Note: Descriptions are shown in the official language in which they were submitted.
CA 02326272 2000-11-17
SUB-BASE DRAINAGE DEVICE
Technical Field
The invention pertains to water drainage systems and, more
particularly, to materials for filling water drainage beds having high
water-carrying capacity.
Back round
In the construction of water drainage beds, for example
around building foundations, under playing fields, for roof gardens,
etc., it is common to form the bed by placing gravel or crushed rock in
an excavated trench or by spreading it on the area to be drained, placing
a sheet of water-permeable geotextile over the gravel and covering the
sheet with soil. The geotextile keeps the fine soil particles from filling
the spaces between the gravel pieces and the spaces provide a volume
into which water drains and a channel through which water can flow
away from the area to be drained, for example to a drainage pipe or
field.
There are several disadvantages to these conventional
drainage beds. Although the spaces between the gravel (or crushed
rock) pieces provide a volume into which water can flow, the pieces
themselves occupy the great majority of the total volume in a conven-
tional drainage bed and, being solid, do not provide a volume for the
receipt of water. Also, gravel is a very heavy material and, for applica-
tions such as roof gardens, requires correspondingly strong structural
support in order to hold a drainage bed containing it. Further, the
porous geotextile sheet that is required to prevent fine soil particles
from settling into and filling the spaces between the gravel pieces can
become clogged with the particles, severely reducing the permeability of
the sheet and therefore the effectiveness of the drainage bed.
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Summary of Invention
It is an object of the invention to provide a drainage fill
material that permits water to flow into and through it, while being
strong enough to support the soil or other material placed over it.
It is a further object of the invention to provide a light-
weight drainage fill material that is accordingly inexpensive to transport
and that is useful in applications, such as roof gardens, where light-
weight material is desired.
It is a further object of the invention to provide a drainage
fill material that does not require the use of a geotextile sheet over it to
keep out fine soil particles.
It is a further object of the invention to provide a drainage
bed, and a method of constructing a drainage bed, using drainage fill
material according to the invention.
According to one aspect of the invention, there is provided
a water drainage element comprising a hollow shell with a plurality of
holes in it permitting water to flow into and out of the shell. The shell
may be substantially spherical and made of molded plastic or metal.
The holes in each shell may be a mixture of sizes, some relatively
smaller and some relatively larger.
According to a further aspect of the invention there is
provided a sub-base water drainage bed comprising a space, such as an
excavated trench, having a mass of water drainage elements as afore-
said.
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These and other objects and features of the invention will
be apparent from the following description of the preferred embodi-
ments, considered along with the accompanying drawings.
Brief Description of Drawing
Figure 1 is a perspective view of a first preferred embodi-
ment of a water drainage element according to the invention.
Figure 2 is a cross-sectional view on the line II - II of
Figure l;
Figure 3 is a perspective view, partly cutaway, of a second
preferred embodiment of a water drainage element according to the
invention;
Figure 4 is an end elevational view of a drainage bed with
the water drainage elements of Figure 1; and
Figure 5 is a perspective view of a portion of a drainage
bed.
Description
Referring to Figures 1 and 2, in a first preferred embodi-
ment of the invention a drainage element 10 comprises a hollow shell 12
having a plurality of holes 14 therein. Shell 12 is preferably made of
plastic, such as recycled polyethylene or polypropylene, and can be
formed by conventional molding processes. It is preferably about 8 mm
to 12 mm in outer diameter.
There is a plurality of round holes 14 which permit the
drainage of water into and through the elements 10. The holes 14 are
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preferably about 1 to 2 mm in diameter and are spaced generally evenly
about the shell 12 to facilitate such drainage. There are preferably at
least four holes 14 and, more preferably, many more holes, for example
to 15 holes, in order to facilitate the flow of water with minimal
5 obstruction. In this specification, a "plurality of holes" 14 means four
or more holes.
Holes 14 are preferably a variety of sizes in each drainage
element 10, some relatively larger and some relatively smaller. For
10 example, half of the holes may be 1 mm and half may be 2 mm in
diameter, arranged in a mixed or random array about the surface of the
shell, as shown in Figure 1. It has been found that fine soil particles are
less likely to lodge in the interior of elements 10 when the holes 14 are
of different sizes, an effect which, it is believed, is due to the more
turbulent flow and the differences in flow rate through relatively larger
and smaller holes.
Drainage element 10 is randomly oriented when placed in a
drainage bed, as described below, so holes 14 are evenly spaced about
the surface of the shell 12 so as to facilitate water flow through the
holes however the element is oriented.
Shell 12 is constructed to be strong enough to resist crush-
ing when placed in a sub base drainage bed and covered with soil or
other material and subject to the weight of such material and anything
else that may ordinarily exert pressure on a drainage bed.
Figures 4 and 5 show the use of drainage elements in a
drainage bed. A "drainage bed" in the specification includes channels,
building foundation and roof garden drainage structures and drainage
bed of any size, including a drainage bed under an entire field, such as a
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playing field. Drainage bed 30 is normally formed by excavating a
space 32 in ground 36. Space 32 may be a trench, channel, foundation
drainage area, etc. of any type for a given application. Space 32 may
cover the entire, or substantially the entire, surface of a field such as a
sports field or golf green. For some applications, of course, excavation
of a bed is not required as, for example, in a roof garden, where the
drainage bed is made by filling a constructed space with drainage
elements 10 and laying topsoil, etc. over it to form a garden.
A mass of drainage elements 10, comprising a large num-
ber of such elements, is dumped into space 32 to form a volume suffi-
cient for a particular application. The elements 10 may be uniform in
size or a mixture of different sizes. Once in place, they are covered
with a particulate covering material 34, which is typically soil but which
may be crushed rock or other material as may be desired for a particu-
lar application. In a preferred embodiment, covering material 34 is
topsoil, or includes topsoil in its upper portion, for planting with grass
for other ground cover.
When soil 34 is put on top of the drainage elements 10 in
space 32, some fine soil particles 38 fall into the interstices between
elements 10. Likewise, over time, by the effects of gravity and water
movement, further soil particles 38 settle in the interstices. Some soil
particles will enter holes 14 in the drainage elements 10. It has been
found that this does not significantly affect the effectiveness of the
drainage system according to the invention. As shown in Figure 5,
when water flows through drainage bed 30 in the direction indicated by
arrow A, it flows in and out of holes 14. Small dirt particles that fit
through holes 14 are accordingly washed through the drainage bed and
do not cause significant blockage.
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It will be apparent that the mass of drainage elements 10,
by virtue of the volume of the elements and the relatively free flow of
water through them, can hold and accommodate the flow of a larger
amount of water for a given volume of elements 10 than would an
equivalent volume of gravel or crushed rock, which permits water to
flow in the interstices between the gravel or rock pieces but not through
the pieces themselves.
The water drainage elements of the invention can also be
mixed with gravel or crushed rock to form a fill material for use in
water drainage beds. This could be done, for example, if gravel or
crushed rock is less expensive than the water drainage elements in a
particular local, in order to produce a less expensive fill material.
Various proportions of the two components could be used, such as
50/50 water drainage elements and gravel (or crushed rock), by volume.
The water drainage elements of the invention can also be
mixed with pieces of polystyrene or similar plastic foam material for use
in the drainage beds. The function of the foam pieces is to cushion and
protect the water drainage elements from damage when they are being
dumped into a drainage bed and covered with soil, etc. For example,
foam pieces roughly comparable in size to the water drainage elements
can be mixed with them in a proportion of less than 30 % foam pieces
by volume in a mixture of foam pieces and water drainage elements and
more preferably about 10 - 20% foam pieces by volume.
A second embodiment of the invention is illustrated in
Figure 3. Here, the drainage element 20 comprises a hollow shell 22
formed of wires 24, arrayed in a generally interwoven configuration
with spaces 26 between adjacent wires. Wires 24 are made of
corrosion-resistant metal. Spaces 26 correspond functionally to holes
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14 in drainage element 10 of Figure 1, permitting water to flow in and
out of the drainage element, as in the embodiment of Figure 1. The
shell 22 may be formed by a single wire or a plurality of wires. Drain-
age element 20 is used in a drainage bed in the same manner as dis-
cussed above for drainage element 10. Drainage element 20 may
include an inner frame to strengthen and support the shell, if desired.
It has been found that the drainage elements of the inven-
tion have utility in an application unrelated to water drainage.
The drainage elements can be used in place of gravel or
crushed rock around heating pipes placed in the floors of buildings.
Gravel or crushed rock are conventionally used in such applications
because quicker transfer of heat from the pipes (typically hot water or
steam pipes) to the flooring (typically wood strips), and longer
maintenance of heat in the floor, are achieved than where the pipes are
in an empty air space under the flooring. The same benefits are
achieved by the use of the water drainage elements of the present
invention in place of gravel or crushed rock. In such an application, of
course, water does not flow through or around the elements. The space
around the pipes is filled with elements 10, 20, 30 and heat from the
pipes is transmitted to the floor, through and around the elements. The
substantial weight of gravel or crushed rock in the floor is accordingly
avoided by this use of the present invention.
While the preferred embodiments of the invention have
been described herein, it will be apparent to persons skilled in the art
that various changes and modifications may be made that are within the
scope of the invention. For example, the drainage element is preferably
spherical, to provide optimum structural strength to resist crushing and
to provide ample interstitial spaces between adjacent elements, but the
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drainage elements may be other shapes if desired. The elements may
also be larger or smaller than the preferred sizes described herein. In a
drainage bed, space 32 is normally excavated but it may be simply the
space on top of existing ground, the mass of drainage elements being
placed on the ground and then covered with soil or other particulate
covering material. The drainage elements do not need to be covered
with a porous geotextile sheet as in most prior art drainage systems, but
such sheet may be placed over the mass of drainage elements if desired.
These and other variations will occur to persons skilled in the art and
are mentioned merely by way of example, the invention being limited
only by the scope of the following claims.
