mine the required length of well screen W to achieve

computing seepage through a permeable deposit are

based on the assumption that the permeability of the

following procedure can be used. This method is used

deposit is isotropic. However, natural soil deposits are

in analyses to determine penetration depths needed to

stratified to some degree, and the average permeabil-

obtain required discharge from partially penetrating

ity parallel to the planes of stratification is greater

wells or wellpoints. Each stratum of the previous foun-

than the permeability perpendicular to these planes.

dation or aquifer with thickness d and horizontal and

Thus, the soil deposit actually possesses anisotropic

vertical permeability coefficients kh and kv, respective-

permeability, with the permeability in the horizontal

ly, is first transformed using equation (E-1) into an

direction usually the greatest. To construct a flow net

or make a mathematical analysis of the seepage

through an anisotropic deposit, the dimensions of the

deposit and the problem must be transformed so that

the permeability is isotropic. Each permeable stratum

The transformed coefficient of permeability of each

of the deposit must be separately transformed into iso-

stratum from equation (E-2) is

tropic conditions. If the seepage flows through more

than one stratum (isotropically transformed), the

The thickness of the equivalent homogeneous isotropic

analysis can be made by a flow net constructed to ac-

aquifer is

count for permeability of the various strata.

(E-3)

m=1

anisotropic stratum can be transformed into an iso-

where n equals the number of strata in the aquifer.

tropic stratum in accordance with the following equa-

The effective permeability of the transformed aquifer

tion:

is

m-n

(E-1)

where

E-4

y = actual vertical dimension

where n equals the number of strata in the aquifer.

kh = permeability in the horizontal direction

The effective well-screen penetration into the trans-

kv = permeability in the vertical direction

formed aquifer is

The horizontal dimensions of the problem would re-

main unchanged in this transformation. The permea-

bility of the transformed stratum, to be used in all

equations for flow or drawdown, is as follows:

(E-2)

bility.

fied aquifer, the effective well penetration usually dif-

fers from that computed from the ratio of the length

of well screen to total thickness of aquifer. To deter-

Integrated Publishing, Inc. |