(a) This section sets forth the criteria that shall be considered on a mine-by-mine basis in the formulation and approval of roof control plans and revisions. Additional measures may be required in plans by the District Manager. Roof control plans that do not conform to the applicable criteria in this section may be approved by the District Manager, provided that effective control of the roof, face and ribs can be maintained.
(b) Roof Bolting.
(1) Roof bolts should be installed on centers not exceeding 5 feet lengthwise and crosswise, except as specified in § 75.205.
(2) When tensioned roof bolts are used as a means of roof support, the torque or tension range should be capable of supporting roof bolt loads of at least 50 percent of either the yield point of the bolt or anchorage capacity of the strata, whichever is less.
(3) Any opening that is more than 20 feet wide should be supported by a combination of roof bolts and conventional supports.
(4) In any opening more than 20 feet wide -
(i) Posts should be installed to limit each roadway to 16 feet wide where straight and 18 feet wide where curved; and
(ii) A row of posts should be set for each 5 feet of space between the roadway posts and the ribs.
(5) Openings should not be more than 30 feet wide.
(c) Installation of roof support using mining machines with integral roof bolters.
(1) Before an intersection or pillar split is started, roof bolts should be installed on at least 5-foot centers where the work is performed.
(2) Where the roof is supported by only two roof bolts crosswise, openings should not be more than 16 feet wide.
(d) Pillar recovery.
(1) During development, any dimension of a pillar should be at least 20 feet.
(2) Pillar splits and lifts should not be more than 20 feet wide.
(3) Breaker posts should be installed on not more than 4-foot centers.
(4) Roadside-radius (turn) posts, or equivalent support, should be installed on not more than 4-foot centers leading into each pillar split or lift.
(5) Before full pillar recovery is started in areas where roof bolts are used as the only means of roof support and openings are more than 16 feet wide, at least one row of posts should be installed to limit the roadway width to 16 feet. These posts should be -
(i) Extended from the entrance to the split through the intersection outby the pillar in which the split or lift is being made; and
(ii) Spaced on not more than 5-foot centers.
(e) Unsupported openings at intersections. Openings that create an intersection should be permanently supported or at least one row of temporary supports should be installed on not more than 5-foot centers across the opening before any other work or travel in the intersection.
(f) ATRS systems in working sections where the mining height is below 30 inches. In working sections where the mining height is below 30 inches, an ATRS system should be used to the extent practicable during the installation of roof bolts with roof bolting machines and continuous-mining machines with integral roof bolters.
(g) Longwall mining systems.
(1) Systematic supplemental support should be installed throughout -
(i) The tailgate entry of the first longwall panel prior to any mining; and
(ii) In the proposed tailgate entry of each subsequent panel in advance of the frontal abutment stresses of the panel being mined.
(2) When a ground failure prevents travel out of the section through the tailgate side of the longwall section, the roof control plan should address -
(i) Notification of miners that the travelway is blocked;
(ii) Re-instruction of miners regarding escapeways and escape procedures in the event of an emergency;
(iii) Re-instruction of miners on the availability and use of self-contained self-rescue devices;
(iv) Monitoring and evaluation of the air entering the longwall section;
(v) Location and effectiveness of the two-way communication systems; and
(vi) A means of transportation from the section to the main line.
(3) The plan provisions addressed by paragraph (g)(2) of this section should remain in effect until a travelway is reestablished on the tailgate side of a longwall section.