Engineering Rock Mechanics

Question and answers: permeability 153

Q9.7 The following rock mass hydraulic conductivity data were ob-

tained from four sets of tests on fractured rock samples with volumes

1 m3, 5 m3, 10 m3, and 15 m3. In each case it was assumed that

the hydraulic conductivity was a scalar quantity. The data values are

in units of 1 x lo-* m/s. As the test volume increased, so did the

difficulty and the cost of the tests, so there are fewer data for the

tests at larger volumes.

DUM for test size of 1 m3

2.122 1.156 3.696 1.165 1.649 2.886 1.652 2.876 1.197

2.593 2.114 2.771 16.214 2.529 1.700 7.658 10.928 0.627

9.854 0.847 0.670 1.623 2.274 5.163 2.209

Dcrtu for test size of 5 m3

1.630 1.981 2.436 3.700 1.215 1.767 0.909 0.450 3.512

1.314

Dcrtar for test size of 10 m3

1.369 1.188 2.037 1.688

Dufu for test size of 15 m3

1.487 1.343 1.473 1.738

Using the data above, estimate the REV value5 for the hydraulic

conductivity of the fractured rock mass tested.

A9.7 The rock property data, together with the mean value for each
sample volume, are plotted in the diagram below. We can see that there
is a larger variation for the smaller sample sizes, and that the mean value
progressively decreases as the sample size increases (i.e. from 3.53 x
m/s, through 1.89 x m/s and 1.57 x m/s to 1.51 x IOp6 m/s).

0 2 4 6 8 10 12 14 16

Size of test sample, m3

Visual inspection of this plot shows that there does seem to be a stable

value for the conductivity at larger volumes, of about 1.5 x m/s

The REV definition is given in Section 9.1.