Presentation on theme: "Scaling and Bolting or Shotcrete 56 & 57.3000 Definitions. The following definitions apply in this subpart. Rock burst. A sudden and violent failure."— Presentation transcript:
Scaling and Bolting or Shotcrete
56 & 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.
56 & 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.
56 & 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.
56\ 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.
56\ 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.
56\ 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.
56 & 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.
56 & 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.
Hand verses Mechanical Scaling Scaling Bar Mechanical Scaler Scaling
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. Economical Effectiveness dependent upon the skill and experience of personnel
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
Data from underground mines in Sweden
Rock Bolt Installation Limited More versatile Inexpensive Costly
56 & 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--
56 & Rock Fixtures. (1) Obtain a manufacturer's certification that the material was manufactured and tested in accordance with the specifications of ASTM ; and, Where does MSHA test these bolts?
56 & Rock Fixtures. (2) Make this certification available to an authorized representative of the Secretary.
56 & Rock Fixtures. (b) Fixtures and accessories not addressed in ASTM F 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
56 & 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.
56 & Rock Fixtures. (c) Bearing plates shall be used with fixtures when necessary for effective ground support.
56 & Rock Fixtures. (d) The diameter of finishing bits shall be within a tolerance of plus or minus 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.
Roof Bolting Support PrinciplesSupport Principles Support ParametersSupport Parameters ShotcreteShotcrete
Bolting Principles Beam buildingBeam building SuspensionSuspension KeyingKeying Surface control - natural archSurface control - natural arch What is the Bolt System Designed to do?
Beam Building Weak Strata LaminatedStrata Individual laminations bound together to form a single beam Support Principles
Suspension Competent Strata Weak Strata Anchorage Zone Support Principles Suspended layer
Keying Weak Strata Fractured Rock Rock Support Principles
Surface Control Highly jointed, altered or weathered rock Support Principles
Bolting Principles Beam buildingBeam building SuspensionSuspension KeyingKeying Surface control - naturalarchSurface control - natural arch
Critical Parameters Bolt TypeBolt Type StrengthStrength –Grade –Diameter LengthLength Density (spacing)Density (spacing) PlatePlate
MECHANISMS OF FRICTION ANCHOR BOLTS LOW PLATE LOADS LOW ANCHORAGE DEVELOPED ALONG BOLT LENGTH NO CLAMP LOADS LITTLE OR NO SHEAR RESISTANCE ALONG SLIPS AND JOINTS UNLESS INTERSECTED BY BOLT
Split Sets Inexpensive Easy to Install No resin cartridges Can be installed in soft or shifting ground
Friction Anchor Bolts
Critical Parameters Bolt TypeBolt Type Strength –Grade –Diameter Length Density (spacing) Plate
EXPANSION SHELL ANCHOR BOLT
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
PARTS OF A BOLT cont. WASHER –ACTS AS LUBRICATION BETWEEN PLATE AND BOLT HEAD
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
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
ROOF BOLT HEAD MARKING 5 Grade 55 5/8 INCH DIAMETER
ROOF BOLT MARKINGS GRADE DIAMETER DESIGNATION 40 3/4 INCH UP NONE 55 5/8 INCH UP 60 5/8 INCH UP 75 5/8 INCH UP X 100 5/8 INCH UP
Plugs Shell Leaves Support Nut Bolts Bail BAIL STANDARD
STANDARD 4 LEAF TYPE EXPANSION SHELL
THREE PRONG EXPANSION SHELL
TWO LEAF BAIL TYPE EXPANSION SHELL
JAM NUT TO STRONG
JAM NUT TOO STRONG ( DOES NOT BREAK AWAY AND DEFORMS THE SHELL )
JAM NUT TOO WEAK
JAM NUT TOO WEAK ( BREAKS AWAY TOO SOON AND DOES NOT EXPAND SHELL )
56 & Rock Fixtures. (f) When rock bolts tensioned by torquing are used as a means of ground support, (1) Selected tension level shall be- (i) At least 50 percent of either the yield point of the bolt or anchorage capacity of the rock, whichever is less; and
56 & Rock Fixtures. (ii) No greater than the yield point of the bolt or anchorage capacity of the rock. WHAT IS ANCHORAGE CAPACITY OF THE ROCK & HOW DO WE MEASURE IT?
WHAT IS THE RELATIONSHIP BETWEEN THE WASHER AND THE TENSION IN THE BOLT ? THE “K” FACTOR IS THE RELATIONSHIP BETWEEN THE WASHER & TENSION IN BOLT NO WASHER K = 40 HARDENED WASHER K = 50 ANTIFRICTION WASHER K = 75 > 125 »HARD PLASTIC
K FACTOR cont. TENSION IN BOLT = K x TORQUE FOR A BOLT USING A HARDEN WASHER AND HAS A TORQUE OF 150 FT- LBS TENSION IN BOLT = 50 x 150 TENSION IN BOLT = 7500 LBS
MECHANISMS OF MECHANICAL BOLTS MODERATE CLAMP LOADS MODERATE PLATE LOADS MODERATE TO HIGH ANCHORAGE DEPENDING ON THE STRATA CLAMP LOADS DEVELOP SOME SHEAR RESISTANCE ALONG BEDDING PLANES, SLIPS AND JOINTS
56 & Rock Fixtures. (2) The torque of the first bolt, every tenth bolt, and the last bolt installed in each work area during the shift shall be accurately determined immediately after installation. If the torque of any fixture tested does not fall within the installation torque range, corrective action shall be taken.
56 & Rock Fixtures. (g) When grouted fixtures can be tested by applying torque, the first fixture installed in each work place shall be tested to withstand 150 foot-pounds of torque. Should it rotate in the hole, a second fixture shall be tested in the same manner. If the second fixture also turns, corrective action shall be taken.
56 & Rock Fixtures. (h) When other tensioned and nontensioned fixtures are used, test methods shall be established and used to verify their effectiveness. (i) The mine operator shall certify that tests were conducted and make the certification available to an authorized representative of the Secretary.
56\ Rock Fixtures PPM This standard contains the requirements for installation and testing of all rock fixtures and accessories used for ground support. In all cases where rock fixtures are selected as the method used to support ground, they must meet the requirements of 56/
56\ PPM Cont. All bolts tensioned by torquing must be within the torque range set out in paragraph (f)(1). Mine operators are required to test the first, tenth and last bolt installed in each work area during the shift as a check on whether or not the torquing requirements are being achieved. When the testing process reveals that a fixture is not properly torqued, steps must be taken to determine the extent of defective installation and to correct all improperly installed fixtures.
56\ PPM Cont. The ground conditions in many active face areas require the installation of only a few bolts during each blasting cycle. Testing of the first and last bolts in each work area will help ensure the integrity of the ground in these instances. Where large numbers of bolts are installed on a continuing basis, testing of the first, tenth and last bolt in each work area would normally provide the frequency of testing necessary to identify a bolting problem and enable the operator to take corrective action.
56\ PPM Cont. The mine operator must certify that all tests required by this standard have been conducted. In the case of testing of the ASTM bolts and accessories by the manufacturer of the devices, the mine operator's certification responsibility is satisfied by obtaining a copy of the manufacturer's certification and making it available to the inspector
56\ PPM Cont. The correction of improperly installed fixtures will also help to ensure compliance with standard which requires that wall, bank and slope stability be maintained at surface mines where miners are exposed, and standard , which requires that ground support systems at underground mines be designed, installed and maintained to control the ground where miners are exposed.
MECHANISMS OF FULLY GROUTED BOLTS LOW PLATE LOADS HIGH ANCHORAGE DEVELOPED ALONG BOLT LENGTH NO CLAMP LOADS LITTLE OR NO SHEAR RESISTANCE ALONG SLIPS AND JOINTS UNLESS INTERSECTED BY BOLT HIGH SHEAR RESITANCE ALONG RESIN/ROCK INTERFACE
RESIN ANCHOR TORQUE TENSION BOLT IN THE FIRST TYPE OF INSTALLATION, TWO FOOT OF FAST SETTING RESIN IS USED, AND THE REST OF THE HOLE IS LEFT OPEN
RESIN ANCHOR TORQUE TENSION BOLT SECOND TYPE, ONE TO TWO FOOT OF FAST SETTING RESIN IS PUT IN THE BACK OF THE HOLE, WHILE SLOW SETTING RESIN IS PUT IN THE BOTTOM OF THE HOLE
Aluminum Plug Cast Dome Shear Pin Tension Nut Threaded Deformed Bar TENSION NUTS
MECHANISMS OF TENSIONED REBAR BOLTS VERY HIGH PLATE LOADS EXTREMELY HIGH ANCHORAGE REGARD- LESS OF STRATA VERY HIGH CLAMP LOADS CLAMP LOAD DEVELOPS VERY HIGH SHEAR RESISTANCE ALONG SLIPS AND JOINTS HIGH SHEAR RESISTANCE ALONG RESIN/ROCK INTERFACE
Compression Tube Deformed Bar Mechanical Bolt
RESIN POINT ANCHOR WITH REBAR SUPPLEMENT
RESIN POINT ANCHOR WITH STEEL PIPE SUPPLEMENT
RESIN POINT ANCHOR WITH SHEAR PIN & COMPRESSION RING
HIGH CLAMP LOADS MECHANISMS OF POINT RESIN ANCHORED BOLTS HIGH PLATE LOADS HIGH ANCHORAGE EVEN IN SOFT ROCK CLAMP LOADS DEVELOP MODERATE SHEAR RESISTANCE ALONG BEDDING PLANES,SLIPS AND JOINTS
MECHANISMS OF COMBINATION BOLTS VERY HIGH CLAMP LOADS VERY HIGH PLATE LOADS EXTREMELY HIGH ANCHORAGE REGARDLESS OF STRATA GROUTED LENGTH REINFORCES THE STRATA LIKE A FULLY GROUTED BOLT CLAMP LOADS DEVELOPS HIGH SHEAR RESISTANCE ALONG BEDDING PLANES, SLIPS AND JOINTS
Support Characteristics Fully Grouted Mechanical Combination Point Anchor Tensioned Rebar Very High Moderate Very High Very High Low Moderate Very High Very High Low Medium/ High Low/ Medium Very High Medium/ High Low High Medium Very High AnchorageClamping Vertical Stiffness Horizontal Stiffness Frictional Anchors Low Bolt Type