TM 5-818-5/AFM 88-5, Chap 6/NAVFAC P-418
and one new spare pump and controls shall be at the
PVC pipe cement. The top of the riser shall be cut off
job site at all times. The electrical system and controls
30 inches above the ground surface and provided with
shall be designed so that failure of any one pump, or
a threaded cap with a `/,-inch hole in the side. The up-
the need to disconnect and replace a pump, does not
per part of the piezometer shall be protected by install-
adversely affect operation of any other pump.
ing a 6-inch I.D. cardboard casing around the riser em-
(e) The Contractor shall be responsible for re-
bedded 2 feet below the ground surface and filling the
cording the results of the pumping tests on the well
casing with concrete. After removal of the cardboard
system and furnishing them to the Construction Man-
casing, the top 30 inches of each piezometer shall be
ager. He shall also advise the Construction Manager at
painted day-glo orange, and the piezometer number
least three days in advance of making this test so that
marked in 3-inch-high black characters.
a representative of the Government can observe the
(b) Each piezometer shall be pumped after in-
stallation and then checked to determine if it is func-
test.
(f) Because of the importance of preventing any
tioning properly by filling with water and observing
significant artesian head in the semipervious stratum
the rate of fall. For the piezometer to be considered ac-
above the bottom of the excavation, tees shall be in-
ceptable it shall pump at a rate of at least 0.5 gallon
stalled in the riser pipe for the deep wells to provide
per minute, or when the piezometer is filled with wa-
ter, the water level shall fall approximately half the
relief of this artesian pressure in event of any pump or
electrical failure. These tees shall be provided with
distance to the groundwater table in a time less than
plugs during installation of the wells; as the excava-
the time given below for various types of soil:
tion is carried down to each tee, the plug in that tee
Type of Soil
Approximate time
Period of
shall be removed and a 2-inch pipe with brass check
observation
of 50 percent
in which piezometer
valve inserted in the tee so that water can flow into the
fall, minutes
screen is wet
minutes
excavation. As each tee is connected into the excava-
30
30
Sandy silt (>50% silt)
tion, the tee above shall be sealed.
Silty sand (<50% silt,
5
10
>12% silt)
(g) Installation of the wellpoint and the relief
1
Fine sand (<12%silt)
5
well systems shall be supervised by someone with at
least 5 years actual experience in installing such sys-
If the piezometer does not function properly, it shall be
tems. A log of each relief well shall be maintained by
developed by air surging or pumping with air if neces-
the Contractor; forms for logging installation of the
sary to make it perform properly.
wells will be furnished by the Contracting Officer.
d. Available soil data. Generalized soil profiles and
(6) Piezometers. Piezometers shall be installed at
logs of boring were made for Government. Samples of
are
the locations specified to measure the groundwater ta-
the soils from the borings made by
ble in the line of wellpoints and in the excavation (A
available for inspection by bidders at
piezometers), and to measure the hydrostatic water
e. Damages. The Contractor shall be responsible and
level in the semipervious stratum beneath the excava-
shall repair any damage to the excavation, including
tion (B piezometers). The tips of the A piezometers
damage to the bottom due to heave, that may result
shall be set at the top of the Cockfield formation; the
from his or her negligence, improper operation of the
tips of the B piezometers shall be set in the middle of
dewatering and pressure relief systems, and any me-
the semipervious stratum. The A piezometers shall be
chanical or electrical failure of the systems.
surrounded with Filter Sand A; the tips of the B pie-
f. Maintaining excavation unwatered and pressure
zometers shall be surrounded with Filter Sand B. The
relieved. Subsequent to completion and acceptance of
A piezometers shall be installed using the same equip-
all work in the excavated area, the Contractor shall
ment and procedure specified for installing the well-
maintain the excavation unwatered and the water lev-
points; the B piezometers shall be sealed with an ex-
el in the B piezometers at or below elevation 250.0 feet
panding cement bentonite grout up to at least eleva-
until placement of the structural mat is complete and
tion 252.0 feet. After sealing around a B piezometer,
the backfill has been placed to elevation 256.0 feet,
the sanding casing shall be checked to see if there is
and a written directive to cease pumping has been re-
any bentonite or cement in the casing; and if such ex-
ceived from the Contracting Officer. The Contractor
ists, the casing shall be thoroughly washed prior to in-
shall be responsible for maintaining the excavation un-
stallation of the next piezometer.
watered and pressure relieved during this period as set
(a) The piezometers shall consist of a 1.50-inch
for above except for operation of the wellpoint system.
inside diameter (I.D.) (Sch 40 or 80) PVC screen with
0.025- to 0.030-inch slots connected to 1.50-inch I.D.
g. Removal of wellpoint system. After excavation to
(Sch 40 or 80) PVC riser pipe. Screens shall be 5 feet
grade, installation of drainage ditch, sump pump, and
long. The joints of the screen and riser shall be flush
placement of the "mud" mat, the wellpoint system may
(inside and outside) and shall be glued together with
be removed. Removal of the wellpoint dewatering sys-
G-7
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