U.S. patent application number 10/344775 was filed with the patent office on 2003-10-09 for structural module.
Invention is credited to Marshall, Richard Granville.
Application Number | 20030188505 10/344775 |
Document ID | / |
Family ID | 11042657 |
Filed Date | 2003-10-09 |
United States Patent
Application |
20030188505 |
Kind Code |
A1 |
Marshall, Richard
Granville |
October 9, 2003 |
Structural module
Abstract
A sub-base layer for use in construction, comprises a plurality
of connected substantially cuboid modules each having spaced-apart,
substantially parallel top and bottom walls joined by a peripheral
sidewall defining an enclosed volume. The connection between the
modules is effected by a plurality of tie members which prevent
lateral movement of the modules relative to one another. The layer
is particularly useful as a lightweight replacement for aggregate
sub-base layers in foundations, roadways, pavement, carparks, and
the like.
Inventors: |
Marshall, Richard Granville;
(Dublin, IE) |
Correspondence
Address: |
David G Parkhurst
Fulwider Patton Lee & Utecht
Howard Hughes Center
6060 Center Drive 10th Flr
Los Angeles
CA
90045
US
|
Family ID: |
11042657 |
Appl. No.: |
10/344775 |
Filed: |
February 18, 2003 |
PCT Filed: |
August 17, 2001 |
PCT NO: |
PCT/IE01/00106 |
Current U.S.
Class: |
52/606 |
Current CPC
Class: |
E03F 1/005 20130101;
E01C 3/006 20130101; E02D 27/02 20130101 |
Class at
Publication: |
52/606 |
International
Class: |
E04C 002/10 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 17, 2000 |
IE |
S2000/0648 |
Claims
1. A sub-base layer for use in construction, said layer comprising
a plurality of connected, substantially cuboid modules each
comprising spaced-apart, substantially parallel top and bottom
walls joined by a peripheral sidewall defining an enclosed volume,
the connection between said modules being effected by a plurality
of tie members which prevent lateral movement of the modules
relative to one another.
2. A sub-base layer according to claim 1, wherein each module is
formed from a top half which includes said top wall and the upper
part of said peripheral sidewall, and a bottom half defining said
bottom wall and the lower part of said peripheral sidewall.
3. A sub-base layer according to claim 2, wherein the top and
bottom halves are each provided with a set of half-pillars
extending within the enclosed volume towards one another, whereby
the two sets of half-pillars co-operate with one another to form
pillars extending between the top and bottom walls to resist
vertical crushing of the module.
4. A sub-base layer according to claim 2 or 3, wherein the top and
bottom halves are two substantially identical integral plastics
moulded components which are fitted one inverted on top of the
other.
5. A sub-base layer according to any preceding claims, wherein the
height of the peripheral sidewalls is substantially less than both
the width and the length of the top and bottom walls.
6. A sub-base layer according to any preceding claims, wherein each
module further comprises a network of bracing members extending
between the pillars within said enclosed volume to resist geometric
deformation of said module in a horizontal plane.
7. A sub-base layer according to claim 6, wherein said sidewall and
said network are apertured to allow fluid flow both vertically and
horizontally through said module.
8. A sub-base layer according to any preceding claim, further
comprising an infill medium disposed within the enclosed volume of
one or more of said modules.
9. A sub-base layer according to claim 8, wherein said infill
medium is a medium which provides biological and/or chemical
treatment of water stored in or passing through the modules.
10. A sub-base layer according to any preceding claims, wherein
said tie members are adapted to clamp together abutting sidewalls
of a pair of adjacent modules.
11. A sub-base layer according to claim 10, wherein the peripheral
sidewall of each module is provided with a keyway for receiving one
half of a tie member.
12. A sub-base layer according to claim 11, wherein said keyway is
in the form of a female dovetail groove extending through the
height of the sidewall.
13. A sub-base layer according to claim 12, wherein each tie member
is an elongate member having a cross sectional outline of a pair of
adjoined symmetrically identical trapezoids connected along the
shorter of their parallel sides.
14. A sub-base layer according to claim 13, wherein an elongate
reinforcing member is disposed within the interior of the tie
member.
15. A sub-base structure comprising at least two sub-base layers
according to any preceding claim, said layers being disposed one
above the other, and a plurality of reinforcing struts connected
between the layers.
16. A sub-base structure according to claim 15, wherein each strut
is hollow to provide a fluid passageway through the strut.
17. A sub-base structure according to claim 16, wherein said struts
extend between opposed surfaces of two sub-base layers, and wherein
said opposed surfaces are provided with formations to engage the
struts and retain them in position relative to the modules.
18. A sub-base structure according to claim 17, wherein said
opposed faces of the modules are provided with fluid ports in the
vicinity of the struts whereby the enclosed volumes in the two
levels are in communication via the interior of the hollow
struts.
19. A sub-base structure according to claim 17 or 18, wherein each
strut is in the form of a hollow cylinder having a central support
post and a plurality of planar supports extending radially between
the support post and the internal surface of the cylinder.
20. A sub-base structure according to any one of claims 15-19,
wherein said at least two sub-base layers define upper and lower
faces of a cage structure having an internal space in which said
struts are located, and further comprising one or more side modules
disposed perpendicular to the modules in said layers and extending
between said upper and lower faces at the periphery of said layers,
whereby said side modules define at least a part of a side of said
cage structure.
21. A sub-base structure according to any preceding claims, wherein
one or more surfaces of the modules are at least partially covered
by a geomembrane or geotextile.
22. A structural module comprising spaced-apart, substantially
parallel top and bottom walls joined by a peripheral sidewall
defining an enclosed volume, a plurality of pillars extending
within said enclosed volume substantially vertically between the
top and bottom walls to resist vertical crushing of the module, and
a network of bracing members extending between the pillars within
said enclosed volume to resist geometric deformation of said module
in a horizontal plane, said top and bottom walls, said sidewall and
said network being apertured to allow fluid flow both vertically
and horizontally through said module.
23. A module according to claim 22, wherein the geometrical shape
of the module is such that a plurality of such modules may be
disposed closely adjacent one another along their sidewalls to form
an extensive, substantially continuous layer of modules, the module
further including means for rigid connection of said module to
adjacent modules in said continuous layer.
24. A module according to claim 22 or 23, wherein the module is
made of two substantially identical integral plastics moulded
components which are fitted one inverted on top of the other.
25. A module according to any one of claims 22-24, further
comprising an infill medium disposed within the enclosed volume
26. A module according to claim 25, wherein said infill medium is a
medium which provides biological and/or chemical treatment of water
stored in or passing through the modules.
27. A module according to claim 23, wherein said means for rigid
connection comprises a keyway in said peripheral sidewall for
receiving one half of a tie member.
28. A module according to claim 27, wherein said keyway is in the
form of a female dovetail groove extending through the height of
the sidewall.
29. A module according to claim 27 or 28, wherein said keyway is
tapered along its length to provide a progressively tighter fit for
said tie member as it moved into the keyway.
30. A tie member for connecting a pair of structural modules, said
tie member comprising an elongate member having a substantially
constant cross sectional outline of a pair of adjoined
symmetrically identical trapezoids connected along the shorter of
their parallel sides.
31. A sub-base layer according to claim 30, wherein an elongate
reinforcing member is disposed within the interior of the tie
member.
Description
TECHNICAL FIELD
[0001] This invention relates to a structural module for use, for
example, in the creation of a structural sub-base layer within a
pavement, building foundation or soft landscaping area, and to
sub-base layers and structures.
BACKGROUND ART
[0002] Traditional forms of sub-base layers have comprised
particulate materials (usually natural aggregates) to provide the
necessary structural and drainage characteristics within a pavement
construction. For example, in GB2294077 a bed of gravel is
used.
DISCLOSURE OF INVENTION
[0003] The invention provides, in one aspect, a sub-base layer for
use in construction, said layer comprising a plurality of
connected, substantially cuboid modules each comprising
spaced-apart, substantially parallel top and bottom walls joined by
a peripheral sidewall defining an enclosed volume, the connection
between said modules being effected by a plurality of tie members
which prevent lateral movement of the modules relative to one
another.
[0004] The sub-base layer according to the invention provides an
inexpensive, lightweight, and strong layer with particular
application as a replacement for aggregate layers in foundations,
pavements, roadways, carparks, and the like. Unlike aggregate
layers, the sub-base layer of the invention provides an inherently
level base on which to lay further materials.
[0005] In a further aspect the invention provides a sub-base
structure comprising at least two sub-base layers according to the
invention, said layers being disposed one above the other, and a
plurality of reinforcing struts connected between the layers.
[0006] The invention also provides a structural module comprising
spaced-apart, substantially parallel top and bottom walls joined by
a peripheral sidewall defining an enclosed volume, a plurality of
pillars extending within said enclosed volume substantially
vertically between the top and bottom walls to resist vertical
crushing of the module, and a network of bracing members extending
between the pillars within said enclosed volume to resist geometric
deformation of said module in a horizontal plane, said top and
bottom walls, said sidewall and said network being apertured to
allow fluid flow both vertically and horizontally through said
module.
[0007] An advantage of the invention is that the modules can be
fabricated off-site and a sub-base layer built up rapidly on-site
from the pre-fabricated modules.
[0008] The modules according to the invention can be used to form a
non-particulate sub-base layer under any type of surface, permeable
or impermeable, porous or non-porous, and in both trafficked and
non-trafficked situations, to provide the dual function of
structural layer and shallow storage reservoir. Inherent within the
structure is a system of connectors which eliminates the potential
for short-term and long-term creep of the sub-base layer. Further,
their voided internal structure (typically >90%) enables the
modules to be used as a lateral drainage system with integral flow
control and water treatment capabilities.
[0009] The modules can include infill media to provide biological
and/or chemical treatment of water stored in or passing through the
modules. Further, they can be used for infiltration and attenuation
incorporating geotextiles and geomembranes to suit the
application.
[0010] While the primary application of the modules is envisioned
to be in the construction of structural sub-base layers as
described above, other uses are possible.
[0011] A non-exclusive list of examples of other uses might include
the following, all of which are provided in the scope of the
invention:
[0012] a) Load bearing systems in general for fluid containment,
transportation and/or treatment;
[0013] b) Lightweight load distribution systems for weak
sub-grades, capping layers and floating pontoons;
[0014] c) Structural retaining wall systems;
[0015] d) Lightweight raft formations for foundations;
[0016] e) Channel line drainage systems
[0017] f) Temporary structural formwork systems;
[0018] g) Acoustic and thermal insulation systems;
[0019] h) Structural cavity forming systems;
[0020] i) Temporary structural flooring and seating systems;
[0021] j) Leak detection systems;
[0022] k) Hydraulic flow control and energy dissipation
systems;
[0023] l) Cable ducting and troughing systems;
[0024] m) Air conditioning ventilation formers;
[0025] n) Raised flooring systems having integral drainage,
particularly for use in "wet" industrial environments.
[0026] In a further aspect the invention provides a tie member for
connecting a pair of structural modules, said tie member comprising
an elongate member having a substantially constant cross sectional
outline of a pair of adjoined symmetrically identical trapezoids
connected along the shorter of their parallel sides.
BRIEF DESCRIPTION OF THE DRAWINGS
[0027] An embodiment of the invention will now be described, by way
of example, with reference to the accompanying drawings, in
which:
[0028] FIG. 1 is a perspective view of a structural module
according to the embodiment of the invention;
[0029] FIG. 2 is a plan view of the module of FIG. 1;
[0030] FIG. 3 is a horizontal cross-section through the module in a
plane parallel to the top wall of the module;
[0031] FIG. 4 illustrates the location of parabolic bracing webs
extending between the pillars of the module;
[0032] FIG. 5 is a vertical cross-section of the module taken on
line 5-5 of FIG. 3;
[0033] FIG. 6 is a side elevation of an alternative embodiment of
module to that shown in FIG. 1.
[0034] FIG. 7 is a plan view of a plurality of modules of FIG. 1
connected into a continuous sub-base layer by tie members;
[0035] FIG. 8 is a view, similar to FIG. 5, showing the two halves
from which the complete module is assembled;
[0036] FIG. 9 is a perspective view of the two halves of FIG.
8;
[0037] FIGS. 10A and 10B are perspective end views of two
alternative tie members according to the invention;
[0038] FIG. 11 is a plan view of the tie member of FIG. 10A;
[0039] FIG. 12 is a plan view of a further alternative tie member
according to the invention;
[0040] FIG. 13 is a plan view of the tie member of FIG. 12 with a
reinforcing I-bar in place.
[0041] FIG. 14 is a detail of two modules connected by the tie
member of FIG. 10A;
[0042] FIGS. 15 and 16 are perspective views of a reinforcing strut
used in the sub-base structure according to the invention;
[0043] FIG. 17 is an exploded sectional elevation of the upper and
lower halves of the strut of FIGS. 15 and 16;
[0044] FIG. 18 is a sectional elevation similar to that of FIG. 17,
showing the two halves assembled together;
[0045] FIGS. 19 and 20 are plan views of the upper and lower halves
respectively of the strut;
[0046] FIG. 21 is a perspective view of two modules separated by
reinforcing struts;
[0047] FIG. 22 is a sectional elevation of a sub-base structure
according to the invention;
[0048] FIG. 23 is a schematic view of a sub-base layer according to
the invention used in an infiltration mode; and
[0049] FIG. 24 is a schematic view of a sub-base layer according to
the invention used in an attenuation mode.
DESCRIPTION OF PREFERRED EMBODIMENTS
[0050] In the present specification expressions of orientation such
as top, bottom, vertical, etc., are used for convenience only and
refer to the normal orientation of the module as seen in the
accompanying drawings. However, such expressions are not to be
regarded as limiting the orientation of the module in use, and
indeed, as will be described below, sub-base structures according
to the invention can include modules disposed on their sides or
ends, at right angles to their "normal" orientation.
[0051] Referring to the drawings, a structural module 10 comprises
spaced-apart, substantially parallel top and bottom walls 12, 14
joined by a substantially vertical peripheral sidewall 16 defining
an enclosed volume. In the present embodiment the top and bottom
walls 12, 14 are rectangular so that externally the module 10 has
the general shape of a rectilinear box. The top and bottom walls
have a large number of clustered rectangular apertures 13 (those in
the bottom wall are not visible in the figures but are arranged the
same as those in the top wall), and likewise the peripheral
sidewall 16 has a large number of clustered rectangular apertures
17. These apertures 13, 17 allow fluid flow into and out of the
module 10 in any direction, vertical or horizontal.
[0052] Internally, the module 10 contains a rectangular array of
hollow, generally cylindrical pillars 18 extending vertically
between the top and bottom walls 12, 14 to resist vertical crushing
of the module 10. In this embodiment the module 10 is assembled
from two substantially identical integral components 10A, 10B (see
especially FIGS. 8 and 9) moulded from a rigid plastics material
and which are fitted one inverted on top of the other. Each pillar
18 thus comprises two half-pillars or male and female parts 18A,
18B respectively, one part being integral with one component 10A or
10B and the other part being integral with the other component 10A
or 10B. The male parts 18A alternate with the female parts 18B in
each component 10A and 10B such that when the two components are
fitted together the male parts 18A of each component enter the
respective female parts 18B of the other component to form the
complete pillars 18. To avoid over-insertion of the male parts into
the female parts, and to maintain the top and bottom walls 12 and
14 at their correct separation, each male part has a shoulder 18C
which abuts against the open end 18C of the respective female part
when the components 10A and 10B are fully engaged.
[0053] Internally, the module 10 also contains a network of bracing
members 20, 22 to resist geometric deformation of the module in a
horizontal plane. The bracing members 20, whose locations are shown
in FIG. 4, extend directly or diagonally between adjacent pillars
18 and comprise vertical webs having apertures 20C to allow fluid
flow horizontally through the module 10 in any direction (since the
webs 20 are orientated vertically they do not obstruct fluid flow
in the vertical direction). Each web 20 is formed of upper and
lower halves 20A, 20B integral with the upper and lower components
10A, 10B respectively, and have facing concave edges 20D defining
the apertures 20C. In this embodiment the edges 20D are
parabolic.
[0054] The bracing members 22 serve to break down voids within the
box. As viewed from above in FIG. 3, they extend substantially
normally between the bracing members 20 and supplement the bracing
effect of the latter. As viewed in FIG. 3, members 22 are 5 mm
thick and extend upward from the base (in a direction normal to the
page) by 3 mm.
[0055] To allow a plurality of modules 10 to be rigidly connected
together to form a layer of such modules, for example, for use as a
structural sub-base layer, the peripheral sidewall 16 comprises a
plurality of substantially vertical keyways in the form of dovetail
slots 24 each for slidably receiving a respective reinforced tie
member 26 (FIGS. 10-13) having a "bow tie" cross-section. As seen
in FIG. 7, when connecting two modules 10 together, a single tie
member 26 slidably engages two opposing keyways 24 in the two
modules. This connector eliminates the potential for short-term and
long-term creep of the system.
[0056] As seen in FIG. 7, the rectangular shape of the modules 10,
in plan view, allows the modules to be disposed closely adjacent
one another along their peripheral sidewalls 16 to form an
extensive, substantially continuous layer of modules of any desired
area. That is to say, the layer of modules is without significant
gaps between the modules. However, the same effect can be obtained
using modules of different geometrical shape in plan view, for
example, the modules could be hexagonal or triangular. Either
alternative will allow an extensive, substantially continuous layer
of modules to be built up, with connectors eliminating short-term
and long-term creep.
[0057] Finally, to allow a layer of connected modules to be built
up which is more than one module thick, the ends of the pillars 18
are open at the top and bottom walls, as seen at 28. This allows
reinforced pegs 30 (FIG. 1) to be inserted partially into the open
pillar ends 28 in the top wall 12 of one module and partially into
the open pillar ends 28 in the bottom wall 14 of a module overlying
and in register with the first module, to maintain them against
relative lateral displacement.
[0058] An example of a module 10 made as above had overall
dimensions approximately 710 mm long.times.355 mm wide.times.250 mm
deep. The pillars 18 were spaced on approximately 105 mm centres,
had an outside diameter of about 40 mm and a thickness of about 5
mm. All walls 12, 14 and 16, and webs 22 and 22, were about 3 mm
thick.
[0059] FIG. 6 shows an alternative embodiment of a module according
to the invention, in which the pattern of apertures 17 in the
sidewall 16 is more open, to allow greater lateral fluid flow
between adjoining modules and out of the outermost edges of a
sub-base layer formed of a plurality of adjoined modules. The
larger apertures can be incorporated without significantly
compromising the strength of the modules due to the fact that when
used as a structural sub-base the lateral compressive forces are
significantly less than the vertical forces, and most of the
vertical strength is derived from the pillars rather than the
sidewalls.
[0060] FIGS. 10A and 11 show an embodiment of tie member in
perspective view from one end, and in plan view, respectively. The
tie member 26 has a substantially constant "bow-tie" cross-section,
i.e. the shape is that of two symmetrically identical trapezoids
40,42, sharing a common side 44, which is the shorter of the two
parallel sides 44,46 of each trapezoid.
[0061] The tie member of FIG. 10B is identical in outline, but the
shared wall is omitted.
[0062] FIG. 12 shows the cross-section of a further embodiment of
tie-member in which the shorter shared side of the trapezoids has a
gap 48 to accommodate a reinforcing I-bar section of steel 50 (FIG.
13). The ends 52 of the I-bar abut against a pair of ridges 54
running down the longer of each of the parallel trapezoid sides 46,
to hold the I-bar firmly in place in the tie member.
[0063] FIG. 14 shows the tie member 26 of FIG. 10A in position in a
pair of keyways 24 to hold two adjacent modules 10a, 10b in
position relative to one another.
[0064] Advantageously the keyways 24 which extend through the
height of the peripheral sidewall (see FIG. 1, for example), may
incorporate a slight taper narrowing from the top and bottom
surfaces towards the centreline. In this way, a pair of tie
members, each having a length equal to the height of one of the
halves making up the module, may be inserted from the top and from
the bottom. As they move into the keyways, the taper grips them
more tightly, and thereby holds them firmly in place without
allowing any play between the tie members and the modules.
[0065] Instead of stacking modules directly on top of one another
as previously described, reinforcing and separating struts can be
used to define a void between layers of modules in a sub-base
structure. A reinforcing strut is shown in FIGS. 15-20. As seen in
FIGS. 15 and 16, the strut 60 comprises a generally hollow
cylindrical body 62 having a central support post 64 therein which
extends above and below the ends of the cylinder. A plurality of
planar supports 66 extend radially from the support post 64 to the
body 62. These planar supports define generally wedge-shaped
hollows 68 running through the length of the strut, allowing fluid
flow through the strut.
[0066] As seen in FIGS. 17 and 18, the strut is formed in two
halves 70,72 (shown in plan view in FIGS. 19 and 20). The planar
surfaces within upper half 70 terminate at an end edge 74 against
which the end edge 76 of the corresponding planar surface in the
lower half 72 abuts. This upper end edge 76 fits into a collar 78
of the upper half 70, thereby enabling the two halves to fit
together as seen in FIG. 18.
[0067] By manufacturing the strut in two halves, the length of the
strut (and hence the distance between the layers separated by the
strut) can be varied. Thus, only the upper half could be used,
making a male connection with the module above it and a female
connection with a peg fitted into the module below it, or the full
strut (FIG. 18) could be used to make a male connection with the
modules above and below. It will be appreciated that the strut can
be extended as required.
[0068] The wedge-shaped hollows 68 can advantageously be used to
retain infill or filtration media of any suitable type (e.g. simple
physical strainers, or chemical or biological purifiers), to treat
water or other liquid passing down through the strut from an upper
module to a lower module.
[0069] FIG. 21 illustrates how the struts 60 may be disposed
between an upper module 10a, and a lower module 10b (both shown in
simplified form as a pair of connected box sections) separated by a
plurality of struts 60. In practice, rather than just two modules,
a more extensive structure will be formed from two or more stacked
layers (such as the layer of FIG. 7 extended outwards), with struts
60 between these layers. FIG. 22 shows such a structure.
[0070] As seen in FIG. 22, three sub-base layers 80,82,84 each
comprising a plurality of modules 10 connected by tie members (not
shown) are disposed one above the other. Struts 60 separate the
upper layer 80 from the middle layer 82, and the middle layer 82
from the lower layer 84. The structure is shown in section but will
extend in three dimensions, with struts disposed periodically
across the extent of each layer.
[0071] The edges of the structure are bounded by a series of
modules 10' which are identical to the modules 10 of the layers but
which are disposed on their sides. The modules and struts are
dimensioned so that the height of the strut equals the width of a
module, i.e. when disposed on their sides, modules 10' have a
"height" which exactly fills the gap between the peripheries of the
layers. In this way a "cage" structure can be created which defines
an internal void 86 (or with more than two layers a number of such
voids 86) in which the struts are located.
[0072] The cage provides a large open volume to receive waste water
or other fluids, and the structure is sufficiently strong to
support constructions such as building foundations and paved
surfaces.
[0073] The structure will generally be disposed in the earth so
that the modules 10' are prevented from falling outwards by the
lateral inward pressure exerted by the surrounding soil. The
positions of the struts are chosen so that the modules 10' cannot
move into the cage since they abut against struts 60, and in this
way the cage structure is maintained in use.
[0074] Referring to FIG. 23, a first application of the sub-base
layer according to the invention is shown. A sub-base layer of
modules 10 is placed on a sub-grade 90. This sub-base layer takes
the place of aggregate such as gravel which is often used as a
sub-base layer. Surface layers 92,94 are then laid on top of the
modules in conventional manner to provide a finished surface 96
which receives precipitation 98 and surface water.
[0075] The top wall 12 and bottom wall 14 of the modules are
covered by a pervious geotextile which acts to filter water
entering the modules and to prevent soil fines from migrating
through the modules. Although the geotextile is preferably provided
above and below the layer, one or both of these geotextiles may be
omitted as appropriate.
[0076] If the surface layers 92,94 are both pervious, then
precipitation 98 falling on the surface can seep through the
surface layers into the sub-base layer and from there into the
underlying sub-grade 90. In addition to providing structural
strength and a level top surface, the sub-base layer provides a
temporary storage tank for holding and dissipating large volumes of
water. It also enables water to be redistributed away from
localised areas where a lot of water collects.
[0077] Furthermore, by including infill media in the modules,
filtration and/or chemical or biological treatment of the water may
be achieved before it reaches the local water table or watercourses
via the sub-grade.
[0078] The single layer of modules 10 shown in FIG. 23 can be
replaced by a number of stacked layers or by a multi-layer sub-base
structure of the type shown in FIG. 22.
[0079] If one or more of the surface layers is impervious, then
water can arrive at the modules laterally from a section of the
layer which lies under pervious layers, or 10 via pipes, gullies
and the like.
[0080] FIG. 24 shows another application, in which the modules 10
are again disposed in a layer above a sub-grade 90 and below
surface layers 92,94 which may be pervious or impervious as
discussed above. In this embodiment, the bottom wall 14 is covered
by an impermeable geomembrane which prevents water from flowing out
of the bottom of the layer. Instead, the layer acts to store water
and channel it to a suitable drainage structure by lateral
drainage. This arrangement may be required if local geological
conditions or environmental regulations preclude the direct
drainage of water into the sub-grade. The top surface 12 can also
be covered by an impermeable geomembrane (if water arrives via
conduits, pipes or gullies) or by a permeable geotextile (if water
is to seep directly into the modules from above). Again, the single
layer of modules can be replaced by a multi-layer structure.
[0081] Referring back to FIG. 22, a further modification of the
structure can be described for use in such applications as those
described for FIGS. 23 and 24. The cage structure, in this
variation, is covered above and below by a permeable geotextile
(not shown). Water arrives into the structure by seeping from above
into the top layer 80 of modules 10. The bottom wall 14 of this top
layer is covered externally by an impermeable membrane (not shown)
which is held in place by being clamped between the struts 60 and
the modules 10. This prevents water from draining directly through
the apertures 13 (FIG. 1) in the bottom wall 14 into the void
86.
[0082] The impermeable membrane is provided with apertures in the
region 100 where it is covered by the cylindrical struts abutting
against the bottom wall 14. These apertures in the impermeable
membrane provide the sole means of water draining from the upper
layer 80, i.e. all of the water draining from the upper layer does
so via the hollow struts. Water drains through the wedge-shaped
channels in the struts which are filled with filtration and/or
water treatment infill media. The treated or filtered water reaches
the middle layer 82 from where it can drain into the bottom layer
either from the bottom wall 14 of the middle layer 82 or via the
struts 60 supporting the middle layer 82.
[0083] The bottom wall of the middle layer may be provided with a
similarly apertured impermeable membrane, in which case the lower
set of struts can provide a second stage treatment. In this way, a
coarse filtration medium could be provided in the upper set of
struts and a fine filtration medium in the lower set of struts.
Water entering the top layer 80 would be coarsely filtered and
could flow at high rates into the middle layer 82. Since the only
egress from the middle layer to the bottom layer 84 is through the
lower set of struts and since these struts may be provided with low
flow-rate fine filters, large volumes of water could be temporarily
held in the middle layer and in the void 86 between the middle and
upper layers (this void being in free communication with the
apertures in the top wall of the middle layer modules). After
collecting in the middle layer and upper void, the coarsely
filtered water can then seep more slowly through the fine filters
into the lower layer 84 and the void 86 between the lower and
middle layers, before finally seeping out of the lower layer into
the sub-grade, or laterally from the lower layer through drainage
channels (not shown). A combination of filters and
chemical/biological treatment media could also be used as
required.
[0084] The invention is not limited to the embodiments described
herein which may be modified or varied without departing from the
scope of the invention.
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