Field Tests - Rock Mechanics Based on an Anisotropic Jointed Rock Model - page 507

Figure 15.34 Slug test in an unconfi ned aquifer, calculation of equivalent rock mass permeability k RM
normal to a vertical test hole

The falling head test is a modifi ed slug test that requires a minimum of equipment. The
test section can be sealed by a single packer or a double packer system. Alternatively,
the borehole may be cased to at least 2 m below the water table.
In both test types, from the linear range of the ln( h 0 ) versus time plot (Fig. 15.34,

lower right) the rock mass permeability is determined, assuming transient, laminar, ra-
dial fl ow. For an unconfi ned aquifer, the equivalent rock mass permeability k RM and
transmissibility T normal to the test hole can be calculated from the excess heads

Δ h(t)/ Δ

Δ h 1

and Δ h 2 at two points in time t 1 and t 2 as follows (Hvorslev 1951):

(15.52)

where r t is the radius of the standpipe (Fig. 15.34, left) and is the dip angle of the test

hole (ISRM 1977a). For a confi ned aquifer in (15.52) the test section length must be
replaced by the radius of infl uence R (Bauwer & Rice 1976, ISRM 1977a, Thompson
1987). Formulas for the estimation of R for a slug test are given in Bauwer & Rice

β