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Back fill - Prior to construction of the block wall, the <br />Z'6AT~A~TOR shall completely backfill a minimum 25 feet long <br />section of the mine opening beginning immediately behind the <br />position of the block wall. Fill material shall consist of <br />non-combustible, non-coal earth fill material only and shall be <br />placed such that no voids or air passages remain between the <br />fill and the roof, walls, or floor of the back filled portion of <br />the mine opening. After construction of the block wall is <br />completed and mortar has had sufficient time to cure, the <br />CONTRACTOR shall backfill the remaining portion of the mine <br />entry beginning at the front of the wall and extending out to <br />the surface. This portion of the backfill work shall be <br />combined with regrading work covered under Section III,4 of the <br />Special Conditions such that no voids or air passages remain <br />between the fill and the roof, walls, or floor of the mine <br />entry and any portion of the ventilation fan facility remaining <br />after structural demolition work has been completed. However, <br />a partial void shall be left immediately in front of and <br />immediately behind the block wall in order to prevent excessive <br />side pressure on the masonry units, <br />B. Main Mine Entry Behind Wash Plant <br />1. Backstop - It will not be necessary to construct a backstop for <br />i~Fe 6Tock wall seal for this mine opening. <br />2. Concrete Block Wall - The CONTRACTOR shall construct a solid <br />concre oc wa within the mine opening positioned between <br />25 feet and 30 feet from the concrete portal face-up at the <br />surface. The wall shall be constructed to completely seal the <br />mine opening by extending the wall to fully contact the shell <br />or plate steel portion of the arch roof and side walls, The <br />rear of the wall shall be positioned against the front of one <br />of the curved structural steel arch frame pieces such that the <br />framing serves as a backstop for the perimeter of the wall. <br />A level trench or keyway for the base of the wall shall be <br />excavated into the floor of the mine entry a minimum of 24" <br />below existing floor grade, or to competent rock if encountered <br />less than 24" below existing floor grade. ALL voids remaining <br />between th wall and the steel arch lining of the mine opening <br />shall be filled with grout. Block courses shall be alternated <br />and laid in the configuration shown on Exhibit 6F. Masonry <br />units shall be laid plump, level and true to line in full beds <br />of mortar. Remaining specifications for construction of this <br />wall shall be the same as those specified in paragraph 2 of <br />Section III.3.3.A.2 of the Special Conditions. <br />-16- <br />