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Cross Mine(M1977-410) Technical Revision No.5 <br /> Mesh is another commonly used passive underground mining reinforcement method.Welded wire mesh <br /> and chain link mesh are the most utilized varieties.The main difference is that welded wire mesh is quite <br /> rigid while chain link is flexible.Both types are fastened to rock faces with bolts and washer plates. Mesh <br /> is exceptionally effective at retaining loose material while letting moisture and gasses dissipate. <br /> • Rock Bolts <br /> Rock bolts work by'knitting'the rock mass together sufficiently before it can move enough to loosen and <br /> fail by unraveling(piece by piece). Rockbolts should be long enough to reach the natural pressure arch <br /> when the failure zone is small.The bolt length should be at least 3 ft beyond the failure zone. In the case <br /> of an extensive failure zone,tightly spaced short rockbolts are installed to establish an artificial pressure <br /> arch within the failure zone and long cables are anchored on the natural pressure arch. In this case,the <br /> rockbolts are usually less than 10-ft long in mine drifts,but can be up to 20-ft in large-scale rock caverns. <br /> Bolt spacing is more important than bolt length in the case of establishing an artificial pressure arch. <br /> • Slot-and-wedge bolt <br /> A <br /> This type of anchor relies on a bolt,slotted at the distal end, into which a wedge is placed.As the bolt is <br /> pushed into the top of the hole,the wedge is pushed into the slot,which in turn applies pressure to the <br /> sides of the drill hole.Tension is then applied to the bolt by torqueing the nut at the proximal end,and in <br /> effect stretching the bolt,to apply a compressional force to the rock unit. Slot and wedge bolts are usually <br /> 1 inch in diameter and placed on 4-foot centers. <br /> • Mechanical anchor bolt: <br /> An improvement of the slot and wedge bolt is the mechanical anchor bolt. Prior to installation,one end <br /> of the bolt is screwed into a mechanical anchor plug.The bolt is placed to the back of the hole and rotated <br /> which causes the plug to be pulled forward into the slotted portion (leaves) of the anchor. The slotted <br /> leaves then apply pressure to the walls of the drill hole which anchors the end of the bolt.Tension is then <br /> developed in the bolt with the application of further rotation to pull the bearing plate against the rock. <br /> • Frictional rockbolts: <br /> Frictional rockbolts or friction bolts attribute their name to their support mechanism. The bolt is <br /> maintained in the rockmass by friction created along the length of the bolt. Due to this characteristic, <br /> friction bolts can slip in the hole when ground movement occurs.This makes friction bolts very efficient <br /> in dynamic conditions although they are subject to corrosion and have a lower load bearing capacity <br /> compared to mechanical and grouted bolts. The two main varieties of friction bolts are SwellexT", <br /> developed by Atlas Copco,and Split-setsT',developed by Ingersoll-Rand. <br /> o Swellex <br /> SwellexTM bolts develop frictional contact with the rock wall by inflation with high water pressure. <br /> Instead of adding torque to expand the bolt once its been inserted, high water pressure is forced <br /> into the bolt which inflates it to the contours of the drill hole profile. This secures the bolt in the <br /> hole and creates frictional resistance between the bolt and rock wall. <br /> o Split-sets <br /> 12 <br />