RQD length threshold used in RQD calculation

RQD length threshold used in RQD calculation

• A. 5 cm
• B. 10 cm
• C. 15 cm
• D. 20 cm

Answer: (B)

The main idea is that RQD uses a cutoff length to decide which drill-core fragments count toward the quality measure. Only core pieces that are at least 10 cm long are included in the numerator; shorter pieces are discarded because they often result from drilling damage or minor breakage and don’t reflect the true continuity of the rock mass. The calculation is the sum of the lengths of all fragments ≥10 cm divided by the total core length, multiplied by 100 to give a percentage. This 10 cm threshold is standardized to provide a consistent, meaningful assessment of rock quality across samples, filtering out small fragments that could obscure the actual integrity of the rock mass.

The main idea is that RQD uses a cutoff length to decide which drill-core fragments count toward the quality measure. Only core pieces that are at least 10 cm long are included in the numerator; shorter pieces are discarded because they often result from drilling damage or minor breakage and don’t reflect the true continuity of the rock mass. The calculation is the sum of the lengths of all fragments ≥10 cm divided by the total core length, multiplied by 100 to give a percentage. This 10 cm threshold is standardized to provide a consistent, meaningful assessment of rock quality across samples, filtering out small fragments that could obscure the actual integrity of the rock mass.