TM 5-818-5/AFM 88-5, Chap 6/NAVFAC P-418
plug, augering with more or less simultaneous installa-
center the piezometer screen in the hole in which it is
tion of a casing, or using rotary wash-boring methods.
to be placed.
The hole for a piezometer should be kept filled with
(b) The filter sand should be poured down the
water or approved drilling fluid at all times. Bentoni-
hollow stem around the riser at a rate (to be deter-
tic drilling mud should not be used; however, an organ-
mined in the field) which will ensure a continuous flow
ic type of drilling fluid, such as Johnson's Revert or
of filter sand that will keep the hole below the auger
equivalent, may be used if necessary to keep the
filled as the auger is withdrawn. Withdrawal of the au-
drilled hole open. Any auger used in advancing the
ger and filling the space around the piezometer tip and
hole should be withdrawn slowly from the hole so as to
riser with filter sand should continue until the hole is
minimize any suction effect caused by its removal.
filled to a point 2 to 5 feet above the top of the piezom-
When assembling piezometers, all fittings should be
eter screen. Above this elevation, the space around the
tight and sealed with joint compound so that water
riser pipe may be filled with any clean uniform sand
levels measured are those actually existing at the loca-
up to the top of the particular sand stratum in which
tion of the wellpoint screen. Where the water table in
the piezometer is being installed but not closer than 10
different pervious formations is to be measured, the
feet of the ground surface. An impervious grout seal
riser pipe from the piezometer tip must be sealed from
should then be placed from the top of the sand backfill
the top of the screen to the ground surface to preserve
to the ground surface.
the isolation of one stratum from another and to ob-
(2) Casing method. The hole for a piezometer may
tain the true water level in the stratum in which the
be formed by setting the casing to an elevation 1 to 2
piezometer is set. Such piezometers may be sealed by
feet deeper than the elevation of the piezometer tip.
grouting the hole around the riser with a nonshrinking
The casing may be set by a combination of rotary drill-
grout of bentonite, cement, and fly ash or other suita-
ing and driving the casing. The casing should be kept
ble admixture. Proportions of 1 sack of cement and 1
filled with water, or organic drilling fluid, if neces-
gallon of bentonite to 10 gallons of water have been
sary, to keep the bottom of the hole from "blowing."
found to be a suitable grout mix for this purpose. Fly
After the casing has been set to grade, it should be
ash can be used to replace part of the cement to reduce
flushed with water or fresh drilling fluid until clear of
heat of hydration, but it does reduce the strength of
any sand. The piezometer tip and riser pipe should
the grout. The tops of piezometer riser pipes should be
then be installed and a filter sand, conforming to that
threaded and fitted with a vented cap to keep dirt and
specified previously, poured in around the riser at a
debris from entering the piezometer and to permit the
rate (to be determined in the field) which will ensure a
water level in the piezometer to adjust to any changes
continuous flow of filter sand that will keep the space
in the natural water table.
around the riser pipe and below the casing filled as the
casing is withdrawn without "sand-locking" the casing
(1) Hollow-stem auger method.
and the riser pipe. Placement of the filter sand and
(a) After the hole for the piezometer is advanced
withdrawal of the casing may be accomplished in steps
to grade, 1 to 2 feet below the piezometer tip, or after
as long as the top of the filter sand is maintained above
the last sample is taken in a hole to receive a piezomet-
the bottom of the casing but not so much as to "sand-
er, the hollow-stem auger should be flushed clean with
lock" the riser pipe and casing. Filling the space
water and the plug reinserted at the bottom of the au-
around the piezometer tip and riser with filter and
ger. The auger should then be slowly raised to the ele-
should continue until the hole is filled to a point 2 to 5
vation that the piezometer tip is to be installed. At this
feet above the top of the piezometer screen. An imper-
elevation, the hollow stem should be filled with clean
vious grout seal should then be placed from the top of
water and the plug removed. Water should be added to
the sand backfill to the ground surface.
keep the stem full of water during withdrawal of the
(3) Rotary method. The hole for a piezometer may
plug. The hole should then be sounded to determine
be advanced by the hydraulic rotary method using
whether or not the hollow stem is open to the bottom
water or an organic drilling fluid. After the hole has
of the auger. If material has entered the hollow stem
been advanced to a depth of 1 or 2 feet below the pie-
of the auger, the hollow stem should be cleaned by
zometer tip elevation, it should be flushed with clear
flushing with clear water, or fresh Johnson's Revert or
water or clean drilling fluid, and the piezometer, filter
equivalent drilling fluid if necessary to stabilize the
sand, sand backfill, and grout placed as specified above
bottom of the hole, through a bit designed to deflect
for the casing method, except there will be no casing to
the flow of water upward, until the discharge is free of
pull.
soil particles. The piezometer screen and riser should
then be lowered to the proper depth inside the hollow
b. Development and testing. The piezometer should
stem and the filter sand placed. A wire spider should
be flushed with clear water and pumped after installa-
tion and then checked to determine if it is functioning
be attached to the bottom of the piezometer screen to
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