Resin Size, Bolt Size and Hole Size - The size of the bolt relative to the cartridge and hole size is critical. The above chart gives the recommended combinations of bar, hole and cartridge sizes. The numbers in the chart refer to the yield i.e. length of encapsulation of the bolt per 12" resin cartridge. Blank spaces are non-recommended bolt and hole combinations.
Hole Condition - The hole should be cleaned and examined to ensure the resin cartridges and the rock bolt will insert smoothly.
Hole Length - If holes are drilled too short then excessive lengths of the bolt will stick out of the hole. The plate may not be effectively installed. If holes are drilled too long then resin will be wasted at the end of the hole. This will reduce the encapsulation length for a point anchored rock bolt and can reduce the load capacity of the bolt. The bolt may not be able to be tensioned adequately.
Oversize Holes - If the hole size is too large relative to the bolt size, poor mixing of the resin will result. The grout yield per resin cartridge will also be reduced. This is particularly important with point anchored bolts. Oversized holes can be caused by using the wrong bit size, leaving the drill running while flushing the hole, soft ground (faults, gouge, etc.) and bent drill steel.
Undersized Holes - Undersized holes will result in insufficient bonding of the bolt to the rock. Difficulties in inserting the bolt into the hole may also be experienced. Undersized holes are usually caused by worn bits and/or wrong bit sizes being used.
Spinning of the Bolt - refer to Resin and Cement cartridge section.
Underspinning - The bolt is spun into the resin cartridge to mix the two separate components (the catalyst and the resin matrix). Improper mixing will result in a poor installation. Underspinning results in inadequate mixing of the resin and insufficient gelling may occur. Operators will complain the resin will not set up.
No Spinning - If the bolt is simply pushed through the resin cartridge without rotation, a detrimental effect may be caused by the resin catalyst being picked up by the end of the bolt. This may cause both undercatalysed and overcatalysed areas to be created.
Overcatalysed resin yields an understrength crumbly type of anchor. Undercatalysed resin stays soft virtually indefinitely because it does not have enough catalyst to speed up the gelling reaction.
Overspinning - Overspinning will grind up the resin as it sets. Poor anchorage will result. The bolt may not be able to be tensioned properly. Consequently, the operator will once again complain the resin is not setting up!
Tensioning with Fast/Slow Set Resins - As a general guideline, when bolts are to be tensioned, fast set resin should be used at the toe of the hole for 1/3 the bolt length (minimum 24"). Slow set resin is used for the remaining 2/3 length to fully encapsulate the bolt. The slow set must be sufficiently slow to allow the plate washer and nut to be installed and the bar tensioned before the resin set up. Rebar bolts can be tensioned by torquing the nut. Dywidag bolts require a greater torque to achieve adequate tension.