Note: Descriptions are shown in the official language in which they were submitted.
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STORMWATER CHAMBER HAVING MULTI-LAYER MAT
Related Application
[001] This application claims the benefit of priority to U.S. Provisional
Patent
Application No. 61/307,282 filed on February 23, 2010, the entire disclosure
of which is
expressly incorporated herein by reference.
Technical Field
[002] The present disclosure relates to a multi-layer mat for stormwater
chambers that are buried beneath the surface of the earth for receiving and
dispersing
stormwater.
Background
[003] Thermoplastic chambers with arch-shaped cross-sections have been
buried beneath the surface of the earth for receiving and dispersing collected
stormwater. Examples include Stormtech Model SC310 or Model SC740 stormwater
chambers, sold by Stormtech LLC, of Wethersfield, Connecticut. These arch-
shaped
chambers are positioned in an arrangement below ground and configured to
receive a
flow of stormwater. For example, stormwater chambers may be positioned in-line
with
each other, in an array, or both in-line and in an array. Stormwater chambers
may be
provided with an inlet configured to connect to the outlet of a stormwater
collection
system, such as a plurality of drain basins associated with a street, parking
lot, roof, etc.
Stormwater chambers may be configured to desirably distribute collected
stormwater
back into the environment through the ground.
[004] Stormwater often carries with it debris that passes through basins and
other traps normally associated with stormwater collection systems. For
example, the
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water may bear suspended solids, such as dirt, sand, small pieces of leaf,
paper, and
plastic. Stormwater chambers are often designed to allow debris to settle
(e.g., sink to
the bottom of a chamber) before stormwater is released into the ground. State
and
federal regulations may in some cases control the amounts or proportions of
debris that
can be reintroduced into the environment after stormwater collection.
[005] In some cases, stormwater systems include a subsystem by which
stormwater is first flowed to a primary row of chambers dedicated to capturing
a large
amount of the debris. Examples of such primary chamber rows include the
Isolator
row subsystem marketed by Stormtech, LLC. Isolator row chambers are typically
encased in a layer of comparatively fine mesh geotextile, often referred to as
"filter
fabric." Typically, the fabric surrounds the exterior of the chamber and runs
along the
surface of the porous medium, typically crushed stone, which forms the floor
underlying
the arch curve of the chamber. To the extent the entrained debris includes
leaves or
pieces of other sheet materials, those materials may be caught by the filter
fabric and
locally mask openings in the fabric, reducing the capacity of the fabric to
disperse
filtered stormwater downwardly.
[006] As a result, maintenance workers periodically remove the debris that
collects in primary rows, such as the Isolator row, and systems not having a
primary
row. Typically, debris is removed using a special apparatus that involves
water jetting
and vacuuming. For example, a jet, siphon, or both at the end of a hose may be
pushed or pulled along the length of each chamber or string of chambers.
Undesirably,
the cleaning devices may push, snag, tear, gather, or otherwise disrupt the
geotextile
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which lies on the crushed stone floor that defines the bottom of the chamber
interior,
thus upsetting its subsequent functionality.
[007] The present disclosure is directed to addressing the above-referenced
challenges.
Summary
[008] In accordance with an exemplary embodiment, a method is disclosed for
receiving and dispersing stormwater, underground. The method includes
directing
stormwater bearing debris from a source into an interior of one or more
chambers
buried within water-permeable aggregate, wherein the one or more chambers are
supported on a floor of the water-permeable aggregate by opposing side base
flanges
of the one or more chambers, and the floor defines a lower boundary of an
interior
space of the one or more chambers. The method further includes filtering a
portion of
water-borne debris from stormwater flowing toward the floor, by using one or
more
filtering layers; and protecting the one or more filtering layers from damage
during a
cleaning process, by using a water permeable protective layer. The one or more
filtering layers have a finer porosity than a porosity of the protective
layer.
[009] In another exemplary embodiment, an apparatus is disclosed for
receiving and dispersing stormwater beneath the surface of the ground, wherein
the
apparatus accumulates debris carried by the stormwater received. The apparatus
includes an arch-shaped cross-section chamber buried in stone aggregate, the
chamber
having base flanges supported on a stone aggregate floor and an interior space
bounded by the floor; and a mat connected to the chamber and positioned over
the
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floor. The mat includes one or more filtering layers disposed in proximity to
the stone
aggregate floor for filtering and retention of a portion of debris carried by
the
stormwater; and a protective layer disposed above the one or more filtering
layers, for
both filtering debris and for protecting the one or more filtering layers
during a cleaning
process. The first layer has an average pore size that is larger than the
average pore
size of the second; and the first layer allows a portion of debris carried in
the water to
flow with the water to the second layer.
[010] Before explaining certain embodiments of the disclosure in detail, it is
to
be understood that the disclosure is not limited in its application to the
details of
construction and to the arrangements of the components set forth in the
following
description or illustrated in the drawings. The disclosure is capable of
embodiments in
addition to those described and of being practiced and carried out in various
ways.
Also, it is to be understood that the phraseology and terminology employed
herein, as
well as in the abstract, are for the purpose of description and should not be
regarded as
limiting.
[011] The accompanying drawings, which are incorporated in and constitute a
part of this specification, illustrate certain embodiments of the disclosure,
and together
with the description, serve to explain the principles of the disclosure.
[012] As such, those skilled in the art will appreciate that the conception
upon
which this disclosure is based may readily be utilized as a basis for
designing other
structures, methods, and systems for carrying out the several purposes of the
present
disclosure. It is important, therefore, to recognize that the claims should be
regarded as
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including such equivalent constructions insofar as they do not depart from the
spirit and
scope of the present disclosure.
Brief Description of the Drawings
[013] The accompanying drawings, which are incorporated in and constitute a
part of this disclosure, illustrate several embodiments and aspects of the
present
disclosure, and together with the description, serve to explain certain
principles of the
invention. In the drawings:
[014] FIG. 1 is an end view of stormwater chamber showing an exemplary
multi-layered mat at the bottom of the stormwater chamber;
[015] FIG. 2 is an elevation view of an exemplary three-layer mat for use
within
a stormwater chamber;
[016] FIG. 3 is an isometric view of a portion of an exemplary three-layer mat
for use within a stormwater chamber;
[017] FIG. 4 is an end view of adjacent stormwater chambers, including an
exemplary multi-layer mat disposed under one of the stormwater chambers; and
[018] FIG. 5 is a perspective view including a detailed view of exemplary
mechanisms for fastening the exemplary multi-layer mat of FIG. 4 to a
stormwater
chamber.
Detailed Description
[019] Reference will now be made in detail to exemplary embodiments of the
disclosure, examples of which are illustrated in the accompanying drawings.
Wherever
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possible, the same reference numbers will be used throughout the drawings to
refer to
the same or like parts.
[020] In general, the present disclosure is directed to receiving and
dispersing
stormwater using a chamber apparatus that receives and retains suspended
solids in a
way that facilitates periodic removal of debris without disrupting geotextile
lying inside
the chamber. As described above, stormwater may be directed from a collection
source
into an interior of one or more chambers buried within stone aggregate
underground.
Each stormwater chamber may include a plurality of base flanges that rest on a
floor
comprised of stone aggregate, through which water flows downwardly during use.
A
multi-layer mat may be positioned on or just above the floor surface, defining
a bottom
of a chamber interior. The mat may include an upper layer having coarse
openings for
filtering and protecting one or more underlying layers. In particular, the
upper layer may
be configured to keep leaves and other sheet debris out of intimate contact
with the
lower layer(s). The one or more lower layers may have finer porosity than the
upper
layer and therefore filter a portion of the finer debris that passes through
the upper
layer.
[021] As described in more detail below, any or all of the layers may be
fastened to each other. The layers may be positioned under the flanges of a
chamber,
or deformed upwards and fastened to the inside of the chamber. In one
embodiment,
one or more of the layers may run around the exterior of the chamber. In one
exemplary embodiment, the upper protective layer may be a nonwoven high
density
polyethylene (HDPE) netting material, and the one or more bottom layers may be
a
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woven slit film polypropylene (PP) geotextile material. In one embodiment, the
multi-
layer mat may include two layers of the woven slit film polypropylene
geotextile material.
[022] Turning now to the figures, FIG. 1 depicts a cross-section of an
exemplary stormwater chamber 20 having side base flanges 28 positioned on a
floor
34, with a multi-layer mat 18 positioned on the floor 34 under the stormwater
chamber
20. Multi-layer mat 18 may include a plurality of layers of water permeable
material
underlying the arch span of stormwater chamber 20 and defining a lower bound
of an
interior 30 of the chamber. In one embodiment, floor 34 is composed of water-
permeable aggregate, such as stone aggregate. Stone aggregate most commonly
comprises crushed stone or gravel; however, the term as used herein shall
comprehend
any water permeable particulate medium. The spaces between adjacent stormwater
chambers and regions above the stormwater chambers may also comprise stone
aggregate.
[023] As described above, in one embodiment, stormwater chamber systems
may comprise a multiplicity of parallel rows of chambers connected end-to-end.
Thus,
FIG. 1 depicts stormwater chamber 20 being flanked by another stormwater
chamber
20A, suggestive of the other rows that may be present. In one embodiment,
stormwater
chambers 20 and 20A may be Stormtech stormwater chambers, Model SC310 or
Model SC740, both of which are made of injection molded thermoplastic and sold
by
Stormtech LLC, Wethersfield, Connecticut.
[024] In one exemplary stormwater system, a primary row subsystem (e.g.,
Isolator row) first receives stormwater and captures a large proportion of
the
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suspended solids, to keep the suspended solids from being distributed to the
rest of the
system (e.g., adjacent rows of chambers). In one embodiment, the primary row
may
have a circumscribing layer of filter fabric surrounding a top of the chambers
arranged in
the primary row. The primary row may be configured to filter and direct
stormwater into
stone aggregate below the chamber and, if desired, into multiple other
chambers 20A.
For the construction and function of a system having an Isolator -type primary
row of
chambers, see U.S. Pat. No. 6,991,734 of Smith, the disclosure of which is
incorporated
herein by reference. While the present disclosure describes the use of a multi-
layer mat
in relation to a primary row of chambers, multi-layer mats consistent with the
present
disclosure may be used with any chambers of other kinds of stormwater systems;
and
also with chambers having cross sections other than those shown in the present
disclosure.
[025] During use, stormwater first flows into the interior 30 of stormwater
chamber 20. Then, under the influence of gravity, the water flows downwardly
and
sideways. In one embodiment, stormwater chamber 20 may include perforations
(not
shown) in sidewalls of the arch, for allowing stormwater to exit the interior
30 laterally.
Stormwater may also exit the interior 30 through multi-layer mat 18.
Stormwater in
stormwater chamber 20 may therefore flow into interstices of the stone
aggregate
surrounding stormwater chamber 20. Eventually, stormwater may flow into the
soil in
which the stormwater system is contained, or by means of a conduit or outlet
to a
discharge point, such as a pond or stream.
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[026] Multi-layer mat 18 may include a plurality of layers and, in one
exemplary
embodiment, may include three layers. As shown in FIG. 2, in one embodiment,
multi-
layer mat 18 may include two adjacent lower filtering layers 24, which lie on
or in close
proximity to the stone aggregate floor 34 of the chamber interior space; and
an upper
protective layer 26 which lies on top of the lower filtering layers 24. Any or
all of the
layers may be formed from plastic or other water resisting material, and
include a
multiplicity of openings, or pores, which make the multi-layer mat water
permeable. In
one embodiment, lower filtering layers 24 may be made from a woven slit film
polypropylene (PP) geotextile material, while upper protective layer 26 may be
made
from a nonwoven high density polyethylene (HDPE) netting material.
[027] The function of filtering layers 24 may be to catch fine suspended
solids,
and to diminish the propensity for the suspended solids to fill the
interstices in the stone
aggregate below stormwater chamber 20 over time. The function of protective
layer 26
may be to protect filtering layers 24 from mechanical disruption, as can occur
during
water jet cleaning or other modes of cleaning. Protective layer 26 may be a
sturdy
material having coarse openings compared to the openings of filtering layers
24. The
material of protective layer 26 may have openings that are large enough to
allow
smaller suspended solids, such as sand and dirt, to pass through protective
layer 26.
However, the mesh size of protective layer 26 may be fine enough to protect
filtering
layers 24 from snagging or damaging engagement with mechanical cleaning
devices
sliding along the floor of the chamber space, and to resist the forces of
water jets as
they blast loose settled debris. Thus, the average size of the pore openings,
or the
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porosity, of the top protective layer 26 is larger than the average size of
the pore
openings, or the porosity, of the lower filtering layers 24.
[028] In one embodiment, the upper protective layer 26 provides a filtering
function in combination with the lower filtering layers 24. While, in an
exemplary case,
the average opening sizes of the protective layer 26 are several times larger
than the
average opening sizes of the filtering layers 24, the protective layer 26 may
still block, or
filter, larger objects that might mask and reduce the flow capacity of the
filtering layers
24. For instance, the protective layer 26 may stop flat sheet matter, such as
paper and
leaves from coming in intimate contact with the filtering layers 24. Thus, a
portion of the
water-borne debris will be captured on the top protective layer 26; and a
portion of the
debris which passes through the top layer will be captured on the lower
filtering layers
24. In one embodiment, the two filtering layers 24 may nominally have the same
porosity as each other. Even when the filtering layers 24 have the same pore
size,
experimental data shows a significant increase in the capture of the finer
suspended
solids is achieved with two filtering layers, when compared to one filtering
layer.
[029] In one embodiment, protective layer 26 and the filtering layers 24 may
be
fastened to each other by adhesives, mechanical fasteners, stitching, and/or
welding
(when compatibility of the materials allows). Fastening the layers to each
other can
make installation of the multi-layer mat 18 more convenient and can provide an
overall
stronger composite mat structure which resists the forces associated with
installation,
use, and cleaning.
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[030] While filtering layers 24 are pictured as lying on the aggregate floor
34, in
general, the filtering layers 24 may be spaced apart from the floor surface.
Likewise,
spacers may be placed between aggregate floor 34, filtering layers 24, and/or
protective
layer 26. In one embodiment, the layers may be discrete pieces of material
having
lateral dimensions that allow the discrete pieces of material to fit within
the interior
edges of the base flanges 28. Alternatively, one or more layers may be
sufficiently wide
to extend under base flanges 28, so the weight of each stormwater chamber 20
helps to
hold the layers in place.
[031] In yet another embodiment, the layers may be curled up at opposing
ends 18A and 18B, as shown in FIG. 3, for connection to chamber 20. FIG. 4
depicts
another perspective view of a stormwater chamber 20 between adjacent
stormwater
chambers 20A. As shown in FIG. 4, multi-layer mat 18 may be curved up at
opposing
ends and fastened to an inside surface of stormwater chamber 20. FIG. 5 shows
how
multi-layer mat 18 may be fastened to an inside surface of stormwater chamber
20
using one or more fasteners 36 (shown in detail cut-out). Fasteners 36 may be
any
suitable device known to those of skill in the art, including but not limited
to nails,
screws, tacks, staples, push-pins, anchors, and/or hooks.
[032] In one exemplary embodiment of multi-layer mat 18, the one or more
filtering layers 24 may include a non-woven material, such as a geotextile;
and the
upper protective layer 26 may be a woven net-like material of orthogonal
welded
ligaments. In one embodiment, the lower filtering layers 24 may be formed from
a non-
woven material conforming with standard AASHTO M288 Class 2 of American
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Association of Highway Transport Officials; and the protective layer 26 may be
formed
from a woven material conforming with standard AASHTO M288 Class 1.
[033] One exemplary material for the lower filtering layers 24 is Geotex 315ST
woven polypropylene geotextile (Propex Inc., Chattanooga, Tennesee).
Functionally,
the geotextile may have an average opening size of about 0.425 mm, more
nominally
about 0.5 mm. An exemplary material for upper protective layer 26 may include
Skaps
Transnet geonet 220 comprised of 220 mil thick high density woven polyethylene
resin
(SKAPS Industries, Commerce, Georgia), which has an average opening size of
about
0.03 square inches (equivalent to a diameter of about 0.195 inch (3.8 mm)).
Thus, the
nominal opening size of the protective layer 26 may be about 9 times larger
than the
nominal opening of filtering layers 24. Table 1 discloses other exemplary
materials that
may be used in substitution of the foregoing examples.
Table 1: Exemplary materials useful for layers 24 and 26.
AASHTO M288 Class 2 AASHTO M288 Class I
Source Non-Woven, for Layers 24 Woven, for Layer 26
Belton Industries Beltech 977
Carthage Mills FX-60HS, FX-80HS FX-66
GSE Lining
NW6, NW8
Technology
MacTex MX245, MacTex
Maccaferri MX275
Pavco-Amanco NT3000M, NT4000M TR4000
Geotex 651, Geotex 861, Geotex 315ST, Geotex
Propex Geotex 2x2HF, Geotex 250ST
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601, Geotex 701, Geotex 801
SKAPS Industrites GT 160NW, GT 180NW W315
Mirafi 600X, Filterweave
403, Filterweave
Tencate Mirafi Mirafi 160N, Mirafi 180N 404,Geolon
HP570, Geolon HP665,
Geolon HP770
TNS Advanced
R060 , R070, R080, R100
Tech.
US Fabrics US 205NW, US 160NW US 315
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TABLE 2: EXEMPLARY PP GEOTEXTILE PROPERTIES FOR FILTERING LAYERS
24.
Property Test Method English Metric
Physical / Mechanical
Thickness ASTM D 5199 20 mils 0.5 mm
Grab Tensile Strength ASTM D 4632 315 lbs 1,400 N
Grab Tensile Elongation ASTM D 4632 15% 15%
Wide Width Tensile ASTM D 4595 175 lbs/in 30.6 kN/m
Trapezoidal Tear ASTM D 4533 120 lbs 530 N
Mullen Burst ASTM D 3786 600 psi 4134 kPa
Puncture Strength ASTM D 4833 125 lbs 555 N
UV Resistance (at 500 hrs) ASTM D 4355 70% 70%
Hydraulic
70 US Std
Apparent Opening Size ASTM D 4751 Sieve 0.212 mm
Permittivity ASTM D 4491 0.05 sec-1 0.05 sec-1
161
Water Flow Rate ASTM D 4491 4 gpm/ft2 I/min/m2
Table 3: Exemplary HDPE Geonet Properties for Protective Layer 26.
Property Test Method English Metric
Physical / Mechanical
Thickness ASTM D 5199 0.125 in 3 mm
12,400
Tensile Strength at Yield ASTM D 638 1800 psi kPa
Tensile Elongation ASTM D 638 600% 600%
UV Resistance (at 500 hrs) ASTM D 4355 90% 90%
Hydraulic
Apparent Opening Size ASTM D 4751 0.03 in2 19 mm2
[034] As a result of the use of protective layer 26 disposed above one or more
filtering layers 24 having, for example, the properties listed above,
filtering layers 24
may be protected when debris is removed from a stormwater chamber provided
with
multi-layer mat 18. For example, when a jet and/or siphon at the end of a hose
is
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pushed or pulled along the length of each chamber or string of chambers,
protective
layer 26 may prevent filtering layers 24 from being pushed, snagged, torn,
gathered, or
otherwise disrupted from laying on the aggregate that defines the bottom of
the
chamber interior.
[035] It will be appreciated that the above described materials, mechanical
properties, hydraulic properties, and performance estimates are merely
exemplary in
nature, and are not to be construed as limiting.
[036] The many features and advantages of the present disclosure are
apparent from the detailed specification, and thus, it is intended by the
appended claims
to cover all such features and advantages of the disclosure which fall within
the true
spirit and scope of the disclosure. Further, since numerous modifications and
variations
will readily occur to those skilled in the art, it is not desired to limit the
disclosure to the
exact construction and operation illustrated and described, and accordingly,
all suitable
modifications and equivalents may be resorted to, falling within the scope of
the
disclosure.
