TM 5-818-5/AFM 88-5, Chap 6/NAVFAC P-418
zometers, and 5 feet for the N piezometers.
for the N piezometers. Samples shall be obtained using
Method 2. Casing. The hole for a piezometer may
a 13/8-inch (minimum) I.D. split-barrel or 3-inch Shelby
be formed by setting a 6-inch casing to an elevation 1
tube sampler by driving or pushing. The length of
to 2 feet deeper than the elevation of the piezometer
drive or push shall not be less than 3 inches. If there is
tip. The casing may be set by a combination of rotary
insufficient sample recovery to identify the soil prop-
drilling and driving the casing. The casing shall be
erly, another sample shall be obtained immediately be-
kept filled with water, or organic drilling fluid if
low the missed sample. If desired, the sampler may be
necessary, to keep the bottom of the hole from "blow-
advanced using driving jars on a wireline.
ing." After the casing has been set to grade, it shall be
(d) Development and testing. After each pie-
flushed with water or (clean) drilling fluid until clear
zometer is installed, it shall be promptly flushed with
of any sand. The piezometer tip and riser pipe shall
clean water, developed, and pumped to determine if it
then be installed and the filter sand poured in around
is functioning properly. (If an organic drilling fluid has
the riser at a rate (to be determined in the field) which
been used, Johnson's Fast Break, or equivalent, shall
will insure a continuous flow of filter sand down the
be added in accordance with the manufacturer's rec-
casing that will keep the hole around the riser pipe and
ommendations to break down the drilling fluid.) A 10-
below the casing filled with filter sand as the casing is
foot minimum positive head shall be maintained in the
withdrawn without "sand-locking" the casing and riser
piezometer following addition of the Fast Break. After
pipe. (Placement of the filter sand and withdrawal of
at least 30 minutes has elapsed, the piezometer shall
the casing may be accomplished in steps as long as the
be flushed with clear water and pumped. The piezom-
top of the filter sand is maintained above the bottom
eter may be pumped with either a suction pump or by
of the casing but not so much as to "sand-lock" the
means of compressed air. The approximate rate of
riser pipe and casing.) Filling the space around the pie-
pumping during development shall be measured. Pie-
zometer tip and riser with filter sand shall continue
zometers installed in the deep sand formation will be
until the hole is filled to a point about 5 feet above the
considered acceptable if they will pump at a rate of 2
top of the piezometer screen. Above this elevation, the
to 5 gallons per minute or more. Piezometers installed
space around the riser pipe may be filled with any
in the semipervious strata within the top strata will be
clean, uniform sand and the hole grouted as specified
considered acceptable if they will pump at a rate of at
in Method 1 above.
least 0.5 gallon per minute, or when the piezometer is
Method 3. Rotary. The hole for a piezometer may
filled with water, the water level falls approximately
be advanced by the hydraulic rotary method using
half the distance of the groundwater table in a time
water or an organic drilling fluid. The hole shall have a
less than the time given below for various types of soil:
minimum diameter of 6 inches. After the hole has
Approximate
been advanced to a depth of 1 or 2 feet below the pie-
time of
Type of soil in
Period of
zometer tip elevation, it shall be flushed with clear
50 percent fall
which piezometer
observation
water or clean drilling fluid, and the piezometer, filter
minutes
screen is set
minutes
sand, sand backfill, and grout placed as specified in
30
30
Sandy silt (> 50% silt)
Method 2 above, except there will be no casing to pull.
Silty sand (< 50% silt, > 12%
5
silt)
10
Method 4. Self-jetting. The M, R, S, and T piezom-
Fine sand (< 12% silt)
5
1
eters may be drilled to within 4 feet of planned total
depth, then clean water used to advance the self-jet-
If the piezometer does not function properly, it shall be
ting wellpoint to the design grade without the use of
developed by a combination of air surging and pump-
filter sand around the wellpoint. The seal and backfill
ing with air as necessary to make it perform properly.
for the piezometers shall consist of a pumpable
If the piezometer still will not perform properly, it
cement-bentonite grout, with a ratio of 1 gallon of ben-
shall be reinstalled at a nearby location selected by the
tonite per bag of cement, or equivalent cement grout
C.O.R.
approved by the C.O.R. (Only enough water shall be
added to make the grout pumpable.) The tops of the
tor shall read all M and N piezometers at least once a
risers shall be cut off 36 inches above the ground sur-
week, selected piezometers at least twice a week, some
face. The upper part of the piezometer shall be pro-
of the piezometers in the deep sand formation daily,
tected by installing a 6-inch I.D. PVC or corrugated
and the water level in the dewatering and the jet-educ-
metal pipe around the riser cemented in to a depth of 3
tor wells at least once a week for his or her informa-
feet below the ground surface. The number of the pie-
tion and use in operation of the dewatering systems
zometer shall be marked with 3-inch-high black letters
and control of groundwater as specified. The Contrac-
on the pipe guard around the riser pipe.
tor shall record what deep well and jet-eductor wells
Method 5. Sampling. Split-barrel samples shall be
are being pumped when he takes his piezometer or
obtained at 5-foot intervals and at every strata change
water level readings. The C.O.R. will also read the M
G-21
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