Field pumping tests

TM 5-818-5/AFM 88-5, Chap 6/NAVFAC P-418

Table 3-4. Approximate Coefficient of Permeability for Various Sands

C o e f f i c i e n t of Permeability k

Type of Sand (Unified

-4

ft/min

x 10

cm/sec

S o i l Classification System)

10-40

Sandy silt

5-20

40-100

Silty sand

20-50

100-400

50-200

Very fine sand

400-1,000

200-500

Fine sand

l,000-2,000

500-1,000

Fine to medium sand

2,000-3,000

Medium sand

1,000-1,500

3,000-4,000

Medium to coarse sand

1,500-2,000

4,000-10,000

2,000-5,000

Coarse sand and gravel

U. S. Army Corps of Engineers

filter surrounding the well screen, and the rate of in-

pirical relations between D10 and k (fig. 3-4), which

flow or fall in water level must be accurately meas-

were developed from laboratory and field pumping

ured. Disturbance of the soil adjacent to a borehole or

tests for sands in the Mississippi and Arkansas River

filter, leakage up the borehole around the casing, clog-

valleys. An investigation of the permeability of filter

ging or removal of the fine-grained particles of the

sands revealed that the permeability of clean, rela-

aquifer, or the accumulation of gas bubbles in or

tively uniform, remolded sand could be estimated from

around the well screen can make the test completely

the empirical relation:

k = C (D10)2

unreliable. Data from such tests must be evaluated

(3-2)

where

k = coefficient of permeability, centimetres per

second

100 (may vary from 40 to 150)

C

D 10 = effective grain size, centimetres

Empirical relations between D10 and k are only approx-

imate and should be used with reservation until a cor-

relation based on local experience is available.

c. Field pumping tests. Field pumping tests are the

most reliable procedure for determining the in situ

permeability of a water-bearing formation. For large

dewatering jobs, a pumping test on a well that fully

penetrates the sand stratum to be dewatered is war-

ranted; such tests should be made during the design

phase so that results can be used for design purposes

and will be available for bidders. However, for small

dewatering jobs, it may be more economical to select a

more conservative value of k based on empirical rela-

tions than to make a field pumping test. Pumping tests

are discussed in detail in appendix C.

d. Simple field tests in wells or piezometers. The

permeability of a water-bearing formation can be esti-

mated from constant or falling head tests made in

wells or piezometers in a manner similar to laboratory

permeameter tests. Figure 3-5 presents formulas for

determining the permeability using various types and

installations of well screens. As these tests are sensi-

tive to details of the installation and execution of the

Figure 3-4. D10 versus in situ coefficient of horizontal permeability-

test, exact dimensions of the well screen, casing, and

Mississippi River valley and Arkansas River valley.

3-6