Search

To investigate the rolling wave characteristics of overland flow, this study calibrated the accuracy of the depth measurement system for shallow flow on slopes using acrylic sheets and optimized it as a dual-line laser water depth measurement system. Non-contact measurement methods were used to measure the water depth at the mature cross-section position of rolling waves in real time. This experiment designed a total of 5 measurement intervals, namely 0.04, 0.05, 0.10, 0.15, and 0.20 m. Three horizontal gradients were set for the slope, namely 3°, 9°, and 15°, and six horizontal gradients were set for the flow rate, namely 2, 4, 8, 12, 16, and 20 L/min. Each horizontal gradient was repeated for 5 experiments. The results indicated that the accuracy of the depth measurement system for shallow flow on slopes was confirmed to be 0.473 mm per grid, and the optimal spacing for the dual-line laser depth measurement system was 0.04 m. Both flow rate and slope significantly affected the wave speed, wave height, height difference, and frequency of rolling waves. The influence of flow rate (the effect size values were 0.655-0.963) was greater than that of slope (the effect size values were 0.232-0.874). The slope significantly affected the wavelength, while the flow rate did not significantly impact it. Wave speed increased with flow rate but the influence of flow rate on wave speed decreased with increasing slope. Under different slope conditions, wave height responded differently to flow rate. At a 3° slope, wave height initially increased and then decreased with increasing flow rate, whereas at higher slopes (9° and 15°), the wave height increased significantly under low flow conditions (2-8 L/min), with the increases of 3.74 and 4.63 mm, respectively. The difference in wave height between 3° and 9° slopes increased with flow rate, but the difference between 9° and 15° slopes decreased. The variation in height difference with slope was influenced by flow rate, showing a trend of initially increasing and then decreasing. Increased flow rates led to an increase in frequency, with the largest increase at a 15° slope, up to 2.37 Hz. The frequency differences between slopes decreased and then increased as flow rate increased, with a critical flow rate of 8 L/min. At a low slope (3°), wavelength fluctuated with flow rate, whereas at a high slope (15°), higher flow rates inhibited the development of wavelength. Under the high flow conditions (16-20 L/min), the wavelength differences between slopes were significant. This research provides a theoretical basis for improving the accuracy of slope overland flow measurements and further elucidating the dynamic characteristics of overland flow rolling waves. [ABSTRACT FROM AUTHOR]

Ultrasonic pulse velocity (UPV) test is widely used to evaluate rock mass integrity. However, it is rather difficult to conduct a sampling of fractured rocks and acquire a set of rocks with different fracture levels in experiments due to friability and heterogeneity. Consequently, numerical modeling on the UPV test of multi-fractured rock is carried out based on the discrete element method (DEM). A single fracture model and comparison between 2D and 3D models are first carried out for numerical verification. Subsequently, the UPV tests of multi-fractured rock are numerically investigated. The fracture system follows a power-law length distribution and is randomly allocated for fracture position and orientation. The influences of geometric fracture characteristics and related mechanical parameters on the wave velocity are discussed. Finally, a multi-parameter sensitivity analysis is performed. It is found that the 2D and 3D models of the UPV test have almost similar variation regularity at different fracture configuration conditions. Long fractures significantly influence the reduction of wave velocity in rock interior. The fracture intensity, long fracture proportion, and wave velocity value are linearly related. In contrast, the mechanical parameters including fracture stiffness and elastic modulus have a limited influence on the attenuation of ultrasonic waves especially at high stiffness and modulus range, and the power function model could fit the correlation between wave velocity and mechanical parameters. An inversion approach is proposed for estimating the fracture magnitude by adjusting the fracture intensity and long fracture ratio to match the target wave velocity value. Highlights: Ultrasonic wave velocity testing results for 2D and 3D fractured rock models were compared. Impacts of fracture geometric distribution characteristics and mechanical parameters on wave velocity were investigated. A fracture distribution inversion strategy based on wave velocity test is proposed as the future perspective based on the parameter sensitivity analysis. [ABSTRACT FROM AUTHOR]

This study experimentally investigated the wave attenuation coefficient and wave number of the heated granite after water cooling (W-C) and air cooling (A-C) treatments. The granite specimens heated to five temperatures (25 °C, 100 °C, 200 °C, 300 °C and 400 °C) were subjected to the W-C and A-C treatments, respectively. The pendulum impact test was performed on the cooled granite at room temperature to obtain the separated stress pulse. The wave attenuation ratio in the cooled granite was investigated. Propagation coefficients (attenuation coefficient and wave number) were introduced to describe the harmonic wave attenuation in the cooled granite. The effects of W-C and A-C treatments on the attenuation coefficient and wave number were discussed. The results show that the P-wave velocity decreases as temperature increases, while the wave attenuation ratio increases as temperature increases. The P-wave velocity of the granite after the W-C treatment is smaller than that of the granite after the A-C treatment. The wave attenuation ratio, attenuation coefficient and wave number of the stress pulse in the granite after the W-C treatment are larger than those of the stress pulse in the granite after the A-C treatment. The differences of P-wave velocity, wave attenuation ratio, attenuation coefficient and wave number after two cooling treatments increase as temperature increases. [ABSTRACT FROM AUTHOR]

Studying the mechanical properties and failure mechanisms of damaged rocks holds practical significance in guiding tunnel or roadway support and assessing the stability of engineering rock masses. To uncover the failure mechanisms of sandy mudstone with varying degrees of damage, we conducted cyclic loading‐unloading tests to create specimens at different damage levels. Subsequently, uniaxial loading tests were performed to investigate the fundamental mechanical properties, wave velocity, and acoustic emission (AE) parameter evolution characteristics of the damaged specimens. The classification of damaged rocks was based on the energy evolution characteristics of damaged sandy mudstone. Finally, we discuss the damage and deterioration mechanisms of different types of sandy mudstone. The findings contribute to establishing a theoretical foundation for evaluating the degree of rock damage. Highlights: The damage degree of rocks was calculated according to the dissipated energy.The response characteristics of AE parameters of damage samples were revealed.The classification of damaged samples is based on the mechanical parameters. [ABSTRACT FROM AUTHOR]

Copyright of CT Theory & Applications is the property of Editorial Department of CT Theory & Applications and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This article used Guiyang Metro Line 3 under construction as an example to study the application of cross hole seismic computed tomography (CT) technology in the exploration process of Karst complex areas, thereby revealing the characteristics of Karst development in the study area. Through comparative analysis of various algorithms, it was determined that compared to the conjugate gradient least squares (CGLS) algorithm, the sparse linear equations and least square problems (LSQR) algorithm is more sensitive and accurate in identifying low-speed anomalies, and has better convergence and reliability. Drilling verification shows that using the LSQR algorithm and bending ray tracing method for seismic tomography inversion can achieve meter level accuracy in cross hole seismic CT detection, obtain high-quality velocity images, and identify the depth, scale, and extension of Karst between boreholes, neutralizing the limitations of drilling. This indicates that seismic CT technology based on the LSQR algorithm is practical and feasible for detecting Karst.

Increasing hydrocarbon production in Ukraine requires the development and introduction of new promising methodological and technological means of petrophysical support and drilling support for exploration areas based on modern scientific and technological achievements. The analysis of the geological structure of lithological and stratigraphic strata of the Neogene Krukenytska system of the Bilche-Volytska depression of the Precarpathian trough confirmed that each individual case has its own peculiarities both in the structure of the rock matrix and in the conditions of its formation. Based on the results of the analysis and evaluation of the quality of interpretation of physical parameters of geophysical surveys of complexly structured reservoir rocks of Neogene sediments, the influence of clay content, temperature and reservoir pressure on the readings of electrical, radioactive and acoustic measurements of mineralogical composition was established. Electrometric methods, which are part of a typical GDS complex, have their limitations when recording resistivity values, in particular, insufficient resolution and ambiguity in assessing the nature of saturation when studying complex reservoir rocks. In the process of assessing the nature of saturation of complexly constructed reservoir rocks of Neogene sediments, the presence of water-saturated rocks in the roof of gas-saturated formations without a continuous lintel was revealed, which also causes watering of productive horizons, thus reducing gas and condensate production. The sandy rocks of the Lower Dashava subsurface are characterized, in addition to normal interbedding, by the presence of hydrocarbon accumulations in lens-shaped traps with various petrophysical parameters. The established features of the geological structure of Neogene lithologic and stratigraphic strata confirm the complex geology of Neogene and Paleogene rocks and cause complications in geological and geophysical studies in exploration wells.

Temperature is an important factor for the service life of cable insulation. To ensure safety, the operating temperature of cables must be monitored. Since optical fiber temperature measurement technology is difficult to be used widely in medium voltage (MV) cables due to cost, this paper proposes a temperature evaluation method based on wave velocity. Firstly, the dielectric constant of cross-linked polyethylene (XLPE) cable insulation under different temperature is obtained through experiment. Based on the result, the relationship curve between wave velocity and temperature is established. The asymmetry effect due to temperature gradient in the cable insulation is discussed via finite element simulation. The effectiveness of obtaining the average insulation temperature of the cable based on wave velocity is validated. In addition, the mechanism of the temperature influence on the cable insulation material's dielectric constant is analyzed by molecular dynamics simulation, which further deepens understanding of the characteristics of cable insulation materials. [ABSTRACT FROM AUTHOR]

Copyright of Bulletin of the Chinese Ceramic Society is the property of Bulletin of the Chinese Ceramic Society Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Increasing hydrocarbon production in Ukraine requires the development and introduction of new promising methodological and technological means of petrophysical support and drilling support for exploration areas based on modern scientific and technological achievements. The analysis of the geological structure of lithological and stratigraphic strata of the Neogene Krukenytska system of the Bilche-Volytska depression of the Precarpathian trough confirmed that each individual case has its own peculiarities both in the structure of the rock matrix and in the conditions of its formation. Based on the results of the analysis and evaluation of the quality of interpretation of physical parameters of geophysical surveys of complexly structured reservoir rocks of Neogene sediments, the influence of clay content, temperature and reservoir pressure on the readings of electrical, radioactive and acoustic measurements of mineralogical composition was established. Electrometric methods, which are part of a typical GDS complex, have their limitations when recording resistivity values, in particular, insufficient resolution and ambiguity in assessing the nature of saturation when studying complex reservoir rocks. In the process of assessing the nature of saturation of complexly constructed reservoir rocks of Neogene sediments, the presence of water-saturated rocks in the roof of gas-saturated formations without a continuous lintel was revealed, which also causes watering of productive horizons, thus reducing gas and condensate production. The sandy rocks of the Lower Dashava subsurface are characterized, in addition to normal interbedding, by the presence of hydrocarbon accumulations in lens-shaped traps with various petrophysical parameters. The established features of the geological structure of Neogene lithologic and stratigraphic strata confirm the complex geology of Neogene and Paleogene rocks and cause complications in geological and geophysical studies in exploration wells. [ABSTRACT FROM AUTHOR]

In order to study the influence of the primary bedding structure on wave velocity and mechanical properties of coal-rock mass, multilayer and multi-directional ultrasonic and CT scanning tests were carried out in laboratory. It also aims to improve the accuracy, rapidity and convenience of obtaining the wave velocity and mechanical parameters of coal-rock mass in laboratory. Based on the ultrasonic test, the characteristics of wave velocity and wave velocity ratio at different layers of coal-rock mass under the primary bedding dip angle were obtained. Combined with CT scanning and 3D reconstruction technology, the calculation method of CT gray mean value in different layers was proposed by using the data of the gray frequency of coal and rock. And the variation law of gray value and coal and rock content of coal-rock mass in different layers under different primary bedding dip angle was obtained. Meanwhile, the relationships between CT gray mean value and wave velocity, mechanical parameters of coal-rock mass were established. Considering the effect of bedding dip angle and the content of coal and rock, the calculation model of longitudinal wave velocity of coal-rock mass was constructed. Then the correctness of the model is verified by comparing the test data. The results show that: ① the wave velocity and wave velocity ratio of coal-rock mass with primary bedding are linearly related to bedding dip angle; with the increase of bedding dip angle, the longitudinal wave velocity of coal-rock mass decreases linearly, while the distribution range of wave velocity ratio expands; ② the mean wave velocity of CT is linearly correlated under different bedding dip angles, and the wave velocity of coal-rock mass increases linearly with the increases of CT gray mean value; ③ the density of coal-rock mass increases linearly with the increase of CT gray mean value, the dynamic elastic modulus and shear modulus of coal-rock mass have third order polynomial relationships with the mean value of CT gray level, and they tend to increase with the increase of the mean value of CT gray level; ④ compared with the bedding dip angle, the wave velocity of coal-rock mass is more sensitive to the coal and rock content, and the wave velocity changes largest during the content of coal and rock similar.

In many geological conditions, obtaining the static elastic moduli of crustal rocks is an essential subject for accurate mechanical analyses of crust. The elastic wave method may be the best choice if rock specimens cannot be taken since elastic wave propagation can be applied to in-situ environments. Although many signs of progress have been made in the elastic wave method, some issues still restrict the accurate extraction of static moduli and its applications. A review of this method and its further research prospect is urgently needed. With this purpose, this paper summarized and analyzed the published experimental data about the relationship between the static and dynamic Young's moduli of rock, and the frequency dependence of wave velocities and dynamic elastic moduli. P- and S-wave velocities, Young's, and bulk moduli of rock, especially the saturated rock, have strong frequency dependence in a wide frequency range of 10–6–106 Hz. Different rocks or conditions (such as water content, amplitude, and pressure), have different frequency-dependent characteristics. The current elastic wave method can be classified into two methods: the empirical correlation method and the multifrequency ultrasonic method. The basic principle, advantages, and disadvantages of both methods are analyzed. Especially, the reasonability of the multifrequency ultrasonic method was elaborated given the nonlinear elasticity, strain level/rate, and pores/cracks in rock materials. Existing problems and prospects on the two methods are also pointed out, such as the choice of a proper empirical correlation, accurate determination of the critical P- and S-wave velocities, the prediction of Young's modulus at each strain level, and the reasonability of the method under various water contents and fracture structures. [ABSTRACT FROM AUTHOR]

This study investigates the impact of intermediate (s2) and minimum (s3) principal stress unloading on damage behavior and the confining pressure influence on crack initiation stress (sci) in true triaxial stress conditions, utilizing large-scale cubic samples. Two distinct true triaxial tests were executed, examining the effects of confining stress (s2 and s3) unloading on porous sandstone damage and the correlation between confining stress and sci. Acoustic emission (AE) parameters, signal characteristics, and wave velocity variations were utilized to elucidate cracking mechanisms and damage development in the samples. Unloading tests reveal consistent velocities in three orthogonal directions (V11, V22, and V33) during the initial two unloading stages. In the subsequent three stages, confining stress unloading leads to a decrease in wave velocity in the corresponding direction, while velocities in the other two directions remain nearly constant. Notably, s2 unloading generates higher amplitude AE signals compared to s3 unloading, with over 70% of the micro-cracks categorized as tensile. In the incremental loading tests, sci is found to be contingent on confining pressure, with s2 playing a crucial role. During s1 loading, V33 decreases, indicating additional crack formation; conversely, s3 loading results in V33 increase, signifying the continuous closure of existing cracks. Limitations of the experiments are summarized and prospects in this domain are outlined. [ABSTRACT FROM AUTHOR]

Microcracking due to thermal stresses affects the mechanical and flow properties of rocks, which is significant for thermally dynamic environments such as volcanoes and geothermal reservoirs. Compared with other crustal rocks like granite, volcanic rocks have a complex and variable response to temperature; it remains unclear how thermal microcracks form and how they are affected by temperature. We heated and cooled samples of low‐porosity basalts containing different amounts of microcracks and a porous andesite over three cycles, whilst monitoring microstructural changes by acoustic emission (AE) monitoring and measurement of P‐wave velocity (vP; up to 450°C) and thermal expansion coefficient (TEC; up to 700°C). During the second and third cycles, the TEC was positive throughout and the rate of detected AE was low. In contrast to studies on granite, we measured a strong and reversible increase in vP with increasing temperature (by 15%–40% at 450°C), which we interpret as due to microcrack closure. During the first cycle, AE and vP measurements indicated thermal microcracking within the andesite and the basalt with a low initial microcrack density. For these samples, strong inflexions in the TEC indicated stress relaxation during heating, preceding significant thermal microcracking during cooling. The basalt with a high initial microcrack density underwent little microcracking throughout all cycles. Our results and a review of the literature relate the initial microstructure to the occurrence of thermal microcracking and explore the potentially significant influence of temperature on volcanic rock properties. Plain Language Summary: Microcracking due to thermal stresses affects the mechanical and flow properties of rocks, playing an important role within volcanoes and geothermal reservoirs. Volcanic rocks exhibit a complex response to temperature, and it remains unclear how thermal microcracks form and how they are affected by temperature. Here, we repeatedly heated and cooled samples of basalt and andesite with different initial porosities and microcrack content over three heating/cooling cycles, whilst monitoring for laboratory‐scale seismicity and changes in acoustic wave velocity (up to 450°C) and sample length (up to 700°C). During the second and third cycles, we measured a strong, reversible increase in wave velocity with increasing temperature (by up to 40% at 450°C): opposite to measurements on granite, and which we interpret as due to crack closure during heating. During cycle one, we detect thermal microcracking within the andesite and the basalt with a low initial microcrack population. For these samples, anomalous thermal expansion during heating is linked to the significant thermal microcracking during cooling. In contrast, the initially highly‐microcracked basalt underwent little microcracking throughout. We relate the initial microstructure to the occurrence of thermal microcracking, and explore how rock properties may significantly change with temperature. Key Points: One basalt cracked significantly during cooling, following an anomalous thermal expansion, indicative of stress relaxation, when heatedAll samples see an increase in wave velocity with temperature during repeated heating, attributed to microcrack closure during heatingOur data literature study suggest low‐porosity volcanic rocks with high P‐wave velocities are most susceptible to thermal microcracking [ABSTRACT FROM AUTHOR]

Copyright of Coal Geology & Exploration is the property of Xian Research Institute of China Coal Research Institute and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Coal Science & Technology (0253-2336) is the property of Coal Science & Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Rock burst, an important kind of geological disaster, often occurs in underground construction. Rock burst risk assessment, as an important part of engineering risk assessment, cannot be ignored. Liquid nitrogen fracturing is a new technology used in the geological, oil, and gas industries to enhance productivity. It involves injecting liquid nitrogen into reservoir rocks to induce fractures and increase permeability, effectively reducing rock burst occurrences and facilitating the flow of oil or gas toward the wellbore. The research on rock burst risk assessment technology is the basis of reducing rock burst geological disasters, which has important theoretical and practical significance. This article examines the temperature treatment of two types of rocks at 25 °C, 100 °C, 200 °C, 300 °C, and 400 °C, followed by immersion in a liquid nitrogen tank. The temperature difference between the liquid nitrogen and the rocks may trigger rock bursting. The research focused on analyzing various characteristics of rock samples when exposed to liquid nitrogen. This included studying the stress–strain curve, elastic modulus, strength, cross-section analysis, wave velocity, and other relevant aspects. Under the influence of high temperature and a liquid nitrogen jet, the wave velocity of rocks often changes. The structural characteristics and possible hidden dangers of rocks can be understood more comprehensively through section scanning analysis. The stress–strain curve describes the deformation and failure behavior of rocks under different stress levels, which can help to evaluate their stability and structural performance. The investigation specifically focused on the behavior of rocks subjected to high temperatures and liquid nitrogen. By analyzing the stress–strain curves, researchers were able to identify the precursors and deformation processes that occur before significant deformation or failure. These findings have implications for the mechanical properties and stability of the rocks. [ABSTRACT FROM AUTHOR]

Wave velocity is closely related to the transverse propagation direction of rock fracture surfaces. In this study, the directions of the principal stress and principal strain in different height planes of the samples were determined by circumferential ultrasonic measurements. Considering the relationship among the directions of the principal strain, transverse propagation, and in situ stress release, the mechanism of transverse fracture propagation driven by micro-cracks caused by in situ stress is explained. The effects of the confining pressure, initial rock damage, and circumferential wave velocity anisotropy on the incline angle were analysed. The results indicate that the directions of the principal stress and principal strain were approximately perpendicular to the central position of the samples. Significant deflection occurred in the principal stress direction at the top and bottom. The fracture surface transverse propagation direction was close to the principal strain direction at the central position, and the incline angle decreased with increasing confining pressure. The influence of the micro-crack volume proportion on the angle decreased with an increase in the initial damage. In addition, the incline angle and initial damage first decreased and then increased with the fractal dimension. Under different fractal dimensions, the change trend of the lower envelope incline angle exhibited a negative exponential relationship with the confining pressure. The fractal dimension decreased exponentially related to the chlorite content. This study provides a theoretical guidance for predicting failure locations in rock engineering. [ABSTRACT FROM AUTHOR]

This article presents continuous monitoring results of alkali-silica reaction (ASR) development in concrete specimens for over 400 days using ultrasonic testing and expansion measurements. Eight concrete specimens with nonreactive aggregate (Control), reactive coarse aggregate, and reactive fine aggregates were cast with two reinforced confinement conditions. The specimens were conditioned in an environmental chamber with high temperature and humidity (38°C and 90% relative humidity) to accelerate the ASR development. A multichannel ultrasonic monitoring system was developed to collect ultrasonic signals automatically, and the expansions in three directions were measured periodically. Results showed that the relative velocity change could detect the ASR initiation in all reactive specimens and show a correlation with expansion in the early stage. However, these correlations are inconsistent for different ASR specimens, and the velocity change becomes less sensitive to ASR damage in the late stage (after 300 days). Irrecoverable velocity drop was observed during every chamber shutdown period, especially in specimens with higher levels of ASR damage. This phenomenon suggests that the nonlinear ultrasonic response caused by the ambient temperature variation may indicate the ASR damage. [ABSTRACT FROM AUTHOR]

Copyright of Pearl River is the property of Pearl River Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The heterogeneity of concrete is a major challenge for acoustic emission monitoring. A method of active-passive joint acoustic emission monitoring considering the heterogeneity of concrete is presented herein, and the time-frequency-space multi-parameter response characteristics of active and passive acoustic emission signals were studied in relation to the damage evolution of concrete. This method provides an idea of evaluating the damage state of concrete more actively and quantitatively than traditional methods. The results show that the microscopic damage model of concrete based on the acoustic emission penetrating wave velocity and amplitude is in agreement with the damage process of concrete. The standard deviation of the wave velocity up to 1000 m/s and the change rate of the amplitude up to −0.66 can be adopted as two signs that the load of concrete reached 70% of the ultimate load. The time-of-arrival localization based on variable velocity was used to correct the acoustic emission localization results, and the localization accuracy was increased by 44.74%. The damage process of concrete undergoes diverse changes; that is, the distribution of damage changes from heterogeneous to homogeneous and then back to heterogeneous. Hence, it is necessary for researchers to consider the heterogeneity of concrete when using acoustic emission monitoring. The active-passive joint acoustic emission monitoring is an effective method. [ABSTRACT FROM AUTHOR]

Copyright of Chinese Journal of Applied Mechanics is the property of Chinese Journal of Applied Mechanics Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In order to explore the weakening law of mechanical properties of rocks on the top of coalbed methane under high temperature and cyclic loading and unloading, a DDL-200 uniaxial electronic testing machine was used to conduct graded cyclic loading and unloading tests on the rocks, and the weakening laws of mechanical parameters, sound velocity propagation were analyzed. The results show that: at 25-400 ℃, the strain increment is small, the morphological failure is splitting failure, and the internal damage is uneven, and the longitudinal wave velocity propagates quickly; after 400 ℃, the strain increment is large, and the main failure mode is shear failure. The internal debris increases and the pores become larger, the outer layer of the rock has many and irregular fracture surfaces, and the longitudinal wave velocity is slow; during the loading period, the softening coefficient decreases with increasing temperature under the same cycle, and increases with increasing cycle under the same temperature. The degree of deterioration decreases with increasing temperature under the same cycle, and first increases and then decreases with increasing cycle under the same temperature; during the unloading period, the softening coefficient and degradation degree both increase with the increase of the same cycle (or temperature). The research results will provide reference for the stability of the upper rock mass of coal seams during gas mining and the exploration of rocks under complex stress conditions.

Temperature is an important factor for the service life of cable insulation. To ensure safety, the operating temperature of cables must be monitored. Since optical fiber temperature measurement technology is difficult to be used widely in medium voltage (MV) cables due to cost, this paper proposes a temperature evaluation method based on wave velocity. Firstly, the dielectric constant of cross-linked polyethylene (XLPE) cable insulation under different temperature is obtained through experiment. Based on the result, the relationship curve between wave velocity and temperature is established. The asymmetry effect due to temperature gradient in the cable insulation is discussed via finite element simulation. The effectiveness of obtaining the average insulation temperature of the cable based on wave velocity is validated. In addition, the mechanism of the temperature influence on the cable insulation material’s dielectric constant is analyzed by molecular dynamics simulation, which further deepens understanding of the characteristics of cable insulation materials.

Copyright of Journal of Central South University is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This paper presents acoustic integrated uniaxial compression tests on 11 types of rock specimens to investigate their acoustic behavior and brittleness properties. Thin section analysis was used to characterize the mineral composition and structural characteristics of the rocks, and their grain uniformity was quantified using the weighted variable coefficient. The acoustic signals of the 11 types of rock specimens during uniaxial compression were monitored and recorded in real time using ultrasonic and acoustic emission (AE) testing technologies. The relationships between grain characteristics, mineral composition, and acoustic behaviors were investigated. The results showed that the centroid frequency (Fcf) and transmission coefficient (Tcf) of the rocks were generally positively correlated with grain uniformity, and mineral grain size had different effects on igneous and sedimentary rocks. The ultrasonic (Vp,, Fcf, Tcf) and damage (D3) characteristics were significantly influenced by the three main mineral compositions (quartz, plagioclase, and k-feldspar). Additionally, differences in the percentage growth of Fcf and Tcf in igneous, sedimentary, and metamorphic rocks were explored and attributed to differences in the structural construction and abundance of initial microcracks. A novel brittleness index for rocks was established based on the ultrasonic characteristic parameters and mineral composition, and the existing brittleness index based on AE parameters was improved. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Engineering Geology / Gongcheng Dizhi Xuebao is the property of Journal of Engineering Geology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The dependence of piezoelectric wave impedance on the rotation speed is investigated theoretically and numerically. The Coriolis force due to rotation is introduced into the piezoelectric motion equations, which is solved by the harmonic plane wave solution. It is shown that the wave impedance variations of longitudinal and transverse waves due to rotation are clearly different. The longitudinal wave impedance continuously increases with a small rotation ratio and one transverse wave impedance is almost irrespective of a rotation ratio. In contrast, the rotation applies a big impact on the other transversal wave impedances in the piezoelectric crystal which decreases monotonically with the rotation speed. Such characteristics are significant in piezoelectric transducers and sensors.

The rock fracture characteristics and principal stress directions are crucial for prevention of geological disasters. In this study, we carried out biaxial compression tests on cubic granite samples of 100 mm in side length with different intermediate principal stress gradients in combination with acoustic emission (AE) technique. Results show that the fracture characteristics of granite samples change from ‘sudden and aggregated’ to ‘continuous and dispersed’ with the increase of the intermediate principal stress. The effect of increasing intermediate principal stress on AE amplitude is not significant, but it increases the proportions of high-frequency AE signals and shear cracks, which in turn increases the possibility of unstable rock failure. The difference of stress in different directions causes the anisotropy of rock fracture and thus leads to the obvious anisotropic characteristics of wave velocity variations. The anisotropy of wave velocity variations with stress difference is probable to identify the principal stress directions. The AE characteristics and the anisotropy of wave velocity variations of granite under two-dimensional stress are not only beneficial complements for rock fracture characteristic and principal stress direction identification, but also can provide a new analysis method for stability monitoring in practical rock engineering.

A liquid nitrogen cold-shock fracturing method is proposed to resolve the problem of single heat-exchange cracks generated by hydraulic fracturing in an enhanced geothermal system. A complex crack network can be constructed from the great thermal difference between cryogenic fluids and hot rocks. In this work, damage characterization that combined resistivity, ultrasonic wave, and nuclear magnetic resonance (NMR) was undertaken. The matrix continuity was analyzed ultrasonically, the fracture channel was analyzed by resistivity, and the pore structure was analyzed by NMR. The high-temperature granite damage after liquid nitrogen cold-shocking was evaluated quantitatively. The ultrasonic velocities of the granite cores decreased with high temperature, especially over 400 °C. The resistivity decreased and the largest drop was 81.86% for granite C at 600 °C. According to the NMR T2 spectra, liquid nitrogen cold-shocking expanded the pore volume and increased the pore number. The porosity after cold-shocking increased exponentially with heating temperature, where the porosities of granites A, B, and C reached 7.21%, 4.29%, and 3.10%, respectively. The damage variables calculated by wave velocity and resistivity increased with heating temperatures. The correlation of porosity with resistivity and wave velocity was established by multiple linear regression. Liquid nitrogen cold-shocking induced a developed pore-fracture network in hot dry rocks. [ABSTRACT FROM AUTHOR]

Tunnel Boring Machines (TBMs) have been the main equipment for tunneling and underground construction due to their high safety performance and tunneling efficiency. However, the unknown and changing geological conditions during construction pose a challenge to TBM construction. As one of the essential parameters of rock properties, accurate acquisition of uniaxial compressive strength (UCS) is crucial for TBMs to adapt to changing ground conditions in a timely manner. Therefore, this study proposes a Catboost intelligent model based on Bayesian Optimization to predict UCS. Rock mass are velocity information and key TBM operational parameters are used as model input variables. The Gaussian data augmentation method is used to compensate for the difficulty of obtaining field data in large quantities. The Zhujiang Delta Water Resources Allocation Engineering field data are used in the model, and the obtained evaluation indicators MAPE, RMSE, VAF and a20-index are obtained as 9.91%, 499.38 MPa, 90.7% and 0.95, respectively. In addition, another project is selected to verify the applicability of the model. The validation results also confirm that the model is valid and reliable when applied to practical engineering. [ABSTRACT FROM AUTHOR]

3-Dimension (3D) printers are increasingly being used in high-tech industrial applications technology, because they can produce sophisticated products by laminating materials with less time and cost compared to cutting processing, such as conventional machine tools. However, since the reliability evaluation criteria and method for laminated manufacturing products are not clear, accidents cannot be prevented when 3D printed laminates are used as structures and machined parts. In this paper, ultrasonic wave propagation characteristics were evaluated on the specimens manufactured by laminating acrylonitrile butadiene styrene resin materials with a stereo lithography apparatus 3D printer using the ultrasonic inspection method among non-destructive techniques. Specimens were laminated in units of 0.1 mm, and thicknesses of 1, 2, 4, 6 and 8 mm were applied as variables. In addition, the ultrasonic characteristics according to laminating direction were analyzed by laminating diagonally and vertically, including laminating in the horizontal direction, and defect specimens were produced to check whether defects were read. It was found that the ultrasonic velocity of the horizontally laminated specimen having a thickness of less than 4 mm was slower than the ultrasonic reference velocity, and that the ultrasonic velocity was affected according to the laminated direction. In addition, by arranging the defect location of the specimen differently, it was determined whether the defect was detected, and whether it was possible to check the location. Based on the results of this study, it will be possible to broadly apply this technique to advanced industrial technologies through evaluation of the condition and reliability of laminated manufacturing products manufactured with 3D printers. [ABSTRACT FROM AUTHOR]

Key Message: Due to the simplifying assumptions used to analyze acoustic wave propagation in trees, the accuracy of sonic tomograms varies significantly according to the geometry of the measured tree part. For trees growing in communities, arborists routinely check for evidence of damaged wood during tree risk assessment, and sonic tomography is occasionally used to measure the amount of internal damage in trees. Existing studies investigating the accuracy of commercially available sonic tomography devices have mostly considered a limited range of measurement conditions, limiting their application in practice. Using measurements incorporating greater variability in test conditions, this study examined the accuracy of sonic tomography by comparing the percent damaged cross-sectional area in tomograms with the destructively measured internal condition of trees. Although the accuracy of tomograms differed between the examined temperate and tropical tree species, the variation was largely explained by underlying differences in the cross-sectional geometry of the measured tree parts. The amount of decay was repeatedly underestimated in measurements of small, circular cross sections, and, conversely, it was consistently overestimated in measurements of large, irregularly shaped cross sections. Using different approaches to generating and interpreting tomograms, a wide range of decay estimates was obtained for a given set of measurements. By adjusting software settings, it was possible to obtain tomograms with the least error for a given cross-sectional geometry, and the tomograms could be visually interpreted to similarly compensate for the anticipated measurement error. Although practitioners can use the identified strategies to compensate for the expected measurement error in different situations, there is also a fundamental need to develop improved measurement and analysis routines for sonic tomography relying on physically realistic assumptions about acoustic wave propagation in wood. [ABSTRACT FROM AUTHOR]

Abstract The wave velocity analysis of rock medium is the main method used to explore the internal compositions in the crust and research seismic. In this paper, a compression–shear coupled nonlinear elastic constitutive relation is established, which is consistent with the mechanical properties of rock and mineral medium under high pressure. On this basis, numerical solutions of the wave equation and plane wave analytical solutions for the primary and secondary wave velocities are obtained. As is indicated by the comparison with the linear elastic constitutive theory, the results reflect the compression–shear coupling characteristics of the rock, including the stress path effect and the compression–shear coupling wave effect. With different parameter values, the velocity of the secondary wave changes from lower than that of the elastic shear wave, to higher than that of the elastic shear wave. The research results are expected to provide meaningful explanations for the physical mechanisms of the supershear wave and sub‐Rayleigh wave, and guidance for the detection of rock and soil composition and the observation of seismic waves.

The movements of a reinforced net are considered. Mesh systems are used in various areas of modern technology, aviation, fishing, and construction. In recent years, much attention has been drawn to the complete equations that describe the motion of a deformable thread. In accordance with the studied task, the reinforcement of the net is carried out by adding terms in the equations of motion. In the planar case, the static behavior of the structure is investigated, and equations of motion are derived that allow the study of motion. The problem of wave propagation in deformable filament systems, taking into account a significant deviation of the filament shape from the original rectilinear one, is mathematically very difficult, since the equations of motion are a system of nonlinear differential equations in partial derivatives. To solve the problem, the method of characteristics is used. As well the method of characteristics solves the problem of the propagation of unloading waves (in the case of a load, shock waves arise). Depending on the velocity distribution at the boundary, the distribution of the strain constant on the characteristics is determined. The results are constructed by numerical integration of the integrals of the characteristics found by the method. The solution using the characteristic equations shows the occurrence of traveling waves.

This paper presents a numerical model for the evaluation of the active and passive seismic earth pressure coefficients against the retaining structures subjected to pseudo-dynamic loading using the lower bound limit analysis coupled with finite element discretization and second-order cone programming. The active and passive pseudo-dynamic earth pressures are formulated as functions of the earthquake non-dimensional wavelength as well as the local site effects originated from the backfill damping characteristics and the elastic properties of the underlying foundation. Results generally show that the retaining wall tends to instability by increasing the seismic intensity. In particular, it is shown that when the input acceleration at the base of the wall increases, the active and passive lateral earth pressure coefficients undergo increment and decrement, respectively. Moreover, the pseudo-dynamic active and passive earth pressures are bounded between their static and pseudo-static equivalents. Indeed, it is revealed that when trivial wavelengths are encountered, the influence of seismic loading vanishes due to the counteracted inertia force increments and the static solution is reached. On the contrary, when very high wavelengths are assumed, especially for shorter walls, the acceleration fields become homogeneous lending support to the contention that the pseudo-dynamic earth pressure starts from the pseudo-static asymptote values. The soil-wall interface friction angle is also observed to considerably affect the limit earth pressure coefficients due to the augmented shear resistance provision. Furthermore, foundation elasticity is shown to be as important as the backfill damping characteristics in the pseudo-dynamic site response analysis. [ABSTRACT FROM AUTHOR]

To study the strength deterioration and fracture mechanism of rock under the microwave irradiation, the experiments on the wave velocity and Brazilian splitting tensile strength of sandstones after different microwave irradiation time were carried out. The microstructural evolution of sandstone were studied by means of thermogravimetric (TG) analysis and electron microscope scanning (SEM). The results show that the surface temperature of sandstone increases rapidly under microwave irradiation. The P-wave velocity and tensile strength decreased continuously with the increase of irradiation time under 3 kW power. Considerable macroscopic cracks appeared on the surface of the sandstone after microwave irradiation for 6 min. The high temperature generated by microwave irradiation leads to physical and chemical changes of rock minerals, and the selective heating of microwave results in thermal stress. All these have caused damage to the rock, and led to the deterioration of macro physical and mechanical properties of sandstone. [ABSTRACT FROM AUTHOR]

Rock burst, an important kind of geological disaster, often occurs in underground construction. Rock burst risk assessment, as an important part of engineering risk assessment, cannot be ignored. Liquid nitrogen fracturing is a new technology used in the geological, oil, and gas industries to enhance productivity. It involves injecting liquid nitrogen into reservoir rocks to induce fractures and increase permeability, effectively reducing rock burst occurrences and facilitating the flow of oil or gas toward the wellbore. The research on rock burst risk assessment technology is the basis of reducing rock burst geological disasters, which has important theoretical and practical significance. This article examines the temperature treatment of two types of rocks at 25 °C, 100 °C, 200 °C, 300 °C, and 400 °C, followed by immersion in a liquid nitrogen tank. The temperature difference between the liquid nitrogen and the rocks may trigger rock bursting. The research focused on analyzing various characteristics of rock samples when exposed to liquid nitrogen. This included studying the stress–strain curve, elastic modulus, strength, cross-section analysis, wave velocity, and other relevant aspects. Under the influence of high temperature and a liquid nitrogen jet, the wave velocity of rocks often changes. The structural characteristics and possible hidden dangers of rocks can be understood more comprehensively through section scanning analysis. The stress–strain curve describes the deformation and failure behavior of rocks under different stress levels, which can help to evaluate their stability and structural performance. The investigation specifically focused on the behavior of rocks subjected to high temperatures and liquid nitrogen. By analyzing the stress–strain curves, researchers were able to identify the precursors and deformation processes that occur before significant deformation or failure. These findings have implications for the mechanical properties and stability of the rocks.

Seismic refraction technique is an increasingly useful geophysical tool for geotechnical studies in civil engineering work including the mapping of different soil formation of subsoil and detection of the bed rock. Additionally, wave velocity is a key parameter which correlates directly with significant geotechnical parameters of soils and rocks. Today, the evolution of the measurement technique in the field and the data processing allows to obtain tomographic images which increases its potential for applications to evaluate structuration of rock mass. This work describes the basic principles of seismic tomography and a case history of an application in civil works used to evaluate the foundation conditions of a site were a new structure for a spillway for the Gatun lake, north Panama, was projected. The study allowed to detect a destructured band sector in the bedrock which was covered by more modern sediments and vegetation just in the site of interest for the foundation of a project. The magnitude of the destructured bedrock forced to relocate the structure.

The heterogeneity of concrete is a major challenge for acoustic emission monitoring. A method of active-passive joint acoustic emission monitoring considering the heterogeneity of concrete is presented herein, and the time-frequency-space multi-parameter response characteristics of active and passive acoustic emission signals were studied in relation to the damage evolution of concrete. This method provides an idea of evaluating the damage state of concrete more actively and quantitatively than traditional methods. The results show that the microscopic damage model of concrete based on the acoustic emission penetrating wave velocity and amplitude is in agreement with the damage process of concrete. The standard deviation of the wave velocity up to 1000 m/s and the change rate of the amplitude up to −0.66 can be adopted as two signs that the load of concrete reached 70% of the ultimate load. The time-of-arrival localization based on variable velocity was used to correct the acoustic emission localization results, and the localization accuracy was increased by 44.74%. The damage process of concrete undergoes diverse changes; that is, the distribution of damage changes from heterogeneous to homogeneous and then back to heterogeneous. Hence, it is necessary for researchers to consider the heterogeneity of concrete when using acoustic emission monitoring. The active-passive joint acoustic emission monitoring is an effective method.

Longitudinal (P) waves have been widely employed for estimating concrete compressive strength based on correlation models between wave velocity and strength. However, P-wave based methods show high uncertainty because of the challenge of identifying the weak first arrival of P waves and the sensitivity of P waves to air voids and moisture. Shear-horizontal (SH) waves are superior to P waves because of their velocity stability in concrete at various air void and moisture levels. Moreover, SH waves exhibit a high signal-to-noise ratio without mode conversion after reflection and refraction. In this study, an SH-wave based method was developed to measure the shear-wave velocity (Vs) of concrete directly using SH-wave transducers and then establish a correlation between Vs and compressive strength. The proposed method was verified using concrete specimens produced with four water-to-cement ratios and different strength grades. The results indicate that the proposed method can significantly improve the accuracy of first arrival identification and enhance the preciseness of strength evaluation. [ABSTRACT FROM AUTHOR]

Considering the elastic–plastic deformation, the wave propagations and energy transmissions of the one-dimensional three-segment composite granular chain are studied. The axial symmetry model for elastic-perfectly plastic materials is built by using the finite element method. Six materials with different yield strengths are selected for the adjustable segment. The results show that the repeated loading and unloading behaviors, as well as the wave propagations in the elastic–plastic granular chain, are complex and significantly different from those in the purely elastic granular chain. The yield strength of the granular materials in the adjustable segment has significant effects on energy dissipation and wave velocity, which could be used to design the impact buffer. The studies show that taking lower yield strength for the adjustable part than the non-adjustable part, the energy dissipation could be increased, and the wave velocity could be reduced, then the arrival time of the impact waves could be delayed. These characteristics of the elastic–plastic granular chain could be used to design metamaterials for impact absorbers in impact protection. [ABSTRACT FROM AUTHOR]

We investigate the effect of temperature on the elastic properties of rocks by combining the thermal-damage factor (TDF) with the Gassmann equation. The resulting model is tested in carbonate samples by analyzing the ultrasonic wave velocity. A comparison between the estimated and measured TDF shows that the model quantitatively describes the behavior of carbonates at relatively low temperatures, while the high-temperature one is underestimated. The dry- and wet-rock TDF difference increases significantly with increasing temperature, and the TDF is highly affected by the rock permeability and microcrack aspect ratio. [ABSTRACT FROM AUTHOR]

In order to understand how the in-situ primary stress state has evolved with subsidence and uplift in a granitic rock mass for anticipated of a radioactive waste repository in Hungary, the authors investigated the applicability of seismic tomography as an interpretive tool. Very high P wave velocity (Vp) values were obtained during the tomographic scanning of the study area of the repository, and these were compared with existing findings of in-situ and laboratory seismic measurements. Apart from seismic tomographic survey, dynamic FEM numerical modelling, empirical calculations of residual stresses, laboratory measurements of compression wave (ultrasonic) velocities on intact rock cores, in-situ primary stress measurements as well as site geological model were integrated to evaluate the use of seismic tomography for identifying possible in-situ stress increases around the excavation. A detailed calibration modelling was carried out based on the site seismic tomography measurements and during the large-scale modelling. It was observed that the increasing Vp is directly related to simulated increasing directional loadings on the rock mass. Using a measured wave raypath it was possible to check the different in-situ stress parametrizations which resulted in the best approximation to the measured Vp values. It was concluded that the rock mass under investigation to extend the repository must have higher in-situ stress values than the area of the constructed deposition chambers nearby. The results of this research indicated that seismic tomography is a useful tool for determining relative stress around and within the vicinity of underground excavation. [ABSTRACT FROM AUTHOR]