Precursor Of Failure Research Articles

Mechanical Properties and Acoustic Emission Characteristics of Weakly Cemented Sandstone With Different Grain Sizes

The weakly cemented sandstone is widely distributed in the Western Mining Area, which is mainly formed by mineral grains and cemented minerals through compaction and cementation. To study the influence of grain size on the mechanical properties and acoustic emission (AE) characteristics of weakly cemented sandstone, uniaxial compression and Brazilian splitting AE tests were carried out on four weakly cemented sandstone specimens with different grain sizes. The physical properties, mechanical behaviors, and AE characteristics of sandstone under two conditions were analyzed, and the microfailure mechanism was investigated. The results show that the P-wave velocity, density, uniaxial compressive strength (UCS), and tensile strength of weakly cemented sandstones with different grain sizes decrease with the increase of grain size. The medium sandstone and coarse sandstone exhibit ductile failure, while the siltstone and fine sandstone exhibit brittle failure under the two conditions. The distribution of AE signal strength is nearly Gaussian in the time domain. The peak frequency and upper limit of signal strength are negatively correlated with grain size, and the occurrences of lots of high-strength AE signals can be used as the precursor of sandstone failure. The damage evolution shows the trend of low-speed damage-accelerated damage-low-speed damage, and the damage increase at the peak load is negatively related to the grain size. The microfailure mechanism is the tension-shear mixed failure, which is dominated by tensile failure, with few shear failures. The proportion of shear cracks is positively correlated with the grain size under uniaxial compression, while there is no significant correlation between shear cracks and grain size under Brazilian splitting.

Influence of temperature on the transformation and self-control of energy during sandstone damage: Experimental and theoretical research

The surrounding rock in tunnelling engineering and coal mining will sometimes be exposed to high temperature. Rock failure is the result of energy dissipation, and the study of the evolution and transformation behavior of energy is of great significance for the in-depth understanding of the deformation and failure of rock after high temperature. This study analyzed the intrinsic connection between mechanical properties and acoustic emission (AE) energy under temperature effect. Based on the energy dissipation and release theory, the distribution and transformation of energy was analyzed, and the energy self-incentive and self-inhibition (EII) model was further established. The main findings are that temperature effect affects the confidence interval trend and the value of AE energy rate, which is related to the change in mechanical properties. The ability of sandstone to store elastic strain energy after exposure to high temperature is independent of the mechanical properties. In this study, the ratio of dissipated energy to elastic energy is used to characterize the stable state of the sandstone system, which can be used as the energy indicator of rock failure precursor. During the absorption, storage, and release of energy before the peak stress, there exists self-incentive and self-inhibition of energy (control behavior).

Numerical Investigation of the Scale Effects of Rock Bridges

Due to the challenge of measuring rock bridges in the field and the negligence of progressive damage and changes in stresses within a rock mass when defining rock bridges, it is questionable to evaluate mechanical properties of rock bridges using only geometric parameters. A demonstration is the scale effects of rock bridges, because the same geometric parameter may refer to different sizes and numbers of rock bridges, leading to erroneous equivalent rock mass responses. In this context, in-plane rock bridges in rock slope engineering were equivalent to rock bridges subjected to direct shear by conducting numerical simulations employing the Universal Distinct Element Code (UDEC) and described by constant geometric parameters, i.e., joint persistence, while the sizes and numbers of rock bridges were variant. In this way, the scale effects of rock bridges were investigated from the perspective of load–displacement curves, stress and displacement fields, crack propagations and AE characterizations. The results revealed that the mechanical properties of rock bridges deteriorated with decreasing scales. More specifically, the shear resistance and the area and value of stress concentration decreased with decreasing scale. Furthermore, an uneven distribution of displacement fields in an arc manner moving and degrading away from the load was observed, indicating the sequential failure of multiple rock bridges. It was also found that the propagation of tensile wing cracks was insensitive to scale, while the asperity of macro shear fracture mainly formed by secondary cracks decreased with decreasing scale. In addition, increasing the dispersion of rock bridges would overlap the failure precursors identified by intense AE activities. Based on the abovementioned results, the scale effects of rock bridges were characterized using existing rock bridge potential (RBP) index and degree of persistence (DoP) index. Interestingly, a scale threshold to possibly identify a rock bridge was found.

Changes in resonance frequency of rock columns due to thermoelastic effects on a daily scale: observations, modelling and insights to improve monitoring systems

Summary Slope instabilities, including prone-to-fall rock columns, are known to exhibit clear vibrational modes. The resonance frequencies of these modes can be tracked by seismic instrumentation, allowing the rock column's mechanical and structural properties to be monitored, as well as providing precursors of imminent irreversible failures. In previous studies, superficial thermoelastic effects were assumed to drive daily fluctuations in resonance frequencies, but no qualitative or quantitative evidence was provided. The results presented here corroborate this hypothesis and quantify the physical processes involved. We interpreted daily variations of resonance frequencies in the Les Arches study site (Vercors, French Prealps) using a thermo-mechanical finite-element model. Modelled fluctuations of the resonance frequencies over a day closely matched experimental observations, reproducing the daytime frequency increase of around 2 per cent. In addition, our model provides explanation of the various behaviours observed across study sites: the frequency response strongly depends on solar exposure, as well as the timing and intensity of both radiative and convective heat fluxes. We highlight acousto-elastic constants as key parameters of our semi-quantitative model, although they remain poorly constrained here. For future instrumentation, we therefore recommend the deployment of pyranometers on rocky sites to accurately invert these parameters over time, thus allowing rock fracturing to be quantitatively tracked by acousto-elastic monitoring.

Failure behaviors of fractured granite during loading and unloading under high confining pressure based on acoustic emission multi-parameter analysis

To investigate failure and mechanical behaviors of fractured rocks during loading and unloading under conditions of high ground stress, a series of loading and unloading tests were conducted on granite containing prefabricated fractures under high confining pressure. Results indicate that the evolution of acoustic emission (AE) events of fractured granite during loading and unloading under high confining pressure is strongly correlated with the deformation and failure and the energy evolution process in the rock, the peak values of AE cumulative energy and AE cumulative count rate in the pre-peak deformation stage decrease first and then increase with the dip angle (the minimum value is reached at 60°), when the dip angle is 0° to 60°, the number of AE events increases abruptly due to closure of the prefabricated fracture in the early stage of loading(only about 30 % of the main fracture time). After the fractured granite enters the unstable crack propagation stage, the crack tips are subject to a dynamic cycle of stress concentration, crack propagation, and stress release, accompanied by significant fluctuations in the energy rate before and after the point of peak AE energy rate. Therefore, the cracks propagate in an intermittent or a stepped manner. Under the unloading path, the process of crack development, gathering, and coalescence in the granite happens earlier, and there are more high-energy AE events in the failure process. The value of the brittleness index Bd is larger under the unloading path under high confining pressure, which reflects more significant brittle failure characteristics. The research provides a basis for judging failure precursors of rocks using AE characteristics in the failure process.

Investigation on Acoustic Emission Characteristics of Hole-Joint Contained Granite under a Compressive Disturbance: Experimental Insights

Abstract Uniaxial compression experiments were performed in cross-jointed granite samples with a hole, together with acoustic emission (AE) observations, to investigate AE variability and precursory information during sample failure. The variability characteristics of multiple AE time-series parameters (including AE counts, accumulated counts, energy, accumulated energy, and b-value) and frequency domain parameters (including AE frequency and amplitude) were systematically analyzed, the variations in different parameters and precursor characteristics were compared, and the AE parameters suitable for rock failure prediction in a cavern were discussed. The results indicate that the variability characteristics of different AE parameters are different, and each parameter has a precursor phenomenon of specimen fracture. The peak value of specimen AE counts does not necessarily appear at the peak stress, but the AE counts decrease significantly when the samples are damaged. The accumulated AE count curve makes it easier to identify the precursors of sample failure. The AE energy is released at an accelerated speed when the samples are near complete failure, and a critical energy release exists in the samples. The abrupt increase in AE energy has potential as a precursor to sample failure. The b-value shows a fluctuating decline during the whole loading process and a rapid decline before sample failure. The low-frequency with high-amplitude and the high-frequency with low-amplitude signals exhibit distinct characteristics at different specimen deformation stages and are sensitive to the change in specimen stress state, so they can be used as the crucial signal source for predicting specimen failure. The joint analysis of these AE parameters can better capture the precursory information of rock failure.

Study on Crack Classification Criterion and Failure Evaluation Index of Red Sandstone Based on Acoustic Emission Parameter Analysis

The acoustic emission (AE) characteristics of rock during loading can reflect the law of crack propagation and evolution in the rock. In order to study the fracture mode in the process of rock fracture, the AE characteristics and crack types of red sandstone during fracture were investigated by conducting Brazilian indirect tensile tests (BITT), direct shear tests (DST), and uniaxial compression tests (UCT). The evolution law of AE event rate, RA and AF values, and the distribution law of RA–AF data of red sandstone samples in three test types were analyzed. Based on the kernel density estimation (KDE) function and the coupling AE parameters (RA–AF values) in DST and BITT, the relatively objective dividing line for classifying tensile and shear cracks was discussed, and the dividing line was applied to the analysis of fracture source evolution and the failure precursor of red sandstone. The results show that the dividing line for classifying tensile and shear cracks of red sandstone is AF = 93RA + 75. Under uniaxial compression loading, the fracture source of red sandstone is primarily shear source in the initial phase of loading and tensile source in the critical failure phase, and the number is far greater than shear source. K = AF/(93RA + 75) can be defined as the AE parameter index, and its coefficient of variation CV (k) can be used as the failure judgment index of red sandstone. When CV (k) < 1, it can be considered that red sandstone enters the instability failure phase.

Electromagnetic radiation signal monitoring and multi-fractal analysis during uniaxial compression of water-bearing sandstone

Rockburst disasters seriously threaten the safety of deep coal mining. Electromagnetic radiation (EMR) is a powerful means of rockburst monitoring and early warning. However, the current related research often ignores the fact that the rock mass in engineering is frequently in a water-bearing state. Therefore, in this paper, the EMR signals of sandstone samples with different water contents were monitored under uniaxial compression. The experimental results showed that with the increase of water content, the EMR signals of sandstone weakened as well as the mechanical strength. Compared with dry samples, the total EMR energy and peak EMR energy of saturated samples decreased by 71.41% and 76.06% respectively. Moreover, higher moisture content would lead to lower dominant frequency and amplitude of EMR signals under various stress levels. Through multi-fractal analysis, it is found that with the rise of moisture content, the non-uniformity of signal (Δα) and the frequency diversity of minimum and maximum signals (Δf) decreased. These reflect some changes in the generation mechanism of EMR signal. The abrupt changes of Δα and Δf can be regarded as precursors of rock failure. The research results can provide guidance for the frequency band selection and precursor identification of rockburst monitored by EMR.

Carbon deposition and argon post-treatment of polyurethane surface: Structural-mechanical and fracture properties

Modification of polymeric surface by plasma ions has perspectives in creating flexible functional materials; their deformation behavior is one of the most important properties, as poor fracture resistance cancels all advantages. Carbon ions were deposited on the surface of elastic polyurethane with subsequent argon treatment. Created carbon-containing nanolayer has increased wettability and nonuniform local mechanical properties. Uniaxial extension to strains >100% induces discontinuous microcracks of carbon-modified surfaces but their propagation is constrained by inhomogeneities of the modified layer. Argon post-treatment improves wettability further but makes local mechanical properties uniform that decreases the fracture resistance. Multi-cycle uniaxial loading to 50% doesn't damage the surface but forms in the modified layer weakened domains – precursors of failure; this improves crack resistance at strains >100% a mesh of disordered microcracks appears preventing propagation of long cracks.

Study on cross-scale pores fractal characteristics of granite after high temperature and rock failure precursor under uniaxial compression

High temperature can make the rock physical properties change significantly. In this study, the fractal dimension of cross-scale pores of the granite after high temperatures is first obtained. It is found that the fractal characteristics of mesopores and macropores are significant, while that of micropores are opposite. Secondly, the dual effects of high temperatures on the mechanical properties are studied, and the fractal dimension of cross-scale pores is closely related to the mechanical properties of rock. Then, it is found that when the rock is about to break, the abnormal changes in energy rate and frequency can be used as the rock failure precursor, but this method also has certain limitations. Finally, the correlation dimension is obtained based on acoustic emission (AE) time series. When the correlation dimension decreases to the local minimum after the fluctuation stage, it can effectively predict the imminent large-scale failure.

Damage spreading in quasi-brittle disordered solids: II. What the statistics of precursors teach us about compressive failure

We investigate numerically and theoretically the precursory intermittent activity characterizing the preliminary phase of damage accumulation prior to failure of quasi-brittle solids. We use a minimal but thermodynamically consistent model of damage growth and localization developed by Berthier et al. (2017) that accounts for both microstructural disorder and non-local interactions. Its numerical implementation permits performing a complete scaling description of the failure precursors. In particular, we show that their size, duration and spatial extent are related to each other by robust scaling laws and that these three quantities diverge close to failure. By developing a theoretical model of damage growth in disordered elasto-damageable specimen, we demonstrate that these scaling relations emerge from the physics of elastic manifolds driven in disordered media, while the divergence of these quantities close to failure is reminiscent of the loss of stability of the specimen at the localization threshold. Our study sorts out a long-standing debate on the nature of the compressive failure and the origin of the universal statistics of the precursors preceding it. Our analysis rules out a critical-point scenario in which the divergence of the precursors size close to failure is signature of a second-order phase transition governed by the microstructural disorder. Instead, we show that while the jerky evolution of damage prior to failure results from the presence of material disorder, the latter does not significantly change the nature of the localization process, which is an instability well described by standard bifurcation theory of homogeneous systems. Finally, we harness our detailed understanding of the precursory statistics to design a methodology to estimate the residual lifetime of a structure from the statistical analysis of precursors. This method relevant for structural health monitoring is shown to perform rather accurately on our data.

New insights into the 2020 Sardoba dam failure in Uzbekistan from Earth observation

On 1 May 2020, the Sardoba Reservoir in Uzbekistan breached its western wall, and the uncontrolled release of water caused casualties, environmental damages and economic losses. We investigate the dam failure based on three sets of Earth observation data, including: (i) satellite altimetry products, i.e., ICESat-2 data, with the aim of understanding the topographic features in the study area; (ii) multi-geometry Sentinel-1 SAR data to retrieve the pre-failure deformation along the vertical and horizontaleast-west directions between 2017 and 2020; (iii) optical images from Sentinel-2 satellites and Global Precipitation Measurement (GPM) products, which are involved in exploring the environmental status before the failure. We analyse the possible causes of the collapse in terms of both physical and human factors. The differential settlement of ∼60 mm revealed by InSAR at the failure section is a sign of internal erosion through the embankment, which is the physical factor contributing to the failure. The opportunity to prevent the collapse were missed due to the human factor of ignorance brought by limitations of the conventional monitoring methods. Neither ground observations nor satellite-based GPM products show extreme precipitation in the region, ruling out the likelihood of rainfall-induced overtopping. The settlement rate of the embankment shows no decaying trend, indicating that the dam is undergoing the primary consolidation phase of total settlement. Maximum settlement of ∼270 mm (∼0.8% of the dam height) has happened on the north bank since the reservoir impoundment, which should raise concern in future monitoring and surveillance. The results reveal that InSAR can discern the failure precursor by detecting surface motion, and that the deformation signals can help to warn of risks and avoid dam damage. We recommend InSAR deformation monitoring be included in future safety programs, providing detailed deformation and resisting risks of ignorance.

Research on Failure Precursor Based on Characteristics of Energy Dissipation Rate for Rock

Research on early warning of rock disaster based on the energy theory is closer to the essence of rock failure. In this paper, static compression tests and acoustic emission (AE) tests of coal rock under 0, 8, 16, and 25 MPa confining pressures were carried out on the MTS815 test system. Energy evolution law in the rock failure process was analyzed according to the relationship between mechanical parameters, AE parameters, and energy dissipation rate (EDR) in the rock failure process. Eventually, a new index for evaluating rock failure precursors was proposed based on EDR. The results show that the EDR has a good correlation with mechanical strength and AE events under different confining pressures. The deformation and failure characteristics of coal rock can be truly characterized by EDR. The variation of EDR can be divided into a quiet stage, a stable increasing stage, an active stage, and a stable stage. The EDR level in the quiet stage is obviously enhanced by confining pressure. When EDR reaches the peak, AE events increase rapidly. In the active stage, the EDR peak value is concentrated and large, the AE event is highly active, and stress drops abruptly, indicating that the EDR is reliable for evaluating the rock failure process. Compared with AE test results, it is found that the warning stress and warning time of the EDR failure precursor occur later than that of the AE failure precursor, and the former is closer to the peak stress of rock, which is more universal in engineering and could provide a better reference value for preventing rock disaster.

Multi-Source Information Monitoring Test of Fractured Rock Mass Destruction Characteristics and Sensitivity Analysis of Precursor Phenomena

The accuracy of the monitoring information is particularly important for exploring fractured rock mass deformation and failure mechanisms and precursor characteristics. Appropriate monitoring methods can not only timely and effectively reflect the failure laws of fractured rock masses but also play an early warning role. To explore more reasonable monitoring methods, uniaxial compression experiments and real-time non-destructive monitoring on prefabricated fractured rock specimens through DIC, AE, and IRT were conducted; the strain field, temperature field, ringing frequency, standard deviation, etc. were analyzed; and correlation between the three methods in the information of audience was explored. The results show the following. (1) The failure evolution process of fractured rock mass can be divided into four stages. DIC can detect the initiation and propagation of cracks near the fractures of the specimen at the earliest stages. (2) The order of occurrence of precursor phenomena in multi-source monitoring information is different, which is vertical strain field > shear strain field > horizontal strain field > temperature field > ringing times. (3) The dispersion degree of standard deviation of each field is obviously different; the infrared temperature field is greater, but the strain field and temperature field show the same trend. (4) There are obvious precursors before the specimen is on the verge of instability; acoustic emission detected two consecutive increases in the cumulative number of ringing before destruction, which means the most obvious precursors. The research results can provide a theoretical basis for the precursory information capture and damage early warning of the fractured rock mass destruction process.

Association of nocturnal subconjunctival hemorrhage and non-dipper blood pressure pattern: A benign clue for serious diseases.

To evaluate the association between non-dipper blood pressure pattern and subconjunctival hemorrhage (SCH). Twenty-seven consecutive patients with nocturnal SCH and 27 age, sex-matched controls were enrolled. Demographic, blood parameters, office blood pressure measurements, 24-h ambulatory blood pressure monitoring (ABPM) were evaluated. Mean diastolic blood pressure (DBP) for nighttime (65.03 ± 7.1 vs. 70.78 ± 10.5, p: 0.22), mean heart rate for nighttime (64.54 ± 8.26 vs. 69.93 ± 9.85, p: 0.034), Minimum Systolic Blood pressure(SBP) and DBP values for nighttime (92.44 ± 9.72 vs. 99.44 ± 10.66, p:0.015 and 51.15 ± 8.31 vs. 57.7 ± 11.2, p: 0.018) were higher, nocturnal fall ratio of SBP and DBP were significantly lower in the SCH ( + ) group compared to SCH (-) group (5.38 ± 8.39 vs. 10.34 ± 6.08, p: 0.016 and 4.26 ± 8.92 vs. 13.78 ± 6.97, p < 0001 respectively). Ten patients (37%) in the SCH (-) group and 18 patients (66.7%) in the SCH ( + ) group were non-dippers (p: 0.029). Mean daytime SBP and DBP were higher compared to office measurements of 4 patients (14.8%) in the SCH (-) group and 11 patients (40.7%) in the SCH ( + ) group (p: 0.033). SCH had a strong association with non-dipper blood pressure pattern, higher nocturnal heart rate and masked hypertension which are precursors of myocardial infarction, stroke and renal failure. So, SCH should be considered as a clue for serious diseases such as coronary artery disease, myocardial infarction, stroke and patients should be evaluated for ABPM.

Influence of Graphite Powder on the Mechanical and Acoustic Emission Characteristics of Concrete

In this paper, uniaxial compressive strength (UCS) test and three-point bending (TPB) test, together with an acoustic emission (AE) system, were performed to investigate the mechanical properties and AE characteristic changes of concrete with different graphite powder (GP) content. The results show that: (1) Poor adhesion and low interlocking of graphite with cement stone increase the initial defects of concrete, reducing its elastic modulus and the cyclo-hoop effect, and thus weakening the compressive strength. (2) For concrete with a low graphite content, the second sharp rise in ringing counts or energy released during the compressive process can be regarded as a failure alarm. However, as GP content increases, the second sharp rise fades away, while the first sharp rise becomes more visible. At high GP content, the first sharp rise is better for predicting failure. (3) The initial defects caused by GP significantly lower the initial fracture toughness, but its bridging effect greatly increases the critical crack mouth opening displacement and thus significantly enhances the unstable fracture toughness of concrete, by up to 9.9% at 9% GP content. (4) In contrast to compressive process, the sharp increase in AE signals preceding failure during the fracture process cannot be used to predict failure because it occurs too close to the ultimate load. However, as GP can significantly increase the AE signals and damage value in the stable period, such failure precursor information can provide a safety warning for damage development.

Translational Control in Liver Disease

Chronic liver disease is one of the biggest threats to public health worldwide. Worryingly, the incidence of liver disease is dramatically rising due to the aging of the population and the global epidemics of obesity. Both are major risk factors for chronic liver disease and adverse prognostic factors, causing an increase in mortality rate. It is of great concern that 80–95% of obese people have non-alcoholic fatty liver disease, the major precursor for liver failure and a global health challenge. Currently, the only curative treatment for advanced chronic liver disease is liver transplantation, which is, however, hampered by high treatment costs and the scarcity of donor organs. New strategies are therefore urgently needed to prevent and reverse chronic liver disease. And for that it is essential to understand better the molecular mechanisms underlying human disease. This review focuses on the abnormalities in the regulation of translation by RNA-binding proteins during chronic liver disease and their pathological impact on portal hypertension, fibrosis, steatosis, neovascularization, and cancer development.

Abstract 13664: Identification of Myocardial Scar Using Deep Residual Network Integration of CMR Images in Ischemic Cardiomyopathy

Introduction: Ischemic scar development is a potential precursor of lethal arrhythmias and heart failure, conditions with exceptionally high mortality rates. Contrast-enhanced cardiac magnetic resonance imaging (CMR) is frequently used in clinical practice to quantify myocardial scar. With the advance of machine learning, increasing amounts of information can be garnered from CMR scans, including information that has both diagnostic and prognostic value for patients with ischemic cardiomyopathy. Hypothesis: We hypothesize that deep residual network integration combined with an augmented CMR scan selection can more accurately differentiate between patients with and without myocardial ischemic scarring. Methods: CMR scans from 170 patients, 138 with ischemic scarring and 32 controls without myocardial scarring, were collected from a tertiary care facility. CMR scans were selected to include those that had a clear visualization of the left ventricle and the surrounding myocardium. This region of interest (ROI) was then cropped. Images from patients with no myocardial scarring were additionally rotated 3 times to improve class balance. The final dataset was composed of 9,840 images from the patients with no myocardial scarring and 10,480 images with ischemic scarring. Results: Applying a ResNet-50-based convolutional neural network machine learning algorithm, we were able to identify patients with ischemic scarring at an accuracy of 75.9%. Sensitivity and specificity were 76.2% and 75.7%, respectively, with an F1 Score of 76.7%. By introducing targeted ROI selection, we were able to further improve accuracy to 81.7% with an F1 score of 82.4%. Sensitivity and specificity were also higher at 83.4% and 79.8%, respectively. The data acceptance rate of the short axis images for this implementation was 22.0%. Conclusion: Application of our residual network integration algorithm- along with targeted ROI selection- can significantly enhance the accuracy of myocardial scar detection in patients with ischemic cardiomyopathy. When tested in larger samples this is expected to aid clinical adjudication and enhance workflow.

Comparative analysis of acoustic and electromagnetic emissions of rocks

Comparative analysis of acoustic and electromagnetic emissions recorded during the intact rock samples deformation and dynamic rupture of simulated crustal fault is presented. Specialized machines for uniaxial compression and shear tests of rock samples with identical data acquisition systems for both test cases were employed. Increase of acoustic emission was observed accompanied by significant rise of intensity and amplitude of electromagnetic signals at high stress of the rock samples under the uniaxial compression or dynamic failure in the spring-block model. Such correlation is consistent with the previous conclusions that an increase of electromagnetic emission may be considered as a rock failure precursor. Any specific characteristics of the detected electromagnetic signals to be used for prediction of impending rock failure or the earthquake fault rupture were not found. The similarity of electromagnetic signals and their spectra obtained at the press equipment and the spring-block model suggests that in both cases, the signals observed are generated by the crack formations and shear. The electromagnetic emission appeared only in dry samples. The samples saturated by water with the salinity of over 0.1% demonstrated no electromagnetic emission.

Experimental Study on the Shear Band of Methane Hydrate-Bearing Sediment

The occurrence of a shear band is often thought as the precursor of failure. To study the initiation of shear banding in gas hydrate-bearing sediments, two groups of triaxial compression tests combined with a CT (computer tomography) scan were conducted by triaxial CT-integrated equipment under two confining pressures and seven hydrate saturations. The macro stress–strain curves and the corresponding CT scanning images of the micro-structure and the distribution of the components were obtained. The geometric parameters of the shear bands were measured based on the CT images at four typical axial strains, respectively. The distribution characteristics of soil particles, water, hydrate and gas were also analyzed. It is shown that the existence of methane hydrate changes the mechanical property of hydrate-bearing sediment from plastic failure to brittle failure when the hydrate saturation is over 13%, which occurs in the range of the tests in this paper. The peak of the deviatoric stress increases with the hydrate saturation. The shear band is in either a single oblique line or inter-cross lines depending on the hydrate saturation, the effective confining pressure and the initial distribution of the gas hydrate. Most of the shear band surfaces are not straight, and the widths of the shear bands are almost non-uniformly distributed.