SAMPLE BIAS AND THE SCALING OF HYDRAULIC CONDUCTIVITY IN FRACTURED ROCK

Compilations of the hydraulic conductivity of fractured rock suggest a n increase in conductivity between laboratory and field scales. This s caling is inconsistent with recent suggestions that natural fracture n etworks are near the percolation threshold as the effective conductivi ty of networks near the percolation threshold decreases with increasin g scale. The predicted decrease in conductivity with increasing scale may not be apparent in laboratory data due to a systematic bias in lab oratory scale samples; many laboratory scale samples may not contain f ractures that are larger than the size of the sample. When this bias i s accounted for, the conductivity of simulated networks near the perco lation threshold is consistent with the compiled data and increases wi th the sample dimension. Therefore, observed scaling in conductivity c an be interpreted as consistent with the idea that many fracture netwo rks are near the percolation threshold.