Infiltrator IM™- and TW™- Series Septic Tank Buoyancy Control

Infiltrator IM™- and TW™- Series
Septic Tank Buoyancy Control Guidance
septic tanks
Before you Begin
Concrete Deadmen
This document presents recommended buoyancy control methods for
Infiltrator Systems Inc.’s (Infiltrator’s) IM- and TW-Series tanks (TW300, TW-500, TW-900, TW-1050, IM-1060, TW-1250, and TW-1500). Tank
buoyancy control methods must be implemented according to state
and/or local regulations, which may supersede the guidelines in this
document. If unsure of the requirements for a particular site, contact the
local health department or permitting authority.
Types of concrete deadmen recommended for use in buoyancy control of
Infiltrator tanks include filled plastic half pipe, filled Infiltrator chambers, precast
parking bumpers and traffic barriers, and poured blocks. The inherent weight of
these deadmen combined with the weight of soil above them provide buoyancy
control when properly strapped across an Infiltrator tank. Deadmen are placed
at the bottom of the tank excavation on opposite sides of the tank’s proposed
installation location. The deadmen are fastened to each other with tie-down
straps placed up and over the tank at the locations specified for each tank
model (See Step 3: Strapping).
This document provides a simple procedure to determine if tank buoyancy
control is required based on installation conditions. You must know the
following measurements to establish if control is necessary and what methods
are applicable:
15 [315 mm] to
18 [450 mm]
• Infiltrator tank model
• Height of seasonal high groundwater above the tank bottom elevation
• Depth of soil backfill over the tank top
Once tank buoyancy control measures are determined to be required
and a method has been selected and implemented, refer to Infiltrator IMand TW-Series Septic Tank Installation Instructions and Riser Connection
Guidance documents, as applicable, for completing the installation.
How to Use this Document
1. F
amiliarize yourself with the descriptions in the Compatible Devices and
Products section.
2. D
etermine if buoyancy control is required for your Infiltrator tank installation
using Step 1, Table 1. Representative examples are provided following Table
1. If buoyancy control is required, proceed to Step 2.
STEEL
REBAR
Use commercially available steel-reinforced
parking bumpers with typical dimensions of
12-inches wide by 6-inches high (300 mm x 150
mm). Weight is 58 lbs/foot (86 kg/m) minimum.
INFILTRATOR SYSTEMS INC.
6 Business Park Rd. Old Saybrook, CT 06475
(800) 221-4436
SEPTIC TANK BUOYANCY
ConcreteCONTROL
trafficGUIDANCE
barrierDETAIL
Drawn by: LMB
The parts and supplies necessary for buoyancy control of Infiltrator tanks
must be purchased separately from the tank. All parts and supplies are
either commercially available or available through Infiltrator’s network of
tank distributors. Some parts may require fabrication on site using common
construction practices. Contact Infiltrator’s Technical Services Department or
your local Infiltrator tank distributor for assistance obtaining parts and supplies.
Poured Blocks
Concrete precasters can pour blocks of
various dimensions and weights. Blocks
are often an affordable option if they
satisfy the weight requirements for use as
buoyancy control (see Tables 2–5 and the
Supp-lemental Force section of Step 2 for
more information).
Compatible Devices and Products
•H
elical anchors (Chance™ No-Wrench Screw Anchors with min. 4” [100 mm]
helix and 48” [1,200 mm] shaft length)
Tie-Down Straps
Straps are commercially available in varying
lengths and with assorted hard-ware and
tightening options. Nylon or polyester strapping
with minimum 10,000-lbs-capacity (4,500 kg) is
required for buoyancy control use with Infiltrator
tanks. Place straps up and over the tank at specified locations only (See Step 3:
Strapping). Tighten straps snugly with a ratchet or turnbuckle system to remove
slack and slightly pre load the system. All connections, fittings, and hardware
must be corrosion resistant or coated with epoxy or other corrosion-resistant
materials to inhibit deterioration in the subsurface environment. Consider
encapsulating such components in heat-shrink tubing or painting on additional
corrosion-resistant coatings prior to burial.
Date: X/X/XXXX
XXXXX
Parts and Supplies
•C
oncrete deadmen (concrete-filled plastic half pipe or chambers, precast
parking bumper, precast traffic barrier, or poured block)
Drawing No. 1
Scale:
Checked by: XXX
Sheet: 1 of 1
Use commercially
available
steelreinforced concrete traffic barrier or
equivalent. Typical dimensions include a
24-inch-wide base tapering to a 6-inchwide top, with a height of approximately
32 inches (600 mm x 150 mm x 800 mm).
Weight is min. 390 lbs/foot (580 kg/m).
4. O
nce a preferred buoyancy control method is selected, follow the procedures
for implementation provided in Step 3.
•T
ie-down straps (high-tensile-strength webbing, 10,000-lbs [4,500 kg]
minimum capacity, nylon or polyester, corrosion-resistant hardware)
Use Schedule 40 PVC plastic pipe having a
minimum inside diameter of 15 inches (375 mm)
or HDPE corrugated pipe having a minimum
inside diameter of 18 inches (450 mm) cut in half
lengthwise. Fill with concrete having a minimum
unit weight of 145 lbs/ft3 (2.32 metric tons/m3)
reinforced with three equally spaced 40-grade,
1/2-inch-diameter (13 mm) steel bars. Weight is
61 lbs/ft (91 kg/m) minimum.
Concrete parking bumper
3. U
se the respective table for your IM- or TW-Series tank model from Tables
2–5 in Step 2 to determine the appropriate buoyancy control methods for
your installation conditions.
Infiltrator tanks are compatible with the following devices or products used for
buoyancy control:
Concrete-filled plastic half pipe
Helical Anchors
Chance™ No-Wrench Screw Anchors with a
single 6-inch-diameter (150 mm) helical flight
are recommended for use in buoyancy control
for Infiltrator tanks. These anchors rely on the
shear strength of the soil combined with the
weight of the soil above the flight to provide
holding strength. Proper installation is to 4 feet
(1.2 m) below the bottom of the tank excavation
and to within 5° of alignment with the webbing
load. Determine the proper locations for anchor
installation to ensure that tie-down straps will be
aligned properly for each tank model (See Step
3: Placement of Anchors), and follow anchor
manufacturer installation instructions. Contact
Infiltrator’s Technical Services Department for
anchor sourcing.
Contact Infiltrator Systems’ Technical Services Department for assistance at 800-221-4436.
Step 1 – Determine Need for Buoyancy Control
You must know the maximum height of the estimated seasonal high groundwater above the tank
bottom AND the depth of proposed cover fill above the tank top for your installation conditions to
complete Step 1. Tank buoyancy control may be required if the seasonal high groundwater has
the potential to rise 24 inches (600 mm) or more above the bottom of the tank, AND less than 24
inches (600 mm) of soil cover is to be placed as backfill over the tank top. Otherwise, no buoyancy
control is required
Seasonal High Groundwater Elevation
Groundwater elevation, or water table, fluctuates seasonally based on various factors including:
soil type and porosity, rainfall amounts, frost/thaw cycles, proximity to sources such as springs and
gutter downspouts, and uptake from plants (evapotranspiration). The seasonal high groundwater
elevation represents the highest point the water table has the potential to reach at any time of
the year, and is not necessarily the level at which groundwater may be observed seeping from the soil at the time of tank installation. In general, a qualified soil
evaluator can estimate the seasonal high groundwater elevation from careful examination of the soil profile. This information is critical to the design of a successful
on-site wastewater treatment system, including installation of the septic tank.
Table 1 Instructions
1. In the left-hand column, locate the row corresponding to the height of the estimated seasonal high groundwater elevation above the tank bottom (Parameter I)
for your conditions.
2. Follow that row to the right until you reach the column corresponding to the depth of soil cover proposed above your tank top (Parameter II).
3. If your tank model is described in that cell, buoyancy control is required as described for your tank model in Step 2. If your tank model is not listed in that cell,
no buoyancy control is required.
PARAMETER II
DEPTH OF SOIL
COVER ABOVE TANK TOP
PARAMETER I
SEASONAL HIGH GROUNDWATER
HEIGHT ABOVE BOTTOM OF TANK
1. Infiltrator tank models include: TW-300, TW-500, TW-900, TW-1050, IM-1060, TW-1250, and TW-1500
2. Groundwater height corresponds to seasonal high groundwater elevation
3. Minimum 6 inches soil cover backfill required above all Infiltrator tanks
Example 1
A contractor plans to install an IM-1060 tank in a location where the
seasonal high groundwater has the potential to rise to 45 (1,125 mm) inches
above the tank bottom (Parameter I), and the design plan calls for 9 inches
(225 mm) of soil cover above the top of the tank (Parameter II). 45 inches
groundwater height corresponds to row 3 (42 inches [1,050 mm] to less than
48 inches [1,200 mm]). 9 inches of soil cover corresponds to column A (6
inches [300 mm] to less than 12 inches [600 mm]). Cell 3A lists “All models”.
The IM-1060 would require buoyancy control when installed under these
conditions. The contractor would refer to Table # in of Step 2 to determine
the appropriate control method.
Example 2
STRAPPING
(TYPICAL)
PROVIDE ADE
BACKFILL PLA
DEADMAN ANC
DEADMAN
A contractor plans to install a TW-300 tank in a location where the seasonal
high groundwater has the potential to rise to 36 inches (900 mm) above the
tank bottom (Parameter I), and the design plan calls for 20 inches (500 mm)
of soil cover above the top of the tank (Parameter II). 36 inches groundwater
height corresponds to row 4 (36 inches to less than 42 inches [1,050 mm]).
20 inches of soil cover corresponds to column C (18 inches [450 mm] to less
than 24 inches [600 mm]). Cell 4C does not list any Infiltrator tank models;
no buoyancy control is required when a TW-300 is installed under these
conditions.
Contact Infiltrator Systems’ Technical Services Department for assistance at 800-221-4436.
Step 2 – Determine Buoyancy Control Method
Step 2 is used if the Step 1 analysis shows that buoyancy control is required for your tank model and the conditions of your installation. As before, you must
know the maximum height of the estimated seasonal high groundwater above the tank bottom AND the depth of proposed cover fill above the tank top for your
installation conditions to complete Step 2.
Tables 2–5 Instructions
The tank model tables are presented below and grouped together wherever appropriate. For each tank model table, find the Case row on the left side of the
table that corresponds to both the groundwater height (Parameter I) and soil cover measurements (Parameter II) for your tank installation conditions. Note: If the
groundwater height and soil cover measurements for your installation are not included on the table, then the tank installation does not require buoyancy control.
Follow the row to the right for a listing of the appropriate buoyancy control methods for your installation conditions under each method description column. Refer
to the compatible devices and products and Step 3 – Implementation sections of this document for additional information.
Table 2 – TW-300 / TW-500 Buoyancy Control
Case
1
2
3
4
Parameter I
Groundwater height
above tank bottom
30” (750 mm) to
40” (1,000 mm)
41” (1,025 mm) to
50” (1,250 mm)
36” (900 mm) to
50” (1,250 mm)
42” (1,050 mm) to
50” (1,250 mm)
Poured block or
Parameter II
minimum supplemental
Soil cover depth above
force required
tank top
@ F.S. = 1.51
Buoyancy Control Methods (minimum per side of tank)
Concrete-filled
half pipe
(minimum length)
Concrete
parking bumpers
(minimum length)
Concrete
traffic barriers
(minimum length)
Helical
anchors
(min. no.)
6” (150 mm)
2,200 lbs (998 kg)
8’ (2.4 m)
10’ (3.0 m)
6’ (1.8 m)
2
6” (150 mm)
3,000 lbs (1,360 kg)
11’ (3.4 m)
14’ (4.3 m)
8’ (2.4 m)
4
12” (300 mm)
2,100 lbs (953 kg)
8’ (2.4 m)
10’ (3.0 m)
6’ (1.8 m)
2
18” (450 mm)
1,100 lbs (499 kg)
4’ (1.2 m)
5’ (1.5 m)
3’ (0.9 m)
2
1. See Supplemental Force disucssion below
Table 3 – TW-900 / TW-1050 Buoyancy Control
Case
1
2
3
Parameter I
Groundwater height
above tank bottom
32” (750 mm) to
39” (975 mm)
40” (1,000 mm) to
51” (1,275 mm)
45” (1,025 mm) to
51” (1,275 mm)
Buoyancy Control Methods (minimum per side
Poured block or
Parameter II
minimum supplemental
Soil cover depth above
Concrete parking
Concrete
force required
Concrete-filled half
tank top
bumpers
traffic barriers
@ F.S. = 1.51
pipe (minimum length)
(minimum length)
(minimum length)
of tank)
Helical
anchors
(min. no.)
6” (150 mm)
2,500 lbs (1,150 kg)
3’ (0.9 m)
4’ (1.2 m)
3’ (0.9 m)
2
6” (150 mm)
7,500 lbs (3,400 kg)
10’ (3.0 m)
12’ (3.5 m)
7’ (2.1 m)
3
12” (300 mm)
2,450 lbs (1,100 kg)
3’ (0.9 m)
4’ (1.2 m)
3’ (0.9 m)
2
1. See Supplemental Force disucssion below
Table 4 – IM-1060 Buoyancy Control
Case
1
2
Parameter I
Groundwater height
above tank bottom
36” (900 mm) to
54” (1,350 mm)
48” (1,200 mm) to
54” (1,350 mm)
Buoyancy Control Methods (minimum per side
Poured block or
Parameter II
minimum supplemental
Soil cover depth above
Concrete
Concrete
force required
Concrete-filled half
tank top
parking bumpers
traffic barriers
@ F.S. = 1.51
pipe (minimum length)
(minimum length)
(minimum length)
of tank)
Helical
anchors
(min. no.)
6” (150 mm)
7,000 lbs (3,200 kg)
8’ (2.4 m)
10’ (3.0 m)
6’ (1.8 m)
2
12” (300 mm)
2,100 lbs (960 kg)
3’ (0.9 m)
3’ (0.9 m)
2’ (0.6 m)
2
1. See Supplemental Force disucssion below
Table 5 – TW-1250 / TW-1500 Buoyancy Control
Case
1
2
3
Parameter I
Groundwater height
above tank bottom
32” (750 mm) to
39” (975 mm)
40” (1,000 mm) to
51” (1,275 mm)
45” (1,025 mm) to
51” (1,275 mm)
Buoyancy Control Methods (minimum per side
Poured block or
Parameter II
minimum supplemental
Soil cover depth above
Concrete
Concrete
force required
Concrete-filled half
tank top
parking bumpers
traffic barriers
@ F.S. = 1.51
pipe (minimum length)
(minimum length)
(minimum length)
of tank)
Helical
anchors
(min. no.)
6” (150 mm)
4,850 lbs (2,200 kg)
6’ (3.6 m)
8’ (2.4 m)
5’ (1.5 m)
3
6” (150 mm)
12,000 lbs (5,450 kg)
15’ (4.6 m)
15’ (4.5 m) TW-1250
18’ (5.5 m) TW-1500
10’ (3.0 m)
4
12” (300 mm)
5,100 lbs (2,300 kg)
7’ (2.0 m)
8’ (2.4 m)
5’ (1.5 m)
2
1. See Supplemental Force disucssion below
*Supplemental Force
The minimum supplemental downward counter-buoyancy force required is included for installers and design engineers to develop custom buoyancy control
methods as needed. These values include a factor of safety of 1.5 applied to the calculated force required to restrain the tank. Custom-designed buoyancy
control methods shall consider fully saturated conditions. So long as buoyancy control is provided that supplies the weight listed in the table (for poured-concrete
blocks or other methods designed by third parties), the tanks will be stable for the corresponding groundwater and soil cover conditions. All Infiltrator strapping
and fastening recommendations would still apply for alternate control methods. Contact Infiltrator’s Technical Services Department with any questions regarding
supplemental force requirements.
Contact Infiltrator Systems’ Technical Services Department for assistance at 800-221-4436.
Step 3 – Implementation
Strapping Locations
Effective buoyancy control of Infiltrator tanks requires careful preparation,
thorough excavation, precise placement, secure strapping and proper backfilling
as described and illustrated below.
(Table 2)
(Table 2)
Excavation Requirements
It is recommended that the excavation width provide a minimum of 36 inches
(900 mm) clearance beyond the tank on all sides when utilizing buoyancy
control. This will allow sufficient room within the excavation to place deadmen
and to fasten strapping. The excavation should provide a minimum of 48 inches
(1,050 mm) when using Chance™ No-Wrench Screw Anchors to allow for
room to properly install the screw anchors. The actual excavation size shall be
determined by the installer. Refer to Infiltrator IM- and TW-Series Septic Tank
Installation Instructions for additional excavation procedures.
(Table 3)
(Table 3)
Concrete-filled Half Pipe Construction
Concrete-filled half pipe shall be supported with soil or other stabilizing means
below the pipe haunches prior to concrete placement. The stabilization shall
prevent the pipe from rolling during placement and curing of the concrete.
Concrete shall be allowed to cure for a minimum of one day prior to tank
backfilling.
Placement of Deadmen and Anchors
Concrete deadmen are to be installed at the bottom of the tank excavation,
parallel to the long axis of the tank (See PLAN VIEW below).
PLAN VIEW
(Table 4)
(Table 5)
PARAMETER II
DEPTH OF SOIL
COVER ABOVE TANK TOP
PARAMETER I
SEASONAL HIGH GROUNDWATER
HEIGHT ABOVE BOTTOM OF TANK
(Table 5)
The deadmen should be placed close to, but not touching, the tank on both
sides of the tank to allow the placement of backfill between the deadman
anchor and tank sidewall. (See SECTION VIEW below).
SECTION VIEW
STRAPPING
(TYPICAL)
PROVIDE ADEQUATE SPACE FOR
BACKFILL PLACEMENT BETWEEN
DEADMAN ANCHOR AND TANK
DEADMAN
Backfill and Cover
Helical anchors should be installed so that the eye loop is level with the bottom
of the tank excavation. They must be in line with the tank model strapping
locations (See Step 3: Strapping) or lifting lugs, as appropriate. Anchors must
also be installed at such a distance from and angle to the tank so that the
strapping is within 5° of alignment with the anchor shaft per manufacturer’s
recommendations.
Strapping
Preparation and fastening of webbing to/over the tanks is critical for tank
stability under constant and fluctuating high groundwater conditions. Straps
must be placed at the specified strapping locations for each model as illustrated
in the following views. These locations correspond to the top lifting lugs for the
TW-300 and TW-500 tank models, and to corner lifting lugs and alignment with
interior structural bulkheads for the remaining TW-Series models. The IM-1060
strapping locations correspond to alignment with interior structural posts. The
IM-1060 tank does not have corner lifting lugs for fastening strapping. Straps
must never be placed over access openings, lids, or inlet/outlet piping. Straps
must be tight-ened with a ratchet or turnbuckle system to remove slack and
slightly pre-load the system.
Place backfill between deadman anchor and tank sidewall to fully fill void.
A minimum 6” layer (150 mm) of suitable cover material is required over
all Infiltrator tank installations. Mound cover for proper drainage. Establish
appropriate vegetative cover as necessary. Refer to Infiltrator IM- and
TW-Series Septic Tank Installation Instructions for additional backfilling and
cover procedures.
General Specifications
• P
rior to ground disturbance, check for subsurface obstructions and utilities in
conformance with applicable requirements.
• Excavations shall conform to applicable safety regulations.
• F
ollow manufacturer instructions for all products and devices used for
Infiltrator tank buoyancy control.
• B
uoyancy control methods described herein do not account for unanticipated
conditions such as surface flooding or other natural disasters, unintended
removal of cover fill over tank, etc.
• B
uoyancy control methods described herein are recommendations only;
consult a professional engineer if desired.
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