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Standard components and properties of Steel Roof bolts to be used in mines

Standard components and properties of Steel Roof bolts to be used in mines

1.0 Physical properties : (a) shape and size : The roof bolt shall be of MS steel or TMT Rebar having circular cross section with ribs on circumferential region. The manufacture of the roof bolt shall specify the design, calculations, yield strength and ultimate tensile strength along with elongation at yield and the factor of safety of the roof bolt manufactured by them.

(b) Length Length of roof bolt shall not be more than the designed length of + 05 mm.

(c) Diameter Diameter of roof bolt shall not be more than the designed diameter ± 04% by mass.

(d) Straightness : The roof bolt shall be straight without any joint, welding, deviation or deflection. However if the deflection or deviation cannot avoided due to practical reasons, it shall not be more than + 0.1% per metre length of the bolt.

(e) Rib The rib of the roof bolt shall be as per the design of the rib with the objective to maximise the surface area without reducing the core diameter of the roof bolt and having maximum grip with the grout. 2.0 Physico-mechanical properties : Steel for the roof bolt : The roof bolt shall be of thermo-mechanical treated (TMT) rebar manufactured from MS Grade Fe-500, Fe-600 or above. Minimum load bearing capacity (anchorage load) of the roof bolt shall be 160 KN. 3.0 Chemical Composition : chemical constituents of the steel which influence the required properties of steel are carbon, sulphur, Phosphorus, manganese and other alloying / micro alloying elements.

Thread on the Roof Bolt : (a) The minimum length of the thread shall be 150 ± 05 mm. As a routine test, one thread in every 50 produced shall be checked using a go / no- go gauge.

(b) Non-threaded end The non threaded end of the rock bolt shall be formed by cropping or sawing and shall be free from burrs and edge which protrude beyond the profile of the rock bolt. As a routine one rock bolt in every 200 produced shall be checked for straightness.

(c) The nuts shall be hexagon shape of thickness not less than 30 mm.

(d) Pull test : Thread and the nut on the roof bolt shall be subjected to pull test which should not slip at the yield strength / load of the room bolt. Bearing plate

(a) The bearing plate of the roof bolt shall be Dome Washer Plate of dimension 150 x 150 x 8 mm with compatible central hole of required size and angled side to accommodate the conical seat and nut.

(b) The minimum load at which the Domed Washer Plate will become flat should be at least 14 tonnes. Conical seat

(a) Conical seat shall be of forged steel of required dimension.

(b) The conical seat shall not be deform at 1.20 times the yield stress of the roof bolt. Tensile test of roof bolt assembly

(a) The roof bolt assembly shall be subjected to tensile test and should not fail up to 16 tonnes load. Subject to the condition that system stiffness of the roof bolt assembly shall be within 20 KN/mm. System stiffness between 50 to 150 KN.

Other properties and parameters (a) Weatherability : The roof bolts and its components are parts shall be subjected to a Accelerated Weathering Test in mine water condition for 20 days. No deterioration should occur on the assembly. (b) Accelerated Weathering Test : AWT shall also be conducted in acidic water condition for 20 days during which no deterioration should occur on the assembly. [Note the AWT under mine water condition generally is at ph > 4 and that under acidic water condition is considered at pH - 2 (05% HCL aqueous solution) during testing. The test limit is that the loss of weight shall not be more than 05%] (c) Corrosion resistance test : The roof bolt assembly shall also be subjected to Fixed Exposure and Corrosion Resistivity Test as per IS - 5555 : 1970 to test the resistance to corrosion of the steel of the roof bolt and its parts. The roof bolt should pass the required test. 6.0 Sampling and testing : In order to check the composition and required parameters during manufacture, it shall be required that the random sampling be done at the rate of 02 roof bolts per 1,000 pieces of roof bolts and its accessories manufactured in a batch which shall be subjected to the required set of tests. In case the roof bolts or any of its accessories fail to pass the required test at the users end, that batch or lot of the manufacture shall not be used in the mine and intimation thereof shall be sent to the manufacture. (Cir Approval 03/2010)