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Copyright © 2009 GEBEL Aquasafe. • All Rights Reserved • May 2010 • Pub. No. MAN 200
FIBREGLASS WETWELL INSTALLATION
!
D. BED AND BACKFILL
Proper backfill selection and compaction is required for a
proper installation. The allowed backfills are shown in Table
D-1 along with the degree of compaction required.
Table D-1
Bed and Backfill Compaction
Soil type-pipe bedding material
(Unified Soil Classification System
See Table D-2)
Minimum Degree of
Compaction Required*
Fine - grained soils (Liquid Limit < 50)
with medium to no plasticity with less
than 25% coarse grained particles.
CL, ML, ML - CL,
High
Fine grained soils (Liquid Limit <
50) with medium to no plasticity
with more than 25% coarse grained
particles.
CL, ML, ML - CL
Moderate
Coarse grained soils containing more
than 12% fines.
GM, GC, SM, SC
Moderate
Coarse grained soils with less than
12% fines.
GW, GP, SW, SP
Slight
Coarse grained soils with less than
12% fines.
GW, GP, SW, SP
Dumped
* Degree of compaction:
• Dumped - No compaction effort.
• Slight - Some compactive effort. In-place density <85%
standard compaction. Or < 40% modified compaction.
• Moderate - Intermediate level of compactive effort, In-place
density >/=85% and < 95% standard compaction, or
>/=40% and <70% modified compaction.
• High - Considerable compactive effort. In-place density >/=
95% standard compaction, or >/= 70% modified compaction
• The difference in the “dumped” and “slight” degree of compac
-
tion values are significant and are based on the method of con
-
struction, not the measured densities.
“Dumped” means that there is absolutely no compaction of the
embedment soil. “Slight” means there was something done
that increased the soil density, even if minor, such as water settling,
jetting, flooding, equipment travel, and in some cases, foot traffic.
Letter and Definition
Second Letter and Definition
G . . . . . . . . . . . . .
Gravel
S
. . . . . . . . . . . . . . .
Sand
M
. . . . . . . . . . . . . . .
Silt
C . . . . . . . . . . . . . .
Clay
O
. . . . . . . . . . . . .
Organic
P . . . . . . . . . . .
Poorly Graded
(uniform particle sizes)
W
. . . . . . . . . . .
Well Graded
(diversified particle sizes)
H . . . . . . . . . . . .
High Plasticity
L . . . . . . . . . . . . .
Low Plasticity
Table D-2
• For stable soils (cohesion ≥ 36 kpa and / or a bearing
capacity ≥ 170 kpa a minimum 300mm of backfill must be
placed around the wetwell.
• For unstable soils (cohesion ≤ 36kpa and ultimate bearing
capacity ≤ 170 kpa).
- Wetwells 1200mm diameter or smaller require a
minimum 600mm of backfill around the entire
circumference of the wetwell.
- Wetwells larger than 1200mm diameter require
a minimum backfill of ½ the wetwell diameter around
the entire circumference of the wetwell.
• If muck, bog or peat are present, consult with a Geotechnical
Engineer for backfill and excavation requirements.
• For permafrost conditions, consult with a Geotechnical Engi
-
neer for backfill and excavation requirements.
Keep backfill dry and free of ice in freezing conditions. Ensure
that no foreign objects such as large stones,
concrete clumps, tree roots/limbs, or debris is in the backfill
surrounding the wetwell.
Prevent large surges of backfill from displacing the wetwell.
E. WETWELL INSTALLATION WITH A
FIBREGLASS UNDERGROUND TANK
CAUTION
Not using approved backfill material may result in tank failure
and environmental contamination.
If the wetwell is installed in the same excavation as an under
-
ground fibreglass tank, the backfill around the wetwell must
also meet the tank backfill requirements so as to not compro
-
mise the tank installation. Tank backfill requirements are more
restricted and strict conformance to the tank backfill requirments
in MAN 600 must be met for both the wetwell and tank.
Goodnal STP ST041 Pre Treatment (KSB Amenities Pump Station OM Manual) Vendor Manual
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