RQD value
The RQD value or RQD number is a value in geotechnics and engineering geology to classify drill samples (drill cores) of a rock and means "Rock Quality Designation Index". The rock or mountain classification according to the RQD value goes back to Deere (1963).
definition
RQD is defined as the quotient:
- * 100%
- = Sum of the lengths of the drill core pieces that are longer than 10 cm
- = Total length of the drill core
The total length also includes lost fragments. - The RQD value should be determined as soon as possible after drilling.
Classification table
| RQD | Rock quality |
|---|---|
| <25% | very low |
| 25-50% | low |
| 50-75% | medium |
| 75-90% | Well |
| 90-100% | excellent |
application
Using the RQD value can with experience formulas to the compressive strength of the rock ( rock strength close), for example with the aid of the RMR value .
disadvantage
A drill core 1 m long, which breaks up into eleven fragments 9 cm long, is assessed very poorly according to this criterion. But if it breaks up into nine fragments 11 cm long, it has an excellent RQD value, although both cores are actually almost the same.