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Scaling and Bolting or Shotcrete

Scaling and Bolting or Shotcrete. 56 & 57.3000 Definitions. The following definitions apply in this subpart.

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Scaling and Bolting or Shotcrete

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  1. Scaling and Bolting or Shotcrete

  2. 56 & 57.3000 Definitions. • The following definitions apply in this subpart. • Rock burst. A sudden and violent failure of overstressed rock resulting in the instantaneous release of large amounts of accumulated energy. Rock burst does not include a burst resulting from pressurized mine gases.

  3. 56 & 57.3000 Definitions. • Rock fixture. Any tensioned or nontensioned device or material inserted into the ground to strengthen or support the ground. • Travelway. A passage, walk, or haulageway regularly used or designated for persons to go from one place to another.

  4. 56 & 57.3200 Correction of Hazardous Conditions • Ground conditions that create a hazard to persons shall be taken down or supported before other work or travel is permitted in the affected area. Until corrective work is completed, the area shall be posted with a warning against entry and, when left unattended, a barrier shall be installed to impede unauthorized entry.

  5. 56\57.3200 PPM • This standard prohibits work or travel, other than corrective work, in areas where hazardous ground conditions exist. Posting of a warning against entry is required until corrective work is completed if workers could enter the area inadvertently.

  6. 56\57.3200 PPM Cont. • In addition, barriers are required if the area is left unattended prior to the completion of the corrective work. The mode of travel in the area must be evaluated to determine what type of barrier is appropriate to "impede" unauthorized entry.

  7. 56\57.3200 PPT Cont. • Examples of barriers would be piles of muck, piles of large boulders or a timber barricade. These barriers would have openings to allow access for persons who are correcting the hazardous conditions. These posting and barrier requirements do not apply to underground face areas under development where the corrective work is performed on a continuing basis as a part of the mining cycle, and the only workers exposed are those engaged in the corrective activity.

  8. 56 & 57.3201 Location for Performing Scaling. • Scaling shall be performed from a location which will not expose persons to injury from falling material, or other protection from falling material shall be provided.

  9. 56 & 57.3202 Scaling Tools. • Where manual scaling is performed, a scaling bar shall be provided. This bar shall be of a length and design that will allow the removal of loose material without exposing the person performing the work to injury.

  10. Scaling Hand verses Mechanical Scaling Scaling Bar Mechanical Scaler

  11. Hand Scaling Allows for a detailed assessment of rockmass integrity by close observation and “feeling the rock” Allows the back to be sounded by hand. Effectiveness dependent upon the skill and experience of personnel Economical

  12. Mechanical Scaling Allows operators to maintain a safer distance from area being scaled. Can reach higher into back or fall cavities. Applies greater force to loose blocks

  13. Data from underground mines in Sweden

  14. ROOF BOLTING Scaling Shotcrete

  15. Rock Bolt Installation More versatile Costly Limited Inexpensive

  16. 56 & 57.3203 Rock Fixtures. • (a) When rock bolts and accessories addressed in ASTM F432-95, "Standard Specification for Roof and Rock Bolts and Accessories", are used for ground support, the mine operator shall--

  17. 56 & 57.3203 Rock Fixtures. • (1) Obtain a manufacturer's certification that the material was manufactured and tested in accordance with the specifications of ASTM 432-95; and, • Where does MSHA test these bolts?

  18. 56 & 57.3203 Rock Fixtures. • (2) Make this certification available to an authorized representative of the Secretary.

  19. 56 & 57.3203 Rock Fixtures. • (b) Fixtures and accessories not addressed in ASTM F432-95 may be used for ground support provided they- • (1) Have been successful in supporting the ground in an area with similar strata, opening dimensions and ground stresses in any mine; or

  20. 56 & 57.3203 Rock Fixtures. • (2) Have been tested and shown to be effective in supporting ground in an area of the affected mine which has similar strata, opening dimensions, and ground stresses as the area where the fixtures are expected to be used. During the test process, access to the test area shall be limited to persons necessary to conduct the test.

  21. 56 & 57.3203 Rock Fixtures. • (c) Bearing plates shall be used with fixtures when necessary for effective ground support.

  22. 56 & 57.3203 Rock Fixtures. • (d) The diameter of finishing bits shall be within a tolerance of plus or minus 0.030 inch of the manufacturer's recommended hole diameter for the anchor used. When separate finishing bits are used, they shall be distinguishable from other bits.

  23. Roof Bolting Roof Bolting • Support Principles • Support Parameters • Shotcrete

  24. Bolting Principles What is the Bolt System Designed to do? • Beam building • Suspension • Keying • Surface control - natural arch

  25. Laminated Strata Weak Strata Support Principles Beam Building Individual laminations bound together to form a single beam

  26. Anchorage Zone Support Principles Suspension Competent Strata Weak Strata Suspended layer

  27. Support Principles Keying Fractured Rock Weak Strata

  28. Surface Control Support Principles Highly jointed, altered or weathered rock

  29. Bolting Principles • Beam building • Suspension • Keying • Surface control - naturalarch

  30. Critical Parameters • Bolt Type • Strength • Grade • Diameter • Length • Density (spacing) • Plate

  31. Types of Bolts • Friction Anchored • Mechanical • Fully Grouted • Tensioned Rebar • Combination/Point Anchored • Mechanically Anchored/Resin Assisted

  32. Support Characteristics * Anchorage * Clamping * Vertical Stiffness * Horizontal Stiffness

  33. Friction Anchored Support Splitsets or Swellex Bolts Split sets provide minimal support (~1 ton per foot of anchorage) when utilized in a suspension application.

  34. FRICTION ANCHORED BOLTS SPLIT TUBE EXPANDING TUBE

  35. MECHANISMS OF FRICTION ANCHOR BOLTS LOW ANCHORAGE DEVELOPED ALONG BOLT LENGTH LITTLE OR NO SHEAR RESISTANCE ALONG SLIPS AND JOINTS UNLESS INTERSECTED BY BOLT NO CLAMP LOADS LOW PLATE LOADS

  36. Split Sets Inexpensive Easy to Install No resin cartridges Can be installed in soft or shifting ground

  37. SPLITSET

  38. RADIAL FORCE

  39. SWELLEX

  40. DYWIDAG BOLT

  41. Friction Anchor Bolts

  42. Critical Parameters • Bolt Type • Strength • Grade • Diameter • Length • Density (spacing) • Plate

  43. EXPANSION SHELL ANCHOR BOLT

  44. PARTS OF A BOLT • SHELL • STANDARD ( HARD ROOF ) • BAIL ( SOFT ROOF ) • PLUG • SPREADS SHELL • SUPPORT NUT (PAL NUT or JAM NUT) • HOLDS SHELL IN PLACE - THEN BREAKS AWAY

  45. PARTS OF A BOLT cont. • WASHER • ACTS AS LUBRICATION BETWEEN PLATE AND BOLT HEAD

  46. WHAT DOES GRADE OF A BOLT MEAN ? • GRADE 75 MEANS THE BOLT HAS A TENSILE STRENGTH 75,000 PSI • TENSION BOLTS • GRADE 60 MEANS THE BOLT HAS A TENSILE STRENGTH 60,000 PSI • NONTENSION BOLTS

  47. WHAT DOES THE TERM #5 REBAR MEAN ? • THE DIAMETER OF BOLT ARE STAMPED IN 1/8 INCH INCREMENTS • SO A #5 HAS A DIAMETER OF 5/8 INCH • A CIRCLE AROUND THE NUMBER MEANS IT IS A DEFORMED BAR • 5/8 INCH REBAR = 5

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