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ranged from 1035 to 1576 psi. Specifications for concrete will call for 3000 <br />psi minimum. Garrett end Campbell Pitt used a factor of safety of 4 to 5 when <br />` assigning a safety factor to concrete's compressive strength. The allowable <br />compressive strength, fc, used in these calculations will be 400 psi or approx- <br />imately 1/5 of (1035 psi + 3000 psi)/2. <br />The following is a table of the calculated lengths of plugs: <br />Portal Mine a b <br />Rock slope ~ #1 16 10 <br />Belt slope ~ #1 13 8 <br />Track entry ~ #1 24 12 <br />B-Seam Return Entry ~. #1 14 8 <br />Track Entry #3 ~ 18 15 <br />Belt Entry #3 16 12 <br />Return Slope #3 14 8 <br />Minimum Plug Length <br />1.5' <br />1.2' <br />2.0' <br />1.3' <br />7.2' <br />6.0' <br />4.5' <br />The lengths of these plugs may vary depending on where they are located and <br />the resulting dimension after scaling the roof, ribs and floor. This concrete <br />design method does not require steel reinforcing or additional anchorage into <br />the roof, ribs or floor. Contact grouting will be done between the seal and <br />the roof, ribs and floor. A minimum plug length of 3' will be used to assure <br />a tight seal. Either a Portland cement grout or a chemical grout will be <br />used. <br />Exoloration Holes and Wells <br />Exploration holes, when no longer needed, will be plugged or sealed to prevent <br />acid or toxic drainage and to minimize any disturbance to the hydrologic balance. <br />Figure 4.4.2-2 shows a sealed hole in cross section. <br />• <br />4-66b New 5/11/87 <br />_~ <br />