrounding rock are identified, and the corresponding optimized design of the bolt support is presented, which has achieved good support effects. The research results can provide important theoretical guidance and practical engineering value for risk avoidance, disaster identification and targeted prevention and control of dangerous rock fall and chain collapse instability disasters in jointed rock body tunnels.

Experimental Study on the Shear Failure Properties and Damage Constitutive Model of Rocks.

In the construction of underground geological engineering, a variety of rocks were often encountered, and the engineering surrounding rocks was prone to shear fracturing. Shear mechanics tests were conducted on a variety of rocks under various joint angles. By studying the shear mechanical characteristics, acoustic emission behavior, and damage degree of the different rock types, we can obtain an insight into their bearing capacity and fracture mechanisms. An obvious inflection point from the elastic to plastic behavior can be observed for the specimens during the process of shear mechanics tests, and the shear behavior was divided into three phases. The acoustic emission signals significantly increased for coal during the second phase, while those of sandstone and shale start to increase during the third phase, which is from the peak point to fracture. The analyses of the shear failure and acoustic emission properties showed that the crack propagation angle increases as the normal stress of rock increases. It was proved that the joint angles and normal stresses of rock could effectively hinder the development of vertical fractures. Based on the shear failure and acoustic emission properties, a constitutive model capable of describing the shear behavior of different types of rocks was developed. This constitutive model can accurately describe the shear fracture properties of the various rocks. The shear failure properties and damage constitutive model of rocks in this study can be used to reduce engineering surrounding rock instability caused by shear.

A novel approach to assessing precarious rock instability in high-cold regions considering freeze-thaw forces

A novel approach to assessing precarious rock instability in high-cold regions considering freeze-thaw forces

Analysis of cracks development and damage evolution in red sandstone under dry-wet cycles based on temporal and frequency characteristics of acoustic emission

Utilizing the goafs of underground reservoirs (underground buildings) in western coal mines as storage spaces plays a crucial role in ecological environment protection and energy transition in mining areas. Hence, it is crucial to recognize the repeated erosion of reservoir water levels on the deformation and damage mechanisms of the roof and floor rock masses in the underground building dams. This paper intends to study the instability failure mechanisms and precursor responses of red sandstone samples with 0–3 dry-wet cycles during uniaxial loading-unloading under acoustic emission (AE) monitoring. The AE time-frequency features were analyzed, and the crack three-dimensional spatial extension and tensile-shear crack evolution were explored. The b-value and entropy value of AE events were presented for evaluating crack expansion damage status during loading-unloading. The findings suggest that the peak strength, elastic modulus, and crack thresholds of red sandstone exhibit a positive exponential decline with growing dry-wet cycles. Conversely, the peak strain and strain-softening modulus exhibit an opposite trend. With growing dry-wet cycles, AE signals from low-frequency, high-amplitude, and large-scale cracks decline, exhibiting a multi-frequency simultaneous response effect before sample instability. Meanwhile, the proportion and concentration of localization events with energy exceeding 104 aJ rise, and the failure instability gradually shifts from tensile-shear failure to tensile cracks. The sudden decline in b-value and the significant fluctuation in entropy value serve as short-term precursors to imminent rock instability failure, with the system energy following an ordered-disordered-ordered pattern. The research findings offer certain experimental foundation and novel judgment indicators for rock structure safety warning, including the stability of underground building dams, support for water-rich roadways, water hazard prevention, and utilization of abandoned mine spaces.

Influence of filling materials on mechanical properties of fissured sandstone treated by tailings water

Fissured rocks deteriorate with increasing water content, and the mechanical behavior is significantly influenced by the filling materials within their fissures. Understanding the effects of tailings water on the mechanical properties and failure modes of rocks under different filling conditions is crucial for assessing the stability of tailings ponds. In this study, uniaxial compression tests were conducted on single-fissured sandstone filled with gypsum, cement, and epoxy resin at various immersion heights, and acoustic emission signals were monitored. The results indicate that the mechanical properties of sandstone deteriorate significantly upon immersion, but the rate of deterioration decreases with increasing immersion height. The use of stronger and more cohesive filling materials can improve the mechanical properties of fissured sandstone, but there remains a gap compared to intact samples. Differences in physical properties and uneven stress distribution between immersed and dry portions lead to the formation of complex crack networks in partially immersed samples. The strong bonding between epoxy resin and sandstone results in local stress exceeding the sandstone's bearing limit, leading to increased fragmentation. The acoustic emission activity generally exhibits a pattern of gradual increase, quiescence, and then activation. As the immersion height increases, the number of acoustic emission events and energy release decrease. The average frequency and rise angle analysis reveals that tensile cracks dominate the failure process. Near failure, the b-value drops sharply and exhibits intense fluctuations, accompanied by the emergence of numerous high-frequency signals. These phenomena provide a basis for predicting rock instability and failure.

Integrated early warning and reinforcement support system for soft rock tunnels: A novel approach utilizing catastrophe theory and energy transfer laws

The initial support strength of deep-buried soft rock tunnels during excavation is often inadequate, and the timing of reinforcement support is inappropriate. This inadequacy leads to significant deformations in the tunnel, causing the energy released by the surrounding rock to exceed the energy that the support system can absorb, ultimately resulting in tunnel collapse. Tunnel deformation monitoring and anchorage support, when combined with energy transfer laws, are thus imperative for studying collapse prediction, the timing of reinforcement support, and parameters of the reinforcement support system of the surrounding rock. In this paper, a novel approach for early warning and support control in tunnel construction facing large deformations is introduced, and a predictive model for surrounding rock instability utilizing catastrophe theory and energy transfer laws is developed. By analyzing the correlations of rock deformation and energy dissipation, the timing of anchor reinforcement support was determined using function fitting techniques. Further, an energy transfer model under reinforced anchoring support was established, and the energy absorption parameters of the support body were determined. Also, the support parameter design scheme was proposed. The results indicate that the early warning and reinforcement support scheme proposed in this paper reduces the release of potential energy by 35.71 %; decreases the number of steps needed to reduce kinetic energy to zero by 66.67 %; reduces the total dissipated energy in joint shear by 33.68 %; increases the total stored strain energy in the material by 5.70 %; and reduces the total dissipated work in plastic deformation by 26.15 %. Additionally, this plan effectively controls the originally predicted large deformation area of the meter level to within 350 mm.

Surrounding rock instability mechanism for fault-crossing tunnels in water-rich soft rock

Surrounding rock instability mechanism for fault-crossing tunnels in water-rich soft rock

Quantitative Risk Assessment of Rock Instabilities Threatening Manazan Caves, Karaman, Türkiye

Located in the southern part of Central Anatolia Region, Manazan Caves is situated in the east of Yeşildere Valley. It is a five-storey mass dwelling carved into a human-made high rock mass. Although there are no exact data to determine when the caves were carved, it is assumed that the caves were carved and settled in the Byzantine period during the 6th − 7th centuries. The geological and geotechnical data analyses were conducted in Manazan Caves. As a result of these analyses, it was observed that rock blocks of different sizes fell into the field in various times of the year, and there were instabilities in some individual rock blocks. In the study area, the movement mechanisms of rock slopes due to discontinuity were analysed by using various computer programs (DIPS, RockFALL, GEO5); and in order to ensure the safety of life and property and to protect this heritage cave, the current rockfall potential and risk along with slope instabilities were determined, and the fundamental prevention measures to be taken were discussed.

Investigation on the multidirectional crack vibration induced by rock fracture

Understanding crack vibrations in rock under load is crucial for comprehending and predicting rock failure. With this motive, a novel multidirectional crack vibration (MCV) monitoring experiment is carried out using miniature vibration acceleration sensors with directional sensing. The obtained results show that the crack surface produced by uniaxial compression failure of rock is rough and its direction is variable. Furthermore, the volume distribution of the sample after failure is uneven, and there is a noticeable difference in mass between the broken samples on either side of the crack. Different directions of crack vibration signals were detected during rock failure, all exhibiting a strong temporal correspondence with the stress drop, but the amplitudes and main frequencies of the vibrations differ across directions. The fracture-induced crack vibration is a typical low-frequency signal, with the highest recorded frequency at 55.63 kHz and the lowest being 0.86 kHz, with the main frequency mostly below 25 kHz, which is notably lower than acoustic emission. This difference suggests that fracture-induced crack vibration and acoustic emission are distinct physical quantities. The disparities in rock vibration amplitude and main frequency among different directions, especially those perceived by opposing sensors, indicate that the two sides of the crack cannot be considered as the same vibration system. The analysis shows that the fracture-induced crack vibration of rock under load is damped vibration with a small and variable damping. Besides, due to the difference in vibration parameters on both sides of the crack, their vibration amplitude and frequency are also different. The miniature acceleration sensors used in this work can effectively capture MCV during rock failure and can be employed to further investigate the vibration precursor of rock instability failure, so as to develop appropriate assessment and prediction methods for underground dynamic disasters.

Creep Energy Evolution of Red-Bed Soft Rocks in South China under Chemical-Stress-Seepage Coupling

The red-bed soft rocks in South China have obvious creep characteristics and are prone to engineering geological disasters such as landslide and foundation settlement under the action of rainfall, groundwater, and load. In order to reveal its creep characteristics and mechanism under complex conditions, a step-loading creep test was carried out under chemical-stress-seepage coupling, and the energy evolution law of the whole creep process was analyzed based on linear energy storage and energy dissipation theory. The results also show that the acid chemical solution has the greatest influence on the triaxial strength and creep strength, and the creep damage and energy evolution of red-bed soft rock are universal. The creep damage and total strain increase with the increase of acidity, the decrease of confining pressure, and the increase of seepage pressure. The evolution law of creep damage shows the characteristics of slow-acceleration-rapid growth, and with the increase of load level, it has obvious transfer and accumulation. After entering the constant velocity creep stage, the damage rate begins to accelerate. The proportion of instantaneous strain and creep strain in the total strain increment is about 50%, and confining pressure has little influence on their respective proportions. The instantaneous strain is more sensitive to the acidity of the chemical solution, and the proportion of creep strain increases gradually with the increase of seepage pressure. The relationship between elastic energy density and total energy density is linear. The elastic energy density and dissipated energy density in the loading stage and creep stage all increase nonlinearly with loading time. The density of dissipated energy in the creep phase is lower than that in the loading phase, but the opposite is true in the higher stress phase, and the law of energy dissipation can explain the hardening damage effect in the creep process of soft rock samples. The research results provide a new perspective for us to reveal the mechanical properties and failure mechanism of red-bed soft rocks and provide an important theoretical basis for predicting and evaluating the creep instability and long-term stability of such rocks.

Experimental Study on Energy Release Mechanism and Crack Propagation Evolution of Sandstone under True Triaxial Loading

The instability of hard and brittle rock often leads to disastrous consequences in underground engineering. Under various surrounding rock pressure conditions, in situ stress induces corresponding deformation and damage to the floor post-mining. Therefore, it is crucial to examine the effects of mining under different confining pressures on rock disturbance, damage characteristics, and their distribution. Consequently, triaxial loading experiments under varying intermediate principal stress conditions were conducted on red sandstone specimens, using an acoustic emission monitoring system to track energy changes during rock damage and failure. This approach aids in studying crack generation, propagation, and fracture damage evolution. The results indicate that rock deformation results in axial compression and dilatancy, aligned with the direction of minimum and intermediate principal stresses. Ductility in rock failure becomes more pronounced with increased stress, primarily manifesting as shear failure. Internal cracks in the specimen lead to stress concentration and marked plastic deformation under compression, yet do not result in macroscopic surface cracks. The fracture angle θ of specimens post-failure generally exceeds 45° and varies with stress changes; at consistent burial depths, the angle of the sandstone failure surface increases with intermediate principal stress. This paper preliminarily establishes the informational linkage between rock failure and energy release, analyzing the rock samples over time and space. This research offers insights for analyzing and mitigating sudden rock instability.

Micro-cracking morphology and dynamic fracturing mechanism of natural brittle sandstone containing layer structure under compression

The failure and instability of sedimentary rocks are related to internal weak surface and potential damage. To explore the influence of layer structure on the crack expansion law and deformation characteristics of sandstone, this study investigated the effect of layer structure on apparent crack degree, microscopic damage law, acoustic emission and deformation field under uniaxial compression. The fracture modes include tensile fracture Ⅰ, tensile fracture Ⅱ, shear fracture and composite fracture with an anisotropic characteristics. The apparent crack degree and stress show a simultaneous evolution feature and the sandstone with significant layer deterioration effect have greater damage degree. The peak stress and elastic modulus have nonlinear exponential relation with layer angles. The acoustic emission (AE) behavior has a phased response to the aging fracture, and AE energy warning points and AE b-value dropping abruptly generally occur near the continuous stress drops or peak stress. The deformation field reveals the principal strain and resultant displacement has a spatiotemporal response characteristic and there is a typical damage competition relationship in the deformation concentration area. The fracturing effect intensifies the dissimilation behavior of deformation field, formation of strain concentration zone and banded dissimilation zones indicate the cracks penetration. The displacement field at the fracture tip shows a significant suddenness and strain concentration region is often pregnant with high-level displacement. These findings on the dynamic fracture mechanism are helpful in the deterioration characteristics of sedimentary rock in underground space engineering.

Damage evolution and destabilization precursors in granite under splitting load at different temperatures

Brazilian splitting acoustic emission (AE) tests were conducted on the granite specimens that were heated at the temperatures from 50 to 600 °C to investigate the mechanical and damage characteristics of granite under high temperatures and splitting load in deep drilling. The results indicate that temperature variations significantly alter the mechanical characteristics and AE properties of granite, thereby influencing the evolution of fractures. At the temperature above 500 °C, the tensile strength of granite decreases significantly and the proportion of shear-induced damage modes increases. Furthermore, the rate of fracturing also exhibits a noticeable increase. Damage parameter mutation points on the damage parameter evolution curves of hit counts and energy counts were defined to determine the rock damage precursor. Mutation points based on hit counts arrive earlier than rock instability signals. The greater the damage is, the earlier the mutation points arrive. This time difference can be used to identify rock destabilization signals.

Study of Time–Frequency Domain of Acoustic Emission Precursors in Rock Failure during Uniaxial Compression

Predicting rock bursts is essential for maintaining worker safety and the long-term growth of subsurface infrastructure. The purpose of this study is to investigate the precursor reactions and processes of rock instability. To determine the degree of rock damage, the research examines the time-varying acoustic emission (AE) features that occur when rocks are compressed uniaxially and introduces AE parameters such as the b-value, γ-value, and βt-value. The findings suggest that the evolution of rock damage during loading is adequately reflected by the b-value, γ-value, and βt-value. The relationships between b-value, γ-value, and βt-value are studied, as well as the possibility of using these three metrics as early-warning systems for rock failure.

Prediction of water inflow and analysis of surrounding rock stability in unfavorable geological mountain tunnel

During the construction of a mountain tunnel, water inflow and rock instability are common occurrences due to unfavorable geological conditions, posing serious threats to construction safety. This study focuses on a proposed mountain tunnel and employs multiple formulas to predict potential water inflow during excavation. Based on the amount of water inflow and deformation of surrounding rocks, comprehensive determinations are made for the thickness of grouting rings and permeability coefficients. The results demonstrate that: 1) Different formulas yield slightly varied outcomes but overall trends remain consistent; considering various calculations, the normal water inflow for this tunnel is approximately 115.5908×103 m3/d with a maximum at 210.9100×103 m3/d 2) Increasing grouting ring thickness or decreasing permeability coefficient can effectively reduce water inflow, but the reduction range is gradually narrowed. 3) Pre-grouting curtains have an evident effect in enhancing stability; however, their effectiveness decreases with increased thickness. 4) Taking into account both safety and economic factors, it is recommended that the grouting ring thickness be set at 8 m with a permeability coefficient equaling one 100th that of surrounding rocks for this tunnel project.