Laserfiche WebLink
For the East subdrain, the majority of the rock drain will have 3 square feet of <br />3/4" screened or washed rock. The upper section of the rock drain will have up <br />to 200 square feet of screened or washed rock. The drain will have a slope of <br />1.6%. Darcy's Law 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 (0.1 to 9.6 cubic feet per minute) <br />k = hydraulic conductivity of clean gravel (2.0 to 200 ft/minute)2 <br />A = column cross sectional area (3 SF) <br />dh/dl = hydraulic gradient, the change in head over the length of interest (0.016). <br />The estimated flow rate through the rock drain is 0.72 to 71.8 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 0.72 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 underdrain will discharge into ditch D -J11. A screen shall be placed over <br />the 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 />2 Principles of Geotechnical Engineering, Braja M. DAS, 1985, page 84. <br />Volume XI <br />TR -114 - 8 - 10/17 <br />