Rock Mass Damage Research Articles

Monitoring stress-induced brittle rock mass damage for preventative support maintenance

Stress-induced brittle fracturing near an excavation boundary results in a volume increase, known as bulking. Excessive bulking places added demand on the rock support, which, if not detected and addressed through preventative support maintenance (i.e., proactively added reinforcement), can cause the support to fail, leading to a safety hazard and costly production delays for underground mining operations. For caving mines, these project risks are exacerbated during cave establishment due to the large abutment stress from undercutting that redistributes and concentrates stresses near excavations critical for production. This paper reports the findings from research conducted to develop and improve geotechnical monitoring practices to support preventative support maintenance in deep mining operations. This research uses a unique geotechnical monitoring database collected for the Deep Mill Level Zone panel cave mine. The data was collected across a large footprint during the mine's ramp-up period and represents an initial step toward best practices for data collection at cave mines operating in high-stress environments. Borehole camera surveys supplemented by multi-point borehole extensometers have been used to determine the depth of stress fracturing in pillar walls as a function of the distance away from the undercut. Convergence measurements and LiDAR scanning are used to characterize the corresponding rock mass bulking. The results show that the interpretation of monitoring data can be used to identify the long-term depth of stress fracturing and bulking trends in response to undercut advances. These show that direct measures of stress-induced fracturing damage provide an early indication of excavations vulnerable to bulking and that LiDAR scanning is an effective method for capturing the onset of bulking and anticipating local areas likely to experience greater deformation demand as bulking progresses. Proactive and strategic geotechnical monitoring based on the long-term depth of stress-induced fracturing trends is proposed to assist with preventative support maintenance practices.

Dynamic Response and Rock Damage of Different Shapes of Cavities under Blasting Loads

In order to investigate the dynamic response and rock mass damage characteristics of cavities with different shapes under blasting loads, this paper, through a combination of model tests and numerical simulations, studies the stress distribution, strain, failure modes, and blasting fragment size distribution of cavities with different shapes subjected to blasting loads. The results show that under the action of blasting loads, the presence of cavities with different shapes significantly affects the blasting effects and rock mass damage. Spherical cavities exhibit excellent blast resistance, whereas rectangular and triangular cavities are prone to stress concentration at their tips, which in turn promotes rock mass damage and failure. Subsequent analysis of the blasting fragment sizes reveals that rectangular and triangular cavities yield more favorable blasting results than spherical cavities. The research findings provide important theoretical foundations and practical guidance for the design and construction of underground engineering blasting, contributing to enhancing engineering safety and promoting the sustainable development of the underground engineering industry.

Characteristic analysis of tunnel collapse arch in weak rock mass

The stress of surrounding rock and supporting structure is very complicated during the construction of a loose rock tunnel. The characteristics analysis of collapse arch is very important for the construction safety. This paper compares and analyzes the applicability of the full section method and the three-step method under shallow buried loose surrounding rock, reveals the influence law of tunnel excavation height span ratio on the stability of a pseudo-collapse arch of surrounding rock under shallow buried loose surrounding rock, and rationally chooses the three-step method as the dominant construction method of tunnel construction under this geological condition. For the three-step construction method, the optimization study of the excavation height of the upper step is carried out, the relationship between the excavation height of the tunnel and the stress concentration area under the condition of shallow buried loose surrounding rock is revealed, the influence of surrounding rock stress release on the stability of the tunnel surrounding rock is explored, and the damage of tunnel rock mass caused by the stress concentration phenomenon is analyzed. It is determined that the optimal excavation height of the upper step is 0.4H under the geological conditions of the DS project in Sichuan province, China, under construction. This paper analyzes the influence of structural plane spacing on the stability of a tunnel collapse arch under shallow buried loose conditions and reveals the law that the smaller the structural plane spacing, the worse the self-bearing capacity of the collapse arch, and the higher the risk of engineering accidents such as rock collapse or even collapse in the tunnel, which effectively guides the safe construction of the tunnel under shallow buried loose geological conditions.

Fracture characterization of fractured rock bodies based on acoustic and optical characteristics

Crack propagation is an important cause of damage to rock bodies. In this study, uniaxial compression tests were conducted on specimens with rock-like mass containing fissures with different inclination angles to study the effect of crack angle on the crack evolution and fracture characteristics of rock bodies. The specimen surface deformation and internal response characteristics during fracture were analyzed via digital image correlation (DIC) and acoustic emission (AE) techniques. The results indicated that the AE characteristics of the fractured specimens exhibited a high degree of activity during the pore compaction and crack propagation stages. The prefabricated fissure configuration affected the stress state at the fissure tip, leading to differences in the crack evolution paths and rupture modes of fissure specimens with different angles. Under the uniaxial peak intensity, the relative position of the normalized global strain curve peak point gradually shifted from the specimen tip to the middle of the specimen as the crack angle increased, which corresponded to the shear damage-tension-shear mixed damage-tension damage modes of the specimen. The findings of this study indicate that normalized global strain curves can reflect the characteristics of crack evolution and provide a basis for the discrimination of fissured rock mass damage modes.

Acoustic emission characteristics and fracture mechanism of sandstone in open-pit mines under different types of cyclic loads

Rock mass is one of the most important load-bearing media in geotechnical engineering. It has been continually vulnerable to geological tectonic movements, natural calamities, and human excavation activities. Its inherent weak surfaces such as primary pores, joints, and fissures have resulted in varying damage degrees. In mining operations, the damaged rock mass has a variety of negative impacts on the stability of its overlying structures and is frequently disturbed by the load. To study the damage law of rock mass under cyclic loading, in this paper, an acoustic emission (AE) device was employed to monitor the rock under the action of two types of cyclic loads: the variable upper and lower pre-loads, and the fixed upper and lower pre-loads. The damage of the loaded rock was split into three stages in this research, based on the features of the AE signals of the rock under uniaxial load, and the damage evolution of the loaded rock was analyzed in distinct stages. The AE signals of the rock under cyclic loading were mainly emitted in the first loading stage. When the stress did not exceed the maximum stress value in the stress history of the loaded rock, few new AE event was generated in the loaded rock. After the low-frequency cyclic static load, the AE signals varied with the load-bearing stress of the rock during the whole process from initial loading to failure, which was consistent with the characteristics of the AE signals of the loaded rock. The research results can be adapted to rock mass in open-pit mines stability analysis and risk prediction while providing some references for the early warning and danger relief of rock masses in engineering.

Damage and Fragmentation of Rock Under Multi-Long-Hole Blasting with Large Empty Holes

The technique of multi-long-hole blasting with large empty holes has been used in practice to break rock mass. However, the damage mechanism of rock mass surrounded by empty holes and boreholes under this type of blasting has not yet been well-understood and identified, which may lead to inappropriate design of the configurations of empty holes for multi-long-hole blasting. The present study investigates the damage modes and mechanism of rock mass under multi-long-hole blasting with large empty holes by conducting a field test and numerical simulations. The results show that multi-long-hole blasting with empty holes mainly causes compressive damage of rock mass around boreholes, reflected tensile damage near empty holes and ground surface, bending-induced tensile damage between empty holes and boreholes, shear damage along the side tangents and bottom of empty holes and boreholes, and tensile damage along the connection of boreholes caused by the superposition of stress waves. In addition, parametric studies are conducted to examine the effects of depths and diameters of empty holes and the spacing between boreholes and empty holes on the damage and fragmentation of rock mass under blast loads. It is found that the flexural stiffness and confined levels of rock mass can be greatly influenced by the variation of configurations of empty holes, which thus induces different damage and fragmentation under multi-long-hole blasting. Analytical formulas for the evaluation of shear and bending-induced damage of rock mass under multi-long-hole blasting are finally proposed to provide references for the design of empty holes in multi-long-hole blasting.

Study on the mechanism of energy evolution and bearing degradation in pre-cracked sandstone under non uniform cyclic loading

The engineering rock mass is affected by the original cracks, which increases the uncertainty of instability and failure mechanisms. Under the action of excavation unloading or other disturbance loads, its bearing properties are more complex and the deformation characteristics is more special, which has always been a difficult issue in the analysis of rock mechanics. In order to explore the propagation and failure mechanism of spatial micro cracks in fractured rock masses, acoustic emission (AE) experiment of sandstone was carried out under pre-static loading and low-frequency stepwise cyclic loading–unloading. The research results indicate that the peak strain and crack initiation stress of rocks with different pre-cracked positions have the highest differences of 12.62% and 18.65%, respectively. The difference between peak stress and crack initiation strain is within 4%. The pre-cracked position mainly affects the peak strain and crack initiation stress of pre-cracked rocks, and its effect on peak stress and crack initiation strain is limited. The crack initiation angle of prefabricated cracks is mainly distributed within the range of 45° − 90°, and it decreases with the increase of quantities of prefabricated cracks. The crack initiation angle of rocks with prefabricated three cracks is 30% lower than that of single crack. The research results have deepened the analysis of energy evolution and deformation damage of fractured rock masses.

Study on the Stability of Large Retrogressive Landslide and Treatment Technology

To study the catastrophic mechanisms of retrogressive landslides and assess the stability post treatment, it is essential to examine the internal factors contributing to landslides. This involves a detailed analysis of the characteristics of engineering geology, environmental conditions, and the impact of engineering construction activities on the landslide area. The comprehensive treatment schemes for landslides are determined using deep displacement monitoring and numerical analysis. It has been shown that the process of the landslide mechanism can be divided into four stages, i.e., primary structure breakage, rock mass damage deterioration, rock mass softening in water, and rainfall-induced instability failure. Rock mass damage and rainfall caused by slope excavation are the main causes and inducements of landslide instability. The monitoring results of deep displacement have shown that the sliding surface of a landslide is fully integrated. To mitigate the risk of secondary disasters, this study proposes a comprehensive set of measures based on the mechanisms of landslide instability and the support principle of a compensated traction zone. These measures include the implementation of prestressed anti-slide piles, the application of molten steel pipe grouting, and enhanced drainage techniques. The displacement of the slope was reduced, showing that the treatment scheme had a good reinforcement effect.

The Performance Analysis of Grouting Repair Effect on the Accuracy of Disturbance Stress Test in Damaged Surrounding Rock Mass.

Disturbance stress assessment is crucial for ensuring the safety of deep engineering projects. Currently, the primary technique for continuously monitoring three-dimensional disturbance stress is the stress relief method, but its accuracy can be compromised by rock damage that occurs after excavation. To mitigate this issue, grouting is employed to repair damaged rock masses and enhance their mechanical properties. However, the impact of grouting techniques on improving the accuracy of disturbance stress testing is challenging to evaluate through laboratory and in situ experiments. To address this problem, numerical simulation technology is employed to investigate disturbance stress testing after the repair of damaged surrounding rock through grouting. The simulation results indicate that grouting repair significantly enhances the accuracy of stress testing. As the depth of damaged rock mass repair increases, the error in stress testing decreases. Achieving complete repair of the initial damage zone during grouting is essential to eliminate errors in stress testing. Expanding on the positive effects of grouting repair on stress testing, a segmented testing method for disturbance stress is proposed. The method involves separately testing the initial stress and stress changes, thereby reducing the stress level within the rock, minimizing rock failure, and enhancing the accuracy of disturbance stress testing. This study provides valuable reference methods, and the outcomes of this research will serve as a foundation for enhancing the accuracy of disturbance stress testing in deep hard rock engineering.

Analysis of induced stress during construction and production stages of drawbells in block caving mines

Drawbells are large constructions that allow the flow of the broken ore at the production level within the drawpoints. The results of drawbell construction are crucial for a successful mine plan extraction in a block caving mine. Analysis and integration of all the topics related to a drawbell can improve the performance of the surrounding area of drawbells, particularly the damage associated to induced stress during the different stages of a block caving operation. The improvement of operational aspects related to the drawbells would decrease the risk of failure, particularly in deep mines subject to large stresses, which are more likely to experience sudden violent or progressive failure. A large-scale numerical model was developed to analyse different mining sectors using sub-models. It was found that the geotechnical response is highly correlated to the stress field, which also controlled the resulting seismicity. In a scale of a drawbell, the drawpoint drift roof and the bridge pillar between the drawbell and the undercutting level were found the most critical zones in the design. When geological structures are present, they can be activated in the construction at an earlier stage and, therefore, could easily become critical in the resulting rock mass damage.

Application of seismic methods for determining the depth of the rock mass damage zone around the excavation profile by blasting

Research and determination of the blasting damage zone around the profile of tunnels or underground structures is a platform that would serve to confirm or correct blasting parameters and underground assemblies, that is, geotechnical and main tunnel projects. From the obtained research, the stability of the excavation profile, as well as the safety risk for equipment and personnel on the construction site, would be better understood. Considering the importance of the size of the damage zone of the rock mass in terms of its influence on stability, the amount of primary support elements required to achieve the stability of the excavated space, and the additional costs of stabilization of the excavation and the safety of people and equipment, the aforementioned problem was investigated and processed for specific cases and for the rock mass characteristic for the location in question. From the described research, the change in the elastic characteristics of the rock mass and the depth of the damage zone around the tunnel excavation profile were measured and calculated.

Investigation of the influence of pre-crack number on acoustic emission characterization of red-sandstone short-term creep damage and failure precursors

Rock crack is one of the main factors responsible for rock failure. Uniaxial compression creep tests are performed using acoustic emission techniques, a high-sensitivity, non-radiative, non-destructive testing method to understand the influence of crack number on the precursor characteristics of short-term creep damage in the fractured rock mass. Based on the Grassberger-Procaccia (G-P) algorithm, the calculation step size for the correlation dimension value (D 2) of the acoustic emission ringing count rate is consistent with that for the acoustic emission b-value. The influence of the number of pre-cracks on the Acoustic emission precursor characteristics of red sandstone creep is analyzed. The results show that near the destabilization of the specimen, the Acoustic emission accumulative ringing count surges in a stepwise manner, the Acoustic emission b-value decreases, the D 2-value increases, the Acoustic emission amplitude shows high intensity and high frequency, and the ringing count increases sharply, all with the characteristics of failure precursors. During the accelerated creep stage of the specimens, with the increase of pre-cracks number, the precursory time points of acoustic emission b-value and D 2-value advance, and their acoustic emission ringing counts increase sharply.

Investigation of Sandstone-like Material for Damaged Rock Mass Based on Orthogonal Experimental Method

The investigation of the mechanical properties of rock mass can be effectively carried out through rock-like material experiments. In this study, polystyrene foam particles were utilized as a novel material for simulating initial damage within rocks. Our research involved the development of sandstone-like materials with comparable mechanical properties to actual sandstone. These materials were then subjected to orthogonal mechanical tests, allowing us to identify the key factors that have a substantial impact on the mechanical parameters of sandstone-like rocks. The influencing factors considered in the orthogonal mechanical tests were the proportion of aggregate and binder, the proportion of polystyrene foam in the entire model, the proportion of binder and regulator, and the size of polystyrene foam. Five levels were set for each factor, and mechanical parameters such as compressive strength, tensile strength, elastic modulus, axial strain, and Poisson’s ratio were tested for each group of samples. The changes in mechanical parameters with the levels of the above four factors were studied. The study found that modifying the proportion of aggregate to binder can alter the elastic modulus, tensile strength, and compressive strength values of sandstone-like material. The size of polystyrene foam can be modified to alter the axial strain values of sandstone-like materials. Additionally, adjusting the ratio of binder and regulator can modify the value of Poisson’s ratio. The comparison of mechanical parameters between sandstone-like samples and sandstone reveals that sandstone-like materials can better simulate the deformation and failure mechanisms of sandstone. The error in the main mechanical parameters, such as modulus of elasticity, strength, and Poisson’s ratio, is less than 7%, indicating a greater resemblance between sandstone-like materials and sandstone. Therefore, sandstone-like materials can be used to investigate the deformation law, damage evolution law, and failure mechanism of sandstone. This can help alleviate the difficulty of obtaining specimens of deep damaged rock and the high cost of testing.

Damage deterioration mechanism and damage constitutive modelling of marble after cyclic impact loading

Rock mass in tunnel, underground chamber and other underground engineering is inevitably affected by multiple blasting impact, rock mass cracking and failure are often affected by these damaged rock mass, so it is meaningful to study the rock mass affected by dynamic damage. To explore the influence of cyclic impact on the internal structure of marble, NMR (Nuclear Magnetic Resonance) technique was adopted to test the marble. It was found that the impact would rise the porosity of marble, and the pore size distribution would also change greatly. Then uniaxial compression experiments were conducted on core samples. The results show that the impact will cause significant damage to the marble, and the mechanical properties of the marble will be obviously degraded. With the increase of impact times, the peak strength and tangential deformation modulus tend to decrease. The impact effect promotes the initiation and development of rock microcracks, pushes forward the development of the compaction stage, and increases the strain at the full compaction point. In addition, the damage constitutive model with the combination of different disturbances and loads was constructed in stages according to the principle of statistics, and the experimental results were used to verify the damage constitutive model. The crack closure and failure of the samples subjected to different impact times were well reflected in the model, and the practical significance of the parameters in the model was analyzed. The failure mode of the sample subjected to different impact times is discussed and verified by acoustic emission technology.

Damage creep model and application for sandy mudstone considering the effect of immersion deterioration

Abstract Aiming at the problem of performance degradation and large deformation of sandy mudstone after immersion in water, the compression test is carried out. The damage and deterioration law of strength and elastic modulus of immersed rock mass is analyzed, and the function relationship between rock damage variable and soaking time is obtained by fitting. Combined with the Hoek-Brown criterion and Mohr-Coulomb criterion, the calculation method of instantaneous cohesion and instantaneous internal friction angle of damaged rock mass is derived based on the tangent method, and the equivalent Mohr-Coulomb criterion which can effectively characterize the nonlinear strength characteristics of damaged rock mass is given. Based on the built-in creep model Cvisc of Flac3D, a damage creep model is given by introducing the damage factor and nonlinear strength criterion of immersed rock mass, which is more suitable for describing the creep characteristics of immersed sandy mudstone. The validity of the model is verified by comparing with the measured results.

Research on the Cumulative Damage Law of Surrounding Rock under Cyclic Blasting Action

In order to study the cumulative damage characteristics and laws of rock masses under cyclic blasting loads, based on the finite element software ANSYS/LS-dyna and the HJC constitutive model, a single blasting damage analysis is conducted first, and the accuracy of the results is verified. On this basis, numerical simulation studies on the cumulative damage of rock masses under cyclic blasting are carried out separately. The results indicate that the cumulative damage evolution cloud map of the rock mass under cyclic blasting is similar to that of a single blasting action, showing an inverse S-shape overall. The damage increment of the rock mass decreases with the increase of blasting times, and in the central area of the damage zone, the rock mass is particularly affected by the superimposed effect of cyclic blasting loads. Cyclic blasting fully reflects the accumulation of damage to the rock mass under multiple cyclic blasting loads, and there is a certain relationship between rock mass damage and the distance between the blasting centers. As the distance between the blasting centers increases, the amount and increment of rock mass damage generated by blasting continue to decrease.

FORMATION OF THE NEAR-FAULT DAMAGE ZONE DURING DYNAMIC RUPTURE IN A CRYSTALLINE ROCK MASS

Many models for analyzing the dynamic propagation of seismogenic ruptures are based on solving classical problems of fracture mechanics. It is assumed that the fault is a shear fracture mode with uniformly distributed friction and stresses at the crack tip. Known fracture mechanics theories do not describe the formation of laterally oriented damage zones, i.e., in the direction perpendicular to the crack plane. Observational data indicate the presence of a fairly extensive zone of damaged material in the vicinity of the fault. This is the zone of dynamic influence where the material has an increased number of fractures, higher permeability and lower elastic wave velocities. A correct assessment of the properties and sizes of zones of dynamic influence is crucial for constructing adequate earthquake preparation models. This paper analyzes the development patterns and quantitative characteristics of the damage zone during dynamic earthquake rupture and quasi-static evolution of the fault. To estimate the size and mechanical characteristics of the near-fault damage zone caused by movement along the slip surface, it is convenient to use the value of the second invariant of the deviatoric stress tensor (shear intensity). Matching of the calculated value with one or another degree of rock mass damage can be done using measurement data from large-scale explosions, by comparing them with the calculation results. It is shown that coseismic movement along the fault leads to insignificant changes in the properties of the host rock mass. Although the longitudinal wave velocity near the fault decreases markedly by 30-35%, the permeability increases only by approximately a factor of three, and the increase in the degree of fracturing is almost unnoticeable. This means that the properties of the rock mass change due to the opening of preexisting cracks. Repeated movements do not radically change the characteristic dimensions and properties of the damage zone. It is concluded that the fault-affected zone is formed mainly at the quasi-static stage of the formation of a single main fault zone through the coalescence of individual macrofractures, and future seismogenic movements add to the already existing amount of fractures.

Influence of Joint Orientation and Spacing on Induced Rock Mass Damage due to Blasting in Limestone Mines

Influence of Joint Orientation and Spacing on Induced Rock Mass Damage due to Blasting in Limestone Mines

Failure mechanism and deformation forecasting of surrounding rock mass in an underground cavern based on engineering analogy method

The underground powerhouse of Lianghekou hydropower station is deeply buried with high ground stress and complicated geological conditions. To delineate rock mass damage zones and analyze the stability of underground powerhouse subjected to excavation disturbance, an ESG monitoring system was applied to carry out real-time monitoring against the inner micro-fracture activity of surrounding rock mass. In order to solve the problem that the deformation of surrounding rock mass cannot be monitored due to the failure of multipoint displacement meters, the engineering analogy method is adopted to forecast the deformation of surrounding rock mass by comparing the similar projects of Houziyan and Baihetan hydropower stations. Research results show: (1) The failure of surrounding rock mass was stress-driven failure, and was primarily characterized by a medium degree of stress-induced failure. (2) During the monitoring period, microseismic (MS) events clustering area formed, which was both related to blasting excavation disturbance of the bus tunnel and the formed crossed free surfaces. (3) The seismic source parameters during the deformation of surrounding rock mass in similar projects were analyzed, and the variation characteristics of the frequency, energy, b-value, central frequency, apparent stress, and apparent volume of MS events were summarized. (4) The engineering analogy method was adopted to forecast that the deformation period of surrounding rock mass of Lianghekou hydropower station is from April 25 to May 2, 2016. The present achievements can provide some references for similar deep underground excavation 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.