TM 5-818-1 / AFM 88-3, Chap. 7
reading should be taken 24 hours or more after drilling is
determined should be sealed off with well-tamped clay or
stopped. Water level readings obtained in drill holes
cement, or chemical grout. In granular soils where a
should be shown on the boring log with the date of the
more permanent system is desired, a 2-foot section of
reading and the date when the drill hole was made.
well-point screen can be attached to the bottom of the
b. Piezometers.
Piezometers provide an
pipe. A well-point screen should be selected that will
prevent entrance of foundation materials into the screen,
accurate means for determining the groundwater level
or else a suitable filter material should be used. For all
over a period of time. In pervious strata, a temporary
piezometers, seal the top several feet below ground
piezometer may consist of a section of riser pipe, the
surface around the riser pipe to prevent infiltration of
open bottom end of which is placed in a bag (filter) of
surface water. In granular soils, the riser pipe is normally
coarse sand or gravel. The annular space between the
about 1 1/4-inches inside diameter and generally made
piezometer riser pipe and the drill hole immediately
of plastic. In cohesive soils, a Casa-
above the stratum in which the water level is to be
(Courtesy of L Bjerrum, "Embankment on Soft Ground, "
Proceedings, Conference on Performance of Earth and Earth-
Supported Structures. Purdue University. Lafayette, Ind.,
Vol2, 1975. Reprinted by permission of the American Society
of Civil Engineers, New York.)
Figure 4-3. Correction factor for vane strength.
4-7
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