Pressure Relief Effect Research Articles

Analyzing method to evaluate effect of roadway pressure relief

Analyzing method to evaluate effect of roadway pressure relief

Calculation Model of High-Pressure Water Jet Slotting Depth for Coalbed Methane Development in Underground Coal Mine

In underground coal mines, high-pressure water jet slotting is effective at improving coal seams’ permeability. The slotting depth determines the effect of pressure relief and permeability enhancement in coal seams. However, there is no effective and feasible way of determining the slotting depth; thus, the operational parameters and borehole layout are unknown. This study determined the effects of key parameters, including the nozzle diameter, jet pressure, rotation speed, and slotting time, on the slotting depth. A water jet slotting depth calculation model was established and verified according to the slotting experiments under different operational conditions. The slotting depths were investigated based on the results of field slotting experiments. The results revealed that there exists an optimal nozzle diameter for a higher jet impact velocity. The slotting depth linearly increased with the jet pressure and decreased as a power function with the increase of the jet translation speed. The slotting depth increased with the slotting time, but the growth rate gradually decreased and tended to be stable. As the rotation speed increased, the slotting depth became greater at the initial period and the limit depth was reached faster. Laboratory and field slotting experiments were conducted to verify the model, and the experimental results are approximately in agreement with the theoretical predictions. The results of this study can be useful as guidelines for the hydraulic parameter selection of water jet slotting and for optimizing the layout of coal gas drainage boreholes.

Experimental investigation on the permeability, acoustic emission and energy dissipation of coal under tiered cyclic unloading

Because of periodic disturbance during coal seam excavation and support, the surrounding rock is subjected to cyclic unloading-reloading. To study the effect of pressure-relief on coal fields during gas drainage and mining, the permeability, acoustic emission (AE) and energy dissipation properties of coal under tiered cyclic unloading were experimentally investigated. Permeability enhancement rate (PER), AE signal change rate and a damage variable were defined to describe this process. Hysteresis, memory and Felicity effects are revealed. These results show that, the step-wise increase of strains and permeability display a hysteresis effect under tiered cyclic unloading. The axial residual strain increases exponentially, while the radial residual strain increases as a quadratic function, and the PER increases. The AE signals show Kaiser effect when the unloading capacity is small. Conversely, the Felicity effect is displayed when the unloading capacity is large. The cumulative AE signal and the axial strain exhibit good synchronisation and memory characteristics. The dissipated energy increases as a quadratic function, and the developed damage variable also increases, the critical damage variable of coal failure is estimated to be Dc ≈ 0.8.

A novel technology for high-efficiency borehole-enlarging to enhance gas drainage in coal seam by mechanical cutting assisted by waterjet

ABSTRACT Although the effect of pressure relief and permeability increasing achieved by the technology of traditional hydraulic flushing (enlarging hole by high-pressure water jet) is great significance, it has some shortcomings, such as low efficiency, large consumption of water resources, and being difficult to guarantee the sizes of holes. The limitations of water jet are known as the main factors that would restrict the effective pressure relief in soft and low-permeability coal seam. For the purpose of solving the problems existing in the traditional technology, a new technology of mechanical cutting assisted by waterjet has been developed. Then, a numerical simulation method was employed to illustrate the flow field and the force characteristics of equipment equipped with new technology. Finally, the new technology and its supporting system were tested in the Xinjing Coal Mine, Shanxi Province, China. The test results obtained are as follows: the efficiency of mechanical cutting is much higher than that of hydraulic flushing; the maximum equivalent to enlarge hole radius is increased by 83.3% (t = 30 min), and the efficiency of the new technology is 3 times more than that of the traditional hydraulic flushing; the time used for gas drainage is increased by 19.3%, and the drainage efficiency is increased by 28%; the cost spent on gas control in one working face decreases by more than 14.7%. It is concluded that the new technology can efficiently enlarge borehole so as to enhance gas drainage in coal seam and decrease the cost of coal mining.

Definition of Pressure Relief Range and Effect Analysis of Regional Measures in Long-distance Mining of Protective Seam

Based on the engineering background of the protection layer mining of the long distance and near horizontal coal seam group in Zhujixi Coal Mine, by means of theoretical analysis, numerical simulation and field investigation, the scope of pressure relief protection of the protected layer after the protection layer mining is studied and determined, and the effect of regional measures of surface drilling and underground perforation extraction measures is evaluated. The results show that the pressure relief angles in strike and dip directions are 63.7° and 80.8° respectively. The maximum residual gas content is 5.28m3/t and the gas extraction rate is 81.4%. The pressure relief protection effect is remarkable, effectively eliminating the outburst risk of the protected layer.

Experimental Research on Directional Blasting in Pre-cutting Hard Coal Seam Roof

Aiming at the problem of impact ground pressure caused by the hard roof of goaf in coal mining face, the research on pre-cutting of hard coal seam roof by directional blasting was carried out. According to the principle of energy accumulation in directional blasting, a similar simulated experiment was designed on the basis of theoretical analysis of stress wave propagation law, crack development law and forced roof caving distance. The experimental results show that the roof is pre-cut by directional blasting, the integrity of the roof in front of the working face is reduced, effective pressure relief effect is obtained, the large area of overhanging roof in goaf is prevented, and the impact ground pressure disaster of the working face is relieved.

Intermediate coal pillar instability and permeability evolution in extremely thin protective seam by auger mining

Protective seam mining method is an effective way to eliminate the coal and gas outburst hazard. Auger mining (AM) is adopted to protective seam thinner than 1.0 m. The key of AM is to set intermediate coal pillar (ICP) because they have two functions: on the one hand, ICPs have to support the roof temporarily to avoid coal auger crushing; on the other hand, they have to be broken subsequently to release the pressure of protected layer above. Theoretical analysis and numerical simulation are used to study the instability mechanism of the ICPs. On this basis, the effect of ICPs on the pressure relief and permeability evolution of the protected layer was analyzed. Results show that the reasonable ICP width is related to many factors, such as AM width, AM height, and ICP strength. The single ICP instability mode is compressive failure and the ICPs collapse one by one gradually instead of collapsing wholly and suddenly. The reasonable ICP width of Chiyu Coal Mine is 2.0 m with the conditions of 1.0 m AM height and 10.0 m AM width, namely when 4 AM rooms are mined by the coal auger and three ICPs are set. These ICPs collapse one by one and the sequence is No. 2, No. 1, and then No. 3. With the AM face advancing, the amount of ICPs increase and the pressure relief effect is also gradually improved. When some of ICPs collapse, the stress within the overburden above the goaf is released rapidly which significantly improves the performance of pressure relief.

Acoustic Emission Characteristics of Graded Loading Intact and Holey Rock Samples during the Damage and Failure Process

Rock burst is the result of the development and extension of micro-cracks during the loading process of large-scale rock mass in underground space engineering. Dynamic monitoring results by acoustic emission (AE) can accurately perceive the inner fracture evolution of rock mass and effectively warn about its induced disasters early. By contrastive testing the AE parameters in the whole fracture process of the intact and holey rock samples under graded loading, their spatiotemporal evolution rules were analyzed in this paper, and the damage model of rock samples based on AE localization events was established to analyze the relationship between rock damage and loads. The results show that: (1) Under the condition of grading loading, AE parameter increases with the increase of axial stress and show three states, respectively, which are slow-growth, stabilization and rapid increasing; meanwhile, the damage of the sample has a cumulative effect with time. (2) The AE counts and energy are highly correlated with the fracture of the sample that the more severe the damage of the sample, the faster the crack propagation as well as the higher the acoustic emission counts and the energy amplitude. The damage state of granite sample can be accurately judged by two parameters to character the damage evolution process and fracture mechanism. (3) Compared with the intact rock sample, due to the pressure relief effect of the hole, the rock sample containing the hole takes a long time in the compaction stage and with higher load stress level. Although the AE counts and energy were lower in the damage process, the general law of their response during damage and instability process still exists.

The effect of anionic surfactant (SDS) on pore-fracture evolution of acidified coal and its significance for coalbed methane extraction

Adding the compound solution included hydrochloric acid and hydrofluoric acid into coal seam, the pore structure of coal can be destroyed by acidizing treatment, and the permeability of coal seam can be improved. In order to increase the acidification damage effect, in this paper, the effects of anion surfactant named Sodium Dodecyl Sulfate (SDS) on the pressure relief and enlarge permeability effect of compound solution acidified coal were studied from four aspects: mechanical characteristics, porosity and pore distribution of coal samples, retention effect of fracturing fluid and microscopic morphology of coal sample surface. The results show that the SDS promotes the pressure relief effect of acidified coal body and reduces the strength of the treated coal sample. At the same time, the SDS increases the reaction area of acid fracturing fluid and impurity minerals in the fractures of coal sample, enhancing the acidification effect of HCL and HF on coal sample and increasing the porosity of coal. In the aspect of pore distribution, through the acidification synergism of SDS, the macropores and fractures of coal samples increase obviously. With the addition of SDS, the reversible work required for HCL and HF compound solution to break away from coal molecules is reduced by 18.45 J, which can significantly reduce the water blocking effect caused by the fracturing fluid retention, and improve the efficiency of coalbed methane extraction. After the compound solution erodes the coal sample, the microscopic morphology of coal sample surface has changed greatly, and the destruction degree of acidizing erosion is the highest after SDS synergism. The results of this paper are great significance for studying the mechanism of pressure relief and enlarge permeability effect of acidified coal.

Analysis of the tempo‐spatial effects of hydraulic fracturing by drilling through underground coal mine strata on desorption characteristics

AbstractTo elucidate the tempo‐spatial effect and the corresponding mechanism of hydraulic fracturing on gas desorption, the experiments of the hydraulic fracturing in the field and the gas adsorption‐desorption in the laboratory were carried out, respectively. The difference of the effects on the total amount of gas desorption, desorption proportion, moisture content, and in situ gas drainage concentration of the original and fracturing coal samples were studied. The results show that coal moisture increase in the 29 m area of hydraulic fracturing, the greater moisture content and the smaller amount of gas desorption, and the 9 m coal samples moisture content is 2.77 times greater than that of the original coal samples, and whose total amount of gas desorption for 29.8% of the original coal samples. In addition, the closer to the fracturing borehole, the smaller the desorption velocity, which is the fastest in the initial 5 minutes. The desorption velocity of the original coal samples is 5.6 times greater than that of the 9 m coal samples. The desorption proportion of the coal samples is high in early stages, η30 min is 64% (ηi is the proportion of the instantaneous total of gas desorption to the total gas desorption, %), and for η6 h‐12 h is 10%. The tempo‐spatial effects of desorption characteristics can be expressed as the time‐delay effect and a space‐reduction effect. Furthermore, the upper limit of deformation of the coal seam is 3.3‰ and the ability of gas desorption in coal seam significantly decreases. The time of gas drainage concentration exhibits more than 30% increases from the 10 days in the nonfracturing area to 90 days in the fracturing area. Finally, hydraulic fracturing crushes coal, replaces absorption gas, increases the moisture content of coal, reduces various stresses, makes coal shrink, and ultimately achieves the effects of pressure relief and permeability improvement.

Practice of outburst prevention by pre-driving rock roadway unloading pressure of coal roadway strip in Fengcheng mining area

In view of the new characteristics of the coal and gas outburst disaster of single serious outburst dangerous coal seam in the deep mining area of Fengcheng mining area, the article puts forward regional outburst prevention measures of unloading pressure by pre driving rock roadway and constructing wear layer drilling to pump coal roadway strip gas, a complete set of technical system of regional outburst prevention in coal roadway strip by pre driving and unloading floor roadway in the Fengcheng mining area is obtained. The field practice shows that after entering the deep mining stage, under the conditions of high stress, high gas, high temperature and low permeability, the situation of outburst occurrence is more and more serious, and the mechanism is more complicated, although coal roadway of B4 coal seam has taken the measure of construction of drilling for pre pumping gas along B4 coal seam, but the damage of the high ground stress has not been completely eliminated, the proportion of in-situ stress dominated outburst is increased. Regional outburst prevention is carried through pre driving of floor roadway layout in the rang of 8∼12m which just below the coal roadway to carry on the pressure relief combined with crossing drilling drainage gas, it can greatly improve the permeability of coal seam and the effect of pressure relief, and ensure the safe and fast roadway driving.

Research on Roof Cutting and Pressure Releasing Technology of Directional Fracture Blasting in Dynamic Pressure Roadway

Affected by mining activities, 3−1103 tailgate of Hongqinghe coal mine is seriously deformed. The floor of tailgate cracking and tilting, and two ribs appearing in the net bag, which affects normal transportation and pedestrians. To solve this difficulty, this paper study on the technology of directional fracturing blasting for pressure relief of dynamic pressure roadway. First of all, taking method of theoretical analysis, the mechanical mechanism of directional blasting and the relevant calculation formula are expounded. Afterwards, the mechanical model of roof cutting of roadway is established. In order to analyze the evolution and propagation of effective stress, directional blasting model is established by using LS-DYNA numerical calculation software. In the next part, the roof control technology of directional cut blasting is put forward. In the end, the blasting effect is observed, and the deformation of the roadway before and after pressure relief is monitored and analyzed. The results shows that directional fracture blasting have obvious effect of joint formation, and the effect of pressure relief is remarkable, effectively controlling the deformation of surrounding rock under dynamic pressure.

Analysis of Pressure Relief Effect on the Protective Layer of Hard Roof and Extra-Thickness Coal Seam Mining

The roof of Tashan coal mine was hard and difficult to fall. In the process of fully mechanized coal caving in the Carboniferous extra-thick coal seam, the strong pressure and rock burst appeared in the working face. To obtain the pressure relief effect of the exploitation of Shan 4# protective seam in Tashan coal mine, The stress distribution and displacement variation of the roof and floor of Shan 4# protective layer were obtained by numerical simulation. And by mine pressure observation in the 8107 working face of the un-mining protective seam and in the 8108 working face of mining protective layer, the pressure relief effect of mining Shan 4# protective layer was analyzed. It was shown that the lateral of the open-off cut and the rock mass in front of the working face produced stress concentration when 3–5# coal was mined separately. The stress concentration coefficient of k was 3. The liberated layer was in the floor relief area from the open-off cut after the upper protective layer being mined owing to internal misaligned arrangement of the liberated layer when the protective layer and the liberated layer were mined. The stress concentration of the lateral of open-off cut and working face of the liberated layer was greatly reduced, and the stress concentration coefficient was about 1.5. The middle of the goaf would be re-compacted with the advance of the working face. The maximum principal stress of the liberated layer was W type distribution. The expansion deformation of 3–5# coal was M type distribution. The working resistance of the 8107 working face was mainly distributed in 8000–12,000 kN. The working resistance of the 8108 working face was mainly distributed in 4000–10,000 kN. The vertical stress of the roof of the 3–5# coal was decreased by about 30% after mining the protective layer. The mining of the protective seam effectively reduced the pressure strength of the roof of the fully mechanized coal seam. The reference was provided for the rational layout of coal seam safe mining with impact tendencies.

Modeling of gas migration in water-intrusion coal seam and its inducing factors

Formation water intrusion into the coal seam through cross drainage boreholes seriously affects the gas extraction efficiency. Particularly in the downward boreholes, the formation water cannot be discharged through the drain. Using the conventional seepage model to estimate the effect of gas drainage will cause that the coal seam residual gas pressure is underestimated. In this paper, we construct the gas migration models in a water-intrusion coal seam, which include the gas seepage in original coal seam and the gas diffusion in water-saturated coal seam. By comparing with the field data, the mathematical models are authenticated. Then, the influences of diffusion coefficient, permeability, Henry’s constant and the radius of water-saturated coal seam on the residual gas pressure and gas production are analyzed by numerical calculations. The results show that the gas pressure decreases with the increase of the diffusion coefficient, while increases with the increase of Henry’s constant and the radius of the water-saturated coal seam. The impact of permeability is more complex. In the high permeability coal seam, the overall pressure relief effect is better. However, in the low permeability coal seam, the pressure relief effect around the borehole is better. Finally, the influence mechanism of each factor is analyzed to revel the gas production in the water-intrusion coal seam. The results of the work are of great significance to enrich the theory of gas migration and the prevention and control of mine gas disaster.

Mechanical analysis of effective pressure relief protection range of upper protective seam mining

This paper analyzes the control mechanism of coal and gas outbursts and proposes the concept of an effective pressure relief protection range, based on the stress relief of the underlying coal-rock mass and the development of a plastic zone. Also this study developed a stress change and fracture development model of the underlying coal-rock mass. In addition, the stress and depth of fracture of any point in the floor were deduced with the application of Maple Calculation Software. The specific engineering parameters of the Pingdingshan No. 12 colliery were applied to determine the relationship between the depth of fracture in the floor and the mining height. The pressure-relief principle of the underlying coal-rock mass was analyzed while varying the mining height of the upper protective seam. The findings indicate that as the depth of fracture in the floor increases, the underlying coal-rock mass experiences a limited amount of pressure relief, and the pressure relief protection range becomes narrower. Additionally, the stress distribution evolves from a “U” shape into a “V” shape. A 2.0m mining height of protective seam situates the outburst-prone seam, Ji15, within the effective pressure relief protection range. The fracture development and stress-relief ratio rises to 88%, ensuring the pressure-relief effect as well as economic benefits. The measurement data show that: after mining the upper protective seam, the gas pressure of Ji15 dropped from 1.78 to 0.35MPa, demonstrating agreement between the engineering application and the theoretical calculation.

Diabetic Foot Ulcer: A Review

Diabetic foot problems are common throughout the world, resulting in major medical, social and economic consequences for the patients, their families, and society. Foot ulcers are more likely to be of neuropathic origin, and therefore eminently preventable. People at greatest risk of ulceration can easily be identified by careful clinical examination of the feet: education and frequent follow-up. Infection when complicates a foot ulcer, combination can be limb or life-threatening, and infection is defined clinically, but wound cultures assist in identifying the causative pathogens. Tissue specimens are strongly preferred to wound swabs for wound cultures. Antimicrobial therapy should be guided by culture results, and although such therapy may cure the infection, it does not heal the wound. Alleviation of the mechanical load on ulcers (offloading) should always be a part of treatment. Plantar neuropathic ulcers typically heal in 6 weeks with irremovable casting, because pressure at the ulcer site is mitigated and compliance is enforced. The success of other approaches to offloading similarly depends on the patients’ adherence to the effectiveness of pressure relief.

Permeability Improvement Technology of Directional Hydraulic Fracturing in Low Permeability

According to the conventional fracturing could easily lead to the local stress concentration of coal, the effect of pressure relief and permeability improvement is not ideal. The mechanism of directional hydraulic fracturing is analyzed and the parameters such as the layout of directional hole, the fracturing hole sealing, the minimum cracking pressure are discussed, then the field application tests are carried out. The results show that the directional hydraulic fracturing effect is better than that of ordinary fracturing hole and the maximum concentration and the average drainage scalar is respectively 3.75 times and 4 times of the ordinary hole pumping gas fracturing effects. The effect of permeability improvement is remarkable.

The Effect of the Relief Wave on the Uniformity of an Air Blast Load

AbstractIn most blast loading structure analyses, it is assumed that the load acts uniformly on a target area. For the rationable design, it is useful to have a quantitative criterion to determine at which maximum distance the standoff can be placed to assume a uniform pressure distribution. Surprisingly, no standard criterion was found in the literature and the effect of blast wave clearing was not considered as well. In this paper, pressure histories applied on structures are calculated considering the non‐uniform loading characteristic as well as pressure relief from the edges. Additionally, the effects of various parameters on uniformity of impulse distribution are investigated. The results have shown that the effect of pressure relief on impulse uniformity is very important, especially when the blast wave is attenuated. This phenomenon leads an optimum distance at which impulse distribution is the most uniform.

Study on Underlying Coal and Strata Pressure-Relief Principle and the Gas Extraction Technique under Upper Protective Layer Mining

By study on underlying coal and strata pressure-relief principle and the gas extraction technique under upper protective layer mining, we obtain the stress change and distribution law of underlying coal-rock mass. We analyze the deformation law and fracture development characteristics of underlying coal-rock mass movement. With mining proceeding ahead, the total floor coal and rock experiences compression deformation first, then expansion deformation and re-compaction of the continuous periodic destruction. Based on different development characteristics and status of underlying coal-rock mass, the underlying coal-rock mass under an effect of upper protective layer mining was divided into the floor heave fracture zone and the floor heave deformation zone in this paper. The permeability coefficient of change law of underlying the coal seam as follows: the original value-small decreasing-increasing greatly-reducing-stability at last. The field test for upper protective layer mining of Zhang-ji coal mine of Huainan shows that the effect of pressure relief of protected seam is very good. So it eliminates the risk of gas outburst, ensuring safety mining of the protected seam. The research has an important significance for safety and efficient production under similar exploitation conditions of low-permeability with high gas and outburst risk coal seam.

Numerical Simulation Research and Application on Protected Layer Pressure Relief Affection Under Different Coal Pillar Width

In order to research protected layer pressure relief effect under influence of different width of coal pillar, this paper carried on FLAC3D numerical simulation of vertical stress field and deformation field under different coal pillar width. The protected layer evolutional characteristics of vertical stress, vertical displacement and pressure relief affection which coal pillar affected were analyzed. The results show that: (1) Coal pillar affected zone is high stress concentrated zone. Because of coal pillar width influence, trended vertical stress distribution is from “v shape” to “partial saddle shape”; tendency vertical stress distribution is “flat disc shape”. Vertical stress is non-linear with coal pillar width, vertical stress is most concentrated when coal seam reserved 20m coal pillar, vertical stress distribution is from “single peak shape” to “double peak shape”. (2) Coal pillar affected zone is low strain region. Coal pillar decreases protected layer overall deformation, not just reduce deformation of coal pillar affected zone. Vertical deformation is negative correlation with coal pillar width. Trended vertical displacement distribution is “▪” shape; tendency vertical displacement distribution is “flat disc shape”. (3) Unprotected range increases with the increase of coal pillar width, pressure relief angle is 49°–60°, pressure relief angle of both sides is negative correlation with mined out areas. ▪ Engineering measurement shows: simulative results and experimental results are consistent. Research results have theoretical reference and practical significance on unprotected layer effect measurement and outburst elimination.