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In order to solve the problems such as small influence range, fast decay rate, difficulty in gas disaster control and long treatment period of gas extraction drilling in Hebi Mining Area, a technological process of coordinated stamping operation was put forward, and the technical mode of drilling and stamping coordinated operation with automatic drilling rig group drilling - temporary sealing hole pre-pumping - stamping joint operation after pre-pumping is formed, and industrial test is carried out in Hebi No.6 Coal Mine for industrial trials, the field application results show that: the technology mode gives full play to the advantages of automatic drilling rig continuous drilling, fast operation, reducing staff and improving efficiency, realizes the specialization, continuity and scale of gas extraction drilling construction operation and hydraulic stamping coordinated penetration operation, and makes the construction work efficiency of construction of penetration drilling in the bottom rock tunnel for gas treatment increase by 48% under the same geological conditions; meanwhile, the at the same time, after the construction of extraction holes by automatic drilling rig is completed, the temporary sealing of the extraction holes is carried out, so that the free gas in the holes is greatly reduced after extraction, which greatly reduces the frequency of gas overrunning accidents in the roadway during the construction of hydraulic measures and effectively guarantees the safety of construction; the average gas extraction concentration of the test borehole is 1.31 times of that of the conventional hydraulic ramming measure, and the average daily pure extraction volume of the test unit borehole is 1.79 times of that of the conventional hydraulic ramming measure.

In order to explore the influence of environmental media on the characteristics of water jet coal breaking, ALE algorithm and LS-Dyna software are used to carry out numerical simulation of continuous water jet impact coal breaking and the characteristics of water jet propagation, coal breaking characteristics and time-varying characteristics of the relationship between the two coal breaking depths under the submerged and non-submerged environments are analyzed. The results show that because of the large loss of water jet, the jet velocity in submerged environment is much lower than that in non-submerged state. Under the obstruction of environmental medium, the submerged jet diverges and increases the area of broken coal, resulting in the increase of the area of broken coal and the decrease of the depth, but the damage element does not change much. It is necessary to prolong the impact time reasonably or reduce the spacing of boreholes when coal caving is carried out in submerged environment.

To enhance gas drainage in the soft and hard interbedded (SHI) coal seam, it’s necessary to unload the in-situ stress and improve its gas migration performance. In this research, a directional hydraulic flushing (DHF) technology was carried out. The stress-unloading and gas migration improvement mechanism was analyzed through numerical simulation, and systematic engineering tests were conducted to verify the gas drainage effect. The results show that the improvement of gas migration performance in the SHI coal seam is caused by a combined effect of seepage-improving and diffusion-improving. After DHF, stress-unloading and plastic failure could be achieved both in the soft coal (SC) sublayer and in the hard coal (HC) sublayer. However, the gas diffusion capacity improves significantly in the SC sublayer, while the gas seepage capacity improves notably in the HC sublayer. Meanwhile, the stress-unloading and gas migration improvement effect improves with the flushing radius and the thickness of the SC sublayer. Besides, after adopting the DHF technology, the gas drainage effect improved markedly. The borehole number dropped by 49%, the gas drainage ratio increased from 26.0% to 48.2%, and the average coal roadway excavation speed increased from 2.4 to 5.6 m/d.

This article provides a comprehensive review and best practices for numerically simulating hydraulic flushing for reservoir sediment management. Three sediment flushing types are discussed: drawdown flushing, pressure flushing, and turbidity current venting. The need for reservoir sediment management and the current practices are reviewed. Different hydraulic drawdown types are described in terms of the basic physical processes involved as well as the empirical/analytical assessment tools that may be used. The primary focus has been on the numerical modeling of various hydraulic flushing options. Three model categories are reviewed: one-dimensional (1D), two-dimensional (2D) depth-averaged or layer-averaged, and three-dimensional (3D) computational fluid dynamics (CFD) models. General guidelines are provided on how to select a proper model given the characteristics of the reservoir and the flushing method, as well as specific guidelines for modeling. Case studies are also presented to illustrate the guidelines. [ABSTRACT FROM AUTHOR]

At present, in drilling design and evaluation, the shape of hydraulic flushing hole is usually equivalent to cylinder, which is one of the important bases to determine the effective extraction radius. However, the shape of hole is subject to the joint action of many factors, so the scientific nature of the equivalent shape to cylinder remains to be discussed. By adopting the factors of gravity, friction, water force and in-situ stress of coal and rock mass, and introducing the parallel Bergmark-Roos equation and PKN model, the BR-PKN equation describing the pore shape is established, and the pore shape is reconstructed by MATLAB. In order to verify its accuracy, data are collected and analyzed by using YZD18.5 logging tool in the field, and the hole section is drawn. The equivalent ellipsoidal and cylindrical holes are simulated by COMSOL. The results show that the shape of the holes drawn by MATLAB is ellipsoid with different three axes. The shape of the drawn hole is basically consistent with that in MATLAB. Compared with cylindrical holes, the extraction radius, desorption surface area and effective extraction volume of quasi-ellipsoid holes are 93%, 80% and 117% respectively, which provides a basis for drilling layout.

To realize the precise stress relief and permeability enhancement of the coal seam with non-uniformly distributed gas, the criterion and optimization method of key construction parameters of hydraulic flushing was studied by modeling, numerical simulation and field tests. First, the multiphysics coupling model for stress-relieved coal seam was developed and index of optimal coal discharged was analyzed. Then the criterion and determination method of optimal coal discharged was put forward. Finally, the determination map of key construction parameters of hydraulic flushing was drawn, and a precise permeability enhancement technique for coal seam with non-uniformly distributed gas was proposed. The main conclusions are shown as follows: ① for a given gas extraction time, the residual gas content decreases while the residual gas pressure reduces followed by an increase with a rise of coal discharged; ② the criterion of optimal coal discharged includes the constraints of gas extraction reaching standard and minimization of roadway instability risk and construction cost. When the residual gas content and pressure are less than the critical values, it is considered that the gas extraction reaches the standard. On the premise of meeting the standard of extraction, the coal discharged should be reduced as far as possible to ensure the stability of coal roadway and reduce the project cost; ③ The optimal coal discharged decreases with the increase of ground stress, and increases with the increase of cohesion, gas pressure and borehole spacing. For a given coal seam, there is a maximum value of coal discharged and a minimum value of extraction time reaching standard; ④ comprehensively considering the correlation between coal seam gas pressure, coal yield, borehole spacing and extraction time reaching standard, the optimization map of key parameters of hydraulic flushing is drawn. Based on the map, a precise pressure relief and permeability enhancement technology for coal seams with non-uniformly distributed gas is put forward. In this technique, the construction parameters of hydraulic flushing corresponding to various gas occurrence areas can be determined, with the combination of gas occurrence and optimization map of key parameters, realizing the precise permeability enhancement of the coal seams with non-uniformly distributed gas.

Reservoirs are a crucial part of the human water supply system. The effectiveness and service life of a reservoir is decided mainly by its storage capacity, and as such, preventing reservoir capacity loss is of high interest worldwide. Due to climate change in recent years, precipitation types have changed, and heavy rainfall events have become more severe and frequent. Rainfall causes soil erosion in slope lands and transports large amounts of sediment downstream, forming deposition. This causes reservoir storage capacity to fall rapidly and decreases reservoir service life. The Sediment–Sluice Tunnel can reduce rapid deposition in reservoirs and is, thus, widely employed. By simulating sediment transportation in reservoirs, deposition reduction after building the Sediment–Sluice Tunnel can be evaluated. This study used the Physiographic Soil Erosion–Deposition (PSED) model to simulate the flow discharge and suspended sediment discharge flowing into the Zengwen reservoir then used the depth-averaged two-dimensional bed evolution model to simulate the sediment transportation and deposition in a hydrological process. Simulation results showed that the Sediment–Sluice Tunnel effectively reduced deposition and transported sediment closer to the spillway and Sediment–Sluice Tunnel gate. The deposition distribution with the Sediment–Sluice Tunnel built is more beneficial to the deployment of other dredging works. [ABSTRACT FROM AUTHOR]

This article provides a comprehensive review and best practices for numerically simulating hydraulic flushing for reservoir sediment management. Three sediment flushing types are discussed: drawdown flushing, pressure flushing, and turbidity current venting. The need for reservoir sediment management and the current practices are reviewed. Different hydraulic drawdown types are described in terms of the basic physical processes involved as well as the empirical/analytical assessment tools that may be used. The primary focus has been on the numerical modeling of various hydraulic flushing options. Three model categories are reviewed: one-dimensional (1D), two-dimensional (2D) depth-averaged or layer-averaged, and three-dimensional (3D) computational fluid dynamics (CFD) models. General guidelines are provided on how to select a proper model given the characteristics of the reservoir and the flushing method, as well as specific guidelines for modeling. Case studies are also presented to illustrate the guidelines.

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.)

To enhance the safety of coal mining operations and improve the efficiency of gas extraction, hydraulic flushing technology has been widely used in low permeability coal seams. This study aims to investigate the mechanism of hydraulic flushing by conducting experiments focusing on four aspects: sample strength, punching pressure, punching position and vibration direction. The results show that an increase in hydraulic flushing pressure leads to a deeper impact groove, whereas higher sample strength results in a shallower groove. Additionally, the amplitude of stress wave is positively correlated with the density of the sample, with low-strength samples exhibiting extensive stress wave propagation and minimal attenuation. The stress wave vibration is multi-directional, which can maximize the instability and destruction of the internal structure of the coal body. To validate the practical efficacy of hydraulic flushing, a field test was conducted at the Yuwu Coal Mine in Changzhi City, Shanxi Province. The field trial shows that the effective influence radius of hydraulic flushing can reach 4 m, with a significantly lower gas flow attenuation coefficient compared to ordinary borehole. Notably, the permeability of coal seam in hydraulic flushing area is close to twice that of ordinary drilling area., Competing Interests: Declarations. Competing interests: The authors declare no competing interests., (© 2025. The Author(s).)

Copyright of Journal of Mine Automation is the property of Industry & Mine Automation Editorial Department 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 solve the problem of the high risk of coal and gas outburst in deep coal working face, taking 12090 working face of Shoushan No.1 Coal Mine as the engineering background, the paper analyzes the deformation and stress variation law of coal body after hydraulic flushing in coal working face under deep-buried and high-stress environment by numerical simulation method. The conclusions are listed as follows. The coal body around the hydraulic flushing hole deforms towards the hole, which is conducive to the development and conduction of cracks in the coal body, thus improving the permeability of the coal body. The horizontal stress of the coal body in the flushing area is effectively reduced. The pressure relief areas formed by each punching hole are interconnected to form a pressure relief strip, which is conducive to gas migration and extraction. According to the numerical simulation results and the actual project, the hydraulic flushing project scheme of 12090 working face in Shoushan No. 1 Coal Mine is determined. The upper side drilling angle is 5-6°, and the lower side drilling angle is −5-−4°. The drilling spacing is 4 m, and the length of each punching hole is 1 m. The spacing of flushing holes in each borehole is 7 m, and no flushing operation is carried out within 30 m from the roadway side. The flushing water pressure is 5-6 MPa, and the flow rate is 120-160 L/min. The practice shows that after adopting this scheme, the number of holes completed per month reaches 40 and the completion rate reaches 80%. The gas extraction concentration in the flushing hole is high and the gas attenuation is slow. After 50 days of extraction, the gas volume fraction in the flushing hole is 40%-60%, which is 2-3 times of that in the ordinary hole. After 120 days of extraction, the gas volume fraction in the flushing hole is still 20%. Hydraulic flushing effectively improves the gas extraction effect and reduces the gas content in coal seams. The average gas volume fraction of return air flow decreases to below 0.5%. The average daily footage of the working face increases from 2.4 m to 3.2 m, which improves productivity.

In coal mine gas extraction in China, the current hydraulic permeability enhancement measures generally have complex processes, low adaptability, long operation time, and high labor intensity. This makes it challenging to meet the requirements of coal mining enterprises for safe and efficient mining, and there is an urgent need to develop new technologies to enhance gas extraction and production. This paper proposed an integrated drilling and stamping technology to enhance gas extraction and production and integrates drilling, hydraulic jet fracturing, and hydraulic punching to enhance the permeability of coal seams. A field test was conducted using the specially-developed integrated drilling and stamping equipment to extract gas from the 16101 bottom pumping lane penetration hole in the Jiulishan Mine, Jiaozuo, Henan. The test results show that compared with the hydraulic punching technology previously used in the mine, the punching time of the soft coal seam was shortened by 66–75%, the coal output was increased by 1.7 times, and the punching hole aperture was increased by 1.3 times. Hydraulic injection fracturing was successfully performed to increase the permeability of the hard coal seams, and the fracturing formed a shot hole depth of 345–539 mm. After the integrated drilling and stamping of the drill holes, the coal output, gas extraction concentration, pure gas extraction volume, and coal seam permeability coefficient increased by 2.4, 2.2, 4, and 37.3 times, respectively. The gas flow decay coefficient of the drills holes was also further reduced, which significantly improved the extractionefficiency. Thus the integrated drilling and stamping technology can transform the process of gas extraction from regular extraction to quick, economic, pure, and clean extraction. Thus, this technology has large applicable value for underground gas management in coal mines. [ABSTRACT FROM AUTHOR]

Structural coal has low permeability and high gas content. The increase of mining depth seriously restricts the safe mining of deep mines. Hydraulic flushing is the main means of gas extraction. The shape of the hydraulic flushing hole is an important basis to determine the pumping radius, which is widely regarded as a cylinder. However, due to the differences in the stress level, water force, friction and external moisture, the pore morphology, and permeability evolution need to be further studied. At present, the hole shape for hydraulic punching is equivalent to a cylinder in drilling design and evaluation, which is one of the important bases to determine the effective extraction radius. However, the hole shape is affected by many factors, so the scientific equivalent to a cylinder remains to be discussed. The BR-PKN equation describing the hole shape is established by introducing and combining the Bergmark–Roos equation and PKN model, and the hole’s shape is shown by MATLAB. To verify its accuracy, YZD18.5 is used as an onsite logging tool for data acquisition and analysis, and the hole section is drawn. The BR-PKN equation and permeability evolution model are simulated by COMSOL Multiphysics, and the permeability evolution law of conventional cylinder with hydraulic flushing is compared and analyzed. The results show that 1) the shape of the hydraulic punch hole is ellipsoid with three different axes, and its horizontal section is approximately an ellipse; 2) within the influence range of quasi-ellipsoid holes, the permeability changes in the long and short axis of quasi-ellipsoid holes are similar. The permeability evolution curve of the coal first increases, then decreases, and finally, flattens with the increase of distance from borehole, and the permeability of the coal body increases with the extension of extraction time); 3) the permeability of the equivalent ellipsoid pore decreases with the increase in coal water content. The effective radius in the long and short axes of the minimum cross section of the quasi-ellipsoid hole is 0.89 and 0.95 times the effective extraction radius of the equivalent cylinder, which provides a basis for a drilling layout.

Accurate prediction of reservoir sediment inflows (Min) and adaptation of feasible sediment management strategies pose challenges in water engineering. This study proposed a two-stage complementary modeling approach for comprehensive reservoir sediment management. In the first stage, artificial neural network-based models provide real-time Min predictions using water inflow, water head, and outflow as input parameters. In the second stage, the parameter estimation method of the RESCON model is applied to hydraulic flushing in a reservoir. This approach was applied to the Sangju Weir and Nakdong River Estuary Barrage (NREB) in South Korea. Results from the RESCON model revealed that hydraulic flushing was effective for sediment management at both the Sangju Weir reservoir and the NREB approach channel. Efficient flushing at the Sangju Weir required a flushing discharge of 100 m3/s for 6 days and 40 m of water head. Efficient flushing at the NREB required a flushing discharge of 25 m3/s for 6 days with 1.8 m of water-level drawdown. The proposed approach is expected to prove useful in reservoir sediment management. [ABSTRACT FROM AUTHOR]

Abstract In China, one or several ultrathin soft coal sublayers are widely developed in the coal seam. Therefore, a method of using hydraulic flushing in soft sublayer to enhance the gas extraction in these particular coal seams is developed in this work. We first established a new fully coupled gas extraction model by combing gas diffusion, gas flow, and a permeability model that considers the effect of stress change and plastic failure. By adopting this model, the gas extraction enhancement mechanism and its main influence factors were studied using the numerical simulation method based on the engineering and geological background in the Yangquan No.5 coalmine. Thereafter, a hydraulic flushing equipment, which could move freely in the underground coalmine, was developed to apply the hydraulic flushing method in soft coal sublayers used in the 8402 working face. Its gas extraction effect was systematically investigated. Our simulation results match well with the field results, suggesting that our model is feasible. Meanwhile, after adopting this method, the gas extraction condition in this coalmine improves significantly. The borehole number decreases by 66.7%, while the gas extraction rate and gas extraction concentration increase by 1.33 times and 3 times, respectively. Moreover, during the coal mining process, the gas adsorption index of drilling cuttings, the quantity of drilling cuttings, and the CH4 concentration also decrease dramatically.

In China, one or several ultrathin soft coal sublayers are widely developed in the coal seam. Therefore, a method of using hydraulic flushing in soft sublayer to enhance the gas extraction in these particular coal seams is developed in this work. We first established a new fully coupled gas extraction model by combing gas diffusion, gas flow, and a permeability model that considers the effect of stress change and plastic failure. By adopting this model, the gas extraction enhancement mechanism and its main influence factors were studied using the numerical simulation method based on the engineering and geological background in the Yangquan No.5 coalmine. Thereafter, a hydraulic flushing equipment, which could move freely in the underground coalmine, was developed to apply the hydraulic flushing method in soft coal sublayers used in the 8402 working face. Its gas extraction effect was systematically investigated. Our simulation results match well with the field results, suggesting that our model is feasible. Meanwhile, after adopting this method, the gas extraction condition in this coalmine improves significantly. The borehole number decreases by 66.7%, while the gas extraction rate and gas extraction concentration increase by 1.33 times and 3 times, respectively. Moreover, during the coal mining process, the gas adsorption index of drilling cuttings, the quantity of drilling cuttings, and the CH4 concentration also decrease dramatically. [ABSTRACT FROM AUTHOR]

Hydraulic flushing technology can rapidly and effectively eliminate coal and gas outbursts and improve the permeability of a coal seam. Its effect mainly depends on the technical parameters of hydraulic flushing. To solve the problems on technical parameters that exist in the application of hydraulic flushing technology, the outburst elimination mechanism of hydraulic flushing technology was expatiated, the hydraulic flushing process was introduced, and a field test was performed on the B1 coal seam in Yi’an Coal Mine by using the pressure drop method. Moreover, the effective influence radius of hydraulic flushing measure was determined, and the technical parameters were analyzed. Finally, a series of relationships was obtained, including the relationships between hydraulic pressure and coal output, critical breaking coal pressure and firmness coefficient, flushing time and coal output, drilling hole angle and coal output, and coal output and effective influence radius. Results showed that the effective influence radius of hydraulic flushing in B1 coal seam was 9 m, and the outburst risk of the coal within the influence region was eliminated. In addition, the time of outburst elimination was shortened and the production rate was improved. The research results could provide technical support for the optimization of the technical parameters and the test scheme of hydraulic flushing measures.

Chinese coal mines often apply hydraulic flushing technology for pressure relief and permeability increase of difficult-to-extract coal seams In order to study effective detection methods for the impact range of hydraulic flushing on coal seams, we first experimentally investigated the response characteristics of the apparent resistivity of small-scale coal mass to hydraulic flushing, then theoretically analyzed the characteristics of its temporal variation and spatial distribution, and lastly measured the changes in apparent resistivity in the Hydraulic flushing process at Nuodong Coal Mine, Guizhou Province, China, and the effective range of Hydraulic flushing in the coal bed. The experimental results showed that the spatial distribution and variation of coal and rock mass structure could be reflected by apparent resistivity. Under high-pressure water, coal structure was changed (loosen, broken, or out-washed), forming cavities and a network of cracks in the surroundings of the drilling borehole, which reduced the conductivity of coal and caused a significant increase in apparent resistivity. In both laboratory and field experiments, the coal/rock apparent resistivity was relatively consistent, and the apparent resistivity in the hydraulic flushing impact region significantly grew. The hydraulic flushing impact range was gradually increasing, and the response of apparent resistance was closely associated with the role of high-pressure water and the evolution of the fracture field. [ABSTRACT FROM AUTHOR]

Hydraulic flushing has the advantages of reducing coal stress and improving coal seam permeability, so it is widely used in high gas outburst coal seams in China. However, the effect evaluation of stress relief and permeability enhancement will be necessary before coal mining. In this paper, an acoustic emission (AE) experiment system of coal seam hydraulic flushing was established, and the AE characteristics of coal during hydraulic flushing were studied. The results show that the changes in AE signals are basically consistent with those in load and water pressure. In addition, the quantitative relationship between the signals and the damage of coal around the borehole is revealed by the theory of damage mechanics. The in-situ AE test of hydraulic flushing was performed in the Liangbei Coal Mine, by measuring gas flow and coal stress simultaneously. The variation of AE activities and the effect evaluation of hydraulic flushing were analyzed. The results reveal that the changes in coal seam stress are basically consistent with those of AE signals. After the flushing has been completed for 1−3 h, the coal seam stress decreases rapidly, and the AE counts and intensity reach the peak. Therefore, this study proposes a new method for evaluating the effect of coal seam hydraulic flushing by AE, which has a very important practical significance.

To study the variation of the pressure relief scope and the stress around hydraulic flushing borehole, the theory of coalrock damage was utilized to distinguish the interaction area of water-jet and coal-rock into the coal-rock crushing area, the water-jet pressure stagnation area, the transition area and the original stress recovery area of coal-rock. Based on the actual occurrence conditions of the coal seam, the pressure variation and relief scope around the hydraulic flushing borehole were analyzed and simulated by RFPA2D-Flow software. The results showed that a relief area with the radius of 5.0 ~ 6.0 m around the borehole formed due to the hydraulic flushing with the pressure relief of 0.038 ~ 6.545 MPa, and the maximum principal stress is 15.85 MPa with a distance of 6.8 m from the inspected hole where stress concentration appeared. After hydraulic flushing test, the diameter (441.8 ~ 1171.6 mm) of the hole which can be an expression of coal crushing area size, was calculated based on the examination of the coal amount through the trial process, and it can be drawn that the pressure relief area must be larger than that of the coal-rock crushing area. Meanwhile, the measured pressures relief range(5.96 ~ 6.62 m) is basically consistent with the numerical simulation result (5.0 ~ 6.0 m) which verified the accuracy of the simulation analysis, according to the distance from the inspection drilling to the hydraulic flushing borehole and the decreased degree of the gas content in the inspection hole by the way of Gas Content.

Storage capacity of hydropower reservoirs is lost due to sediment deposition. The problem is severe in projects located on rivers with high sediment concentration during the flood season. Removing the sediment deposition hydraulically by drawdown flushing is one of the most effective methods for restoring the storage capacity. Effectiveness of the flushing depends on various factors, as most of them are site specific. Physical/mathematical models can be effectively used to simulate the flushing operation, and based on the results of the simulation, the layout design and operation schedule of such projects can be modified for better sediment management. This paper presents the drawdown flushing studies of the reservoir of a Himalayan River Hydroelectric Project called Kotlibhel in Uttarakhand, India. For the hydraulic model studies, a 1:100 scale geometrically similar model was constructed. Simulation studies in the model indicated that drawdown flushing for duration of 12 h with a discharge of 500 m/s or more is effective in removing the annual sediment deposition in the reservoir. The model studies show that the sedimentation problem of the reservoir can be effectively managed through hydraulic flushing. [ABSTRACT FROM AUTHOR]

Control of harmful algae in the coves or bays of larger water bodies could be accomplished by hydraulic flushing with algae-free water. This suggestion is examined with a mathematical model of a harmful algal population, parameterized to represent the toxic haptophyte Prymnesium parvum , and its limiting nutrient. A small cove with a hydraulic storage zone and longitudinal advection and dispersion is coupled to a larger lake where ongoing or transient blooms serve as a source for the algal population. This population is transported upstream by dispersion and flushed downstream by advection. Morphometry and hydraulics represent a lake in Texas where blooms of P. parvum have been problematic. When dispersion and hydraulic storage are low to moderate, available pumping technology is predicted to be capable of suppressing the algal population within a variable portion of the cove, under both steady state and transient conditions. This suppression occurs when temperature-dependent algal growth is low. At temperatures high enough to support more rapid growth, flow augmentation carries a risk of stimulating a bloom under some hydraulic conditions. The model presented here complements similar models without population sources, and contributes to theoretical understanding of population persistence in reservoirs and other flowing-water habitats. [ABSTRACT FROM AUTHOR]

By analyzing the stress characteristics around boreholes，the visco-elastic plastic model of coal around hydraulic flushing considering plastic softening and dilatancy was established，the pressure-relief and permeability improvement effect of hydraulic flushing and aperture variation were analyzed，thus the anti-blocking technology and the measures for gas drainage improvement were formulated. The results show that：① Hydraulic punching measures can greatly improve the coal permeability around boreholes，the more punching coal amount，the greater relief range of hydraulic flushing，the higher the permeability of coal is increased；② Shrinkage phenomenon of borehole occurs over time because of rheological properties，the greater the stress，the lower the coal strength，the more intense the creep deformation of coal，once drainage channels are blocked，gas extraction effect will be greatly reduced；③ Anti-blocking technology by installing casting pipe reserves a drainage channel，thus high concentrations gas can be extracted for a long time，the effect of gas drainage increase by 2.7 times；④ By gas injection combined with hydraulic flushing technique，the gas drainage amount of single hole increases by 8.1 times，which can effectively improve gas drainage effect. [ABSTRACT FROM AUTHOR]

Fouling is an inevitable phenomenon with most of the water treatment systems. Similar to RO, NF and other membrane-based systems, fouling also seriously affects the performance of low-cost forward-osmosis (FO) systems and disturbs the overall efficiency of these systems, and various cleaning practices have been evaluated to restore their designed performances. This study evaluates the performance of various physical and chemical cleaning techniques for hollow fibre forward-osmosis (HFFO) membrane. HFFO membrane was subjected to various fouling conditions using different brackish groundwater qualities and model organic foulants such as alginate, humic acid and bovine serum albumin. Results indicated that physical cleaning affects differently the flux restoration according to the type of foulants (i.e. inorganic or organic) and the crossflow rates play an important role in membrane cleaning in both membrane orientation. The higher cross flow Re values at any particular area seem important for the cleaning. With hydraulic flushing, the flux performances of HFFO were recovered fully when operated in AL-FS orientation, as high shear force helps to detach all scaling layers from the surface; however, the lower shear force did not fully restore the flux for the FS membrane in AL-DS orientation. Chemical cleaning was planned for the fouled HFFO membrane, and HCl and NaOH were used in various combination sequences. It was found that HCl did not clean the membrane used for AL-DS orientation for combined fouling. HCl cleaning (at pH 2) was found to be more effective for removing inorganic scale, whereas NaOH cleaning (at pH 11) for a similar period successfully restored the flux for all the membranes used for FS with inorganic and/or organic foulants. ethylenediamine tetra acetic acid (EDTA) was also evaluated for its cleaning performances and it was found that compared to NaOH, EDTA cleaning (1 mM concentration at pH 11) showed superior results in terms of membrane cleaning, as it helped to successfully restore the membrane flux in a very short time. [ABSTRACT FROM PUBLISHER]

To study the variation of the pressure relief scope and the stress around hydraulic flushing borehole, the theory of coalrock damage was utilized to distinguish the interaction area of water-jet and coal-rock into the coal-rock crushing area, the water-jet pressure stagnation area, the transition area and the original stress recovery area of coal-rock. Based on the actual occurrence conditions of the coal seam, the pressure variation and relief scope around the hydraulic flushing borehole were analyzed and simulated by RFPA2D-Flow software. The results showed that a relief area with the radius of 50 ~ 6.0 m around the borehole formed due to the hydraulic flushing with the pressure relief of 0.038 ~ 6.545 MPa, and the maximum principal stress is 15.85 MPa with a distance of 6.8 m from the inspected hole where stress concentration appeared. After hydraulic flushing test, the diameter (441.8 ~ 1171.6 mm) of the hole which can be an expression of coal crushing area size, was calculated based on the examination of the coal amount through the trial process, and it can be drawn that the pressure relief area must be larger than that of the coal-rock crushing area. Meanwhile, the measured pressures relief range(5.96 ~ 6.62 m) is basically consistent with the numerical simulation result (5.0 ~ 6.0 m) which verified the accuracy of the simulation analysis, according to the distance from the inspection drilling to the hydraulic flushing borehole and the decreased degree of the gas content in the inspection hole by the way of Gas Content. [ABSTRACT FROM AUTHOR]

Abstract: Methods based on flow measurement and pressure measurement were employed in this paper to determine pressure relief scope of gas drainage boreholes for coal and gas outburst prevention and control. In order to measure the extent of pressure relief, the principle to choose proper sites was set up based on general gas geology features. The data acquired from underground testing showed that the risk of coal and gas outbursts has been eliminated in the scope of pressure relief. The exclusive method developed in the research could be utilized as the guidance for the future optimization of parameters for hydraulic flushing borehole arrangement [Copyright &y& Elsevier]

In order to search for the gas distribution in the coal seam after hydraulic flushing, introduced a hydraulic flushing field test on the investigation of gas pressure based on Pansan No. 13-1 coal seam occurrence condition. By using RFPA2D-Flow software to simulate the process of coal fracture with hydraulic flushing, studied the effects of hydraulic flushing in seam stress and gas pressure distribution. The results indicate that hydraulic flushing pressure-relief and permeability is a process of the coal around punching holes and rebuild its unstable equilibrium. Around the holes from near and far would form four regions: gas full emission region, gas emission region, gas pressure transition region and natural gas region. The coal in the pressure-relief and permeability region could experience the processes of stress increase, fracture development, stress quick release and recovery equilibrium. [ABSTRACT FROM AUTHOR]

Fish-killing Prymnesium parvum blooms have occurred in south-central USA for at least ∼30 years, with the last decade experiencing recurrent blooms of large magnitude. In the systems reported here, Lakes Possum Kingdom, Granbury and Whitney (Texas), P. parvum blooms were winter phenomena developing under conditions far from the growth optimum. Bloom thresholds of 10 × 106 cells L−1 were observed as a function of inflow and salinity for the period 2000–2009. In Lake Possum Kingdom, blooms occurred only when 7-day accumulated inflows were <10 × 106 m3 and salinities were >1.5 psu. For Lakes Granbury and Whitney, blooms occurred when 7-day accumulated inflows were <20 × 106 m3 and <40 × 106 m3, respectively, and salinities were >0.5 psu. Inflow to these lakes exceeded thresholds during the spring and early-summer months in 8 (Lake Possum Kingdom), 7 (Lake Granbury) and 6 (Lake Whitney) of the 10 years analyzed. Salinities typically exceeded these thresholds during the period of study prior to the spring of 2007. The spring of 2007 was a period of high precipitation, after which salinities were typically below thresholds. The linkage between incidence of P. parvum blooms, inflows and salinity is of concern because combined effects from human population increase and climate change could lead to periods of decreased inflow and increased salinity, which may then increase the frequency and magnitude of P. parvum blooms. [ABSTRACT FROM PUBLISHER]

Hydraulic flushing (HF) is an efficient technique for improving coal mine gas extraction. Although much research has been conducted in recent decades, many problems on its mechanism of enhancing permeability still exist. For example, how does coal strength affect the enhanced permeability by HF? Can a larger borehole generate a higher gas flowrate? Therefore, a coupled gas flow-geomechanics model was developed based on an equivalent fractured-coal model to solve these issues. Plastic volumetric strain was introduced in this model to quantify the coal structure, which can improve the numerical models for coal permeability, gas flow in fracture and diffusion in matrix, respectively. The model was used to describe gas flow in the virgin and disturbed coal seams. Results show that neglecting coal failure can cause erroneous stress and permeability distributions, and lead to an overestimation of gas pressure and an underestimation of gas extraction amount. Effects of coal strength and borehole diameter on the distributions of stress, plastic zone, permeability and gas pressure were systematically studied. It indicates that the stress relief, plastic and enhanced-permeability zones around the boreholes in soft coal are obviously larger than those in hard coal. The stress-concentration level and permeability reduction in soft coal are greater than those in hard coal. After 500 d extraction, gas pressure in soft coal has a higher decrease than that in hard coal, indicating that the enhanced permeability by HF of soft coal is larger than that of hard coal. Besides, the investigation on the effects of borehole diameter shows that there exists an optimal borehole diameter. Gas pressure between the boreholes decreases before the optimal diameter, and increases sharply after the optimal diameter due to the high stress concentration. For the Pingmei 8th mine, the optimal borehole diameter is about 1.0 m. Field tests indicate that the optimized HF can considerably eliminate the risk of coal and gas outburst. [ABSTRACT FROM AUTHOR]

Coal seam gas is a kind of precious energy, but it also will be a terrible disaster in coal mining if not well controlled. Underground coal seam gas drainage is one of the most effective methods for lowering the risk of gas disaster. However, it is difficult to extract gas in many coal seams with low permeability, especially in tectonic coal seams, which were severely crushed or even pulverized by tectonism. The key to improving the gas drainage efficiency is stress relief and permeability increase. There are many conventional technologies to improve the gas drainage efficiency of a single coal seam, but they are inoperative on the special thick coal seam with a soft mylonitic tectonic coal sub-layer at the lower part. In this paper, to enhance gas drainage in this coal seam, we presented a hydraulic flushing gas drainage technology. Numerical simulation was conducted to analyze the stress evolution, plastic damage, permeability changes and gas drainage of the coal after hydraulic flushing. Further, abundant field experiments were carried out to investigate and verify the mechanism of stress relief and permeability increase. The results show that, after adopting the hydraulic flushing gas drainage technology, more tectonic coal in the thick coal seam was flushed out and the big hole in the tectonic coal sub-layer enlarged the range of stress relief and permeability increase, and the gas drainage efficiency increased significantly. [ABSTRACT FROM AUTHOR]

Hydraulic flushing has the advantages of reducing coal stress and improving coal seam permeability, so it is widely used in high gas outburst coal seams in China. However, the effect evaluation of stress relief and permeability enhancement will be necessary before coal mining. In this paper, an acoustic emission (AE) experiment system of coal seam hydraulic flushing was established, and the AE characteristics of coal during hydraulic flushing were studied. The results show that the changes in AE signals are basically consistent with those in load and water pressure. In addition, the quantitative relationship between the signals and the damage of coal around the borehole is revealed by the theory of damage mechanics. The in-situ AE test of hydraulic flushing was performed in the Liangbei Coal Mine, by measuring gas flow and coal stress simultaneously. The variation of AE activities and the effect evaluation of hydraulic flushing were analyzed. The results reveal that the changes in coal seam stress are basically consistent with those of AE signals. After the flushing has been completed for 1–3 h, the coal seam stress decreases rapidly, and the AE counts and intensity reach the peak. Therefore, this study proposes a new method for evaluating the effect of coal seam hydraulic flushing by AE, which has a very important practical significance. [ABSTRACT FROM AUTHOR]