TM 5-818-5/AFM 88-5, Chap 6/NAVFAC P-418
to keep the drilled hole open. The tip of the piezom-
(f) Measure the head loss through the filter and
eters shall be installed at approximate depths or eleva-
well screen for selected wells.
tions as approved by the C.O.R.; piezometers shall also
(g) Read river stages.
The piezometers for monitoring the groundwater table
be installed as instructed. The hole for a piezometer
beneath the slopes and bottom of the excavation shall
shall be kept filled with water or an approved organic
drilling fluid at all times. Bentonitic drilling mud shall
be installed by the Contractor. The pitometers for
measuring the flow from individual wells and from the
not be used. Any auger used in advancing the hole
shall be withdrawn slowly from the hole so as to mini-
complete system will be furnished by the Government.
mize any suction effect caused by withdrawing the
Copies of the data obtained by the Government will be
auger. (Hollow-stem augers shall be filled with drilling
promptly furnished to the Contractor. The Contractor
will furnish and install the pitometer inserts. Opera-
fluid before pulling the plug in the bottom of the
tion and maintenance of the dewatering systems, any
auger.) Drilling and installation procedures shall be as
specified below and shall be in accordance with ac-
supplemental groundwater control facilities if re-
cepted practice and to the satisfaction of the C.O.R.
quired, and surface water control facilities shall be su-
Method 1. Hollow-stem auger. After advancing
pervised by someone trained and with at least 5 years
of actual experience in managing large dewatering sys-
the hole for the piezometer to grade (1 to 2 feet below
the piezometer tip), or after taking the last sample in a
tems and operating pumps and engines.
hole to receive a piezometer, the hollow-stem auger
(2) Piezometers.
shall be flushed clean with water and the plug rein-
(a) Locations. The M, R, S, and T piezometers
shall be installed to measure the groundwater table in
serted at the bottom of the auger. The auger shall then
be slowly raised to the elevation that the piezometer
the deep sand formation beneath the excavation, be-
tip is to be installed. At this elevation the hollow stem
tween the dewatering wells, and on three lines out
shall be filled with clean water and the plug removed.
from the excavation at the approximate locations
Water shall be added to keep the stem full of water
shown on the drawings. The N piezometers shall be in-
during withdrawal of the plug. The hole shall then be
stalled to measure the groundwater table in semiper-
sounded to determine whether or not the hollow stem
vious strata in the bottom of the excavation and mid-
is open to the bottom of the auger. If material has en-
way between jet-eductor wells at the approximate loca-
tered the hollow stem of the auger, the hollow stem
tions. The Contractor shall stake the piezometers at
shall be cleaned by flushing with clear water, or clean
designated locations. The tips of M, R, S, and T pie-
Revert drilling fluid, if necessary, to stabilize the bot-
zometers for measuring the groundwater table in the
tom of the hole, through a bit designed to deflect the
deep sand formation shall be set in clean sand at eleva-
flow of water upward, until the discharge is free of soil
tion -80.0 feet or below as necessary; the tips of the N
particles. The piezometer screen and riser shall then be
piezometers for measuring the groundwater table in
semipervious strata in the top stratum shall be set at
lowered to the proper depth inside the hollow stem
and the filter sand placed. (A wire spider of design ap-
the bottom of the semipervious strata.
proved by the C.O.R. shall be attached to the bottom of
(b) Piezometer materials. The N piezometers
shall consist of a 1.50-inch I.D. (Schedule 80) PVC
the piezometer screen so as to center the piezometer
screen in the hole in which it is to be placed. Use two
screen with 0.025-inch slots connected to a 1.50-inch
I.D. (Schedule 80) PVC riser pipe. The screens shall be
crossed wires just above the plug in the tip.) Filter
10 feet long. The joints of the screen and riser shall be
sand shall be poured down the hollow stem around the
riser at a rate (determined in the field) that will ensure
flush (inside and outside) and shall be glued together
continuous filter sand flow down the hollow stem
with PVC pipe cement. The filter sand (B) shall meet
around the riser and piezometer, and will keep the 8-
the specifications set forth for jet-eductor wells. De-
inch hole below the auger filled with filter sand as the
pending upon the method of installation, the riser and
auger is withdrawn. Withdrawal of the auger and fill-
screens for the M, R, S, and T piezometers shall be as
ing the space around the piezometer tip and riser with
specified above, or 1.5-inch galvanized iron riser pipe
filter sand shall continue until the hole is filled to a
connected to a 1.5- by 30-inch self-jetting wellpoint
with a 30- to 40-mesh stainless steel screen.
point about 5 feet above the top of the piezometer
screen. Above this elevation, the space around the
(c) Installation of piezometers. Holes for pie-
zometers may be advanced by either: using an 8-inch
riser pipe may be filled with any clean, uniform sand
with less than 5 percent passing a No. 100 U.S. Stand-
O.D. continuous flight auger with a 33/8-inch I.D. hol-
low stem with the hollow stem plugged at the bottom
ard sieve up to within 20 feet of the ground or exca-
with a removable plug; augering and more or less
vated surface. An impervious grout seal shall be placed
simultaneous installation of a 6-inch casing; or using a
around the top 20 feet of the ground or excavated sur-
face. An impervious grout seal shall be placed around
rotary wash drilling procedure (6-inch diameter) and
an organic drilling fluid, such as Revert, if necessary,
the top 20 feet of the hole for the M, R, S, and T pie-
G-20
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