Damage Characteristics Of Rock Research Articles

A Study of Constitutive Model of Rock Damage under the Joint Effect of Load and Moisture

To study the mechanical damage characteristics of rock under the effect of subversion, a series of mechanical experiments, including both uniaxial and triaxial mechanical compression experiments under various levels of water content were performed. In this study, researchers investigate the impact of water content on the mechanical characteristics of rock, based on the compliance of the rock damage variants to the Weibull statistic distribution, and Drucker–Prager strength rule, aiming to construct a constitutive model under the joint effect of load and moisture. In addition, the established constitutive model is tested in the experiment. According to the test results, during the initial phase of the submersion, the water content in the rock increases following the exponential function until reaching the threshold. The water content remains stable after the threshold. Under the uniaxial and triaxial loads, the damage detected in the rock and the elasticity modulus decreases linearly as the water content increases. The rock’s mechanical parameters and the damage evolution rate are significantly impacted by the surrounding pressure. As the surrounding pressure increases, the weakening effect of the water in the rock decreases. The theoretic curves developed to describe the rock damage under the joint effect of the water and load are consistent with the curves drafted based on the test, indicating that the constitutive model can accurately describe the stress and strain behaviors of rock under various water contents and loading conditions.

Dynamic damage characteristics of rock under multiple loads during high-voltage pulse fragmentation

To analyze the damage characteristics of rocks during high-voltage pulse fragmentation (HVPF), two kinds of loads, shockwave and cavity, are determined by optical observation, and the pressure–time characteristics of these two and their mechanism of damage to rocks in mesoscopic view are analyzed. A model of dynamic damage characteristics of brittle rock under multiple loads is established, which includes numerical calculation and discrete element simulation. In the discrete element simulation, the rock is simplified as a circular region without reflection boundary with a certain size of the circular hole inside, and the grains in the region are discretized as rigid spheres with a definite bonding relationship. The shockwave is considered the time-varying pressure loaded to the grains of the circular hole, and the cavity is considered the quasi-static pressure loaded to the grains on both sides of the fracture. The results of the model show that shear cracks and tensile cracks are produced during the shockwave action, but tensile cracks are predominant. The shockwave acts as a preload for the expansion of cracks, and the damage radius is small. Most of the cracks in HVPF are caused by the cavity. A comparison of the numerical calculation results with the discrete element simulation results shows that the model can describe the distribution characteristics of cracks under multiple loads, which lays a foundation for further analysis of the internal mechanism of HVPF.

Experimental and Numerical Investigation of the Damage Characteristics of Rocks under Ballistic Penetration

Rock penetration is an inevitable problem in the study of drilling and projectile penetration. The penetration resistance of red sandstone and limestone was investigated at projectile speeds ranging from 600–1200 m/s. The damage characteristics of these rocks were studied via experimental tests and numerical simulations. The damage condition of the target surface, internal damage state and crack distribution were obtained. It was concluded that the maximum error of the numerical simulation and experimental results was not more than 10%. The penetration resistance of limestone was approximately 23.8% stronger than that of red sandstone. However, the energy absorption effect of limestone was weaker than that of red sandstone, and large cracks can be more easily formed. The compaction area of red sandstone was softer, with obvious crack compaction in the crater area, and particle detachment can more easily occur. Red sandstone was more sensitive to the impact angle of the projectile. With oblique penetration, the projectile was more likely to deflect inside the red sandstone target.

Analysis Deformation Failure Characteristics and the Energy Evolution of Varying Lithologies under Cyclic Loading

Deep underground engineering often utilizes cyclic loading. To understand the deformation and damage characteristics of rock under cyclic loading conditions, cyclic loading tests of three different specimens with varying lithology were performed. The dissipated energy method was used to analyze the magnitude of damage and rock failure characteristics during the energy evolution process of cube specimens. The results indicated that the modulus of elasticity of three lithologies were stable prior and subsequent to cyclic loading. While the cyclic loading profile improved the rock’s resistance to deformation, it increased the internal mesostructure defects. Rock damage caused by the cyclic loading reduced the uniaxial compression strength. This was especially true for coal samples. For coal samples, these observations were consistent with internal coal damage calculated by analysis. Under the same lithology and different loading modes, rock damage was caused by cyclic action, and the elastic strain energy released by instantaneous unloading of rock samples with significant damage was reduced. The rupture magnitude for cyclic loading was observed to be less than that of uniaxial compression. Under cyclic loading and varying different lithologies, sandstone absorbed the most energy, resulting in a larger final fracture magnitude compared to other lithologies.

Surrounding Rock Damage Characteristics and Support Optimization of Roadway in Soft Gas-Rich Coal Seam Under the Condition of Penetrating Hydraulic Reaming

The support of roadways in soft coal seams is a challenge in deep coal mines. For gas-rich coal seams, many methods are developed to drain the gas before mining. The penetrating hydraulic reaming (PHR) is one of the most efficient methods to reduce the gas content and pressure in the coal seams. However, the PHR method will cause many large holes in the coal seam, which brings difficulty to in-seam roadways control. The strength parameters of the coal are essential for roadway stability analysis. However, in soft coal seams, the sampling of the coal is difficult, and the direct evaluation of the coal strength parameters is unfeasible. In the present research, the surrounding rock damage characteristics of the holes induced by PHR are first evaluated by ground-penetrating radar (GPR). Then, the strength parameters of the coal are determined via the back-analysis method. After that, the deformation and failure of the roadway are analyzed, and an optimized support scheme is proposed. According to the monitored displacement and measured damage zone of the roadway, the roadway is well controlled by the proposed support scheme.

Mechanical Behavior and Impact Resistance Tendency of Coal Mass with Different Water Content

As a major hidden danger of mine safety production, the impact resistance tendency of rock seriously restricts the safety and high yield of coal mine. At the same time, as one of the puzzles of rock mechanics, it has been perplexing many domestic and foreign scholars since the recorded rock burst in South Stafford coal mine in 1738. At present, this research is relatively weak; so, it is different for economic and social benefits. The study of the impact resistance law and the antishock measures of water-bearing rocks are extremely meaningful. In order to deeply explore the impact resistance law of rock with different water content and the antishock support measures after roadway excavation, based on the previous research results of the previous research, the impact tendency of different coal samples was firstly tested by coal uniaxial compression experiment, judging and then calculating the damage characteristics of rock with different water content according to the obtained data, as one of the judgment basis of the impact law of coal mine. Secondly, according to the experimental data, the energy evolution characteristics are calculated and analyzed with the graph. Finally, the impact tendency of the rock under different moisture conditions is obtained.

The Effect of Blast-Hole Arrangement, Delay Time, and Decoupling Charge on Rock Damage and Vibration Attenuation in Multihole Blasting

Rock damage and vibration attenuation are the basis of blasting design, which will affect rock breaking results and the safety of structures (buildings). In this paper, the effect of blast-hole arrangement, delay time, and decoupling charge on the rock damage and the vibration attenuation in multihole blasting were numerically investigated. Through dynamic analysis software ANSYS/LS-DYNA, the JOHNSON_HOLMQUIST_CONCRETE (JHC) rock model and fluid-solid coupling method were used to establish single-hole and multihole rock blasting models. Based on the analysis of single-hole rock damage and vibration, firstly, the effect of the above three factors on the rock damage characteristics of multihole blasting was analyzed. Then, the extracted peak particle velocity (PPV) data of multihole blasting were fitted to the United States Bureau of Mines (USBM) equation to obtain the blasting vibration attenuation parameters (the site constant K and α). It is found that the blast-hole arrangement, delay time, and decoupling charge have a much smaller effect on α than K. At the same time, a delay-time-dependent model of PPV correction coefficient was proposed, and its rationality was verified by field data. The results obtained in this paper have reference significance for optimizing the blasting design and improving the blasting effect.

A multifrequency ultrasonic approach to extracting static modulus and damage characteristics of rock

Understanding the mechanical behavior of rock is a fundamental requirement for many geological explorations . Based on the frequency dependence of primary and shear wave velocities (P- and S-wave velocities), this work proposed a new approach to obtaining the static modulus of rocks without using empirical correlations. Six group granite specimens are treated by different temperatures, then the P- and S-wave velocities of these specimens at various frequencies were tested. The static moduli of all the specimens were calculated by deriving the newly proposed critical P- and S-wave velocities with a classical formula. The results showed that the static moduli of all the specimens obtained from the ultrasonic approach complied with the initial modulus obtained from uniaxial compression tests , demonstrating the reasonability of the proposed ultrasonic approach. The reasonability of the proposed approach was further proven by using a distinct lattice spring model. Numerical results showed that the calculated modulus is consistent with the true value. In addition, the standard deviation of wave velocities at different frequencies was adopted to describe the damage characteristics in rock, which well explained the change in damage variable during the thermal process. The proposed approach provides a potential method to fast obtain the static modulus and damage characteristics of rock.

Numerical study on rock damage characteristics of multi hole blasting

In this study, a two-dimensional finite element numerical simulation method was used to study the damage characteristics of rock mass under multi-hole blasting load. In the analysis, Drucker-Prager constitutive model was used to characterize the strength of rock mass. The stress acting on the blasting hole was simulated by exponential functions, that the stress could reach the maximum value in a short time and then drop to zero in a relative long time. The damage characteristics of rock under different confining pressures, and the influence of free surface on the damage of rock were examined. The results show that under the same blasting load, increasing the confining pressure of surrounding rock can inhibit the development of rock cracks; The free surface made the explosion stress wave reflect, the rock mass between the blasting hole and the free surface produced a phenomenon of stratification crack which restrained the crack propagation below the blasting hole.

Physical and Mechanical Properties of Transmission Line Galloping under the Action of Freezing and Thawing in Variable Temperature Range

The western part of our country is mostly alpine regions. The rock and soil have been in a strong natural freeze-thaw environment for a long time, and their physical and mechanical properties are easily affected by external loads and external surroundings. Changes due to the influence of the environment will inevitably produce freeze-thaw cycles, damage and destruction, expansion and fracture, etc., resulting in more stable factors than usual. However, there is a lack of theoretical and practical experience in freeze-thaw rocks, especially freeze-thaw hard rocks. Therefore, studying the physical and mechanical properties and damage characteristics of rocks in alpine regions under freeze-thaw cycles has important significance. This paper uses dacite in the alpine region to carry out a freeze-thaw cycle experiment in a variable temperature range. Freezing and thawing cycle test, uniaxial compression test, triaxial compression test, and electron microscope scanning of the rock in the indoor saturated state were carried out. Combining theory with experimental mechanics, freeze-thaw mechanics, and damage mechanics, we studied freeze-thaw cycle in three variable temperature ranges (−20°C–15°C; −30°C–15°C; −40°C–15°C), along with the physical and mechanical properties and damage characteristics of freeze-thaw dacite in the alpine region under cycling. The damage curve of the final theoretical model gradually approaches 1.0 with the increase of strain during the actual test. The rock sample after the medium failure still has a certain bearing capacity, and the rock sample is often destroyed before it reaches the theoretical failure strain.

Investigation on Damage Characteristic and Constitutive Model of Deep Sandstone under Coupled High Temperature and Impact Loads

To investigate the coupling damage characteristics of rock after high-temperature treatment under impact load, dynamic uniaxial compression tests for deep sandstone specimen under laboratory conditions varying with high temperature (i.e., 25°C, 100°C, 300°C, 500°C, 700°C, and 900°C) and strain rate (i.e., 170 s-1, 205 s-1, and 240 s-1) were performed using splitting Hopkinson pressure bar (SHPB) system. Coupling damage variable of deep sandstone was deduced based on the Lemaitre equivalent strain theory. Moreover, the damage parameters of deep sandstone were systematically determined according to the test data, and the effects of high temperature and strain rate on damage growth curves were investigated. Finally, a dynamic compound damage constitutive model, which could consider the coupling damage, was established and verified to describe the dynamic mechanical characteristic of deep sandstone. Theoretical and experimental results indicated that the simulated stress-strain curves matched the test data well and the proposed coupling damage constitutive model could reflect the high temperature-induced weakening and strain rate strengthening effect.

Study on Pressure Relief Effect and Rock Failure Characteristics with Different Borehole Diameters

Rock burst is a common tunnel and mine dynamic disaster, especially for deep buried tunnels, which often leads to tunnel construction delay and even induces tunnel collapse and subsidence of strata. Rock drilling is one of the effective pressure relief methods to prevent these disasters. In order to study the influence of borehole diameter on rock mass pressure relief effect, indoor acoustic emission characteristics and numerical simulation of rock samples with different borehole diameter were studied. The research result shows that with the increase in borehole diameter, the effect of borehole pressure relief is better. Different borehole diameters do not change the overall trend of acoustic emission evolution, but it will lead to different acoustic emission count characteristics of rock damage and failure, especially the maximum acoustic emission count characteristics and corresponding strain values. The existence of drilling will lead to the failure stress of rock in advance. Moreover, the existence of drilling causes a great change in the failure mode of the specimen.

Damage Characteristics of Rocks by Uniaxial Compression and Cyclic Loading-Unloading Test

Damage Characteristics of Rocks by Uniaxial Compression and Cyclic Loading-Unloading Test

Non-linear creep damage model of sandstone under freeze-thaw cycle

To study rock damage characteristics under long-term freeze-thaw cycles and loads, rock freeze-thaw and creep damage factors were defined based on nuclear magnetic resonance porosity and volume strain, respectively. The damage factor is introduced into the basic rheological element, and the non-linear creep damage constitutive model and freeze-thaw rock equation are established to describe non-linear creep characteristics under a constant load. Simultaneously, the creep test of freeze-thaw rock under step loading is performed. Based on the test data, the applicability and accuracy of the creep damage freeze-thaw rock model are analyzed and verified. The results show that freeze-thaw cycles result in continuous rock pore structure damage and deterioration, and nuclear magnetic resonance porosity enhancement. The constant load induces increasing rock plastic deformation, volume, and creep aging damage. As the loading stress increases, the instantaneous rock elastic parameters increase, and the rheological elastic and viscosity parameters decrease. Furthermore, the damage degradation of freeze-thaw cycles weakens the rock viscoplasticity, resulting in a rapid decrease in the viscosity parameter with an increase in freeze-thaw cycles. Generally, the continuous damage of the rock is degraded, and the long-term strength decreases continuously.

Explosion propagation and characteristics of rock damage in decoupled charge blasting based on computed tomography scanning

Blasting in rocks typically causes the remaining rock mass to be subjected to varying degrees of damage and failure, leading to a decline in the mechanical properties and bearing capacity of the surrounding rock. In this study, a decoupled charge blasting experiment for small-charge small-scale red sandstone specimens was conducted in a laboratory; the damaged specimens (after blasting) were scanned and reconstructed using computed tomography (CT) scanning and three-dimensional reconstruction technology. The relationship between the gray-scale change characteristics of the CT images and the decoupling coefficient was analyzed. Additionally, the analysis dimensions and damage degree of the damaged specimens (after blasting) were calculated and the damage degree of the indoor small-scale samples (after blasting) was quantitatively evaluated. Furthermore, the relationship between the decoupling coefficient and the blasting action was examined using the LS-DYNA simulation software. The results indicated that the gray-scale value tended to increase with the decoupled coefficient, and the decoupled coefficient demonstrated a significant influence on the blasting action. Thus, the proposed method serves as a suitable means for the evaluation of the failure mechanism through the reconstruction of the spatial distribution of internal cracks.

Prevention Technology for Strong Mine Pressure Disaster in the Hard-Roof Large-Mining-Height Working Face

The movement and destruction of the hard roof in a stope is an important reason for the occurrence of strong ground pressure disasters at the working face. Considering Tongxin Coal Mine as the engineering background, the stress distribution law of the surrounding rock and the overburden rock damage characteristics of a large-mining-height working face under the hard roof were investigated. To solve the problem whereby the stope’s hard roof is difficult to collapse, the hard rock key stratum of the roof was hydraulically fractured to weaken the mechanical properties of the roof rock stratum. Additionally, microseismic monitoring technology was used to monitor the cracking effect of the rock stratum. The theoretical calculation and numerical simulation results reveal that, after hydraulic fracturing, a crack with a more consistent trend formed inside the hard rock stratum and a large area of the rock stratum was damaged. According to the monitoring results of the stope stress after hydraulic fracturing, the law governing the occurrence of the leading bearing pressure was in effect. In contrast, the influence range and peak strength of the leading bearing pressure were considerably reduced at the working face after hydraulic fracturing. After performing hydraulic fracturing on the roof of the working face, the bearing pressure of the working face can satisfy the production requirements better. Finally, the results obtained through this study can be used as a reference for determining the width of coal pillars under similar mining conditions.

Cyclic shock damage characteristics of electrohydraulic discharge shockwaves

To improve the quality of electrohydraulic discharge (EHD) shockwaves cracking effect and reduce its damage, the study examines the cumulative damage characteristics of rock induced by shockwaves generated by EHD. Voltage, current, energy, efficiency, wave velocity, and peak value of incident and transmission shockwave of a liquid–solid interface at different discharge energies are given based on the observation of the shockwaves of established discharge platform. The cyclic impact cracking test is conducted on cement samples. The cement samples are effectively cracked, and the surface formed several cracks. The tests results indicate that the cumulative effects of different cyclic loading modes exist under the action of EHD shockwaves. An upper limit exists on the cumulative effect, and the breakdown voltage affects the maximum effective number of discharges and affects the depth of action. Particle flow code 2D (PFC2D) simulation is used to simulate the cement samples under the same experimental conditions. The development process and shape distribution of the internal microcracks under different loading energies and loading times are analyzed. The results indicate that there are three cumulative effects of microcrack development stages (i.e. microcrack accumulation, cracks development, and slowing down and cessation of crack development). Simultaneously, the results suggest that the cumulative damage effect of EHD shockwave on rock materials can be divided into three zones (i.e. crushing zone, crack zone, and elastic zone), which can be effectively adjusted via controlling the loading voltage, loading times, and working distance. Finally, an experiment-simulation combined control strategy is proposed to avoid the crushing zone and raise the crack zone. The study provides theoretical, experimental and simulation guidance for the application of EHD shockwaves.

Peridynamics simulation of surrounding rock damage characteristics during tunnel excavation

The improved peridynamics is introduced to analyze the stability of surrounding rock in tunnel excavation process. By introducing short-range repulsive force into peridynamic equation of motion, the tensile and compression failure characteristics of rock materials is simulated. In order to simulate the process of tunnel excavation, the material point dormancy method is proposed in this paper. By simulating the distribution characteristics of excavation damage zone (EDZ) during the excavation of a circular tunnel with high stress difference, the relationship between the distribution position of EDZ and the direction of maximum principal stress is revealed. The v-shaped notches developed on the tunnel periphery at the direction of perpendicular to the maximum principal stress. The predicted EDZ distribution characteristics is consistent with the results of previous studies. And the displacement field of surrounding rock after tunnel excavation is also in good agreement with FEM simulation result. The simulation results show that this method not only has good stability, but also has high computational efficiency. By analyzing the deformation, damage and failure characteristics of surrounding rock under different buried depths, different lateral pressure coefficients, different excavation methods and different section shapes, the evolution process of rock instability caused by tunnel excavation and unloading is revealed. Which provides reference for the design and optimization of surrounding rock support scheme in deep buried tunnels.

Inversion Method of In-situ Stress and Rock Damage Characteristics in Dam Site Using Neural Network and Numerical Simulation—A Case Study

In mountain and ravine region of southwest China, several hydropower stations have been built in this area. It is the main national base for hydropower energy development, but under the influence of geological structure and surface erosion, the in-situ stress environment in this area is more complex. The main purpose of this paper is to establish the relationship between measured in-situ stress data and numerical calculation by means of neural network. Therefore, it can be used to analyze the distribution characteristics of large-scale in-situ stress and the failure of regional geological bodies under the action of in-situ stress in Xiluodu area. This paper analyzes the geological conditions and the measured data of in-situ stress in Xiluodu area. The results show that there is obvious surface weathering phenomenon in this area, the stress environment is complex. The depth has a positive impact on the level of in-situ stress, but the impact degree is different. The genetic algorithm-BP artificial neural networks (G-P) method is trained by the measured in-situ stress data. Based on the field measurement data, neural network algorithm and numerical simulation technology, the three-dimensional in-situ stress field distribution characteristics of the project area are carried out. The research shows that the scheme of combining the actual measurement, numerical analysis and neural network inversion is reliable; Depth is an important factor affecting the maximum horizontal stress value in Xiluodu area; Under the action of in-situ stress, the fissures of geological body are relatively developed, and three types of original water storage and flow spaces are formed before dam storage period; The flow and storage space of groundwater includes limestone fracture, basalt fracture and slope fracture aquifer; After the impoundment of the reservoir area, the reservoir water is transmitted downward through the vertical fissures, and finally the reservoir water forms a hydraulic connection with the groundwater. After impoundment, the hydrogeological conditions of the reservoir area would be changed.

Multi-scale effect of acoustic emission characteristics of 3D rock damage

Scale effect and acoustic emission characteristics of rock damage are two important topics in rock engineering research. In this paper, considering different rock scales and establishing the 3D numerical rock models by means of PFC software platform firstly, the mechanical properties and acoustic emission characteristics were studied. Finally, based on the acoustic emission, characteristic discussed the damage evolution law of the rock models. The research result shows that the multi-scale mainly affects the peak strength, peak strain, and elastic modulus of the mechanic properties, affects the maximum acoustic emission event number, strain range of serious acoustic emission events of the acoustic emission characteristics, affects the damage rapid increase and damage failure stages of the damage evolution process. The stress-strain curves, acoustic emission events curves, and damage variable curves can be divided into three stages and different scales have different effect on these stages.