Note: Descriptions are shown in the official language in which they were submitted.
.. . - 21$547b
Drainacte Unit
This invention relates to a drainage unit suitable for
use in an elevated structure such as a bridge or a
multi-storey car park. Figure 1 shows a typical drainage
unit 1. This is designed to be placed at the side of a
road on a bridge so that the road s-u~faGe at the edge of
the road is level with the bottom edge of the holes 2_
The camber of the road causes water to run off the road
surface and pass into the drainage unit through the hulas
2_ The hole 3 in the end wall allows water to pass into
an adjacent unit. Onits are placed next to one another to
produce a drain running the length of the bridge.
Figure 2 shows a cross-section through a typical bridge.
A concrete deck 4 is covered with a waterproof membrane 5
and a Layer of red sand asphalt 6 to protect the
waterproof membrane. The road is surfaced With an asphalt
base course 7A and an asphalt wearing course 7B. The
asphalt layers will not lee watertight, and some grater
dill permeate through them. The red sand asphalt layer is
less permeable to water than the other asphalt layers,
and water will accumulate in the asphalt layers 7A, 7B.
This water will hereinafter be referred to as "subsurface
Water" .
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If subsurface water continues to accumulate the asphalt
layers will eventually become saturated; water Will then
appear on the road surface, caus~.ng a driving hazard. Tn
winter, repeated freeziag and thawing of the subsurface
water will damage the road. Furthermore, when a vehicle
passes along the road the weight of the wheel will cause a
pumping action" on the subsurface water in the road
construction. A "bow wave" 8 is pushed through the
asphalt layers 7A, 7H to~rards the side of the. road. The
water cannot enter the drainage unit 1, and it is
defleetAd upwards by the drainage unit, as indicated by
the arrows. This causes rapid deterioration of the road
surface, as the water will tend to carry the binding
particles contained in the asphalt upwards out of the
asphalt layers and deposit them as silt 9 on the road
surface. Such deposits of silt form another driving hazard.
Tt is possible to make some allowance for the relief of
subsurface water by leaving small gaps beneath and/or
between adjacent edge kerbs or drainage units to provide a
drainage path. Although these gaps ini..tially provide a
drainage path they quickl y silt up and block the passage
of water.
Figure 3 shows a drainage unit 1' in which some holes 2'
have a V-shaped lower edge. The unit is positioned so that
the V-shaped portion of the holes are below the road
surface, so subsurface water within the asphalt
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layers can pass through the hole$ into the drainage
unit.
This drainage unit is not satisfactory. If the V-shape
part of the holes is shallow it will not co7.lect all the
subsurface watax from the asphalt layers. If the
V-shaped part extends to the bottom of the drainage
unit, however, it ~ri.ll then be possible far water to
drain off the road surface, enter the drainage unit
through the top part of the holes aad pass back into the
road through the lower part of the hulas.
GB-A-2 257 734 discloses a subsurface bridge drain unit
which has a perforated collection chamber. This is
buried is the load, so that the perforations in the
collection chamber aze in the lower part of the asphalt
base course 7A. The collection chamber has an outlet
which passes through, the bridge deck. Subsurface water
enters the collection chamber and is drained away
through the outlet.
This drainage unit Will not drain surface water
effectively, so it is therefore necessary to provide
conventional drains as well as the subsurface drainage
unit. Furthermore, each subsurface drainage unit
requires a hole through the bridge deck which will
weaken the bridge.
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A first aspect of the invention provides a roadway
comprising a substantially waterproof base, an asphalt
base course and an asphalt weariag course, the asphalt
courses being pervious to water, and a drainage unit at
a side edge of the asphalt courses, the drainage unit
having a side wall facing the asphalt courses and
extending above the upper surface of the weaxing course,
first drainage apertures beiag provided in the side wall
above the asphalt wearing course to receive surface
water for passage into the drainage unit, and second
drainage apertures being provided adjacent the asphalt
base course for passage of sub-surface water into the
drainage unit.
A second aspect of the present invention provides a
dzainage unit comprising at least one aperture for
receiving surface water and at least one aperture for
receiving subsurface water; wherein the aperture(a) for
receiving surface v~ater is/are not in direct fluid
communication With the apertures) for receiving
subsurface water.
This drainage unit is able to collect both surface water
and subsurface Water from a road. The surface water will
pass through the upper apertu~ce(s) into the drainage
unit, and will be drained away. It will not pass back.
into the road construction layers. The subsurface water
will pass through the lower aperture(s), and will be
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drained away.
In a preferred embodiment the two channels are defined
within the drainage unit, one channel being in flui8
communication with the aperturs(s) for receiving surface
water and the other channel beiag in fluid communication
with the apertures) for receiving subsurface water, the
two channels not being in direct fluid communication
with one another.
Since the channel for surface water and the channel for
sub-surface grater do not communicate with one another,
' surface water cannot pass into the road construction.
Preferred embodiments of the present invention will now
be described by way of example with reference to the
accompanying Figures in which:
Figure 1 is a perspective die~ct of a known draiaage unit;
F~.gure 2 shows a cross-section of a road;
Figure 3 is a perspective view of another known drainage
uni t;
Figure 4 is a schematic view of a drainage unit
according to one embodiment of the present invention;
Fi gore 5 ( a ) s hovers cotaponents of another draf page unit of
the present invention;
Figure 5(b) shows the drainage unit of Figure 5(a) in
its assembled state;
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Figure 5(c) shown components of another drainags unit of
the present invention;
Figure 6 shows a further embodinsent of the present
i nventi on;
Figure 7 is a cross-section of a further embodiment of
the present invention;
Figure 8 is a cross-section of a further embodiment of
the present invention;
Figure 9 is a perspective view of a further embodiment
of the present invention; and
Figure 10 is a cross-section of the unit of Figure 9
when installed in a road.
Figure 4 shows a drainage unit 10. The unit is provided
with a wall 13 which defines a closed channel 14.
Subsurface water passes from the road through the lower
apertures 15 into the channel 14, as a result either of
natural drainage or of a "bow wave" caused by a vehicle.
Surface water passes through upper apertures 16 into the
interior 17 of the drainage unit. This drainage unit is
able to drain both surface and subsurface water from the
road. The surface water cannot entex the channel 19 and
so is unable to pass back into the ro8d construction
1 ayers .
For ease of construction, the unit is formed of a base
11 and a cover 12. Figure 5a shows an alternative
embodiment of the invention, and shows the base 11'
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separated from the cower 12'. Ths cover is provided with
prongs 22; when the cover is placed on the base an upper
aperture is defined by a pair of adjacent prongs, as
shown in Figure Sb. Figurs 5(c~ shows an alternative
design for the cover 11' and base 12'.
The cover 12, 12' and the base 11, 11' can be made of
any suitable u~aterial. In one embpdl~nent the base is
manufactured in ductile iron, ~ohich is chosen for its
good finish and strength. The cover is made from a
composite material, and this allows the cover to be
produced in any desired colour. The cover is secured to
the base by any suitable means.
Figure 6 shows an alternative base unit 11". The channel
14 is provided with a hatch 18 which can be removed to
provide access to the channel. This allows the channel
to be inspected or cleaned. 2'he cover can also be
provided with a removable hatch (not shown), to avoid
the need to remove the whole cover to provide access to
the base. In use, it would be advisable if inspection
hatches were provided e~rery 20m or so.
The drainage unit is installed oa a bedding layer of
mortar 19 which has a thickness of, for example, 5mm.
The end face of the unit is coated with a sealant, and
the unit is pushed firmly against the previous unit to
make a watertight seal between the two units.
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The base is provided with projections 20 at one end, and the other
end is provided with complementary recesses. These projections and
recesses provide interlocking between two adjacent units, which
lessens the chance of a unit being displaced if it is struck by a
vehicle.
Figure 7 shows a cross-section of an alternative embodiment of the
present invention. The channel 14 is not closed, but is defined by
a wall 27 and a ledge 21. The ledge 21 extends beyond the channel,
so surface water entering the unit is directed into the interior of
the unit and can not enter the channel (unless the depth of water
in the interior exceeds the height of the wall 27. The ledge 21 is
shown as being part of the base unit in Figure 7, but it could be
part of the cover.
Another embodiment is illustrated in Figure 8. The wall l3'
defining the channel for subsurface water is horizontal, so that
the channel for subsurface water is below the channel for surface
water. This embodiment could also be realised by constructing a
drainage channel for subsurface water and placing conventional
drainage units (as shown in Figure 1, for example) over the channel
for subsurface water to form the drainage channel for surface
water.
It is not necessary for every drainage unit to have
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apertures for receiving both surface and subsurface
water. For example, it would be possible to manufacture
two different drai nags units, one havi.ag only apertures
for receiving surface water and the other having only
apertures for receiving subsurface water_ The drain
would be formed from a combination of both units - for
example, with the two units alternating with one another.
A further embodiment of the present invention is
illustrated in Figure 9. This unit again has a channel
14, and has lower apertures 15 through which surface
water can enter the chancel. The unit is also provided
with upper apertures 16 for receiving surface water.
The drainage unit of Figure 9 is intended for use on
roads for which porous asphalt is specified as the
wearing surface ?B. Porous asphalt is used to reduce
surface water spray, by allowing water to percolate into
the top SOmm of the road construction. Conventional
drainage units as in Figure 1 cannot drain this water
from the top SOmm of the road construction.
The drainage unit shown in Figure 9 is provided with
interesediate apertures 23, provided at a height that ie
intermediate between the lower and upper apertures.
When the drainage unit is installed, the intermediate
apertures will be at the same level as the wearing
surface 7B of the road construction. Water that has
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pexcolatad iato a porous asphalt wearing surface will
drain away through the intermediate apertures into the
drainage unit.
As with the othex drainage units of this invention the
unit has a base ila and a cover 12a. The base cad cover
caa be made of any suitable material - for example, the
base unit could be wads of cast iron or ductile iron,
aad the cover can be made fro~a a composite material. The
intermediate apertures 23 connect With the main interior
drainage channel 17. The apertures 23 are made as large
as possible commensurate with retaining the structural
integrity of the drainage unit 11a, in particular its
resistance to impact by vehicles. The front edges 25 of
the central bars 24 ate pointed cad the side walls 26 of
the apertures chamfred to reduce resistance to the flow
of water.
