for wells are:
1.
Operating conditions of wells,
2.
Corrosive characteristics of soil and water,
3.
Method of installations,
4.
Size and depth of wells,
5.
Type of joints, and
6.
External pressures on well casings.
The riser pipe and screen should be designed in all
cases to withstand, with a suitable factor of
safety, the crushing pressures at depths to which
wells extend. Design of relief wells to be
constructed under structures must consider loads
that will be induced into the well pipe due to
structural settlement. The wells, including screen
and riser pipe, should have a diameter which will
permit the maximum design flow without excessive
head losses but in no instance should the inside
diameter be less than 150 mm (6 inches). Based on
design parameters it may require the designer to
include a minimum collapse strength for the pipe and
well screen and a minimum clear inside diameter
through the fittings and screen to allow the
installation of pumps at a later date.
Because of the large variation in design and wall
thickness of the different types of well screen, no
generic specifications have been included. For
large contracts, specific necessary characteristics
should be presented in detail. References to
manufacturers should be eliminated.
Information on the design of filter packs and relief
wells can be found in the Engineering Manual EM
1110-2-1901, "Seepage Analysis and Control for
Dams". The filter criteria specified in EM
1110-2-1901 should be used to determine the
gradation band of the filter material. To minimize
segregation during installation of the filter pack,
the filter should have a relatively uniform
grain-size distribution band. The gradation band of
the filter material should be more or less parallel
to the gradation curve of the material being
drained. No point on the coarser filter gradation
curve should be greater than 25 times the
corresponding size of the material being drained.
The filter material should have a minimum thickness
of 150 mm (6 inches) measured radially from the
outer circumference of the screen section, and its
gradation should depend upon the gradation of the
strata being drained. Where unusual conditions are
encountered, filter tests should be performed in the
laboratory using the foundation sand and the
selected filter. For examples of laboratory
investigations refer to Technical Report GL-87-22,
dated August 1987, "Laboratory Tests on Granular
Filters for Embankment Dams (Includes Appendixes
SECTION 02525A
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