Part 1.  Using Sand Instead of Blasting Mats: How to Calculate the Required Weight and Apply It Safely

By Petr Explosives Group (PEG)

“If flyrock occurs, the blast design has already failed.”

Blasting mats are one of the most common tools used to control flyrock, airblast, and surface ejection. However, in many field situations—remote projects, limited logistics, or cost constraints—mats may not be available.

In those cases, blasters sometimes turn to sand as a surface cover.

This approach can work—but only if it is treated as an engineered solution, not a guess.

1.  Sand is secondary protection
2.   Blast design is the primary control

What Does Sand Actually Do?

Sand provides:

• Mass loading → resists upward movement

• Momentum absorption → slows rock fragments

• Distributed confinement → reduces surface venting

It is most effective for:

• Collar breakout control

• Small-to-moderate surface ejection

• Supplemental flyrock mitigation

It does NOT fix:

• Poor burden or spacing

• Inadequate stemming

• Excessive charge near the collar

Core Engineering Formula

The required sand weight is calculated using:

Sand weight (lb) = Area (ft²) × Thickness (ft) × Density (lb/ft³)

Recommended Field Value

• Sand bulk density (typical):  100 lb/ft³

PEG Field Shortcut (Very Useful)

Using 100 lb/ft³:   Sand weight (lb) = Area (ft2) × Thickness (in) × 8.3.

                                 Sand weight (tons) ≈ Area (ft2) × Thickness (in) × 0.00417

Quick Reference Table

 Rule of thumb:  1 inch of sand ≈ 8.3 lb/ft²

Example- Given:

• Area = 20 ft × 30 ft = 600 ft²

• Sand thickness = 6 inches

Calculation:

Sand weight (lb) = Area (ft2) × Thickness (in) × 8.3.

600 x 6 x 8.3 = 29,880 lb

29,880 ÷ 2000 = 14.94 tons

Answer:  You need approximately 30,000 lb (15 tons) of sand.

How to Select Sand Thickness

This is the most important engineering decision.

• Key Design Factors:
• Hole diameter
• Charge near the collar
• Burden and spacing
• Decking vs continuous column
• Rock condition
• Free face geometry

• Critical Field Practices

✅ DO:

• Use clean sand (not soil or clay)
• Apply uniform thickness across the entire area
• Cover all holes—no gaps
• Protect the initiation system carefully
• Place sand after the final hookup check

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❌ DO NOT:

• Use wet clay or soil
• Leave thin zones or voids
• Cover only part of the blast
• Use sand to compensate for poor design

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• Sand vs Blasting Mats

• Feature	Sand	Mats
  Confinement	Moderate	High
  Reliability	Variable	Consistent
  Installation	Fast	Labor intensive
  Reuse	No	Yes

  Sand = mass-based protection.     Mats = structural containment.

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• Advanced Insight (Important for Professionals)
• Sand works by reducing velocity, not energy.
• If energy release is too high → sand will fail
• If design is correct → sand performs very well

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 Engineering Rule

Correct Sequence:

• Design the blast properly
  • Burden
  • Spacing
  • Stemming
  • Charge per delay
• Then apply sand cover
  • Select thickness
  • Calculate weight
  • Ensure full coverage

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         Sand (tons) = Area (ft²) × Thickness (in) × 0.00417​

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Conclusion

• Sand can be an effective temporary solution when blasting mats are not available—but only when used correctly.
• The calculation is simple to predict the amount of sand and the weight.
  The engineering judgment is not.
•  If you need excessive sand thickness, stop and redesign the blast.