Accurate hole depth is the foundation of correct charge placement and stemming height. A hole that is shorter than designed changes the charge column. A hole that is longer leaves energy at the toe.
Electronic systems and their limits
Optical and electromagnetic borehole imaging, including LIDAR and RADAR, is being trialled in drill and blast. Research since Schunnesson (2003) shows these systems can struggle with sloughing, water, debris and hole deviation.
That is why sites still use dip tapes as the physical reference to check electronic readings during calibration and QA.
What makes a good dip tape
- Graduations printed on both sides, readable when dirty
- Numbers measured from the weight end (0.0 m)
- A swivel at the weight end to stop twisting and early failure
- Clear PVC coating and around 100 kg tensile strength
- Unaffected by water, dust or deviation in the hole
Building a dipping kit
Pair the tape with a bell-bottom dip weight to find the true bottom or the top of the explosive column, and a canvas hand reel for handling. For longer runs and pattern mark-out, survey ropes up to 150 m cover the distance.
