Selecting the conditions for hydraulic working of caving-resistant roofs in the pechora coalfield

Abstract

To find new effective me~hods for controlling caving-resistant roofs in Pechora collieries, the Pechora Scientific-Research Coal institute has studied some physical properties of rocks: the open porosity, the intergranular and fissure permeability, the moisture capacity, etc.The open porosity and moisture capacity were assessed by established methods. Table 1 gives the resul~ of these determinations.For rocks of both the Vorkuta and Inta coalfields the total porosity is on average 2.18o2.64 times higher than the porosity available for water saturation.The tntergranular permeability of the rocks was determined in an AKM-2m apparatus by the known procedure, modernized so as m record very low flow rates of fluids when working with semipermeable rocks, characteristic of the Pechora region. The permeability was assessed quantitatively by the values of the permeability (Kp, mdarcy) md the filtration coefficient (C, cm/sec). The relation between the filtration velocity and the pressure gradient was taken as linear:where Of is the mean filtration velocity over the cross section, in cm/sec, Kp is the intergranular permeability, In mdamy, grad p is the pressure gradient in the direction of filtration (grad p = Z~p/t ), Z~pis the pressure drop, in kg/cm 2, Z is the thickness of the strata du~ugh which the fluid is moving, in centimeters, and t~ is ~he abmlute viscosity coefficient of the fluid, in centipotse~. The coefficient C was calculated by means of the equation During the experimen~ we inves.tfgated the effect of the orientation of the flow of the liquid (normal or parallel to the stratification) and the effect of the rock pressure on KIt As the working Uquid we used commercial kerosene with surface tension ct 26-27 dyu/cm; the ~t and v values were taken as 1.88 cP and 2.38 cS, respectively.In determining Kp values, we rook account of the effect of mechanical stresses in the undisturbed rock mass in the working hoflmns of the collieries.