Volumetric rock quality designation with lognormally distributed intact lengths

Abstract EN

Rock fragments due to different joint types are classified qualitatively into three categories as bars, plates and prisms.

However in engineering evaluations their quantitative descriptions based on the field observations leading to reliable design values are of prime importance.

Simple conceptual models of rock fragments coupled with the scanline measurements provide objective relationships between the rock quality designation (RQD), volumetric, areal of linear (along scanline) joint counts (JJ and block volumes (V).

The main purpose of this paper is to derive such relevant relationships for the logarithmically distributed intact lengths, Due to the complication of these relationships the results are presented in the form of various charts which are hoped to provide useful tools for any engineering geologist.

The presented charts arc for standard deviation equal to unity, however, charts for any desired value of standard deviation can be prepared from the relevant equations.

The implementation of the methodology is performed for actual field data.

A significant conclusion is that the negative exponential distribution provides a single volumetric RQD value which is different than the directional RQD's.

However, the log-normal distribution gives almost the result within the practical limits both for directional and volumetric RQD values.

This is a valid conclusion that the log-normal distribution represents the field data better than negative exponential.