GGU-SLUGTEST: Determination of shape factor and kf value

F is known as the shape factor and takes into consideration the idealised flow path L, according to the well configuration and aquifer geometry. Because L cannot be exactly calculated, HVORSLEV (1951) determined empirical shape factors for six different test arrangements, which are used in the k_f value equation.

The most frequently used equation is valid for an open, imperfect well in a free aquifer of infinite thickness. The following then applies for the shape factor:

This leads us to the horizontal coefficient of permeability:

or

where:

d : Casing diameter [m]

D : Well screen diameter [m]

L : Length of screen [m]

m :

By modification of the general equation for k_f and using

h₁ = H₀ t₁ = t₀ = 0

h₂ = h(t) t₂ = t

we receive:

Because the parameters A, F and k_f are constant for any given well or aquifer, they can be converted to form:

where

giving:

The function represented by the final equation describes the sinking water level in the well in a slug test after HVORSLEV (1951).