Water Flow In Fractures Research Articles

Predicting Water Flowing Fracture Zone Height Using GRA and Optimized Neural Networks

As coal mining depths continue to rise, consideration of WFFZ elevations is becoming increasingly important to mine safety. The goal was to accurately predict the height of the WFFZ to effectively prevent and manage possible roof water catastrophes and ensure the ongoing safety of the mine. To achieve this goal, we combined the particle swarm optimisation (PSO) algorithm with a backpropagation neural network (BPNN) in order to enhance the accuracy of the forecast. The present study draws upon the capacity of the PSO algorithm to conduct global searches and the nonlinear mapping capability of the BPNN. Through grey relational analysis (GRA), the order of the correlation degree was as follows: mining thickness > mining depth > overburden structure > mining width > mining dip. GRA has identified the degree of correlation between five influencing factors and the height of the WFFZ, among these, mining thickness, mining depth, overburden structure and mining width all show strong correlations, and the mining dip of the coal seam shows a good correlation. The weight ranking obtained by the PSO-BPNN method was the same as that obtained by the GRA method. Based on two actual cases, the relative errors of the obtained prediction results after PSO implementation were 2.97% and 3.47%, while the relative errors of the BPNN before optimisation were 18.46% and 4.34%, respectively, indicating that the PSO-BPNN method provides satisfactory prediction results and demonstrating that the PSO-optimised BPNN is easy to use and yields reliable results. In this paper, the height of the WFFZ model under the influence of five factors is only established for the Northwest Mining Area. With the continuous progress of technology and research, the neural network can consider more factors affecting the height of hydraulic fracturing development zones in the future to improve the comprehensiveness and accuracy of prediction.

Monitoring of Overburden Failure with a Large Fractured-Height Working Face in a Deep Jurassic Coal Seam Based on the Electric Method

The development height of a water-flowing fractured zone is the key parameter to consider when carrying out mining under water pressure and coal mining with water conservation. In this paper, Jurassic coal seam 3-1 in the Menkeqing Coal Mine was taken as the research target, and a three-dimensional mining geological model was established by using FLAC3D to study the deformation and failure rules of overburden. Three roof boreholes were drilled in the auxiliary transportation roadway of adjacent working faces for dynamic monitoring by the resistivity method, which can better observe the whole process from failure to stability of the overburden. The results show that due to the complex sedimentary environment and large buried depth of coal seams in western China, there is a large deviation between the calculation results of the empirical formula of the fractured zone height under the “Regulations of buildings, water, railway and main well lane leaving coal pillar and press coal mining” (three regulations) and the simulation and on-site measurement. Based on the comprehensive analysis, the influence range of mining advance abutment pressure is approximately 60 m. The height of the water-flowing fractured zone is approximately 106 m, and it is located at the interface between sandy mudstone and mudstone. The height of the caving zone is approximately 22 m, and it is located at the interface between fine sandstone and medium sandstone. The ratio of the fractured height and coal seam thickness (Rf) reached 24.4, which was basically consistent with the test result of the adjacent Yushenfu mining area (which was 26 on average). There is no obvious change in the development height of the caving zone and water-flowing fracture zone from the working face to the drilling borehole position of more than 120 m, which reflects that the height of the overburden failure zone is related to the control of lithological combination.

Evolution Laws of Water-Flowing Fracture Zone and Mine Pressure in Mining Shallow-Buried, Hard, and Extra-Thick Coal Seams

Shallow-buried, hard, and extra-thick coal seams are very common in Xinjiang, China, but there are relatively few studies on the mine pressure law and the development characteristics of water-flowing fracture zones (WFFZs) during the mining of such coal seams. In this paper, the mine pressure of the top coal caving face in a shallow, hard coal seam with a hard roof and full bedrock (SHCSHRFB) is analysed, the laws of the surrounding rock deformation and stress of the open-off cut and roadway in the large-mining-height top coal caving face are studied, the characteristics of roof-breaking and overburden fracture development are analysed using the physical similarity simulation method, supporting suggestions for roadways are put forward, and three development stages of the WFFZ are analysed. Field monitoring shows that the hydraulic support stress in SHCSHRFB is weak, but the coal wall and roadway stability are good, which is significantly different from the results in the typical shallow-buried thin bedrock working faces. The measured height of the WFFZ is close to the physical similarity simulation results, but quite different from those arising from use of the empirical formula.

Hydrogeological structures of karst features using hydrographs in an underground river basin formed in a peak cluster depression, southwest China

Understanding of the hydrological behaviors in different karst features is crucial for evaluating the hydrological storage and transfer functions of a karst system. In this study, the Maocun karst underground river system, characterized by typical karst features, was selected as the research area in the southwest region of China. The main objectives of this research are to analyze the hydrogeological structure characteristics of each karst feature and assess water storage capacity in different aquifer media. Frequency distribution curve (FDC) of electrical conductivity (EC) values revealed that recharge sources in the five karst features differed and varied according to the amount of precipitation. All hydrographs of water levels in five karst features were divided into three periods due to the presence of triple aquifer media in the basin. The spatial structure of each feature was interpreted by analyzing the variation characteristics of recession exponential coefficients (λ). Additionally, the ratios of fissure water, fracture water, and conduit water sources were calculated based on the recession curves of water levels. Results showed that fast water flow had the highest proportion in the relatively open subsystem located upstream, while fracture water flow had the lowest proportion. The slow water flow was the main pattern of water storage in the basin. Values of EC in water decreased with a well-connected spatial structure and high hydraulic conductivity. There were significant differences in the values of EC among conduit water, fracture water, and matrix water. These values were calculated using mathematical relationships between EC and water level hydrographs. The results indicated that the EC values in matrix water exceeded 200 μS/cm, while EC values in conduit water/channel water were below 100 μS/cm. Finally, hydrogeological conceptual models were constructed for five karst features based on the depletion characteristics of the aquifer media during each recession period. These characteristics were interpreted using variation curves of EC and hydrographs of water levels. These findings not only elucidated the characteristics of hydrogeological structures in multiple karst features, but also had significant implications for the assessment of karst water sources.

Investigation and evaluation methods of shallow geothermal energy considering the influences of fracture water flow

The energy replenishment and heat convection induced by fracture water flowing through the rock mass impact the shallow geothermal energy occurrence, transfer and storage mechanisms in it. In this article, a suitability evaluation and categorization system is proposed by including judgement indexes that are more closely aligned with the actual hydrogeological conditions in fracture developed regions; an assessment approach of regional shallow geothermal energy is proposed by coupling the influences of fracture water into the calculation methods of geothermal capacity, thermal balance and heat transfer rate. Finally, by taking two typical fracture aperture distributions as examples, the impacts of fracture water on the investigation and evaluation of shallow geothermal energy are quantitatively analyzed. Although the fracture apertures only share 1.68% and 0.98% of the total length of a borehole, respectively, in the two examples, the fracture water convection contributes up to 11.01% and 6.81% of the total heat transfer rate; and the energy replenishment potential brought by the fracture water is equivalent to the total heat extraction of 262 boreholes. A single wide aperture fracture can dominate the aforementioned impacts. The research results can support more accurate evaluation and efficient recovery of shallow geothermal energy in fracture developed regions.

Study of the Catastrophic Process of Water–Sand Inrush in a Deep Buried Stope with Thin Bedrock

Taking the 14,030 panel of Zhaogu No. 2 coal mine as its research object, this paper studies the evolution characteristics of the developing height, propagation track and caving arch shape of water-flowing fractures under the influence of thick alluvium by utilizing a physical experiment, theoretical analysis and field investigation. The results show that the height and limit span of the water-flowing fracture zone experience four stages, which include the initial stage, slow-increasing stage, sudden-increasing stage and stable-increasing stage. With the increase in the mining influence range, the shape of the water-flowing fracture in overburden under the influence of thick alluvium is gradually formed. The water in the thick alluvium and the water in the upper phreatic aquifer of the bedrock penetrate each other to form a concentrated danger zone, and the expansion track of the mining water-flowing fracture connects the hydraulic connection between the upper concentrated danger zone of overburden and the panel of No. 2’s first coal seam. A large amount of water mixed with sandstone flows into the fracture surface of the bedrock’s broken rock block through the water-flowing fracture, leading to the instability of the load-bearing structure composed of the thick alluvium caving arch and the towering roof beam, which illustrates the whole process of water–sand inrush accidents in thin bedrock stope with deep thick alluvium.

Influence of Mining Parameters on the Distribution Law of Separation Layer and Water-Flowing Fracture in Mining Overburden

The internal overburden movement after coal mining may cause many disasters to the on-site production. It is of great guiding significance for the engineering treatment such as separation layer grouting and gas extraction to master the evolution law of separation layer and fracture in the overburden. Combined with the full-columnar overburden of a certain working face, this study established a number of models using 3DEC simulation software and analyzed the influence of different mining heights and widths on the distribution law of separation layer and fracture after strata movement. The simulation results show that the evolution of separation layer in the overburden after mining roughly consists of three stages, namely, initial generation, reaching peak, and tending to close (stable). The development of the separation layer is positively correlated with the mining height and negatively correlated with the mining width. When the mining height increases from 3 m to 5 m, the peak value of cumulative separation increases from 0.7 m to 2.1 m. On the contrary, when the mining width increases from 250 m to 350 m, the peak value of cumulative separation decreases from 2.8 m to 1.1 m. The pre-bearing stress concentration will be formed in the mining process of the working face. The influence of mining width change on the peak of stress concentration is greater than that of mining height change, and the subsidence is mainly affected by mining height. A quantitative analysis method of water-flowing fracture development height was developed by using the penetration height of joint shear displacement. The calculated fracture zone height 117.33 m was in good agreement with the actual measured results 120 m, verifying the validity of this method. These findings are of great reference for mastering the distribution law of separation layer and fracture in the mining overburden.

Study on mechanism of effect of flowing water and transferring heat on rock mass temperature in curved fracture

Domestically and internationally, the effect of fracture flowing water and transferring heat on the temperature field of surrounding rock in high-level radioactive waste repositories is a popular research area. Compared with straight fracture flowing water and transferring heat, there are few relevant literatures about the heat transfer of curved fracture water flow. Based on the conceptive model of flowing water and transferring heat in curved fractured rock mass, the influence of flowing water and transferring heat in “I”, “L”, , and shaped fractures on the temperature field of rock mass is calculated by using discrete element program. The findings indicate that: When the model goes into a stable state under four working conditions, the rock on the x = 0–2 m mostly forms a heat transfer path from left to right; the x = 2–4 m primarily forms a heat transfer path from bottom to top, and the temperature gradient reveals that the isotherm of 40–45 °C is highly similar to the shape of four different fractures, indicating that flowing water and transferring heat in the fracture configuration dominate the temperature field of the right side rock mass. The direction of the flowing water and transferring heat of the fracture exerts a dominant effect on the temperature of the rock mass than the length.

Study on Calculation Method of Heat Exchange Capacity and Thermal Properties of Buried Pipes in the Fractured Rock Mass-Taking a Project in Carbonate Rock Area as an Example

Fractures are developed in carbonate rock areas, and the fracture water flow significantly influences the heat exchange between buried pipes and the rock mass by induing heat convection, providing the carbonate rock area a strong heat exchange capacity and preferable conditions for shallow geothermal development and utilization. In this paper, the calculation method of heat exchange capacity of buried pipes based on fracture distribution characteristics is proposed and deduced, featuring such advantages as quick speed and low cost. Taking an actual project in carbonate rock area as an example, the heat exchange capacity of buried pipes was obtained by the following two methods: in-situ thermal response test and calculation based on fracture distribution characteristics. In the thermal response test, the initial ground temperatures of the two test holes were 15.18 °C and 12.72 °C. By fitting the linear equation of time and average temperature with a linear thermal source model, the heat exchange capacities were 57.21 W/m and 58.22 W/m, the thermal conductivities were 3.56 W/(m·K) and 2.32 W/(m·K), the thermal diffusivities were 1.71 × 10−6 m2/s and 1.12 × 10−6 m2/s, and the volume specific heat capacity was 2.08 × 106 J (m3·K). The test results indicated that the thermal property parameters of rock and soil mass were higher than those of other areas, with obvious wide-range distribution characteristics. Through the statistical analysis of outcrop fracture characteristics, combined with the cube law to calculate the fracture water flow and convective heat transfer, an alternative method for the calculation and optimization of buried pipe heat transfer in fractured rock mass area is also proposed in this paper. According to the measured fracture distribution characteristics of the field outcrop, the heat exchange capacities of the two holes were 57.26 W/m and 58.56 W/m, which were basically consistent with the thermal response test values and verified the reliability of the calculation method of heat exchange capacity of buried pipes based on fracture distribution characteristics.

Research on the Application of Fracture Water to Mitigate the Thermal Imbalance of a Rock Mass Associated with the Operation of Ground-Coupled Heat Pumps

Shallow geothermal energy is a clean and effective form of energy that can overcome the problems associated with the depletion of carbon-based energy carbon emissions. Due to the special hydrogeological conditions in karst regions, the heat transfer between heat exchange boreholes and the ground formation is a complicated, multi-physical process. The abundant groundwater flow plays an important role in the heat transfer process, and even presents an opportunity to mitigate the heat imbalance during the long term operation of ground-coupled heat pumps (GCHP). In this study, both laboratorial experiments and numerical simulations were performed to analyze the mechanism that shows how fracture water impacts on heat capacity and the thermal imbalance of the energy storage rock mass. The results showed that the overall temperature fluctuation of the rock mass was reduced by the fracture water, and the temperature curve with time became gentler, which means in practice that the heat imbalance in the rock mass could be delayed. However, the temperature contour map showed that the impact of the fracture water flow was constrained in the nearby areas and decreased obviously with distance. The temperature field was also dragged along the direction of the fracture water flow. During the shutdown period, the fracture water significantly enhanced the thermal recovery ability of the rock mass. The results will assist in further understanding the mechanism of heat transfer and energy balance in a rock mass with fracture water flow. It is proposed that the U pipes should be located at zones with abundant fracture water if the construction condition permits. U pipes that are near the fractures should share more of the load or a denser layout could be possible as their heat transfer capacity is improved by the water flow.

Evaluation of Groundwater Flow Changes Associated with Drainage within Multilayer Aquifers in a Semiarid Area

In order to evaluate the impact of groundwater drainage on groundwater flow, the Hetaoyu coal field was taken as a case study in the Longdong area, China, where the coal seam was covered with multilayer aquifers. A three-dimensional unsteady groundwater flow model and a one-dimensional fracture water flow model were calculated by joint equations for changing hydrogeological structures under coal mining. According to the results, mine construction had greatly affected groundwater reserves in the Quaternary phreatic aquifer, Cretaceous Huanhe confined aquifer, and Luohe confined aquifer. The groundwater drainage was mainly from the Cretaceous aquifer, in which the aquifer reserves of the Luohe Formation decreased by 30,861.8 m3/m, accounting for about 92% of the total changes in local groundwater reserves. A drop funnel with an area of about 2.3 km2 would be formed under the groundwater discharge of 187.6 m3/h for the main inclined shaft excavation of the Hetaoyu coal mine. With the continuation of mining activities, the mine water flow will reach 806.83 m3/h and would result in descending funnel area of about 4.5 km2, the groundwater level drawdown at least 16 m, which would exceed the limited value regulated by the government. Therefore, in order to ensure the safety of coal mining and protect groundwater resources, the Hetaoyu Coal Mine departments should take some water loss prevention and control projects to reduce the drawdown of groundwater.

Plant water stress monitoring and control system

Precision irrigation is an important component of the water-saving approaches in agriculture and is one of the methods for increasing water-saving efficiency. Detecting water stress in crops accurately is the basis of precision irrigation techniques. In this study, the crop water stress monitoring system was developed to detect the acoustic emission (AE) of plants, associating the three factors of soil, crops, and weather in real-time. The automatic monitoring system, which was developed using the virtual instrument platform, not only affects the water stress and the drought of the atmosphere but can also be used to control the greenhouse environment automatically. The substance subjected to testing was a potted tomato plant (Lycopersicon esculentum). Environmental parameters are monitored in this system using a virtual instrument data acquisition system based on Peripheral Component Interconnect - Data acquisition (PCI-DAQ). The AE sensor was used to fix tomato stems at 1/3 and 2/3 of their overall height in order to detect AE information, which serves as an indirect indicator of the plant's water condition. This system, which could test and record water requirement information for the crops, has been demonstrated to be stable, nondestructive, and easily manipulable. The results showed that the cohesion between water molecules was weak under water stress conditions. The water flow fracture of the conduits resulted in cavitation by rapidly expanding gas bubbles. The cavitation event caused a rapid relaxation of the liquid tension that produced an AE of energy. It was found that crop hydraulic structure and anti-drought indicators were correlated with AE, which resulted from crop adaptation to the environment. The counts of AE change regularly, according to the variation of the environment's temperature, humidity, carbon dioxide consistency, and transpiration. Based on the relationship between AE and crop water stress conditions, the mathematical model of precision irrigation was obtained. As producing AE is a complex biological process, the future work is to build the different crops' information models in different growth periods. The data acquisition based on the AE information should be researched further.

Physical Modeling of the Controlled Water-Flowing Fracture Development during Short-Wall Block Backfill Mining

Abstract Short-wall block backfill mining (SBBM) technology is an effective method to solve the environmental problems in the mining process. Based on the technical characteristics of SBBM technology and the physical similarity criterion, the physical similarity models for comparing the control effects of water-flowing fracture (WFF) development using short-wall block cave mining (SBCM) and SBBM were established, and the deformation and the WFF development of overlying strata above gob were monitored. The test results determined that the composite materials of 5 mm thick pearl sponge+5 mm thick sponge+10 mm thick paper+6 mm thick board were adopted as the similar backfill materials by comparing the stress-strain curves between the similar backfill materials and the original gangue sample. When the backfilling body was filled into the gob, it would be the permanent bearing body, which bore the load of the overlying strata accompanied with the protective coal pillar. At the same time, the backfilling body also filled the collapse space of overlying strata, which was equivalent to reduce the mining height, and effectively reduced the subsidence and failure height of the overlying strata. Compared with SBCM, the test results showed that the maximum vertical deformation, the height of water-flowing fractured zone, and activity range of overlying strata using SBBM were reduced by 91.4%, 82.5%, and 64.9%, respectively. SBBM had a significant control effect on strata damage and WFF development, which could realize the purpose of water resource protection in coal mines.

Determining the Height of Water-Flowing Fractured Zone in Bedrock-Soil Layer in a Jurassic Coalfield in Northern Shaanxi, China

The height of the water-flowing fractured zone is the most important technical parameter for water prevention and control in a coal mine. Due to the numerous factors affecting the water-flowing fractured zone, it is difficult to accurately identify the zone. Currently, no effective way exists for determination of the water-flowing fractured zone in a soil layer. To accurately determine the development law of the water-flowing fractured zone in the bedrock-soil layer of a Jurassic coalfield in northern Shaanxi, China, we conducted a comprehensive study using microresistivity scanning imaging technology, apparent density logging, long-range gamma logging, observation on drilling flushing fluid consumption, physical simulation, and numerical simulation. The following results were obtained: (1) The ratio of the height of the water-flowing fractured zone to the mining height was 28.3–28.5, which was obtained by microresistivity scanning imaging technology, whereas the ratio of the height of the water-flowing fractured zone to the mining height was 28.1–29.1, determined by apparent density logging, long-range gamma logging, physical simulation, and numerical simulation. The microresistivity scanning imaging results were consistent with those obtained by other methods. (2) Based on the thickness of the soil layer and the bedrock, the height model of the water-flowing fracture zone was divided into four regions, that is, the thick bedrock-thick soil layer region, thick bedrock-thin soil layer region, thin bedrock-thin soil layer region, and thin bedrock-thick soil layer region. A mathematical model describing the difference between the thickness of the water-flowing fractured zone and the bedrock and the thickness of the soil under the condition of bedrock-soil was established. (3) We conclude that microresistivity scanning imaging technology can accurately detect the height of the water-flowing fractured zone in a soil layer, and the apparent density logging and long-range gamma logging can precisely detect the height of the water-flowing fractured zone in bedrock. This is a new comprehensive method for research on the height of the water-flowing fractured zone that can provide a reliable basis for water prevention and control in mines.

Control of Water-Flowing Fracture Development with Solid Backfill Mining: Designing a Backfill Body Compression Ratio for Water Resources Protection

Control of Water-Flowing Fracture Development with Solid Backfill Mining: Designing a Backfill Body Compression Ratio for Water Resources Protection

Impacts of hydrogeological characters of fractured rock on thermodynamic performance of ground-coupled heat pump.

Ground-coupled heat pump (GCHP) is used to recovery shallow geothermal energy, a widely distributed green energy source. Due to the imbalance between heat rejection and extraction, heat buildup underground is commonly associated with the long-term operation of GCHPs, which undermine system performance. Heat buildup intrinsically results the irreversibilities (entropy production) in subsurface heat sink, in which thermodynamic and transport properties are largely influenced by hydrogeologic properties, especially the existence of fractures and groundwater. This study investigates the influence of water flow in fractures on the thermodynamic performance of a single borehole heat exchanger (BHX) and heat buildup in the underground heat exchange zone (UHXZ). Potential influence factors were screened out, and new terms were proposed to quantify the scale of fractures and available heat and cold in the heat sink. Governing equations were established to calculate the impacts of vertical and horizontal fractures on the heat exchange rate in BHX as well as on the heat flow across the UHXZ. The analysis results show that water flow in fractures can significantly enhance heat transfer, reduce required number of boreholes, mitigate heat buildup and reduce irreversibilities underground. The results also suggest that the role of fracture scales and water velocity in GCHP operation should be carefully evaluated. Therefore, detailed hydrogeological survey is necessary. The study results provide a guide on more accurately evaluating the risk of heat buildup and how to take advantage of hydrogeological characters to improve the performance of GCHPs.

Study on the Development Height of Overburden Water-Flowing Fracture Zone of the Working Face

Mining-induced fractures in underground coal mining face affect the stability of overburdens and provide preferential channels for water and material transfer in the underground environment. Therefore, to study the development of water-flowing fracture zones in overburdens of working face and goaf is of great significance for roof control, gas drainage, water resistance, disaster reduction, and efficient mining from the mining. In this study, a new method for predicting the development of overburden water-flowing fracture zone height (DHOWFFZ) was proposed based on the characteristics of overburden rock in No. 3 coal seam of Xin’an Coal Mine. First, the stope of No. 3 coal seam exhibits a rock stratum structure of mudstone and sandstone overlapping. Considering this characteristic, the overburden strata of No. 3 coal seam are divided into several “mudstone-sandstone” rock stratum groups. Furthermore, the ultimate tensile deformation of soft rock is greater than that of hard rock. It is proposed to judge the development degree of penetrating fracture in each rock stratum by adopting the elongation rate of mudstone intermediate layer. Meanwhile, the DHOWFFZ of “mudstone sandstone” composite rock stratum structure in the 3402 working face of No. 3 coal seam is calculated to be smaller than 43.1 m according to the actual situation. Finally, the DHOWFFZ in the 3402 working face was measured in the field, which verifies the rationality of the new DHOWFFZ prediction method. The research results provide new ideas for the prediction of DHOWFFZ and are helpful for future research in related fields.

Analysis on the main controlling factors of water-flowing fracture evolution in deep-buried and thick bedrock

The study on the evolution and development law of mining disturbed overlying rock fissures is the basic theory for mine water prevention and gas drainage. In order to reveal the evolution law of water conducting cracks in bedrock after deep burial, through the in-situ measurement of mining cracks in overlying strata in Huanglong mining area, the structural characteristics of overlying strata are calculated and analyzed by using key layer theory. It is found that the development height and shape of mining fissures are controlled by 8 direct influencing factors such as mining thickness and 10 indirect influencing factors such as subsidence space, in which mining size and roof overburden structure are the main control indexes. The development pattern of mining fracture is “trapezoid”. For the structural characteristics of roof overlying strata, this paper puts forward the ratio of soft rock proportion coefficient and permeability coefficient in the key layer load layer based on the key layer theory, which plays an important role in the actual development height of mining fissures and the incidence of water inrush.

Estimate of change in specific cohesion between fracture surfaces by back-calculation: A case study of open pit mine Zhelezny of Kovdor Mining and Processing Plant

This article presents the back-calculation data on bench deformations in open pit mine Zhelezny of Kovdor Mining and Processing Plant. The calculations are performed for 105 rock falls divided into six groups with respect to volume (m3): 0–200 is group 1; >200–500 is group 2; >500–1000 is group 3; >1000–5000 is group 4; >5000–10000 is group 5; >10000 is group 6. The computational method was the single-factor analysis of change in specific cohesion between the surfaces of deformation-limiting fractures. The internal friction angle is assumed to be constant as it is the least of all changeable and is correlatable with laboratory test data. Actual rock falls were simulated in GIS GEOMIX. The simulation correctness was ensured by the high-accuracy referencing and orientation measurements of fractures using 3D models constructed based on laser scanning and drone photography. For all sampled rocks, it is found that specific cohesion between fracture surfaces grows with increasing volume of rock falls. Specific cohesion in case of small volume rock falls (0–200 м3) in all types of rocks, except for olivinite, is approximately the same and ranges as 0.0021–0.011 MPa; for olivinite, this value is higher by 20 % at least. Higher rate slipping along fractures is typical of fenite (almost in all groups, specific cohesion is lower by 10–90 % than in other rock types), which is governed by supergene mineralization of fenites and by down water flow in fractures. The low and approximately equal values of specific cohesion (0.0058–0.0094 MPa) are observed in group 0–200 m3, which is conditioned by the action of blasting on deformation of benches. The study is carried out under State Contract No. 075-03-2020-474/1 от 05.03.2020.

Height prediction of water-flowing fracture zone with a genetic-algorithm support-vector-machine method

Prediction of the height of a water-flowing fracture zone (WFFZ) is the foundation for evaluating water bursting conditions on roof coal. By taking the Binchang mining area as the study area and conducting an in-depth study of the influence of coal seam thickness, burial depth, working face length, and roof category on the height of a WFFZ, we proposed that the proportion of hard rock in different roof ranges should be used to characterise the influence of roof category on WFFZ height. Based on data of WFFZ height and its influence index obtained from field observations, a prediction model is established for WFFZ height using a combination of a genetic algorithm and a support-vector machine. The reliability and superiority of the prediction model were verified by a comparative study and an engineering application. The results show that the main factors affecting WFFZ height in the study area are coal seam thickness, burial depth, working face length, and roof category. Compared with multiple-linear-regression and back-propagation neural-network approaches, the height-prediction model of the WFFZ based on a genetic-algorithm support-vector-machine method has higher training and prediction accuracy and is more suitable for WFFZ prediction in the mining area.