Scale effects in the destructive testing of borehole cores

This paper demonstrates that the uniaxial compressive strength (UCS) values of rock samples from two boreholes in Leicestershire, UK are subject to significant scale effect. The magnitude of these scale effects is shown to be lithologically dependent, as is the Representative Element Volume (REV) — the size of sample above which there will be no further scale effect. The results using the author’s methodology are compared with published data and are found to be in close agreement. However, it is calculated that, for each of three lithotypes, the UCS of the bulk rock mass varies only between 73.7 and 76.6% of that of a 25mm diameter and 50mm long cylinder of the same material. It is therefore concluded that, for the purposes of a wider research programme studying correlations with geophysical values, no correction for this phenomenon is required as only 25mm diameter cylinders are being used in that work.