Laserfiche WebLink
foot wide by two feet deep drain. A perforated pipe will be installed in the rock <br />drain. See Map 21-1 for details. <br />The majority of the rock drain will have 4 square feet of 3/4" screened or washed <br />rock. The upper section of the rock drain will have up to 200 square feet of <br />screened or washed rock. The drain will have a slope of 2% to 8%. Darcy's Law <br />can be used to calculate the flow though the drain. <br />Darcy's Law is Q = kA dh/dl <br />where: <br />Q = rate of water flow calculated by formula (0.16 to 64.0 cubic feet per minute) <br />k = hydraulic conductivity of clean gravel (2.0 to 200 ft/minute)' <br />A = column cross sectional area (4 SF) <br />dh/dl = hydraulic gradient, the change in head over the length of interest (0.02 to 0.08). <br />The estimated flow rate through the rock drain is 1.2 to 479 gallons per minute. <br />The seepage from the Fire Mountain Canal does not have a perceptible flow. <br />Therefore, even if the rock drain can only pass 1.2 gallons per minute, it is <br />adequate for the seepage from the Fire Mountain Canal. The perforated pipe in <br />the rock drain will significantly increase its flow capacity. <br />The rock drain including the upper wide and tapering segment of the drain will be <br />wrapped in geotextile fabric. Twelve inches of common fill will be placed over <br />the rock drain so as to protect against the entrance of surface water or leachate <br />from the coal processing waste. The perforated pipe in the rock drain will extend <br />the full length of the drain except for the final 20 feet which shall be a solid pipe. <br />The solid pipe will discharge into ditch D -J3. A screen shall be placed over the <br />outlet of the solid pipe to keep rodents out of the pipe. <br />1 Principles of Geotechnical Engineering, Braja M. DAS, 1985, page 84. <br />Volume XI <br />TR -105 - 7 - 09/15 <br />