Zerdly

Solid Core Recovery Calculator

Core recovery indices all normalise a recovered length against the drilled run length.

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How to use this calculator

Enter Values

Enter your values and press Calculate to see results.

Before you rely on this: First-pass guide only. Verify safety-critical or regulated work against the relevant standards, your project requirements and a qualified professional.

How to use this calculator

  1. Enter the drilled length of the core run (the distance advanced between logging intervals), then the total length of core physically recovered from that run.
  2. Enter the length of solid, full-diameter (cylindrical) core within the run to get Solid Core Recovery (SCR); optionally enter the summed length of intact hard pieces ≥ 100 mm to also get RQD.
  3. Read SCR, TCR, core loss and, if supplied, RQD with its rock-mass class — all as percentages of the same drilled run.

How it works

Core recovery indices all normalise a recovered length against the drilled run length. Total Core Recovery is TCR = (total core recovered ÷ drilled run) × 100. Solid Core Recovery counts only core recovered as complete full-diameter cylinders: SCR = (solid core length ÷ drilled run) × 100, so it is always ≤ TCR. The difference between the drilled run and the recovered length is core loss.

Rock Quality Designation (RQD) is measured along the core axis, summing only intact, sound pieces at least 100 mm long: RQD = (Σ pieces ≥ 100 mm ÷ drilled run) × 100. RQD is then classed as Very poor (0–25), Poor (25–50), Fair (50–75), Good (75–90) or Excellent (90–100). Because SCR and RQD use different piece criteria, they are reported alongside TCR rather than derived from each other.

Worked example

3 m NQ core run. A 3 m core run recovers 2.85 m of core, of which 2.4 m is solid full-diameter core, and the sum of intact pieces ≥ 100 mm is 1.95 m. SCR = 2.4 ÷ 3 × 100 = 80.0 %, TCR = 2.85 ÷ 3 × 100 = 95.0 %, and RQD = 1.95 ÷ 3 × 100 = 65.0 % — a 'Fair' rock mass. Core loss is 0.15 m.

Common mistakes

  • Dividing by the recovered length instead of the drilled run length — all recovery percentages must be normalised against the length actually drilled, not the length that came back up.
  • Counting broken, fragmented or non-cylindrical core in the solid-core figure. SCR includes only full-diameter cylindrical core; RQD includes only intact hard pieces ≥ 100 mm measured along the core axis.
  • Measuring RQD piece lengths across a mechanical break caused by drilling or handling — those breaks should be reconstructed and the piece measured as if intact.

Frequently asked questions

What is the difference between TCR, SCR and RQD?

Total Core Recovery (TCR) is all core recovered ÷ drilled run. Solid Core Recovery (SCR) counts only full-diameter cylindrical core ÷ drilled run. RQD counts only intact, sound pieces at least 100 mm long ÷ drilled run. TCR ≥ SCR, and RQD applies a stricter piece criterion, so the three values are logged together, not derived from one another.

Why is my SCR lower than my TCR?

TCR includes every scrap of recovered core, including broken and rubbly material, while SCR only counts core that comes back as complete full-diameter cylinders. Whenever a run recovers some fractured or fragmented core, SCR will be lower than TCR. If they are equal, the entire recovered length was solid cylindrical core.

How is RQD classified?

By convention RQD is grouped as Very poor (0–25 %), Poor (25–50 %), Fair (50–75 %), Good (75–90 %) and Excellent (90–100 %). This tool reports the class for the entered RQD, but the boundaries and their engineering meaning should be confirmed against the relevant standard (e.g. ISRM) for your project.

Can recovery exceed 100 %?

No. Recovered and solid core lengths cannot exceed the drilled run, so recovery is capped at 100 %. If your measurements give more than 100 %, re-check the run length and the recovered length — apparent over-recovery usually comes from core swelling, mismeasured runs, or material carried over from a previous run.

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