Baselining Development Mining (Drifting)



Development mining is a challenge in that drifts are required to access orebodies in a timely fashion. If drifting lags, there may be a problem reaching production targets. For the most part, a pictorial view is provided for this process as real world examples.
Baselining process is about process improvement and a great deal of measurement. After any change is made, it becomes important to measure the change in that process and evaluate in numerical terms the % difference in improvement or retrogression.

General Observations

  • Development mining is a process that hasn’t changed much in 60 years – advance about 3.7 m per day (3 shifts) - some operators/contractors can sometimes provide 3 times the 3.7 m advance
  • Batch process with post-shear
  • Geometry similar to VRM but is direction of blast motion is horizontal rather than vertical
  • Timing and sequencing – long timing intervals for generation of free facesA
  • Drill holes are short and nearly parallel, similar to surface sinking cut blasting
  •  profile is that of a normal distribution  and is usually not a big problem providing the cut provides relief
  • ANFO has been dominant as the explosive product of choice
  • Long period NONEL is the detonator of choice however electronic detonator are making real advances into all mining methods since inventory is reduced and delay timing is highly accurate
  • Move to gassed emulsions and electronic detonators is presently creating inroads
  • Current advance about 24 7.3 m per day over 3 shifts
  • Poor perimeter control not only affects ground control but but a larger load on ventilation because of the roughness of a development drive
Typical development mining scenes - fine muck providing good relief is usually the norm, and the use of advanced technology such as electronic detonators and gassed emulsions are important developments in technology for producing generous development advances per shift.
Generating void space is the job of a properly designed 'cut' such that at lease 25% void space is usually the limit that a planner accepts as the lowest limit to adopt. The pictures below show some examples of cut design. New holes to be drilled are marked with either a white or red 'X'  with red painted circles indicating bootlegs.
Typical drive showing bootlegs and positions of new holes.
It is important to keep development mining ahead of production because of the number of workplaces that are required to meet daily tonnage levels. At the present time, there are planning software is able to download the exact drilling
parameters to a jumbo drill so that marking up holes (surveying) takes less time. The pictures below some of the issues with development automation which is problematic if the tool steel does not 'bite' easily or exactly when drilling starts. Rod stiffeners are usually employ to prevent the drill bit from skidding on inclined surfaces.
The left drawing shows a typical drift design with an example of 'cut' holes. The picture on the right includes a drift plan on the left hand side showing what a jumbo drill said it drilled from stored data. However the truth came out as shown by the right hand side drift outline that was actually surveyed. There is a real need to ensure that the drift face remains as smooth as possible to allow correct bit positioning. Smooth backs and sides allow better air ventilation flow.
Perimeter control is paramount in order to prevent cracking beyond the drift wall that would lead to instabilities and raveling of the drift back.  The photographs below illustrate some good examples of perimeter control using gassed emulsions.
Picture at far left shows electronic detonators being used with gassed emulsions for perimeter control. The following picture shows gassed emulsion being loaded into primed holes on the wall perimeter. The next picture shows the result of this trial blast after screening and bolting. The last picture shows the results of a separate perimeter control blasting method using decoupled cartridges in the perimeter holes.

Quality of a Drift can be Quantified in a Number of Ways

  • Measure the number of half-barrels and miss-holes that are visible on the drift walls after a blast (via photography and logsheets
  • Obtaining ‘as-built’ profiles at desired sections throughout a drift to define over-break and under-break
  • Structural geological mapping is a good indicator as to the quality of the existing rock mass

Quality Control Measures in a Drift Can Lead to

  • Reductions in ground support requirements
  • Decreased scaling
  • Reduction in waste-rock hauling
  • Optimum drift geometry (favourable stress conditions at depth)
  • Improvement of the overall working conditions in a drift – ease of installation of ground support
  • Improvements in ventilation air flow quantities - less turbulent, faster volume flow
Typical results from a design profile standpoint and the actual 'as-built' result.
Time studies were completed for a variety of drift operations including the following operations that comprise a development round cycle:
  • Jumbo pre-drilling operations
  • Jumbo drilling operations
  • Explosivs loading
  • Ground support
Jumbo Pre-Drilling Operations - Blastholes
Total Man-Hours for One Operational Cycle (Per Shift)
Note that mucking is left until the back shift at which time proper ground control takes place. The above work would start in the morning shift. The above time study can vary greatly between mines and shifts and is dependent on the mining corporation involved. The rest of the tasks are listed below for various cycle operations.
Jumbo Drilling Operations - Blastholes
Total Man-Hours for One Operational Cycle (Per Shift)
Explosive Loading Operations - Blastholes
Total Man-Hours for One Operational Cycle (Per Shift)
Ground Support Operations - Drilling, Screening and Bolting
Total Man-Hours for One Operational Cycle (Per Shift)
Total Man-Hours Per 0.3 Meter of Advance
See Below for Instructions Regarding Use
This chart represents the major components of development mining as individual processes.
The last chart (Total Man-Hours Per 0.3 Meter of Advance) is an important one. To use this data just select the advance required by a mine for development - for example , 7 meters of advance over a period of 24 hours. Using the data from this charge, 22.50% of the time (24 hours) would be required for blasthole drilling. Similarly, 14.2% of 24 hours would be required for blasthole loading and 63.3% of 24 hours would be allocated to ground control. It is implied by the data, when cost savings is a goal, that the most important items are those that take the greatest time to complete and in this case it would be ground control. Imagine the savings if time to prepare ground control measures could be reduced by adopting a perimeter control methodology that requires little scaling or marking up bootlegs etc. It is always important to look at those process that are high cost/high labour and attempt to reduce these to manageable best practices.

Planned Design Versus As-Built Design

During the collection of the above pie chart data, drift design could be distorted by many differenct issues - drill hole quality, irregular face problems, and even surveying proper location for holes as indicted below.
Plan View of Drift Design - Drill/Blast Worst Case Survey
Plan View of Drift Design - Drill/Blast Best Case Survey