Rock Damage Evolution Research Articles

A new elasto-visco-plastic damage model and numerical simulation method used for time-dependent behavior prediction of deep tunnel

Accurately predicting the time-dependent behavior of surrounding rock is crucial for supporting design, revealing the mechanism of lining cracking and understanding long-term stability in deep-buried tunnels engineering. Based on the component combination model method and continuous damage mechanics theory, a New Elasto-Visco-Plastic Damage (NEVPD) model was proposed considering the characteristics of viscoelastic-plastic and the damage evolution of rocks. Three groups of experimental data were used for validating the model, and the results indicate that the model can effectively describe the time-dependent deformation characteristics of rocks at different stress levels. The dynamic link computer application program of the NEVPD model was procured through the secondary development interface of the FLAC3D software, and its validity was ascertained through test simulations. By investigating the influence of stress levels on creep parameters, a creep simulation approach considering the impact of rock mass stress state on the creep parameters was proposed for used in the long-term stability analysis of underground rock engineering. Finally, the time-dependent behavior of deep tunnel was predicted using two simulation approaches (the traditional method and the proposed method) based on the Burger-Creep Viscoplastic (CVISC) model built-in FLAC3D and the NEVPD model. The findings suggest that the proposed tunnel creep simulation approach provides a more precise reflection of the local deformation features of the surrounding rock compared to traditional methods. The simulation outcomes based on the NEVPD model exhibit the highest agreement with the field monitoring data.

Softening properties and damage evolution of the preloaded building sandstone after exposure to high-temperature

In practical engineering, cyclic stress caused by underground excavation, blasting or seismic waves leads to initial damage to rocks, and the high temperature caused by fire will lead to changes in the mechanical and physical parameters of the initially damaged rock. Therefore, a series of experiments were carried out to research rock properties and damage evolution of the preloading sandstone after exposure to high temperatures. The results demonstrate that the mass decreases gradually at a constant rate when the temperature ranges from 25 °C to 600 °C, but above 600 °C, the quality decreases quickly. As the exposed temperatures and stress amplitude of cyclic preloading rise, the p-wave velocity gradually decreases. At exposure temperatures of up to 800 °C, the p-wave decreases by 27.8%, and it is reduced by 0.93% at the largest pre-stressed condition. Furthermore, the peak strength and elastic modulus decrease with the rise of the preloading stress amplitude and treated temperatures. The area of hysteresis loops increases with the increase of the cyclic preloading stress amplitude, and the plastic deformation of hysteresis loops results in the continuous deterioration of the secant modulus. The preloading stress amplitude and the temperature gradually increase, and the damage factor increases. Meanwhile, to compare the performance of the proposed damage model, the constitutive damage model of the preloading treatment sandstone exposure to high temperatures is established. The model has a good fitting effect for the sandstone subjected to the thermal-mechanical effect.

Assessment method for determining rock brittleness based on statistical damage constitutive relations

The brittleness index of rocks is able to provide crucial guidance to the operation of the drilling and hydraulic fracturing. The definition and evaluation method of the rock brittleness has not yet been unified and standardized due to their diversity. We therefore develop an evaluation method of the rock brittleness based on statistical damage relation. A set of uniaxial compression tests on different rock samples are conducted, and corresponding experimental data is collected and analyzed. Then we establish piecewise damage constitutive models based on different combinations of statistical distribution functions, including power function distribution, Weibull distribution, lognormal distribution and logistic distribution. A new evaluation method of rock brittleness based on energy method and the piecewise statistical damage constitutive model is proposed, and the evaluation results show that the increase of damage variable of peak strain will undermine rock brittleness, and the mineral composition contents have influence on the brittleness of rocks. Comparison work between this proposed method and previous brittleness criteria shows that the brittleness index B43 exhibits enhanced stability and consistency in rock brittleness. This study presents a novel method to studying rock brittleness, enhancing current evaluation methods and deepening our understanding of the rock index. Regarding practical application, some field operations involved with the process of drilling or fracturing lead the continuous damage evolution of rocks under loading conditions. The brittleness index from the proposed evaluation method is comparatively reliable and practical for on-site drilling and fracturing.

Temperature dependence of mechanical properties and damage evolution of hot dry rocks under rapid cooling

Understanding the differences in mechanical properties and damage characteristics of granitoid under high temperatures is crucial for exploring deep geothermal resources. This study analyzes the evolution of the acoustic emission (AE) characteristics and mechanical parameters of granodiorite and granite after heating and water cooling by uniaxial compression and variable-angle shear tests under different temperature gradients. We identify their changes in mesostructure and mineral composition with electron probe microanalysis and scanning electron microscopy. Results show that these two hot dry rocks have similar diagenetic minerals and microstructure, but show significantly different mechanical and acoustic characteristics, and even opposing evolution trends in a certain temperature range. At the temperatures ranging from 100 °C to 500 °C, the compressive and shear mechanical properties of granodiorite switch repeatedly between weakening and strengthening, and those of granite show a continuous weakening trend. At 600 °C, both rocks exhibit a deterioration of mechanical properties. The damage mode of granite is characterized by initiating at low stress, exponential evolutionary activity, and intensified energy release. In contrast, granodiorite exhibits the characteristics of initiating at high stress, volatile evolutionary activity, and intermittent energy release, due to its more stable microstructure and fewer thermal defects compared to granite. As the temperature increases, the initiation and propagation of secondary cracks in granodiorite are suppressed to a certain extent, and the seismicity and brittleness are enhanced. The subtle differences in grain size, microscopic heterogeneity, and mineral composition of the two hot dry rocks determine the different acoustic-mechanical characteristics under heating and cooling, and the evolution trends with temperature. These findings are of great significance for the scientific and efficient construction of rock mass engineering by rationally utilizing different rock strata properties.

Rock damage evolution in the production process of the enhanced geothermal systems considering thermal-hydrological-mechanical and damage (THM-D)

Hot dry rocks (HDRs) geothermal relies mainly on enhanced geothermal systems (EGS) for production. During production, the evolution of rock stress distribution will cause damage to the rock, especially near fractures. The application of damage mechanics in the geothermal field has mostly focused on the process of hydraulic fracturing, with limited reports on damage research related to long-term water injection development. According to previous experimental studies, the effect of rock damage is significant and cannot be ignored. Therefore, based on a thermal-hydrological-mechanical and damage (THM-D) coupling model, it studies the rock damage evolution features and its role in changes in rock physical properties. It also analyzed the effects of the initial temperature, injection flow, fracture curvature/number, and stress difference on damage evolution. Results indicate that the damage area and degree continue to increase with time, but the growth rate becomes slower. There are two methods of damage evolution: the new damage caused by the expansion of the low-temperature region is throughout the process, and the original damage is aggravated in the later stages. Damage will cause changes such as reduced Young's modulus (negative feedback) and increased permeability (positive feedback) of the rock matrix, which in turn affect the damage evolution. More, damage increases with the initial rock temperature, injection mass flow, and stress difference increase, and the impact of the fracture curvature is small. The damage of complex fracture reservoirs is more pronounced than that of single fracture reservoirs. This study provides a tool for analyzing the impact of damage on the production performance of HDRs. The investigation of relevant patterns is expected to offer guidance for production strategies.

Flow–solid coupling analysis of underground reinforced concrete forked pipe enclosing rock and structure

The stability of the surrounding rock for the construction excavation and the reinforcement of the lining structure during operation in the water-rich area is a difficult problem for the design of high-head underground turnout pipes. Firstly, according to the mechanism of excavation load release and surrounding rock damage evolution, the seepage effect of excavation in the construction of the forked caves is coupled to the surrounding rock stress damage, and an iterative method of numerical simulation of the coupled mutual feedback effect of excavation surrounding rock stress and seepage is proposed. Then, based on the cracking characteristics of the high internal water pressure reinforced concrete turnpike lining, a numerical analysis method of the coupling interaction between lining cracking and internal water seepage is proposed by coupling internal water seepage to stress damage in the lining by cracking the forked pipe structure. Applying the aforementioned method to a forked pipe project, the results show that: during the construction period, there is a significant increase in the damage zone, stress, and displacement of the rock around the cavern after considering the coupled iterations; during the operation period, with the increase in internal water pressure, the lining structure accelerates cracking due to the external infiltration of internal water; after the internal water is applied, the surrounding rock bears the main internal water pressure and the reinforcement bears only part of the circumferential force. The method provides theoretical support for the analysis and calculation of the reinforcement of similar underground high-pressure tunnels for rock support and lining structures and has certain theoretical and engineering significance.

Characteristics of Pressure Stimulated Current and Damage Evolution of Granite under Progressive Uniaxial Loading

The application of load on rock materials stimulates a weak current known as Pressure Stimulated Current (PSC). This study focuses on investigating the damage evolution of granite rocks through the analysis of PSC responses. Uniaxial loading experiments were conducted on granite samples, and the accompanying PSC was measured in real-time. The relationship between PSC characteristics and mechanical behaviors of granite was examined to explore precursory information related to granite failure. The damage evolution of granite was assessed using a damage variable defined as the cumulative charge (time integral of PSC). The results clearly demonstrate a close correlation between the variation of PSC and the mechanical behaviors of rock. Specifically, during the compaction and elastic deformation stages, PSC exhibits a slow and linear increase. However, once deformation enters the plastic stage, PSC demonstrates an accelerated upward trend. Additionally, it was observed that a stress drop coincides with an abnormal increase in PSC, which is followed by a rapid decay. The fluctuation observed after the abnormal increase in PSC during the accelerated growth phase can serve as a precursor of rock failure. Furthermore, the cumulative charge quantity effectively correlates with the damage process of granite samples. The stress–strain curve obtained from a theoretical constitutive model, established based on the damage variable represented by normalized cumulative charge, aligns reasonably well with the experimental results, affirming that the defined damage variable accurately reflects the damage evolution process of rocks. It is hypothesized that PSCs are carried by electrons within the rocks, which are stimulated by electron diffusion during deformation and experience a sharp increase upon rock fracturing. The research findings hold theoretical significance for predicting rockburst incidents using the PSC method.

Mode I Microscopic Cracking Process of Granite Considering the Criticality of Failure

AbstractRock failure under tensile loading conditions is significant for rock engineering stability and underground energy development. However, a comprehensive understanding of the rock cracking process and the corresponding failure pattern at microscale remains unclear. Therefore, the cracking process and the damage evolution of rock and their underlying mechanisms were systematically investigated. In this study, the fracture behavior of granite was examined by performing mode I fracture tests. For extensive analysis of the cracking process, the cracks were captured in real‐time by scanning electron microscope, and the two fracture toughnesses of the double‐K model were evaluated. Subsequently, fracture morphologies of the post‐failure specimens were analyzed to further investigate the cracking mechanisms. The experimental results indicated the following: (a) the propagated direction of cracks was controlled by the fracture toughness of mineral grains and grain boundaries; and (b) the ratio of the two fracture toughnesses was correlated with fracture tortuosity. Furthermore, two damage modes of granite were found: catastrophic failure and non‐catastrophic failure modes. The former showed precursory behavior prior to catastrophic failure, while the latter did not. The underlying mechanisms of damage modes were revealed as follows: (a) the increased degree of heterogeneity caused by mineral composition complexity led to the early arrival of precursors; and (b) the occurrence of catastrophic or non‐catastrophic failure mode was determined by the difference in grain‐scale heterogeneity. Our results found at microscale also have implications for understanding the macroscopic failure process of rocks.

Recognition of shear and tension signals based on acoustic emission parameters and waveform using machine learning methods

Acoustic emission (AE) technology is widely used to monitor the damage evolution of rock. Identifying AE signals is crucial to reveal the rock cracking mechanism. The current tension and shear signal discrimination methods primarily rely on AE parameters. However, the differences between AE parameters and waveform images used as inputs require further exploration. Acoustic emission data from Brazilian splitting and direct shear tests of red sandstone were collected. A decision tree was applied to classify the signals based on the AE parameters: Rise time (RT), Counts, Amplitude, Peak frequency (PF), and absolute energy. Three typical CNN-based networks (InceptionV3, ResNet50, and VGG19) were used to classify the AE signals using images of waveforms, reconfigured waveforms, and spectrograms generated by wavelet packets. The results showed that using AE parameters as input to distinguish tensile and shear signals yields an accuracy of up to 88%, increasing recognition accuracy when using PF as input. In addition, increasing the number of input parameters to the decision tree can improve average recognition accuracy, with single, double, and three parameters being 65%, 78%, and 82%, respectively. However, when the number of parameters exceeds three, the accuracy improvement is minimal, with four and five parameters being 84% and 86%, respectively. The CNN-based networks outperform the decision tree in terms of recognition accuracy. It is recommended that the VGG19 network and waveform are adopted as input to identify the tension and shear AE signals. In contrast, using the spectrogram as input enhances the stability of the model, particularly for the validation set, although the improvement is limited.

Stability analysis of jointed rock mass in large underground caverns based on multi-scale analysis method

Random defects at different scales are the crucial cause of damage evolution and cascade transfer in rocks. For a large-scale underground cavern, the rock mesoscopic heterogeneity and macroscopic random joints are inevitable factors of rock stability, which needs to be further studied. In this study, a multi-scale analysis method for the stability of jointed rock mass in large underground caverns is proposed. The statistical damage theory is used to describe the mesoscopic heterogeneous rock damage. Monte Carlo simulation and measured joint geometric information are combined to reconstruct the macroscopic random joint network of rock mass. The integrated analysis of mesoscopic heterogeneity of rock and the macroscopic response of random jointed rock mass is performed by Rock Failure Process Analysis (RFPA) system. The research shows that the existence of joint affects the failure mode of rock mass and strengthens the heterogeneity. The representative elementary volume (REV) of jointed rock mass and its equivalent mechanical parameters are determined and used in the stability analysis of a large-scale underground cavern project. Results show a good agreement with the in-situ monitoring deformation of surrounding rock mass, which verifies the effectiveness of the rock mass multi-scale analysis method.

Microscopic damage evolution of anisotropic rocks under indirect tensile conditions: Insights from acoustic emission and digital image correlation techniques

Microscopic damage evolution of anisotropic rocks under indirect tensile conditions: Insights from acoustic emission and digital image correlation techniques

Experimental investigation of damage evolution and fracture mechanism in rocks with a single flaw under stepwise cyclic compression

Experimental investigation of damage evolution and fracture mechanism in rocks with a single flaw under stepwise cyclic compression

Quantitative assessment of the effect of in-situ stresses on blast-induced damage to rock

In-situ stress significantly affects rock blast damage but there is a paucity of quantitative assessments of damage evolution in rocks affected by confining pressure. The present paper analyses the effect of envelope pressure on blast-induced rock damage through theoretical analysis and numerical simulations. Damage clouds obtained from numerical simulations are processed using image processing techniques. The concept of the damage variable (η) is proposed to facilitate the presentation of the image processing results. The damage variable is found to be negatively correlated with the hydrostatic pressure (Px) at the same moment, in equiaxial in-situ stress fields. In contrast, in anisotropic in-situ stress fields, η is not negatively correlated with Px due to the presence of hoop tensile stresses in the rock. The mathematical relationship between η and Px in equiaxial and anisotropic stress fields are established. An anisotropic damage variable (ηk) is introduced to describe the effect of the anisotropy ratio (K) on rock damage, which is found to increase with increasing values of K. The sharp increase in K equal to 4 and 5 is explained in terms of the state of the rock stress distribution under static loading. This study provides insights into the effect of in situ stress on rock blast damage and presents new approaches for analyzing and presenting the data.

Damage Evolution and Failure Mechanism of Red-Bed Rock under Drying–Wetting Cycles

The rock mass on the bank slope of the Three Gorges Reservoir (TGR) area often suffers from a drying–wetting cycle (DWC). How the DWCs significantly affect the mechanical properties and the stability of the rock mass is worth comprehensively investigating. In this study, the influence of the DWC on the mechanical properties of red-bed rock, mainly purplish red argillaceous siltstone, is explored in detail. Triaxial compression tests were conducted on siltstones that were initially subjected to different DWCs. The results show that DWCs lead to a decrease in mechanical properties such as peak stress, residual stress, and elastic modulus, while an increase in confining pressure (CP) levels leads to an increase in these mechanical properties. Significant correlations are found between the energy parameters and the DWC or the CP. Notably, the total absorption energy (TAE) demonstrates a positive correlation with the CP, but the capability of siltstones to absorb energy shows a negative correlation with DWC. Moreover, the study also examines the damage evolution laws of rocks under different DWCs by proposing a damage variable (DV). Results demonstrate that the effect of the CP on the DV is more pronounced than that of DWCs. A novel brittleness index (BI) was also proposed for estimating rock brittleness through damage strain rate analysis. The effectiveness of the proposed BI is validated by evaluating the effects of DWCs and CP on rock brittleness. Finally, the failure mechanism of the rocks under water–rock interaction is revealed. The weakening of mechanical properties occurs due to the formation of microcracks in response to DWCs. These findings provide valuable guidance for the long-term stability assessment of bank slope engineering projects under DWCs.

Evaluation method of rock damage under uniaxial compression based on unit series-parallel electrical conductive model

The evaluation of rock damage behaviour is an important requirement for ensuring stability control and safety prediction in rock engineering. However, they have not been able to obtain sufficiently accurate and dynamic results due to the insufficient evaluation method. In this study, by means of fractals and unit series division, a unit series-parallel conductive model of damaged rock is derived, and a new evaluation method of rock damage under uniaxial compression was proposed. Rock was damaged by uniaxial compression, while electrical measurements and X-ray microscopy tests were performed to obtain the damaged rock resistivity, porosity, and fractal dimension variation. By establishing the relationship between defined meso-damage factor and resistivity, rock damage evolution law under axial compression was obtained. The results indicate that the growth trend was agree with the classical statistical damage model, which verified the accuracy of the results obtained by the proposed method. Moreover, as the strain increased, the damage factor determined by resistivity gradually decreased to −0.06 firstly and then increased rapidly to 0.79. Different from previous damage evolution law, brittle failure was observed and the cracks development in each stage was considered, including the closure (negative damage) and expansion (positive damage) of cracks.

Study on the Damage Mechanism of Sandstone under Different Water Content States

Understanding the failure mechanisms of rocks that are exposed to different water contents is important for rock stability in rock engineering applications, and the quantitative analysis of rock behavior is necessary for predicting and preventing the occurrence of rock failure due to water effects. Mechanical tests using real-time acoustic emission (AE) technology were carried out to reveal the damage evolution in sandstone rocks in a dried state, natural state, and saturated state, which includes a quantitative analysis of AE characteristics and cracking properties. The testing results indicate that with the growth of water content, sandstone rocks show a decreasing trend in strength and tend to experience gentle damage with relatively fewer fractures. The crack morphology of the main fracture surfaces is quantitatively described, including a fractal dimension calculation and cracking length measurements. As the water content rises, when rock failure occurs, a higher AE b-value can be obtained, revealing an increasing proportion of large-scale cracks. The fractal dimension of the acoustic emission hit rate shows that the evolution of rock damage and deformation has self-similarity, that is, the transformation from order to disorder to order, and it is affected by different water contents. The AE waveforms of the sandstone have two dominant frequency bands (0~75 kHz and 75~150 kHz) no matter which water-bearing state they are in. The increase in rock water content has resulted in the decline of AE waveforms located in the range of 200–300 kHz, whereas the rise of AE waveforms is located in the range of 0–50 kHz. The findings of this study deepen our understanding of the mechanism behind rock failure and provide a meaningful reference for disaster assessment and control.

Infrared radiation response mechanism of sandstone during loading and fracture process

Rock damage and fracture are the fundamental causes of coal mine dynamic disasters such as coal and gas outbursts, rock bursts, and mine water inrush. It is also one of the basic and common scientific problems in the field of rock engineering. Therefore, the reliable precursor information of rock damage and fracture process can be determined for the effective monitoring of the early warning of coal mine dynamic disaster, and early warning of surrounding rock fracture and seepage (water inrush) in mines. In this regard, the researcher failed to describe the mechanism of infrared radiation characteristics for the determination of rock failure precursors quantitatively. Further, the qualitative analysis of the infrared radiation mechanism restricts the use of infrared radiation to characterize the internal damage evolution and permeability characteristics of rocks. Therefore, in this paper, the equivalent plastic strain difference of sandstone is defined based on the plastic strain energy and deformation work conversion equation. The frictional heat effect of loaded sandstone is clarified. According to the Euclidean distance between the plastic zone location and the crack tip, the temperature source density function of the crack plastic zone is characterized. Based on the Fourier law of heat conduction, the thermal effect of crack propagation is deduced and analyzed, and the mathematical model of the infrared radiation response mechanism in the process of sandstone loading and fracture is established. Based on this model, the heat conduction range of sandstone fracture under biaxial loading is determined through the secondary development of finite element software, and the average infrared radiation temperature in the local high-temperature region of loaded sandstone is predicted. The findings of this research can provide a theoretical and experimental foundation for detecting rock failure for the safe and efficient execution of underground engineering projects e.g. mines, tunnels, etc.

Energy and Infrared Radiation Characteristics of the Sandstone Damage Evolution Process.

The mechanical characteristics and mechanisms of rock failure involve complex rock mass mechanics problems involving parameters such as energy concentration, storage, dissipation, and release. Therefore, it is important to select appropriate monitoring technologies to carry out relevant research. Fortunately, infrared thermal imaging monitoring technology has obvious advantages in the experimental study of rock failure processes and energy dissipation and release characteristics under load damage. Therefore, it is necessary to establish the theoretical relationship between the strain energy and infrared radiation information of sandstone and to reveal its fracture energy dissipation and disaster mechanism. In this study, an MTS electro-hydraulic servo press was used to carry out uniaxial loading experiments on sandstone. The characteristics of dissipated energy, elastic energy, and infrared radiation during the damage process of sandstone were studied using infrared thermal imaging technology. The results show that (1) the transition of sandstone loading from one stable state to another occurs in the form of an abrupt change. This sudden change is characterized by the simultaneous occurrence of elastic energy release, dissipative energy surging, and infrared radiation count (IRC) surging, and it has the characteristics of a short duration and large amplitude variation. (2) With the increase in the elastic energy variation, the surge in the IRC of sandstone samples presents three different development stages, namely fluctuation (stage Ⅰ), steady rise (stage Ⅱ), and rapid rise (stage Ⅲ). (3) The more obvious the surge in the IRC, the greater the degree of local damage of the sandstone and the greater the range of the corresponding elastic energy change (or dissipation energy change). (4) A method of sandstone microcrack location and propagation pattern recognition based on infrared thermal imaging technology is proposed. This method can dynamically generate the distribution nephograph of tension-shear microcracks of the bearing rock and accurately evaluate the real-time process of rock damage evolution. Finally, this study can provide a theoretical basis for rock stability, safety monitoring, and early warning.

Influence of defect hole location on acoustic emission characteristics and damage evolution of rocks: a numerical study based on particle flow code

Influence of defect hole location on acoustic emission characteristics and damage evolution of rocks: a numerical study based on particle flow code

Mechanical Properties of High-Temperature Granite under Liquid Nitrogen Cooling

The cooling characteristics of liquid nitrogen can effectively weaken the mechanical properties of dry hot rock reservoirs, improve the porosity and permeability of dry hot rock, and thus improve the development and utilization of geothermal resources. In order to explore the weakening effect of liquid nitrogen cooling characteristics on high-temperature reservoir rocks, uniaxial compression tests, Brazil splitting tests, and three-point bending tests were conducted on high-temperature granite, and synchronous acoustic emission tests were conducted to monitor the damage evolution of rocks. It is found that under the action of liquid nitrogen, the elastic modulus, peak strength, fracture toughness, and other mechanical properties of granite decrease to varying degrees. At different initial temperatures, the damage degree of liquid nitrogen to granite is different. The higher the initial temperature of granite, the greater the damage effect of liquid nitrogen on granite. The low-temperature characteristics of liquid nitrogen not only have the effect of cracking damage on granite but also have the effect of thermal stress on granite. If the temperature difference between the two is large, the heat released in the combination process will be higher. The greater the temperature difference, the greater the damage to granite. Under the action of liquid nitrogen, the acoustic emission characteristics of granite also show different evolution laws, and the ringing count of rock increases significantly, which indicates that liquid nitrogen aggravates the internal damage of granite, making the rock more fractured during fracturing. The research results can provide some scientific guidance for the development and utilization of geothermal energy.