TM 5-818-5/AFM 88-5, Chap 6/NAVFAC P-418
pervious strata as shown by the boring logs, or as en-
and drawings to be submitted shall include, but not
countered, to the depth specified.
necessarily be limited to:
(c) Filter sand. Filter sand around the well
(a) Location and size of sumps, pumps, and
screen shall be washed (clean) uniform sand or crushed
dikes.
stone composed of hard, tough, and durable particles
(b) Height and elevation of dike around
free from any adherent coating. The filter sand shall
excavation.
contain no detrimental quantities of vegetable matter,
(c) Characteristics of sump pumps and
nor soft, friable, thin, or elongated particles, and shall
horsepower of engines.
meet the following gradation requirements:
(d) Location and size of discharge `piping. (Sur-
face water shall not be pumped into the discharge
Filter Sand B
header for the dewatering (well) system).
U.S. Standard
Percent by weight
g. Dewatering perched groundwater in lower
Sieve No.
passing
part or bottom of excavation. The Contractor shall be
8
95-100
fully responsible for design and installation of any sup-
10
92-100
14
75-100
plemental dewatering facilities that may be required
16
65-95
to control any seepage or groundwater in the bottom
20
30-77
or lower part of the excavation in order to assure a sta-
30
10-30
ble subbase and permit work to be conducted in the
40
1-13
"dry." These supplemental measures may include well-
50
0-5
points, sand drains, French drains, and appropriate
(5) Jet-eductor pumps and header pipe. The jet-
pumps, piping, and appurtenances as necessary and
eductor pumps shall have the specified pumping ca-
approved by the C.O.R. subject to satisfactory perfor-
pacities. The pressure pumps for operating the jet-
mance of the facility installed. Pay for any such sup-
eductor pumps shall have a diesel engine with a horse-
plemental dewatering, if required, for the lower or bot-
power of at least 110 and a capacity of 1800 gallons
tom part of the excavation should be included in the
per minute at a total dynamic head of at least 150 feet
price for excavation. There will be no charges or claims
on a continuous basis. The standby pumps shall have
for extra compensation or time extension for any sup-
the same horsepower and capacity. The pressure
plemental dewatering performed in the bottom or
header pipe shall be Schedule 40; the return header
lower part of the excavation.
pipe shall have a minimum wall thickness of 0.20 inch.
h. Monitoring dewatering systems.
The sump pumps for the jet-eductor systems shall be
(1) General. Continuous control of seepage into
an electric, automatic priming type, with a capacity of
and artesian pressure beneath the excavation is essen-
pumping 600 gallons per minute at TDH = 50 feet.
tial for driving the test and foundation piles for the
f. Surface water control
dam, and subsequent construction of the lock and
(1) The Contractor shall be fully responsible for
dam. It is therefore imperative that the dewatering
designing all features of the system for unwatering the
systems have adequate capacity to control the ground-
excavation and controlling surface water that may fall
water beneath the slopes and the excavation as speci-
into the excavation. The sump pumping system shall
fied at all times. In order to check the adequacy and
be designed with sufficient storage and pumping ca-
performance of the dewatering systems, the Govern-
pacity to prevent flooding the bottom of the excava-
ment will make the following measurements and eval-
tion for the dam for at least a 1 in lo-year rainfall in-
uate the data:
tensity, assuming 100 percent runoff, for the follow-
ing periods:
bottom of the excavation by means of M, R, S, and T
Rainfall
piezometers installed in the deep sand aquifer that
Period
Intensity, inch/hour
Amount, inches
underlies the site at specified locations.
30 minutes
4.5
2.25
1 hour
3.0
3.00
2 hours
2.0
4.00
locations where the excavation penetrates silts and
In any event, the Contractor shall be responsible for
silty sands in the top stratum overlying the deep sand
controlling whatever surface runoff occurs, regardless
formation by means of N piezometers installed at the
of rainfall intensity, so as to protect the area for pile
locations.
driving and testing from flooding.
(c) Measure the flow from individual wells and
(2) The Contractor shall submit for approval with-
from the complete dewatering system.
in 15 calendar days, after he or she has received a No-
(d) Measure the water level in the dewatering
tice to Proceed, drawings, design data, and charac-
wells.
teristics of the equipment he proposes to utilize in
(e) Measure sand in the flow from dewatering
unwatering and controlling surface water. The data
wells.
G-19
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