Research on Optimization of Coal Pressure Relief Borehole Parameters under High-Stress Conditions

Determining the parameters of boreholes drilled for relieving pressure in coal seams is the key preventing and controlling rock bursts in boreholes of large diameter. In this study, theoretical analysis, numerical simulation, literature research, and other analysis methods are applied to study the angles of elastic energy dissipation and stress transfer, the distribution law of the pressure relief area, and the areas of stress concentration, energy, stress, displacement, and plastic behavior of large-diameter pressure relief boreholes in coal seams under high-stress conditions. The results are then used to evaluate the relationship between large-diameter pressure relief boreholes and the borehole arrangement. The following results are obtained. (1) A large-diameter results in a large amount of elastic energy released by the surrounding coal, low residual elastic energy density, strong interaction between boreholes, large pressure relief range of the borehole, and high pressure relief efficiency. (2) The main evaluation factor of the borehole pressure relief effect is its thickness and stress concentration area; secondary evaluation is based on the areas of energy, displacement, stress, and plastic behavior. (3) Six evaluation index systems are established to evaluate the effects of borehole pressure relief, which are found to be the thicknesses of the borehole pressure relief area and stress concentration area, reduction degree of energy density, percentage of stress reduction, displacement, and penetration degree of the plastic area. (4) It is determined that when the diameters of the pressure relief boreholes are 100, 120, 180, and 200 mm, a single-row borehole arrangement is adopted; a three-pattern borehole arrangement is adopted with diameters of 140 and 160 mm. These research results can provide theoretical support in selecting reasonable borehole arrangements for pressure relief boreholes of different diameters.

Explicit dynamics based numerical simulation approach for assessment of impact of relief hole on blast induced deformation pattern in an underground face blast

The breakage of rock mass by blasting has many challenges. The optimal breakage in an underground development face/tunnel blast is dominantly dependent on the relief area provided to the blast holes. The cut portion in the burn cut face blast is significantly important to achieve the controlled deformation due to the blast. This paper has discussed the impact of the number and diameter of the relief holes on the breakage pattern of the rock. The numerical simulation with varying numbers and diameter of relief hole was carried out for this purpose. Finite element modeller explicit dynamics of Ansys-Autodyn was used for the simulation work. The isosurface of non-deformed zone was plotted to compare the extent of deformation under varying conditions of relief holes. The analysis shows that the higher number of relief holes with optimum diameter gives more controlled deformation than single relief hole with larger diameter. The nearfield vibration was also recorded by placement of seismograph. The waveform analysis of the recorded vibration was carried out. The redesigning of the blasting pattern was done using the results of numerical simulation and waveform analysis. The redesigned pattern consists of four relief holes of 115 mm diameter. The blasting output with the revised design has resulted into the considerable improvements in the pull and reduction of overbreak. The revised pattern has addressed the issue of the socket formation at the site.

Tectonic deformation and mantle-driven uplift of the Middle Atlas mountain belt (Morocco) during the late Cenozoic

<p>The Middle Atlas mountain range represents the northeastern branch of the Atlas system, which spans approximately 2000 km from the Atlantic coast of Morocco to Tunisia. The Atlas system is a prominent example of active intracontinental mountain belts that developed in the African plate of the Cenozoic Alpine belt.</p><p>The Middle Atlas is an inverted Mesozoic rift that began to rise during the late Cretaceous with limited crustal thickening. It can be divided into two geomorphological provinces: 1) an elevated, low-relief area called Tabular Middle Atlas (TMA), which is located in the north-western orogenic sectors and consists of weakly deformed Mesozoic sediments in stratigraphic contact with the Paleozoic basement of the western Meseta, and 2) a deeply dissected, high-relief area known as Folded Middle Atlas to the southeast, where crustal deformation is dominated by transpressive tectonics induced by a NNW-SSE maximum shortening direction. Seismicity and geomorphic landforms suggest that tectonic deformation is still active, at least in some sectors of the orogen.</p><p>In order to investigate the tectonic evolution of the Middle Atlas, we combined structural and geomorphic analysis. Although the age control of the continental syn-orogenic deposits is limited, the eastern boundary of the orogen shows evidence of recent tectonic deformation and flexural subsidence with the development of a foreland basin. Conversely, the western boundary of the orogen does not include syn-orogenic foreland basins suggesting the lack of flexural subsidence. This boundary is also characterized by alkaline late Miocene-Quaternary lava flows over a wide surface of ca. 960 km<sup>2</sup>. These lava flows cover part of the TMA where they fill valleys crossing the Meseta and draining towards the Atlantic Ocean. The degree of subsequent fluvial incision of the lavas is lower in the TMA than in the Meseta. While incision does not go beyond the stratigraphic contact lava-substratum in the TMA, it goes further down in the Meseta indicating a higher magnitude of uplift. The lack of contractional deformation, however, suggests that such an uplift is not controlled by tectonics.</p><p>Overall, our preliminary observations suggest the occurrence of an asymmetry between the two orogenic flanks. Uplift along the eastern orogenic boundary has been triggered by late Cenozoic contractional deformation, whereas deep-seated, most likely mantle-driven processes essentially control uplift of the western boundary.</p>

Characterizing the Permeability and Methane Release with the Treatment of Pressure-relief Mining: Intensive Field Measurements

Characterizing the permeability evolution and methane release is of great significance for the safe mining of the high gas outburst seams, as well as coal and gas simultaneous extraction. Theoretical analysis, laboratory testing, and numerical simulation are widely used methods to characterize the permeability and methane release with the treatment of pressure-relief mining. However, these methods cannot fully reflect the complexity of filed practice. In this study, we report the effectiveness of protective coal seam (PCS) mining and the pressure-relief area in the protected coal seam (PDCS) based on detailed and integrated field measurements in a Chinese coal mine. To the best of our knowledge, it is the first time to measure the permeability coefficient and gas pressure evolution in the PDCS during the PCS longwall mining. The evolution of the permeability coefficient in the pressure-relief area during PCS mining can be divided into four stages: slowly decreasing, sharply increasing, gradually decreasing, and basically stable. The maximum permeability coefficient is 322 times of the initial value and finally stabilized at 100 times after the goaf compacted. The gas pressure evolution in the PDCS indicates that the strike pressure relief angle is 52.2° at the active longwall face zone, and 59.3° at the installation roadway side. The tendency pressure relief angles at the lower and upper sides of the longwall panel are 75° and 78.9°, respectively. The residual gas content and gas pressure of the PDCS in the pressure-relief area are reduced to less than 6 m3/t and within 0.4 MPa, respectively. The field measurements show that pressure-relief mining can prevent coal and gas outbursts in PDCSs. The field observations in this paper can serve as benchmark evidence for theoretical analysis and numerical simulations, and also provide insights into realizing safety mining in similar conditions.

Sediment Losses in Watersheds in the Western-Center Meso-Region Rio-grandense

The permanent monitoring of sediment losses in small-paired watersheds is still incipient, especially in what concerns the search for information that combines variables that are part of an open and dynamic system. In this sense, this work investigated sediment losses in watersheds in the Western Meso-region Rio-grandense from 07/2010 to 12/2012. The auxiliary variables were composed of rainfall, surface and base flow and kinetic energy – in comparison to the morphometry of each microbasin and its use – to the concentration of suspended sediments and total sediment loss. Statistical analysis of the data was based on descriptive statistics, taking into account the indicators of cumulative, average, standard deviation, standard error and variance, as well as regression analysis. The largest mild to smooth corrugate relief area of the smallest river basins is not sufficient to provide lower superficial runoff values. The increase in rainfall directly contributes to the increase in kinetic energy, and leads to greater sediment losses in both small hydrographic basins. The larger area occupied by natural water reservoirs contributes efficiently to the reduction of suspended sediment losses. The watershed with larger area is more susceptible to the triggering of erosive processes than to the smaller area, in 8 (2010), 6 (2011) and 4 (2012) times.

Temperature-based zoning of the Bordeaux wine region

Temperature is a driving climate variable for grapevine development and grape ripening kinetics. The current study first reports interpolation of daily minimum and maximum temperature data by a weather station network from 2001 to 2005 in the Bordeaux (France) region by means of regression kriging using terrain, satellite and land-cover derived covariates. Second it analyses the interpolation procedure errors in agroclimatic indices by means of cross validation and then it compares the field observations of grapevine phenology to temperature-based predicted phenology applied to interpolated data. Finally it proposes a simple method to perform a zoning of Bordeaux vineyards based upon the spatialized prediction of the day on which grape sugar content reaches 200 g.L-1. The zoning performed shows large potential differences in grape maturity date (up to 20 days) induced by temperature spatial variability in a low relief area.