Engineering Rock Mechanics

434 Questions 9.1-9. IO: permeability

49.8 The values and directions for the principal hydraulic conductivit-
ies in a dolomitic rock, shown below, were obtained from back analysis
of induced drainage discharges at the Morro da Usina Mine, Vazante
District, State of Minas Gerais, Brazil'. These are the mean principal
hydraulic conductivities for a rock mass volume greater than 3 km3.
What geological circumstances could cause these values and orienta-
tions?

N

n

90 E

180

$( K max = 1.596E-4 m/s

K min = 3.0428-6 m/s

K int = 5.927E-6 m/s

Q9.9 (a) Explain the term 'effective stress'.

(b) If a fracture contains water under pressure and the stresses at the

fracture surfaces are being considered, what would be the effect on the

normal stress and on the shear stress in the rock of steadily increasing

the water pressure?

Q9.70 In the photograph below, the water pressure in a borehole in

marble has been steadily increased. In addition to the normal pressure

created at the rock surface, the water pressure in this configuration

also creates a circumferential tensile stress of the same magnitude in

the rock, as in Q4.6. A crack developed and was propagated under

servo-controlled conditions from A to B. The water not only penetrated

the crack but also the intact marble, forming the dark inverted V visible

' The authors are grateful to Prof. E. Quadros and Dr. F. 0. Franciss for permission to

use this example.