TM 5-818-5/AFM 88-5, Chap 6/NAVFAC P-418
U.S. Army Corps of Engineers
Figure 4-15. Flow and drawdown for fully penetrating circular well arrays; circular source; artesian flow.
thickness of the aquifer, distance to the effective
(6) Well or screen penetration W/D.
source of seepage, well or wellpoint radius, stratifica-
(a) Most of the equations and graphs presented
tion, required "wetted screen length," type and size of
in this manual for flow and drawdown to slots or well
excavation, and whether or not the excavation pene-
systems were basically derived for fully penetrating
trates alternating pervious and impervious strata or
drainage slots or wells. Equations and graphs for par-
the bottom is underlain at a shallow depth by a less
tially penetrating slots or wells are generally based on
pervious stratum of soil or rock. Where a sizeable open
those for fully penetrating drainage systems modified
excavation or tunnel is underlain by a fairly deep
by model studies and, in some instances, mathematical
stratum of sand and wells are spaced rather widely,
derivations. The amount or percent of screen penetra-
the well screens should penetrate at least 25 percent of
tion required for effective pressure reduction or inter-
the thickness of the aquifer to be dewatered below the
ception of seepage depends upon many factors, such as
4-16
Previous Page
