Field Tests - Rock Mechanics Based on an Anisotropic Jointed Rock Model - page 501

is fulfi lled. Solving (15.46) for S 0 yields:

(15.47)

This evaluation method was developed by Cooper & Jacob (1946).
The recovery period allows us to determine the equivalent permeability coeffi cient k RM
and transmissibility T from the linear range of a Δ h versus ln(t/t 1 ) plot:

(15.48)

where h 2 is the slope of this line (Fig. 15.30, lower right).

Strictly speaking, this evaluation of the transient pumping and recovery periods is valid
only for confi ned aquifers. However, if the drawdown is small compared with the thick-
ness of the aquifer it can also be applied to unconfi ned aquifers.

Δ

The radius of infl uence R of a pumping test can be important, since pumping tests may
infl uence the groundwater conditions at a larger scale and thus may cause environmen-
tal problems. R can be estimated by setting Δ h(r,t) = 0 and solving (15.43a) for r:

(15.49)

If the pumping period is continued until the drawdown in each piezometer approaches
a constant value, the pumping test can also be evaluated assuming steady state fl ow
condition. This method is based on the analytic solutions of Dupuit (1863) and Thiem
(1870) for an unconfi ned and a confi ned aquifer, respectively. For an unconfi ned aqui-
fer, the equivalent rock mass permeability k RM normal to the test hole can be calculated
as follows:

(15.50)

where h 0 and h(r) are the piezometric heads measured in the pumping well and in an
observation hole at a distance r to the well's axis (Fig. 15.31, left). The corresponding
formula for a confi ned aquifer is (Fig. 15.31, right):

(15.51)

A constant rate injection test is usually carried out as double packer test or as a multiple
packer test and requires the same testing equipment as a Lugeon test. After adjusting