S e c t i o n 4 - P a g e 3 May 2013 Undersize Holes - If the hole size is too small r elative to the friction size then it becomes extr emely dif fcult to install the bolt. The bolt can be damaged i.e. kinked or bent when installed. Undersized holes ar e usually caused by wor n bits and/or wr ong bit sizes being used. If integral steel is used with a stoper or jackleg, the hole diameter decr eases with each change of steel (normal practice r equir es smaller bits be used as one drills deeper into the hole). With each r eduction in hole diameter the anchorage capacity incr eases. Integral steel often r esults in cr ooked holes and should be avoided whenever possible. Drive Times - For a typical 5 or 6 foot friction bolt, a stoper or jackleg will drive the bolt into the hole in 8 to 15 seconds. This drive time corr esponds to pr oper initial anchorages of the stabilizer . Faster drive times should serve as a war ning that the hole size is too lar ge and thus the initial anchorage of the bolt will be too low . Longer drive times indicate smaller holes sizes pr obably caused by bit wear . continued Installation Quality Guidelines Friction Stabilizers The following ar e items to be awar e of when using/installing friction stabilizers: T ype of Gr ound - The natur e of the gr ound must be evaluated. Soft strata r equir es a longer anchorage length to be ef fective. Soft gr ound r esults in lar ger hole sizes for a given bit size (dueto bit rattling and r eaming). Scaling - The gr ound should be thor oughly scaled (i.e. barr ed down) befor e drilling and bolting. Periodic r e-scaling may be r equir ed while drilling. Str ength and Y ield Capacity of Bolt -The mechanical pr operties of the bolt should be appr opriate for the gr ound conditions, bolt length and bolting patter n. Pull tests should be performed to determine initial anchorage of the friction bolts. Pr oper Grade Plates - Thin or weak plates will deform at low bolt tension. The bolt could also rip thr ough the plate during installation or by bolt loading. Plates should meet ASTM F432 specs. Hole Condition - The hole should be cleaned andexamined to ensur e the friction bolt will insert smoothly . V ariation in hole diameters (due to dif fering str engths of r ock strata or excessively fragmented gr ound) can yield variations in anchorage capacities at various elevations. Hole Length - If holes a re drilled too short then the bolt will stick out of the hole and the plate will not make contact with the r ock surface. Damage to the bolt will r esult if an attempt is made to drive the bolt further than the hole length will permit. The hole should thus be a few inches deeper than the bolt length being used. Oversize Holes - The hole size r equir ed for the friction stabilizer is the most crucial aspect of the installation. The holding power of the bolt r elies on the fact that the hole is smaller than the diameter of the bolt. The lar ger the hole r elative to the bolt diameter , the less the holding for ce (at least initially). Oversized holes can be caused by using the wr ong bit size, leaving the drill running while ushing the hole, soft gr ound (faults, gouge, etc.) and bent steel. www .dsiundergr ound.com