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Scaled Span Method

The Empirical Scaled Span Design Method (Carter, 1992, 2014) option in CPillar, is detailed in the paper linked below:

Guidelines for use of the Scaled Span Method for Surface Crown Pillar Stability Assessment

The scaled span empirical approach was initially developed for steeply dipping ore body geometries. The method requires the user to estimate crown geometry and assess whether the stope geometry is steep or shallow, in order to apply the most appropriate empirical relationships. The user must also assess "controlling", not average, rock mass quality (including assigning the stress and water terms within the estimated Q value). These are important considerations in correct application of the method. Accordingly the user should familiarize themselves with the following critical limitations before applying the method.

Critical Limitations

Each of the following critical limitations is described in more detail in the paper "Guidelines for use of the Scaled Span Method for Surface Crown Pillar Stability Assessment". The links below go to the relevant sections of the paper.

  • Revised Scaling Approach - Shallow Stopes (Section 6.1 - pg 14)
  • Estimating controlling rock quality (Section 7.1 - pg 22)
  • Assessing change in rock quality and failure risk with time (Section 7.2 - pg 23)
  • Influence of Structure (Section 7.3 - pg 25)
  • Optimizing definition of water and stress terms (Section 7.4 - pg 26)
  • Accounting for overburden or lake bodies (Section 7.5 - pg 26)

    Modification to the Shallow Dip Correction

    A 10 degree transition zone between the steep scaled span equation (Equation 3 in 2014 paper) and the shallow scaled span equation (Equation 5) has been added to provide a smoother transition between the two. If the dip of the ore body is greater than or equal to 55 degrees, the steep equation is used. If the dip is less than or equal to 45 degrees, the shallow scaled span equation is used. Between 55 and 45 degree, a linear transition between the two is implemented.

    Additional Resources

    A New Approach to Surface Crown Pillar Design (Carter, 1992)

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