Field Tests - Rock Mechanics Based on an Anisotropic Jointed Rock Model - page 500

The standard method for interpreting the transient fl ow phase during pumping tests
with respect to the permeability k RM and the specifi c storage coeffi cient S 0 of the rock
mass assumes laminar and radial fl ow around the well in a homogeneous and isotropic
aquifer of infi nite extent. This method is based on the corresponding analytic solution
of Theis (1935) (Equation (6.67) in Section 6.4.2):

(15.43)

where is the aquifer thickness and W(u) is the well function

The test evaluation is based on an approximation of h(r,t) that is valid for large times,

that is, when u < 0.01 (Equation (6.67a) in Section 6.4.2):

Δ

(15.43a)

Thus, for a suffi ciently large time t, the Δ h versus ln(t) plot at the well and the observa-

tion holes forms a straight line:

From the slope

(15.44)

of this line the equivalent rock mass permeability k RM and transmissibility T normal to
the test hole can be calculated by solving (15.44) for k RM (Fig. 15.30, lower left):

(15.45)

At the intersection point ln(t 0 ) of this line with the ln(t) axis, the condition

and thus

(15.46)