Mine Design: Benching

Mine Design: Benching

Who does what and how?

Elements Of Pit Slope Design

Elements Of Pit Slope Design 300x213 Mine Design: Benching

What Is a Bench?

… a ledge that, in open-pit mines and quarries, forms a single level of operation above which minerals or waste materials are excavated from a contiguous bank or bench face ….
Bench parameters (geometry):

  • height
  • width
  • slope angle

Types of Benches

Working bench
The mineral or waste is removed in successive layers, each of which is a bench, several of which may be in operation simultaneously in different parts of , and at different elevations in, an open pit mine or a quarry…

  • properties & size of equipment defines the width
  • same plus selectivity defines height
  • geotechnics define slope angle

Catch bench
remnant bench left to:

  • catch the material/rock falling down the slope
  • facilitate access to the face

Working Bench, Catch Bench

Working Bench Catch Bench 300x228 Mine Design: Benching

Catch Bench Geometry

Catch Bench Geometry 300x281 Mine Design: Benching

Bench facts:
1. face angle varies from 55o –80o
2. most important design component for

  • optimisation
  • equipment selection
  • production planning

3. types

  • working bench
  • safety bench
  • double bench

Working Bench

Working Bench 300x122 Mine Design: BenchingWorking Bench 1 300x169 Mine Design: Benching

SB= Safety bench ( In the beginning it is approx. 2/3 of bench height. At the end of mine life reduced to approx. 1/3 of bench height)

WB= Working bench

  • Double benches at final pit limits.
  • Avoiding intermediate catch benches facilitates steepening the overall pit slope angle

Typical Berm Design

Typical Berm Design 300x151 Mine Design: Benching

Berm facts:

  • Berm height is usually greater than or equal to 1/2 tire radius.
  • Berm slope is normally 35o

Note: Berm in this context is strictly a safety berm. Many mine design software uses the term “berm” as safety bench or catch bench

Double benching? Triple benching?

Bench height vs. slope angle

Bench height vs. slope angle 221x300 Mine Design: Benching


Wall, bank, and slope stability.

Mining methods shall be used that will maintain wall, bank, and slope stability in places where persons work or travel in performing their assigned tasks. When benching is necessary, the width and height shall be based on the type of equipment used for cleaning of. benches or for scaling of walls, banks, and slopes.

Bench Cleaning?

Bench Cleaning 300x192 Mine Design: Benching

Correction of hazardous conditions.

Ground conditions that create a hazard to persons shall be taken down or supported before other work or travel is permitted in the affected area. Until corrective work is completed, the area shall be posted with a warning against entry and, when left unattended, a barrier shall be installed to impede unauthorized entry.

Pit Design: Benches

Higher and wider benches yield:

  • Less selectivity (dilution, recovery)
  • Fewer working places thus less flexibility
  • Flatter slopes: large machines need wide benches
  • Fewer equipment relocations & set-ups
  • Higher productivity at lower unit cost
  • Improved control and supervision

How High Should a Bench Be?

  • Deposit character and geology: selectivity
  • Production strategy: ore/waste ratios, blending requirements, no. of working faces, operating/capital costs, etc.
  • Slope stability considerations
  • Equipment set / equipment specific optimum geometry

Is this slide a problem?

slope 1 300x202 Mine Design: Benching

Lots of added work ($$$$….) here

Would you drive there?

slope 2 245x300 Mine Design: Benching

Reduced Bench Heights


  • ramp volume reduced (fill ramps)
  • contour areas easier to drill & blast
  • ore grading and selective mining is easier
  • multi-row blasts easier to blast
  • single pass drilling easier


  • poor bench grade control by shovel is accentuated
  • reduced drilling yield and increased drill and blast cost
  • subgrade costs more (relatively larger)
  • reduced shovel productivity

Bench Height – Optimization

Bench Height Optimization 300x191 Mine Design: Benching

Are bench dimensions always important?

bench dimensions 267x300 Mine Design: Benching

Bench Height and Dilution

Bench Height and Dilution 300x178 Mine Design: Benching

Watch Your Blasting!

Blasting 300x165 Mine Design: Benching

Slope Design: Summary

Slope Design Summary 300x215 Mine Design: Benching

Slope Design: Conclusions

  • Maximize the height of the benches

at the expense of mining selectivity?

  • Minimize the width of working benches

at the expense of productivity?

  • Minimize the number & width of catch benches

at the expense of safety?

  • Minimize the width & number of haul roads

at the expense of productivity & safety?

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