Note: Descriptions are shown in the official language in which they were submitted.
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A WATER DETENTION SYSTEM INCORPORATING A COMPOSITE
DRAINAGE MEMBRANE
The present invention relates generally to a composite drainage membrane, and
to
a water detention system incorporating such a membrane.
The present invention finds particular utility in connection with the
provision of
pavement surfaces, that is hard, load-bearing surfaces made from paving
elements
such as slabs or blocks, or continuous material such as concrete or asphalt.
However, the present invention is not limited to application solely in this
field, and
may find utility in connection with a wide range of forms of water run-off
management, storage, and precipitation re-utilisation systems, particularly
those
suitable for use with rainwater, as well as systems for decontamination of run-
off
water and for the use of subterranean water for heat exchange purposes.
The use of SUDS (sustainable urban drainage systems) is increasing with the
increasing awareness of the economy of installation and value in
decontaminating
and managing the, water collection-and drainage systems leading to water
courses
for the disposal of water falling on pavement surfaces. Known drainage systems
are built to cope with a maximum expected precipitation, which may be exceeded
from time to time. Changing meteorological conditions, however, are leading to
situations where the peak rainfall for which a drainage system may have been
designed is being exceeded increasingly frequently. Upgrading of systems to
cope
with increased amounts of run-off is extremely costly. There is also the
CONFIRMATION COPY
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containing and polluting effect of motor traffic resulting in heavy metals,
hydrocarbons,
rubber dust, silt and other fine detritus becoming deposited on the surfaces
of roadways and
car parks and subsequently being washed into the water courses causing long
term pollution.
Sustainable urban drainage systems utilising permeable pavements and
underlying layers of
crushed rock over an impermeable sub-grade, or provided with an impermeable
lining
membrane, may be used to collect and store water for other purposes such as
irrigation. When
used for this purpose, however, especially in regions of high temperature,
evaporation of the
stored water, even though located in subterranean voids, can result in
effective loss of a large
proportion of the water collected.
References to the invention herein relate to embodiments or aspects of the
invention.
The present invention seeks to provide means by which such systems can be
improved to
allow rapid infiltration of water into the voids in the sub-base, without
there being an
opportunity for equally rapid escape by evaporation.
According to a first aspect of the present invention there is provided a water
detention system
comprising a sub-base of particulate material in a layer having a substantial
number of voids
over an at least substantially impermeable sub-grade or a preliminarily
positioned at least
substantially impermeable membrane, with an overlying substantially
unidirectionally porous
layer able to allow water to infiltrate from above into the sub-base but which
is such as
substantially to resist loss of water from the sub-base by evaporation such
that water
collecting on its upper surface can infiltrate into the sub-base to be
retained therein, wherein
said substantially unidirectionally porous layer comprises a membrane having
an upper
nonwoven textile material component the fibres or filaments of which are heat
bonded and a
lower woven textile component the filaments of which are composed of flat
plastics strips,
wherein said woven and non-woven components are bonded together, the weave of
the flat
plastic strips of the lower woven textile component being sufficiently tight
so as to provide
interstices between adjacent woven filaments to allow water to pass
therethrough but which
prevent water vapour from escaping whereby to resist evaporative loss from the
sub-base.
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According to another aspect, there is provided a method of forming a water
detention system
comprising the steps of: laying a sub-base of rigid insoluble hard particulate
material of a
defined size range over an at least substantially impermeable sub-grade or a
preliminarily
positioned at least substantially impermeable membrane; overlaying the sub-
base with a
substantially unidirectionally porous layer able to allow water to infiltrate
from above into the
sub-base but which is such as substantially to resist loss of water from the
sub-base by
evaporation; and overlaying the said substantially unidirectionally porous
layer with a layer of
particulate material, wherein said substantially unidirectionally porous layer
comprises a
membrane having an upper nonwoven textile material component the fibres or
filaments of
which are heat bonded and a lower woven textile component the filaments of
which are
composed of flat plastics strips, wherein said woven and non-woven components
are bonded
together, the weave of the flat plastic strips of the lower woven textile
component being
sufficiently tight so as to provide interstices between adjacent woven
filaments to allow water
to pass therethrough but which prevent water vapour from escaping whereby to
resist
evaporative loss from the sub-base.
There is also provided a method of forming a water detention system comprising
the steps of:
laying a sub-base of particulate material of a defined size range over an
impermeable
sub-grade or a preliminarily positioned impermeable membrane; overlaying the
sub-base with
a substantially unidirectionally porous layer able to allow water to
infiltrate from above into
the sub-base but which is such as to resist loss of water from the sub-base by
evaporation.
A further embodiment provides a water detention system comprising a sub-base
of particulate
material in a layer having a substantial number of voids over-lying an at
least substantially
impermeable sub-grade or a preliminarily positioned at least substantially
impermeable
membrane, the sub-base having an overlying substantially unidirectionally
porous layer able
to allow water to infiltrate from above into the sub-base but which is such as
substantially to
resist loss of water from the sub-base by evaporation such that water
collecting on its upper
surface can infiltrate into the sub-base to be retained therein.
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When used as a separating layer over a sub-base of particulate material
defining a plurality of
voids, therefore, the composite membrane allows the infiltration of water
passing through the
permeable layer into the space between the two layers and then travelling
laterally, towards
the edges of the composite membrane, from which the water can escape into the
sub-base.
The form of the composite membrane may vary depending on the particular
exigencies of use.
For example, in some circumstances it may be quite sufficient for the
individual layers simply
to be placed in juxtaposed relation one over the other loosely without a
bonding between the
layers. Because overlying layers will in practice be placed on top of the
membrane, for
example a laying course and a wearing course, there will be no effective
lateral forces
between the layers requiring them to be bonded together. For convenience in
handling of the
membrane, however, they may nevertheless be held together in fixed relation
and in one
embodiment the components of the membrane are held together by adhesive
bonding.
Alternatively, however, the component may be held together by fixing elements
such as, for
example, staples.
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In a preferred embodiment of the invention the spacer means comprise a mesh or
grid, and in particular a plastics mesh has been found to be particularly
appropriate. Of course, since lateral transport of the water between the two
layers
spaced by the mesh is required a mesh structure which formed closed cells
would
be of little value and it is preferred, therefore, that the mesh is formed in
such a
way as to provide communicating or open cell structure when the mesh is placed
between the two layers. This may be achieved, for example, by using a mesh
fondled of overlapping or "woven" filaments.
Another way in which lateral transport of water may be achieved lies in the
use of
a plurality of discrete elements as the spacer means. Such discrete elements
may
be irregularly spaced over the surface of the membrane between the said two
layers
or, in order to minimise on the material used, may be regularly spaced over
this
surface, it being appreciated that regular spacing allows wider separation of
the
spacer elements. Indeed, it will be appreciated that although the spacer
elements
hold the two layers out of contact with one another in the region of the
elements
themselves, it is possible for the two layers to touch between the regions
contacted
by the spacer elements. In this case the two layers may be secured together
between the discrete elements and this, of course, would assist in maintaining
the
discrete elements in determined positions spaced over the area of the
membrane.
Although discrete elements in the form of studs, pebbles, beads or other
granular
material may be used, these could alternatively be elongate, possibly even
spanning the entire width of the membrane, formed as rods, bars or tubes.
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It is also within the ambit of the present invention for the second,
impermeable
layer to be formed with surface formations acting themselves as the spacers.
Thus
local inspissation, corrugation or embossment of the second layer may serve to
5 hold other regions thereof in the required spaced relation with respect
to the
permeable layer.
Permeability of the first layer may be achieved by forming this as a woven or
non-
woven textile material, in which case the fibres or filaments may be heat
bonded to
make a strong resistant material suitable for use as a geotextile.
The present invention also comprehends a water detention system comprising at
least a sub-base of particulate material in a layer having a substantial
number of
voids, and an overlying composite membrane formed by laying down successive
layers in a substantially unbonded juxtaposition, and so positioned that water
collecting on the surface can infiltrate into the sub-base at least from the
edge of
the membrane or through openings formed therein. The intermediate layer in
such
a structure may be made of stones or crushed rock laid to a depth of between a
few
cm to severall tens of cm.
In a structure suitable for water detention the sub-base may overly an
impermeable
or at least substantially impermeable underlying layer, and this layer may be
a
geological formation such as a sub-grade or may be an introduced at least
substantially impermeable, underlying layer in the form of a membrane.
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The underlying layer need not necessarily be planar, and, indeed, there are
circumstances which will be described in more detail below in which irregular
further cavities or sumps, or at least one cavity or sump, may be of
particular
value.
Above the composite membrane of the water detention system there may be a
further particulate layer and this may be a laying course for a wearing layer
which
may comprise a plurality of paving elements and which, in a preferred
embodiment, may be blocks or slabs having means defining openings between
them when laid in juxtaposed relation.
Alternatively, the wearing layer may comprise a substantially continuous layer
of
permeable material such as asphalt, porous concrete or the like.
A water detention system formed in locations other than under urban pavements
may also be formed, and in such a case the particulate material overlying the
composite membrane may itself constitute a wearing layer (for example, gravel
laid to a path or drive, or a larger standing area). It could also be entirely
unrelated
to any traffic or parking system, in which case the further layer may be
overlain by
soil and/or vegetation. This is of particular value where the water detention
system
is provided primarily for collection and storage of water for purposes other
than
simply management of the water run-off. It may be stored, for example, for
further
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use in irrigation, as wash water or even for use in other agricultural
environments,
such as drinking water for animals.
Infiltration of water resulting from precipitation is achieved particularly
effectively "
if the membrane is laid in strips over the said sub-base, and such strips may
be lain
in such a way that adjacent strips are spaced from one another (in which case
water
infiltration is maximised) although adequate water infiltration may equally be
achieved if the strips of the composite membrane are laid abutting one another
or
overlapping one another. The strips may be laid-on a perfectly horizontal
surface
of the underlying sub-base, or this may be shaped, for example domed or
inclined,
to receive the composite membrane.
The present invention also extends to the provision of a pavement structure
having
an underlying water detention system as defined hereinabove and/or using a
composite membrane as defined herein.
Further, the invention may also be considered to lie in a method of folining a
water
detention system comprising the steps of:
laying a sub-base of rigia insoluble hard particulate material of a defined
size range over an at least substantially impermeable sub-grade or a
preliminarily '
positioned at least substantially impermeable membrane;
overlying the sub-base with a substantially unidirectionally porous layer
able to allow water to infiltrate from above into the sub-base, but which is
such as
substantially to resist loss of water from the sub-base by evaporation; and
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overlaying the said substantially unidirectionally porous layer with a
further layer of particulate material.
The method of the invention may further comprise the steps of compacting the
material of the sub-base prior to application of the said substantially
unidirectionally porous layer.
If the said substantially unidirectionally porous layer is a composite
membrane
comprising at least an impermeable layer, a permeable layer and spacer means
holding the said two layers apart over at least a part of their area, as
described
hereinabove, these may be applied one at a time to the sub-base to build up
the said
at least substantially unidirectionally porous layer. Indeed, the spacer means
may
itself comprise a layer of stones or crushed rock.
Alternatively, the substantially unidirectionally porous layer may be a
composite
membrane as herein defined preliminarily formed 'before application to the sub-
base.
The present invention also comprehends a heat exchange structure comprising:
a substantially enclosed volume bounded by a lower water-impermeable
stratum or layer and containing a sub-base of rigid substantially
incompressible
particulate material, overlain by an at least partly permeable membrane which
allows water to enter the said substantially enclosed volume but resists
evaporative
escape therefrom, and
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one or more heat exchange pipes for directing a heat exchange fluid
therethrough and located so as to pass through water trapped in the said
substantially enclosed volume.
The substantially enclosed volume may include a channel through which the or
each heat exchange pipe passes, and such channel may be formed by the
membrane defining a lower boundary of the said enclosed volume. In order to
ensure that thermal contact is made with the water even in the most adverse
circumstances the channel may be formed as a sump in the bottom of the said
enclosed volume and the pipe or pipes pass through this sump.
The rigid substantially incompressible particulate material may be crushed
rock.
Various embodiments of the present invention will now be more particularly
described, by way of example, with reference to the accompanying drawings, in
which:
Figure 1 is an enlarged cross sectional view of a membrane formed as an
embodiment of the present invention;
Figure 2 is an exploded view of a mesh layer forming part of the membrane
of Figure 1;
Figure 3 is a cross sectional view through a water detention system formed
as an embodiment of the present invention and incorporating a membrane of the
general type illustrated in Figure 1;
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Figure 4 is a schematic view of an alternative membrane having tubes,
rods or bars as spacers;
Figure 5 illustrates the use of beads as spacers;
Figure 6 illustrates one laying configuration for the membrane of Figure 1
5 in a water detention system such as that of Figure 3; and
Figure 7 illustrates a further alternative laying configuration;
Figure 8 is an enlarged cross sectional view of a membrane formed as an
embodiment of the present invention;
Figure 9 is a cross sectional view through a water detention system thrilled
10 as an embodiment of the present invention and incorporating a membrane
of the
general type illustrated in Figure 1;
Figure 10 is a cross sectional view of one laying configuration for the
membrane of Figure 1 in a water detention system such as that of Figure 2;
Figure 11 is a plan view of the configuration of Figure 3;
Figure 12 is a plan view of an alternative configuration of Figure 3;
Figure 13 is a plan view of an alternative laying configuration for the
membrane of Figure 1; and
Figure 14 is a cross-sectional view through a heat exchange structure
fowled as an embodiment of the present invention and incorporating a membrane
of the general type illustrated in Figure 1.
Referring first to Figure 1, the membrane generally indicated 10 comprises a
first
layer 11 of non-woven geotextile fabric comprising a plurality of filaments
bonded
together and having the following properties.
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Thermally -bonded non-woven geotextile meeting the following specifications:
Mechanical Properties
Wide Width Strip Tensile EN ISO 10319
Mean peak strength 8.50kN/m
Elongation at peak strength 28%
CBR Puncture Resistance EN ISO 12236
Mean Peak Strength 1575N
Trapezoidal Tear Resistance ASTM D4533
Mean Peak Strength 325N
Hydraulic Properties
Pore Size EN ISO 12956
Mean AOS 090 0.145mm
Water Flow EN ISO 11058
Mean Flow VI15010-3m.s-1(1/m2s) 80
Water Breakthrough BS 6906: Part 3
Mean Head 50rnm
Air Permeability ISO 9237
Mean Flow 2875 1/m2.s
Typical Physical Properties
Mass EN 965 130 g/m2
Roll width 4.5 & 1.5m
Roll length 100m
Colour Green
The composite membrane 10 also includes a flexible second layer 12 of
impermeable plastics material (such as polyethylene or similar) and sandwiched
between the first and second layers 11, 12 is a geogrid or mesh layer (such as
high
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density polyethylene or similar) 13 spacing the two first-mentioned layers
apart
and providing a plurality of drainage passageways for water to travel parallel
to the
plane of the backing layer 12.
Figures 2a and 2b show two alternative forms of the geogrid 13. This layer is
intended to hold the geotextile layer 11 spaced from the impermeable backing
layer 12 and to provide drainage channels or passages for water to travel
parallel to
the plane of the layer 12. For this purpose the grid must provide spaces
between
itself and the layer 12 when placed in contact with it, and in the embodiment
of
Figure 2a this is achieved by forming the grid 13 of a plurality of
"wovenwarp"
filaments 14 interlaced with a plurality of "weft" filaments 15. After
weaving, the
filaments 14, 15 are pressed together and heated to cause bonding in the
overlap
region such as that identified by the arrow 16 so that the geogrid is stable
dimensionally. Passages for water flow are formed by the overlapping filaments
as
identified by the regions 17 identified in Figure 2a.
A similar, but more economical geogrid is illustrated in Figure 2b where the
warp
filaments 14' are first laid in parallel rows and /or overlaid by the "weft"
filaments
15' which are thereafter pressed and heated to bond the grid together at the
intersections 16'. The heating causes partial interpenetration of the material
of the
warp and weft filaments, but as will be appreciated along the length of either
row
of filaments there are wide spaces through which water can travel even when
the
grid is placed in contact with an impermeable surface.
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Figure 3 illustrates in cross section a typical water detention system formed
utilising the membrane illustrated in Figures 1 and 2. The water detention
system
illustrated in Figure 3 underlies a hard paved surface 18 defined by a
plurality of
individual blocks 19 laid closely spaced with no grouting between them so that
channels (not shown) in the sides of the blocks can allow rainwater falling on
the
surface 18 to pass through into an underlying layer 20 formed as a bedding
course
for the blocks 19 and composed of relatively small particulate material such
as
gravel in the range of about 5mm to about 20mm.
Beneath this is a sub-base 21 of crushed rock of angular form and a size range
of
about 163mm to about 10mm between which are a significant number of voids
providing storage space for water infiltrating through the permeable wearing
surface 18. Between the sub-base 21 and the laying course 20 is a composite
membrane layer generally indicated 22. This may have the same structure as
described in relation to Figure 1 and, in this embodiment, the membrane 22 is
laid
in elongate strips 22a, 22b, 22c With spaces 23 between the edges of adjacent
strips. Over the spaces 23 is laid a protective strip 24 of porous geotextile
material, which may be the same material as that which constitutes the layer
11 of
the membrane 10 of Figure 1. A regulating layer 29 of smaller stones may be
laid
between the sub-base 21 and the composite membrane 22.
The edges of the installation are defined by a kerb 25 in suitable haunching
26, and
escape of water is prevented by a strip 27 of impermeable material laid under
the
adjacent strip 22c of composite membrane and extending up the adjacent face of
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the kerb 25 between that and the layer of blocks 19. The edging strip 27 thus
forms a vertical limb 27a and a horizontal limb 27b. An impermeable layer or
membrane 28 defines the lower boundary of the sub-base 21, lying between this
and the sub-grade 29. The membrane 28 likewise extends up the face of the kerb
25 adjacent the limb 27a of the edging strip 27 to define an enclosed space
below
the wearing surface constituted by the blocks 19.
A sump 30 is formed by a channel membrane 36 beneath the sub-base 21 and
extending downwardly into the sub-grade 29. The sump 30 is filled with a
granular material 32 which is smaller in size than the material of the sub-
base 21.
At the bottom of the sump 30 are laid pipes 33 for a heat exchange system. As
described herein the water detention system may be used for multiple purposes
and
not every feature of this embodiment would necessarily be employed in a
practical
installation. Where the water detention system is provided to act as a heat
sink, for
example, it is convenient to maintain a significant body of water within the
region
defined by the sub-base 21 and the sump 30 so that heat yielded from the pipes
30
(through which, in use, a heat exchange liquid or fluid flows from the
appliance or
installation generating or using the heat which is lost to or drawn from the
surrounding water). A further description of such a heat exchange system is to
be
found in British Patent Application No 0418391.9.
Alternative forms of composite membrane are illustrated in Figures 4 and 5, in
which the same reference numerals have been used as those in Figure 1 to
identify
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the same or corresponding component parts. Thus, the upper geotextile layer 11
is
spaced in the embodiment of Figure 4 from the lower impermeable plastics
membrane 12 by a regular array of rods or bars 40 spaced from one another
along
the length of the strip of membrane 12. The bars 40 extend from side to side
of the
membrane and define elongate channels in the composite membrane encouraging
water to flow in one of two opposite directions. The bars 40 may be secured to
the
membrane 12 by adhesive, friction welding or other technique, or, as shown in
Figure 4a, may be bonded in place by forming the membrane 12 around each rod
40 whilst in a mobile state so that, upon curing or hardening, the membrane 12
itself retains the rod 40 in position.
In Figure 5 the geotextile 11 is spaced from the membrane 12 by an irregular
set of
beads 41 spaced over the surface of the membrane 12 and either secured in
place
by adhesive or located by a direct connection of the geotextile 11 to the
membrane
12 by way of fixing elements such as staples 42 over a defined region to
foiin, in
effect, pockets between which the beads 41 are trapped.
Figure 6 shows a laying pattern for the composite membrane in a water
detention
system similar to that illustrated in Figure 3. Again, the same reference
numerals
have been used to identify the same or corresponding components. Here, the
composite membrane 22 is again laid in strips 22a, 22b, 22c, but in this case
they
are laid overlapping one another over a regulating layer 29 and under a
bedding
course 20 overlain by blocks 19 which allow infiltration of water. This laying
configuration still allows water to permeate through the permeable membrane 22
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since water flowing onto, for example, the strip 22a can exit from each of the
two
opposite edges 22a' and 22a", and in this latter case the water flows onto the
adjacent layer 22b from which it can escape through the edge 22b'. Water
collecting in the sub-base layer 21, however, has an effectively- continuous
impermeable membrane above it, and evaporation of the water contained in the
sub-base 21 even when high temperatures exist above the wearing layer 18 is
strongly resisted.
Figure 7 illustrates another alternative laying configuration in which,
however, the
regulating layer 29 is formed into a cambered or domed configuration matching
the
dimensions of the strips 22a, 22b, 22c so that the infiltration of water
through the
membrane 22 into the sub-base 21 is encouraged by gravity. This laying
configuration has the disadvantage, however, that the cambered regulating
layer 29
must be formed with a shape which is reasonably accurate so as to receive the
individual strips 22 of the composite membrane.
Turning now to Figure 8, there is shown an assembled structure forming a
composite membrane, generally indicated 10 for use in a water detention system
of
the type described above. The membrane comprises a first layer 11 of non-woven
geotextile fabric composed of a plurality of filaments bounded together to
form a
porous web having properties as set out in relation to the web described with
reference to Figure 1.
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The composite membrane 10 also includes a flexible second layer 12 of
impermeable plastics material (such as polyethylene or similar), and
sandwiched
between the first and second layers 11, 12 is a layer 13a of crushed rock or
stone
spacing the two first-mentioned layers apart and providing a plurality of
drainage
passageways for water to travel parallel to the plane of the backing layer 12.
This
layer of stone may have a thickness of about 75mm and have been graded to
include particles predominantly of a size 20mm to 5mm.
The composite membrane 10 may act as an evaporation control membrane as will
be explained in more detail herein.
Figure 9 illustrates in cross section a typical water detention system foinied
utilising the membrane illustrated in Figure 8. The water detention system
underlies a hard paved surface 18 defined by a plurality of individual blocks
19
laid closely spaced with no grouting between them so that channels (not shown)
in
the sides of the blocks can allow rainwater falling on the surface 18 to pass
through
into an underlying layer 20 foinied as a bedding course for the blocks 19 and
composed of relatively small size particulate material such as gravel in the
range of
about 5mm to about 20mm, more particularly 6mm.
Beneath this is a sub-base 21 of crushed rock or stone of angular form and
graded
to have a size range of about 63mm to about 10mm between which are a
significant number of voids providing storage space for water infiltrating
through
the permeable wearing surface 18. Between the sub-base 21 and the laying
course
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20 is a composite membrane layer generally indicated 22. This may have the
same
structure as described in relation to Figure 8.
In this embodiment, between the sub-base layer 21 and the underside of the
composite membrane 22, a thin blinding layer of regulating stone 29 is
provided
having a size range of about 20mm to about 5mm and having a thickness of about
50mm. This layer 29 helps to protect the second layer 12 of the composite
membrane 22 from puncture by the larger and more angular rocks and stones of
the
sub-base layer 21.
Further, the embodiment of Figure 9 has a stabilisation layer 50 shown. This
may
be a geotextile or a geo-grid such as manufactured by Tensar TM. The purpose
of
this layer is to help stabilise the sub-base 21 and prevent it from being
reduced in
thickness, which in turn would reduce the volume of water which could be
stored
within it, due to traffic or natural weathering.
At the base of the structure of Figure 9 a substantially impenneable layer 28
is
shown. This layer 28 may be a man-made impermeable layer such as sheets of
substantially continuous plastics, a naturally occurring sub-grade such as a
competent rock formation, or an imported naturally occurring material such as
clay. This element 28 is not a pre-requisite but does enhance water retention.
Figure 10 illustrates how the second layer 12 of the composite membrane 22 may
be formed of overlapping separate sheets 12a. The sheets are overlapped along
an
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edge 12b and tapes 12c are adhered to the two adjacent sheets 12a at the
overlap
12b to produce a larger continuous sheet. Holes 12d may then be punched
through
the sheets 12a in either a regular pattern as shown in Figure 4 or an
irregular
pattern (not shown).
Figure 11 shows this regular pattern in plan view together with the taped
section
12c and the overlap 12b.
Figure 12 shows alternative openings within the second layer 12. Rather than
holes
12d slices, slashes or cuts 12e are made within the second layer 12.
Figure 13 illustrates another alternative to the holes 12d of Figures 3 and 4.
In this
embodiment, the second layer 12 is made up of adjacent sheets 12a which are
spaced apart with a gap 12f left therebetween. These gaps 12f act as the
openings
to allow water to flow through into the sub-base but to minimise evaporation
from
the sub-base by minimising the area of sub-base which is not covered by an
impermeable layer.
In Figure 14 the water detention system of Figure 9 is adapted to become a
heat
exchange structure. This is achieved by having a sump 30 formed within the
base
of the system. The sump is lined with an impermeable layer 36 which could be
an
extension of the membrane 28. At the bottom of the sump 30 are laid pipes 33
for
a heat exchange system. Within the sump 30 a granular material 32 is placed
CA 02597382 2007-08-09
WO 2006/085095
PCT/GB2006/000474
which is smaller in size than the material of the sub-base 21 to protect the
pipes
from damage due to sharp edges and corners.
The impermeable layer 28 is also shown to continue up one side of the sub-base
5 21, composite membrane 22, bedding layer 20 and pavement 18. If
necessary this
layer can be continued around all sides of the structure so as to make it
waterproof
and to retain as much water within it as possible. Water could then be
regulated to
flow out of the structure by means of a valve (not shown) placed through the
impermeable layer 28 at a selected point.
As described herein the water detention system may be used for multiple
purposes
and not every feature of this embodiment would necessarily be employed in a
practical installation. Where the water detention system is provided to act as
a heat
sink, for example, it is convenient to maintain a significant body of water
within
the region defined by.the sub-base 21 and the sump 30 so that heat yielded
from
the pipes 30 (through which, in use, a heat exchange liquid or fluid flows
from the
appliance, or installation generating or using the heat) is lost to the
surrounding
water. A further description of such a heat exchange system is to be found in
British Patent Application No 0418391.9.
