Dynamic Disasters Research Articles

A novel vehicle path planning method for freight enterprises considering environmental regulation

In the paper of vehicle path planning, it is necessary to factor in both governmental regulation policies and enterprise regulation investments. In this paper, a novel method for vehicle path planning is investigated, which incorporates environmental regulation to determine the transportation path, driver, and vehicle type in a joint manner. The mathematical formulation of the investment decisions related to internal self-regulation is provided, considering four external regulation policies. To address the challenges posed by the multidimensional, discrete, and non-linearity model, an improved dynamic disaster genetic algorithm with elite strategy (ED-GA) is proposed. The numerical results demonstrate the effectiveness of the ED-GA in solving large-scale path planning problems, considering both effectiveness and running time. Moreover, this paper analyzes the variations in internal environmental regulation and external environmental regulation, elucidating the impact of different degrees of internal regulation and exploring the applicability of various external regulations. The proposed method is particularly relevant for freight enterprises that possess their own vehicles and are committed to investing in emission reduction. It offers valuable guidance for decision-making and management in low carbon vehicle path planning.

Experimental study on the interrelation of multiple mechanical parameters in overburden rock caving process during coal mining in longwall panel

In order to comprehend the dynamic disaster mechanism induced by overburden rock caving during the advancement of a coal mining face, a physical simulation model is constructed basing on the geological condition of the 21221 mining face at Qianqiu coal mine in Henan Province, China. This study established, a comprehensive monitoring system to investigate the interrelations and evolutionary characteristics among multiple mechanical parameters, including mining-induced stress, displacement, temperature, and acoustic emission events during overburden rock caving. It is suggested that, despite the uniformity of the overburden rock caving interval, the main characteristic of overburden rock lies in its uneven caving strength. The mining-induced stress exhibits a reasonable interrelation with the displacement, temperature, and acoustic emission events of the rock strata. With the advancement of the coal seam, the mining-induced stress undergoes four successive stages: gentle stability, gradual accumulation, high-level mutation, and a return to stability. The variations in other mechanical parameters does not synchronize with the significant changes in mining-induced stress. Before the collapse of overburden rock occurs, rock strata temperature increment decreases and the acoustic emission ringing counts surges with the increase of rock strata displacement and mining-induced stress. Therefore, the collaborative characteristics of mining-induced stress, displacement, temperature, and acoustic emission ringing counts can be identified as the precursor information or overburden rock caving. These results are in good consistent with on-site situation in the coal mine.

Chemical dissolution of minerals in anthracite after supercritical carbon dioxide immersion: Considering mechanical damage and enhanced porosity

Carbon dioxide injection into in-situ coal seams can effectively enhance coalbed methane recovery and promote carbon sequestration, increasing energy production while reducing greenhouse gas emissions. CO2 is prone to exist in a supercritical state in deep coal seams, so it is of great significance to quantitatively describe the mechanical properties damage of coal caused by supercritical carbon dioxide (SC–CO2). Based on the non-equilibrium thermodynamic framework, a nonlinear model of SC–CO2–coal interaction is developed using the special forms of Helmholtz free energy and energy dissipation. Two damage variables are employed to quantify the irreversible degradation induced by chemical reactions and mechanical loads, respectively. The results indicate that the long-term effect of SC-CO2 can increase the porosity of anthracite by approximately 5.49%, but reduce the elastic modulus and strength by about 58% and 56% respectively. The experimental data confirms that the damage model facilitates an analysis of the interplay among SC-CO2 absorption, porosity, elastic modulus and tensile strength of anthracite. The degradation of anthracite mechanical properties is time-dependent, which means that the risk of coal-rock dynamic disasters increases with the passage of CO2 injection time. This work is expected to study the complex multi-field coupling mechanism of SC-CO2 on in-situ coal seams, providing a theoretical basis for guiding CO2 geological sequestration and CO2 enhanced coalbed methane recovery.

Risk Assessment of Compound Dynamic Disaster Based on AHP-EWM

The coal mine in deep mining can easily form a compound dynamic disaster with the characteristics of rock burst and gas outburst. In this paper, the analytic hierarchy process (AHP) and the entropy weight method (EWM) are combined, and the fuzzy comprehensive evaluation (FCE) secondary evaluation model of compound dynamic disaster is proposed to evaluate the risk of compound dynamic disaster, which avoids the problems of the imperfect evaluation index system and strong subjectivity of index weight. Based on the statistical analysis of typical compound dynamic disaster cases in China, three first-level indicators were established, and sixteen second-level indicators were developed. The verification results show that the accuracy and weight are better than the traditional evaluation methods. Combined with geological and mining data, the compound dynamic disaster risk assessment was carried out on the second mining area of mine B, in the Pingdingshan mining area, and the result was grade II (weak risk). Corresponding prevention measures and parameters were implemented, and no compound dynamic disaster occurred during the working face excavation.

Dynamic characteristics and deterioration mechanism of coal under distinct initial gas pressure

Additional to dynamic and static superimposed loads, gas effects frequently affect coal seams throughout the coal mining process. It is crucial to comprehend coal samples’ mechanical properties and deterioration mechanisms under distinct initial gas pressure conditions. Consequently, the dynamic compression experiment of coal samples was conducted utilizing a self-developed observable combined dynamic and static loading test system of gas-bearing coal (GAS). The mechanical characteristics including failure mode in coal samples under distinct initial gas pressures were studied. Furthermore, the mechanism of gas deteriorated mechanical parameters and aggravated the propagation of cracks when combined with dynamic and static loads was revealed. The conclusions are drawn as follows: The GAS can go through four stages of deformation: elastic stage, elastoplastic stage, plastic stage, and failure stage. Furthermore, the dynamic strength and failure strain deteriorated with increasing gas pressure. Based on computed tomography (CT) technology, it is found that the splitting-spallation composite cracks of impacted samples become more noticeable with rising initial gas pressure, and finally, the two kinds of cracks create a complex reticular crack system. Meanwhile, the crack volume and fractal dimension increase with rising gas pressure, indicating that gas can aggravate the coal’s failure degree. Under combined dynamic and static loads, the deterioration model of mechanical parameters of GAS is obtained, that is, with rising initial gas pressure, the dynamic strength of coal samples reduces and the failure strain rises synchronously. The main reason for the aggravation of compound failure in impacted samples is that the stress intensity factor rises with the rise of gas pressure. These conclusions enrich the basic theories such as the inducing mechanism of dynamic disasters caused by coal-rock-gas compounds and can offer a theoretical foundation for the technology employed in monitoring, early warning, and prevention of dynamic disasters in compounds.

Discrete characteristics of instantaneous frequency of EMR induced by coal and rock fracture

To reveal the discrete characteristics of the instantaneous frequency of the electromagnetic radiation (EMR) waveform induced by coal and rock fracture, the uniaxial compression experiments for coal and rock samples were carried out, and the EMR signals with full waveform were acquainted and stored. The empirical wavelet transform is used to filter and de-noise the EMR waveform, and then the short-time Fourier transform is used to analyze the time-frequency characteristics of the waveform. The discrete characteristics of the instantaneous frequency with a larger amplitude and the relationship between the centroid frequencies and peak-to-peak values (Vpps) of the EMR waveforms are statistically analyzed. The results show that the centroid frequency of 0–100 kHz is negatively correlated with the Vpp, and the relationship between them shows a logarithm function relation. The instantaneous frequency of the EMR waveform of coal and rock fracture has significant discrete characteristics. In detail, for the rock sample, the instantaneous frequencies with relatively large amplitude are mainly 4.5 kHz, 19.5 kHz, 22.0 kHz, and 27.5 kHz; for the coal sample, the instantaneous frequencies are mainly 1.0 kHz, 4.5 kHz, 9.0 kHz, and 74.0 kHz. This discrete characteristic is determined by the natural properties and fracture characteristics of the sample. Compared with the homogeneous rock samples, the internal cracks of the coal samples are well developed and show strong anisotropy, resulting in the discrete characteristics of the instantaneous frequency being relatively weaker. The findings have certain guiding significance for optimizing the design of the EMR monitoring frequency band and improving the pertinence and accuracy of the monitoring and early warning for coal and rock dynamic disasters.

Coal and rock dynamic disaster prevention and control technology in the large mining face of a deep outburst mine

Coal and rock dynamic disaster prevention and control technology in the large mining face of a deep outburst mine

Editorial: Evaluation, projection, and prevention of dynamic geological disasters: advances and applications of geophysical methods and numerical modeling

Editorial: Evaluation, projection, and prevention of dynamic geological disasters: advances and applications of geophysical methods and numerical modeling

Mine Microseismic Signal Denoising Based on a Deep Convolutional Autoencoder

Mine microseismic signal denoising is a basic and crucial link in microseismic data processing, which influences the accuracy and reliability of the monitoring system, and is of great significance with regard to safety during mining. Therefore, this study introduces a deep learning method to improve the mapping function and sparsity of signals in the time-frequency domain and constructs a denoising framework based on a deep convolutional autoencoder to address the denoising problem of mine microseismic signals. First, all noisy microseismic signals are normalized to ensure the nonlinear expression ability of the constructed denoising framework. Then, the normalized signals are transformed into the time-frequency domain using the short-time Fourier transform (STFT), and the real and imaginary parts of time-frequency coefficients serve as the input of the deep convolutional autoencoder to output the masks of the effective and noise signals. Next, these masks are applied to the time-frequency coefficients of the noisy microseismic signals, and the time-frequency coefficients of the potentially effective and noise signals are estimated. Finally, inverse STFT is used to transform these time-frequency coefficients to the time domain to obtain the final denoised effective and noise signals. The constructed framework automatically learns rich features from synthetic data to separate the effective and noise signals, thereby achieving the purpose of fast and automatic denoising. The experimental results show that compared with the wavelet threshold and ensemble empirical mode decomposition, the denoising framework considerably improves the signal-to-noise ratio of mine microseismic signals with less waveform distortion. Moreover, it can achieve a better denoising effect efficiently even in the case of a low SNR, which has obvious advantages. The constructed denoising framework is suitable for microseismic monitoring signals of various mine dynamic disasters and provides strong technical support for intelligent monitoring and early warning concerning production risks in mines.

Study on the energy evolution mechanism of coal and rock with impact tendency under different strain rates

To explore the strain rate effect of deformation and failure of impact prone coal rock, uniaxial compression tests and triaxial compression tests with different strain rates were carried out. The mechanical properties and impact tendency of impact-prone coal rock were studied, and the energy evolution law and pre-peak energy self-promotion-inhibition mechanism of impact-prone coal rock were obtained. The results show that with the increase of strain rate, the peak strength of coal rock under uniaxial compression decreases gradually, and the peak strength of coal rock under triaxial compression increases first and then decreases, and the impact tendency of coal rock increases first and then decreases. The energy evolution of coal rock under uniaxial compression is mainly divided into four stages: initial energy damage, energy hardening, energy softening and failure. With the increase of strain rate, the total energy and elasticity at the peak point of coal rock under uniaxial compression decrease gradually, and the total energy, elastic energy and dissipation energy at the peak point under triaxial compression increase first and then decrease. The elastic energy promotion coefficient of impact-prone coal rock is much larger than the inhibition coefficient, and the increase of strain rate will promote the generation of elastic energy inside coal rock. The research results can provide reference for the prevention and early warning of dynamic disasters of coal and rock mass with impact tendency.

Enhancing Performance of Engineering Structures under Dynamic Disasters with ECC–FRP Composites: A Review at Material and Member Levels

Dynamic loadings arising from impact, explosive, and seismic disasters impose high requirements on the performance of engineering structures during service periods. Engineered cementitious composite (ECC) exhibits exceptional toughness and crack resistance, while fiber-reinforced polymer (FRP) possesses lightweight and high-strength properties. ECC and FRP composites show promising potential in enhancing the resilience of existing structures under dynamic disaster scenarios. However, most research on ECC and FRP has primarily focused on static properties, while investigations of dynamic properties are limited. This paper provides a comprehensive review of the dynamic properties of ECC and FRP composites followed by a summary of studies conducted on the dynamic behavior of ECC and FRP strengthened members, which provides valuable insights for further research on these materials and their applications in strengthening structures under dynamic disasters.

Microseismic monitoring and forecasting of dynamic disasters in underground hydropower projects in southwest China: A review

The underground hydropower projects in Southwest China is characterized by large excavation sizes, high geostresses, complicated geological conditions and multiple construction processes. Various disasters such as collapses, large deformations, rockbursts are frequently encountered, resulting in serious casualties and huge economic losses. This review mainly presents some representative results on microseismic (MS) monitoring and forecasting for disasters in hydropower underground engineering. First, a set of new denoising, spectral analysis, and location methods were developed for better identification and location of MS signals. Then, the tempo-spatial characteristics of MS events were analyzed to understand the relationship between field construction and damages of surrounding rocks. Combined with field construction, geological data, numerical simulation and parametric analysis of MS sources, the focal mechanism of MS events was revealed. A damage constitutive model considering MS fracturing size was put forward and feedback analysis considering the MS damage of underground surrounding rocks was conducted. Next, an MS multi-parameter based risk assessment and early warning method for dynamic disasters were proposed. The technology for control of the damage and deformation of underground surrounding rocks was proposed for underground caverns. Finally, two typical underground powerhouses were selected as case studies. These achievements can provide significant references for prevention and control of dynamic disasters for underground engineering with similar complicated geological conditions.

Integrate Assignment of Multiple Heterogeneous Unmanned Aerial Vehicles Performing Dynamic Disaster Inspection and Validation Task With Dubins Path

The actual performance of a task assignment method of unmanned aerial vehicles (UAVs) shows a considerable dependence on the path planning process coupled with it; however, this topic has been rarely studied in the existing literature. This paper considers the problem of maximizing the task-assignment reward of a fleet of heterogeneous UAVs for a dynamic reconnaissance and confirmation task under constraints of critical time and multi-UAV tasks where the coupled path optimization objectives also need to be considered. The existing consensus-based bundle algorithm is extended with an effective method for managing the multi-task and multi-agent constraints. The proposed method can optimize the inherent coupling path using the Dubins path to reduce the differences between the estimated path and the actual path, shortening the operation time by adopting the distributed genetic algorithm. The proposed method is verified by the sample run tests of a disaster area reconnaissance and confirmation task and Monte Carlo comparison simulations with the two existing algorithms. The results verify both the practicality and advantages of the proposed method.

Failure characteristics and conditions of rock-coal combination structure with weak layer under dynamic and static stresses

To comprehensively understand the mechanical response of a rock-coal combination structure containing a weak layer, a series of laboratory static loading and impact loading experiments were conducted. The results showed that under static load, the sliding process of the rock coal structure was relatively slow, and fragments can be observed. Under the action of horizontal impact loading, the whole coal stratum slipped out rapidly, and the process lasted only 0.05 s. Under the horizontal and axial impact loads, the coal stratum remained stable first, and then it slipped out as a whole under the action of static load. Additionally, a sliding instability criterion of a rock coal structure containing a weak layer was established based on theoretical analysis. The key parameter P value was checked through a numerical simulation experiment. It was found that the value was linearly related to the mechanical properties of the weak layer and overburden stress, and the experimental results coincided with the theoretical results. Finally, the relationship between sliding rockburst and strain rockburst was discussed, and these results can provide an important scientific basis for the prevention and control of dynamic disasters in deep mining.

Experimental Study on Mechanical Properties of Coal-Based Solid Waste Nanocomposite Fiber Cementitious Backfill Material.

Previous studies have shown that coal-based solid waste can be utilized in combination with cement, silica fume, and other modified materials to create a cemented backfill material. However, traditional cemented backfill materials have poor mechanical properties, which may induce the emergence of mining pressure and trigger dynamic disaster under complex mining conditions. In this study, the nanocomposite fiber was used to modify the traditional cemented backfill materials and a new cemented backfill material was developed using coal-based solid waste, nanocomposite fiber and other materials. Specifically, coal gangue, fly ash, cement, and glass fibers were used as the basic materials, different mass fractions of nano-SiO2 were used to prepare cemented backfill materials, and the mechanical enhancement effect of the compressive strength, tensile strength, and shear strength of the modified materials was analyzed. The results show that when the nano-SiO2 dosage is 1%, the optimal compressive strength of the specimens at the curing age of 7 d can be obtained compared with cemented materials without nano-SiO2, and the compressive strength of the modified specimens raises by 84%; when the nano-SiO2 dosage is 1%, the optimal tensile strength and shear strengths of the modified specimens can be obtained at the curing age of 28 d, increasing by 82% and 142%. The results reveal that nanocomposite fibers can be used as additives to change the mechanical properties of cemented backfill materials made using coal-based solid waste. This study provides a reference for the disposal of coal-based solid waste and the enhancement of the mechanical properties of cemented backfill materials.

Influence of Key Strata on the Evolution Law of Mining-Induced Stress in the Working Face under Deep and Large-Scale Mining

When there are multiple key strata in the overburden of a deep coal seam and the surface subsidence coefficient after mining is small, this indicates that the overlying key strata fail to break completely after mining. On this occasion, stress is easily concentrated in the working face, which in turn leads to the occurrence of dynamic disasters such as rock bursts. This study adopted a comprehensive analysis method of field monitoring and numerical simulations to explore the influence of the key stratum on the evolution law of mining-induced stress in the working face. A distributed optical fiber sensor (DOFS) and a surface subsidence GNSS monitoring system were arranged inside and at the mouth of the ground observation borehole, respectively. According to the monitoring results of strain obtained from the DOFS, the height of the broken stratum inside the overlying strata was obtained and according to the monitoring results of surface subsidence, the surface subsidence coefficient was proven to be less than 0.1, indicating that the high key stratum is not broken completely, but enters a state of bending subsidence instead. In order to reveal the influence of the key stratum on the mining-induced stress of the working face, two 3DEC numerical models with and without the key stratum were established for a comparative analysis. As the numerical simulation results show, when there are multiple key strata in the overburden, the stress influence range and the stress concentration coefficient of the coal seam after mining are relatively large. The study revealed the working mechanism of rock burst accidents after large-scale mining and predicted the potential area with a rock burst risk after mining of the working face, which was verified by field investigations. The research results are of great guiding significance for the identification of the working mechanism of rock bursts in deep mining condition and for their prevention and control.

Influence of Overlying Strata Movement on the Stability of Coal in Fully Mechanized Top-Coal Caving Mining

Overlying strata movement has an important effect on the stability of coal along goaf. In order to study the impact of overlying strata movement on the stability of coal during fully mechanized top-coal caving mining, a simulation experiment was conducted on the Liuxiang Coal Mine using digital image correlation (DIC) and stress electric measurement methods. The characteristics of overlying strata movement, stress concentration and deformation evolution of coal, and interlayer sliding between coal and rock are analyzed. The following conclusions could be drawn. The movement of overlying strata can be classified into two stages: the first stage is characterized by vertical displacement, while the second stage is characterized by horizontal displacement. In the first stage, the vertical movement of overlying strata causes the vertical stress concentration of the coal. In the second stage, the horizontal movement causes frictional sliding between coal and rock, which produces a shearing effect on the coal. Under these two effects, the coal along goaf gradually reaches its strength limit, and local deformation occurs, and the micro-cracks are further concentrated and fused in this area. When macro-cracks are formed, occur and expand unstable, the elastic energy is released suddenly, which will lead to dynamic disasters such as rock bursts.

Dynamic behavior of outburst two-phase flow in a coal mine T-shaped roadway: The formation of impact airflow and its disaster-causing effect

The study of the dynamic disaster mechanism of coal and gas outburst two-phase flow is crucial for improving disaster reduction and rescue ability of coal mine outburst accidents. An outburst test in a T-shaped roadway was conducted using a self-developed large-scale outburst dynamic disaster test system. We investigated the release characteristics of main energy sources in coal seam, and obtained the dynamic characteristics of outburst two-phase flow in a roadway. Additionally, we established a formation model for outburst impact flow and a model for its flow in a bifurcated structure. The results indicate that the outburst process exhibits pulse characteristics, and the rapid destruction process of coal seam and the blocking state of gas flow are the main causes of the pulse phenomenon. The outburst energy is released in stages, and the elastic potential energy is released in the vertical direction before the horizontal direction. In a straight roadway, the impact force oscillates along the roadway. With an increase in the solid–gas ratio, the two-phase flow impact force gradually increases, and the disaster range extends from the middle of the roadway to the coal seam. In the area near the coal seam, the disaster caused by the two-phase flow impact is characterized by intermittent recovery. In a bifurcated roadway, the effect of impact airflow on impact dynamic disaster is much higher than that of two-phase flow, and the impact force tends to weaken with increasing solid-gas ratio. The impact force is asymmetrically distributed; it is higher on the left of the bifurcated roadway. With an increase in the solid-gas ratio, the static pressure rapidly decreases, and the bifurcated structure accelerates the attenuation of static pressure. Moreover, secondary acceleration is observed when the shock wave moves along the T-shaped roadway, indicating that the bifurcated structure increases the shock wave velocity.

Automatic recognition of effective and interference signals based on machine learning: A case study of acoustic emission and electromagnetic radiation

Integrated monitoring technology using acoustic emission (AE) and electromagnetic radiation (EMR) is a promising mean for monitoring coal and rock dynamic disasters. However, due to the complex underground environment, blasting, drilling and mechanical operations may generate interference signals that affect the accuracy of early warning. It is essential to study the automatic recognition of effective and interference signals for AE and EMR. For this reason, a field test of synchronous AE-EMR monitoring was conducted in a coal mine. Further, the time domain, frequency domain and fractal characteristics of effective and interference signals for AE and EMR were analyzed, and sensitive characteristics were obtained by the Relief algorithm. Based on this, automatic recognition models of effective and interference signals were established by Fisher's linear discriminant method, support vector machine and ensemble learning method, respectively. Field application showed that support vector machine performed higher recognition accuracy. The AE and EMR warning indicators were obtained based on the signal recognition model, and the results show that the indicators reflect the risk of rock burst more accurately and earlier than the original indicators before the removal of interference signals.

Crack instability in deep coal seam induced by the coupling of mining unloading and gas driving and transformation of failure mode

Coal and gas outburst is a violent mechanical instability of gas-containing coal, and its mechanism is crucial for prevention of gas dynamic disasters. The macroscopic instability of gas-containing coal is the result of the expansion and connection of micro cracks driven by unloading induced tensile stress and gas pressure. This study is aimed at solving the problem of crack instability of gas-containing coal during mining unloading. To this end, first, the governing equations of unloading-induced tensile stress and gas pressure evolutions in cracks were built, and the dynamic evolutions and main controlling factors of tensile stress and gas pressure were revealed. Furthermore, the evaluation indexes of crack stability under tensile stress and shear stress were established, and the variation of crack stability during unloading was investigated. Finally, the phase diagram of crack failure mode was drawn, and the transformation of crack failure mode was analyzed. The results show that unloading-induced tensile stress is generated when θ > 54.73°, and it rises gradually with the increase of original stress, unloading rate, unloading time and crack size and dip angle. Overall, gas pressure in cracks increases first and then decreases during unloading. It increases gradually with the increase of initial gas pressure, gas desorption rate and original stress, while it decreases as the unloading rate gets higher (k from 10−4 to 10−2 s−1) and the dip angle gets larger (θ from 50 to 90°). With the increase of unloading ratio, the crack stability declines slowly first and then plunges rapidly until the crack finally becomes unstable. In addition, burial depth of coal seam, unloading rate, gas desorption rate and mechanical strength of coal have significant effects on this process. Different factors have important influences on the crack failure mode. With the increase of burial depth from 100 to 2000 m, the crack failure mode gradually transforms from tensile failure to shear failure, and the higher the unloading rate is, the more easily tensile failure occurs. With the increase of cohesion (0.1–2 MPa), the scope of the shear failure zone shrinks gradually, and the crack is less prone to shear failure. The desorption rate has a notable effect on the scope of the non-failure zone. Under a higher gas desorption rate, the scope of the non-failure zone becomes smaller, which is due to the greater gas pressure in crack for a given time. The research in this paper has certain reference value for further grasping of the instability failure of gas-containing coal and the mechanism of coal and gas outburst.