On foundation sites, the most expensive mistake I see is the wrong rig for the ground. Not wrong by a factor of ten — wrong by just enough that the rig spins the auger for hours without advancing, the project falls behind schedule, and nobody can quite explain why. Nine times out of ten, the rig was sized by torque alone. Crowd force was ignored, or assumed to be “sufficient.”
The Depth Correction — Why It Gets Harder as You Go Deeper
Both torque and penetration force requirements increase with depth — not just because of the formation, but because of side friction on the Kelly bar and casing as they extend further into the bore. At 10 metres in medium clay, side friction is manageable. At 35 metres in the same clay, side friction adds a meaningful load on top of the cutting resistance at the bit. The calculator applies a depth correction factor that accounts for this — which is why you can’t just use the surface-condition torque figure for a deep pile project.
Formation Resistance Reference
| Formation Type | Specific Cutting Resistance | Penetration Resistance |
|---|---|---|
| Soft clay / loose sand | 80–120 kNm/m² | 40–80 kN/m |
| Medium stiff clay / dense sand | 150–220 kNm/m² | 90–150 kN/m |
| Gravel with cobbles | 220–320 kNm/m² | 150–250 kN/m |
| Weathered rock | 280–380 kNm/m² | 220–350 kN/m |
| Hard rock (basalt/granite) | 450–700 kNm/m² | 350–600+ kN/m |
How to Calculate Piling Rig Torque? Rotary Power & Soil Penetration Force Estimator
Technical Analysis for Foundation Engineers & Rig Operators
🏗️ Drilling Performance Report
| Required Rotary Torque: | kNm |
| Required Crowd Force: | kN |
| Recommended Rig Class: |
Analyse the pilling rig drilling power and assess its operational feasibility.
