Field Tests - Rock Mechanics Based on an Anisotropic Jointed Rock Model - page 508

(1976), Dawson & Istok (1991) and Özgen Karacan & Goodman (2009). According to
Thompson (1987), R can be estimated as R = 200 · r 0 .
Slug tests can also be evaluated by means of type curve methods (Ferris & Knowles
1954, Cooper et al. 1967, Papadopulos et al. 1973, Ramey et al. 1975, Bredehoeft &
Papadopulos 1980, Ostrowsky & Kloska 1989). These methods also allow the determi-
nation of the specific storage coefficient.
Falling head tests in soil are evaluated at steady state condition assuming that flow takes
place through both the wall and the bottom of the test section (USDI 1974).
Transient oscillation method
The transient oscillation method proposed by Krauss (1974) is a special case of a slug
test. With the aid of a packer, the water level in a borehole is lowered by compressed air
and then abruptly released. Depending on the rock mass permeability, this stimulates a
periodic damped oscillation of the water level, or the water level approaches exponen-
tially the undisturbed water table in the test hole. From the damping of the oscillation
of water level, the equivalent rock mass permeability, or transmissibility, can be calcu-
lated. A detailed description of this method is given in Krauss (1974), Krauss-Kalweit
(1987) and Dawson & Istok (1991).
Transient oscillation tests allow rock formations with permeability coefficients ranging
from 10 -7 m/s to more than 10 -2 m/s to be investigated. After installation of packers,
the test duration is in the order of seconds to one minute and thus is a fast and eco-
nomic method. The tests do not interfere with, or change, the groundwater conditions
(Krauss-Kalweit 1987).
Interpretation of monitoring results
A suitable method for determining the large-scale, anisotropic permeability of jointed
rock is the interpretation of monitoring results by means of numerical analyses. As an
example, during excavation of an exploration adit or tunnel, water inflow and the lower-
ing of the water table may be measured. In favorable cases, these measurements provide
information on the distribution of piezometric heads and flow rates at a large scale.
By means of back analyses of the results of these measurements, the determination of
permeability and specific storage coefficients of the rock mass is possible.