Patterns and security technologies for co-extraction of coal and gas in deep mines without entry pillars

Retaining gob-side entryways and the stability of gas drainage boreholes are two essential techniques in the co-extraction of coal and gas without entry pillars （CECGWEP）. However, retained entryways located in deep coal mines are hard to maintain, especially for constructing boreholes in confined spaces, owing to major deformations. Consequently, it is difficult to drill boreholes and maintain their stability, which therefore cannot guarantee the effectiveness of gas drainage. This paper presents three measures for conducting CECGWEP in deep mines on the basis of effective space in retained entryways for gas drainage, They are combinations of retaining roadways and face-lagging inclined boreholes, retaining roadways and face-advancing inclined boreholes, and retaining roadways and high return airway inclined boreholes. Several essential techniques are suggested to improve the maintenance of retained entryways and the stabilization of boreholes. For the particular cases considered in this study, two field trials have verified the latter two measures from the results obtained from the faces 1111（1） and 11112（1） in the Zhuji Mine. The results indicate that these models can effectively solve the problems in deep mines. The maximum gas drainage flow for a single hole can reach 8.1 m^3/min and the effective drainage distance can be extended up to 150 m or more.

Chemical Composition, Characterization and Factors Affecting Household Dust (<20 µm) in Greater Cairo, Egypt

Adverse health and environmental effects of household dust are derived from their chemical composition and properties. In this study, household, stairs and entryway dust (<20 μm) samples from homes located in urban, residential and residential near to industrial area in Greater Cairo during summer 2013 were collected to study their chemical composition, characterization and factors affecting them. Results indicate that the levels of measured anions and cations were higher in the household compared to stairs and entryway dust. The highest concentration of ?, , Cl-?,?, Na+, K+, Ca2+ and Mg2+ in the household and entryway dust was found in urban area. was abundant in household, entryway and stairs dust followed by Cl- and . Its average concentrations were 21.38, 14.57 and 15.83 mg/g, respectively. The household/entryway (I/O) concentration ratios of measured ion components indicate that these species might derive from indoor sources, although outdoor sources could be present as well. pH values of household, stairs and entryway dust ranged from 6.43 to 8.53, indicating that these dusts brought a large amount of crustal species, and might alleviate the tendency of acidification. The relationships between the concentrations of acidic components ( and ) and basic components (, Ca2+ and Mg2+) in household, stairs and entryway dust confirm that the acidity of dust is neutralized. Ca2+ and in household and stairs dust and Ca2+ and Mg2+ in entryway dust are the most dominant neutralization substances.