GB2257734A

GB2257734A - Subsurface bridge drain unit and method of installation

Info

Publication number: GB2257734A
Application number: GB9114679A
Authority: GB
Inventors: Kenneth Roy Harland; Keith Saunders; Raymond Gaskell; Roger William Smith
Original assignee: SIR OWEN WILLIAMS AND PARTNERS
Current assignee: SIR OWEN WILLIAMS AND PARTNERS
Priority date: 1991-07-08
Filing date: 1991-07-08
Publication date: 1993-01-20
Anticipated expiration: 2011-07-08
Also published as: GB9114679D0; GB2257734B

Abstract

A subsurface bridge drain unit comprises a collection chamber (28) with apertures (30) in at least its upper region, an outlet portion for drainage of water from the collection chamber and support means so that the unit is located with the upper region of the collection chamber above a protection layer (16) extending over a bridge deck into a water permeable layer for reception of subsurface water. The outlet portion extends into a bore through the bridge deck. Such a unit allows for better drainage of water which otherwise accumulates in the matrix of the hot mould asphalt of the base and wearing courses of the bridge deck, particularly in the region of bridge deck expansion joints. <IMAGE>

Description

SUBSURFACE BRIDGE DRAIN UNIT AND METHOD OF INSTALLATION DESCRIPTION The present invention relates to a subsurface bridge drain unit and to a method of installing the same within a bridge super-structure, and in particular, but not exclusively, to a bridge drain unit for a bridge structure employing spray-applied waterproofing membranes and impermeable bridge deck expansion joints.

Bridge super-structures generally comprise a reinforced concrete deck, waterproofing membrane having a bituminous protection layer, commonly formed of red sand asphalt, a base course, and/or a wearing course laid in turn thereon.

The wearing course provides the actual road surface and, along with the base course, comprises a region through which surface water can permeate. Any such water is retained in the base and wearing courses since the bituminous protection layer is generally less permeable and, in any case, is separated from the bridge deck by means of a waterproofing membrane. Thus, the negligible amount of water that passes through the bituminous protection layer is prevented from penetrating the waterproofing membrane and the remaining bridge structure.

The water accumulation in the matrix of the hot rolled asphalt of the base and/or wearing courses creates problems in that, as the water continues to accumulate, it eventually rises to the level of the upper surface of the wearing course and, at the lower part of an inclined bridge section appears as surface water. Such surface water particularly appears in the region of the bridge deck expansion joints.

The presence of such surface water is particularly disadvantageous as it creates an unsightly, stained appearance on the road surface and creates hazardous driving conditions, particularly when the temperature drops below freezing. Also, it can lead to a premature failure of the surface adjacent the bridge deck expansion joint due to the pumping action created in the base course and/or wearing course as traffic passes over the saturated material layers and so increases the pressure of the water therein. These problems are particularly exaggerated in bridge superstructures which comprise a spray-applied liquid waterproofing membrane and impermeable bridge deck expansion joints.

Previous attempts to alleviate the above problems have included incorporating drainage pipes within the expansion joint structure. Because of the location of these pipes within the expansion joint structure, these pipes have to be of a disadvantageously small size dictated by the dimensions of the joint. As such, the pipes cannot cope with the volume of water involved. The pipes also become rapidly blocked due to the formation of calcareous deposits and the deposition of silt.

Ventilation/drainage units are known which allow for both vapour and moisture collection at the interface of the waterproofing membrane and the concrete deck surface.

Attempts have been made to use such units solely for drainage purposes, but such use is of limited benefit since they are not designed to fulfil that function. Further, the units are not designed for use with spray-applied waterproofing membranes, the water collection apertures/slots are too small, the general shape of the unit is inappropriate for drainage purposes and the limited dimensions of the unit promote rapid blockage by the bituminous protection layer. Only a negligible amount of water in the base and/or wearing courses reaches the ventilation unit since the bituminous protection layer, below which the unit is located, is relatively impermeable.

Thus, it has become necessary to remove the bituminous protection layer from around the units, immediately after laying, and to replace this layer with a suitably permeable material so as to allow for the passage of water from the base and wearing courses to the drainage unit. This extra step is a time consuming and inefficient attempt to employ the currently available ventilation unit as a drainage unit.

The present invention therefore seeks to overcome problems currently experienced in providing subsurface drainage in bridge structures.

The invention accordingly provides a subsurface bridge drain unit comprising a collection chamber which is apertured in at least its upper region, an outlet portion for drainage of water from the collection chamber, and support means for locating the unit with the upper region of the chamber above a protection layer extending over a bridge deck into a water-permeable layer for reception of subsurface water collected above the protection layer and with the outlet portion extending into a bore through the bridge deck.

Preferably, the support means comprises an external flange or step or other laterally extending portion of the drain unit so that a stable location can be provided by seating the unit on the bridge deck. In particular, the water drainage portion may comprise a funnel member wherein the wider upper portion of which forms said step portion of the unit. As such, the water collection portion may comprise a cylindrical chamber closed at one end by a flat or domed portion and arranged to engage with the inner surface of the upper portion of the funnel member.

In any case, the water collecting portion may comprise a cylindrical member, closed at one end, and having a plurality of apertures provided in the upper regions of the side walls thereof.

Alternatively, the apertures may extend for the whole height of the side walls of the water collecting portion.

The side walls of the water collecting portion may be formed from laterally extending finger portions of an appropriately shaped blank, which portions are bent to extend in a vertical plane so as to form side wall portions separated by vertically extending apertures. In particular, the remote ends of the finger portions may be secured to a support ring or appropriately shaped member.

The uppermost surface of the water collecting portion, or indeed that portion itself, may comprise a hemispherical or domed chamber so as to improve the mechanical strength of the unit.

One particularly advantageous feature of the present invention is that the unit is supported on, or in the bore extending through, the bridge deck. As such the unit can be easily installed in the bridge structure. Also, the drainage unit can be formed of two or less members so as to further enhance the advantages relating to the simple structure and ease of installation of the invention.

The water drainage portion may also be arranged to engage a drainage pipe which extends through the bore in the bridge deck. The lower end of the drainage pipe is then connected to an appropriate drainage system.

According to another aspect of the present invention, there is provided a method of installing a subsurface bridge drainage unit, as described above, in a bridge structure comprising a bridge deck, a protection layer, and/or base and wearing courses, the method comprising the steps of forming a bore- through the bridge deck, locating the water drainage portion of the unit in the bore, disposing the waterproofing layer on the upper surface of the bridge deck, disposing a blanking plug on the water drainage portion so as to cover said portion, overlaying the waterproofing layer with a protection layer, for example red sand asphalt, replacing the blanking plug with a water collecting portion of the unit and laying the base course and wearing course over the protection layer so that the water collection portion can collect water from the base course.

The dimensions of the blanking plug are preferably chosen so that the plug extends at least up to the level of the protection layer and the apertures of the water collecting portion are located so that an opening is provided between the internal region of the chamber and the bridge deck disposed above the protection layer.

Preferably, the water drainage portion is separated from the bridge deck surface by means of an epoxy or acrylic mortar bedding layer.

Preferably, the water drainage portion comprises a funnel member whose upper, and laterally enlarged, portion is arranged to receive the water collecting portion thereon.

Also, the mouth of the bore may be suitably stepped so as to receive the upper portion of the funnel member therein.

The waterproofing layer may be laid in any known manner but the method of the present invention is particularly advantageous when the waterproofing layer is formed from a spray-applied waterproofing membrane.

The invention is described further hereinafter, by way of example only, with reference to the accompanying drawings, in which: Fig. 1 is a sectional view of a subsurface drainage unit embodying the present invention and located within a deck; Fig. 2 is an exploded perspective view of the water collecting portion of the unit of Fig. 1; Fig. 3 is an exploded perspective view of the water drainage portion of the unit of Fig. 1; Fig. 4 is a perspective view of an alternative water collecting portion; and Figs. 5A-5G illustrate the various steps in installing the drainage unit of the present invention.

Fig. 1 shows a section through part of a bridge surface structure 10 which comprises a bridge deck 12, formed of reinforced concrete, a spray-applied waterproofing member 14, a red sand asphalt protection layer 16 and a permeable surface layer formed of a base course 18A and/or wearing course 18B.

The bridge deck 12 has a stepped bore 20, 26 formed therein upon the step of which a water drainage portion 24 of a drainage unit according to the present invention is seated by way of an epoxy mortar bedding layer 22. The water draining portion 24 is formed of a funnel member, as shown in Fig. 3, which forms a close seated fit in the stepped bore 20, 26.

The spray-applied waterproofing membrane 14 extends over the top edge of the water drainage portion 24. During formation, any of the spray-applied material that becomes coated on the upward facing portion of the water drainage section 24 can be removed by a knife or other similar implement. A water collecting portion comprising a cylindrical chamber 28 is seated on the upwardly facing surface of the water drainage portion 24 such that apertures 30, provided in the upper side wall surface thereof, open to the surface structure at a location above the protection layer 16.

The lower region of the water drainage portion 24 comprises a downwardly depending open ended cylinder 24A which extends into the bore 26 extending through the bridge deck 12. A drainage pipe 32 engages the open cylinder 24A and extends through and beyond the bore 26. The drainage pipe 32 can then be connected to a drainage conduit system as required.

As atmospheric precipitation, for example rain water, falls upon the road surface A it passes into the relatively permeable wearing course and base course but is prevented from continuing its downward passage by a protection layer 16 which is relatively impermeable. Accordingly, the lower portion of the base course becomes saturated and this water flows laterally through the apertures 30 and into the accumulated water receiving portion 28 of the drainage unit.

This water then passes down through the water drainage portion 24 and out by way of the open cylinder 24A and drainage pipe 32. Any water that passes between the external side surface of the chamber 28 and to the protection layer 16 is prevented from entering the bridge deck layer 12 due to the spray-applied waterproofing membrane which extends down the inner side wall surfaces of the upper portion of the water drainage section 24. Any such water then passes under the base of the side wall of the chamber 28 and into the open cylinder 24A and drainage pipe 32.

Fig. 2 is an exploded perspective view of the water collecting portion 28 of the drainage unit and, as can be seen, it comprises an upper surface disc 28b having a downwardly depending cylindrical skirt 28A with apertures 30 formed in the upper region thereof.

Fig. 3 shows a similar view of the water drainage portion of the unit of the present invention, which comprises a funnel member formed from an upper cylindrical portion 24C extending from an annular base portion 24B the inner aperture of which has a cylindrical skirt 24A depending downwardly therefrom.

Fig. 4 shows an alternative embodiment of the water collecting portion, or chamber of the present invention.

This embodiment is formed from a material blank, the peripheral regions of which are stamped so as to form laterally extending finger portions 128B which are bent downwardly so as to form side wall portions extending between an upper surface 128A and a base ring 128C. As such, longitudinal apertures are formed between the side wall surfaces 128B which provide for a similar drainage function as the apertures 30 of the chamber 28 of Figs. 1 and 2.

Turning now to Fig. 5, there is illustrated an installation sequence for the drainage unit of the present invention.

This assumes that the invention is to be incorporated into an existing bridge structure but the unit can very easily be used in new bridge construction.

In Fig. 5A the bridge structure is prepared by removing all the surface layers so as to expose the bridge deck 12.

The recess 20 is then cored in the bridge deck 12 as illustrated in Fig. 5B and a drainage bore 26 is cored in the central region of the recess 20 so as to form a stepped bore as in Fig. SC.

In Fig. 5D, an epoxy or acrylic mortar layer 22 is applied to the stepped bore and the funnel water drainage portion 24 is seated thereon; a drainage pipe 32 having been attached to the lower extension of the funnel 24.

As shown in Fig. 5E, the waterproofing membrane 14 is then spray-applied to the upper surface of the bridge deck and also to the inner walls of the upper portion of the funnel. Any over spray which is accidentally applied to the upwardly facing surface and blocks the apertures of the funnel 24 can be removed by way of a sharp knife or similar implement.

As shown in Fig. 5F, a wooden blanking plug 34 is then received in the upper portion of the funnel 24 and the red sand asphalt protection layer 36 is laid upon the waterproofing membrane 14. Advantageously, the wooden blanking plug extends upwardly to a height which corresponds to the upper surface of the protection layer 36. Once the protection layer 36 has been suitably laid, the wooden blanking plug is removed and, as shown in Fig. 5G, the water collecting chamber 28 is located in the space created by the removal of the wooden blanking plug 34.

Next, the base course 18A is laid over the protection layer 36 and the chamber 28 and finally the wearing course 18b is laid upon the base course 18A so as to form the roadway surface.

As a final step, the respective drainage pipes 32 of the drainage units are coupled together and led to a pier or abutment downpipe.

The invention is not restricted to the details of the foregoing embodiment. For example, the top surface of the water collecting portion 24 may'be formed as a dome or, indeed, the water collecting portion 24 may be provided as a hemisphere so as to improve the mechanical strength thereof.

Claims

1. A subsurface bridge drain unit comprising a collection chamber which is apertured in at least its upper region, an outlet portion for drainage of water from the collection chamber, and support means for locating the unit with the upper region of the collection chamber above a protection layer extending over a bridge deck into a waterpermeable layer for reception for subsurface water collected above the protection layer and with the outlet portion extending into a bore through the bridge deck.

2. A subsurface bridge drain unit according to claim 1, wherein the support means comprises an external flange or step.

3. A drain unit according to claim 2, wherein the support means comprises a laterally extending portion of the drain unit constructed and arranged so that a stable location is provided by seating the unit on the bridge deck.

4. A drain unit according to claim 2 or 3, wherein the outlet water drainage portion comprises a funnel member having a wider upper portion which forms the step of the support means.

5. A drain unit according to claim 4, wherein the water collecting chamber comprises a cylindrical chamber closed at one end by a flat or domed portion and arranged to engage with the inner surface of the upper portion of the funnel member.

6. A drain unit according to any one of the preceding claims, wherein the collection chamber comprises a cylindrical member, closed at one end, and having a plurality of apertures provided in the upper regions of the side wall thereof.

7. A drain unit according to claim 6, wherein the apertures extend for the whole height of the side walls of the water collection chamber.

8. A drain unit according to claim 6, wherein the water collection chamber is formed from a blank having laterally extending finger portions, which portions are bent to each extend in a vertical plane so as to form side wall portions of the water collection chamber separated by vertically extending apertures.

9. A drain unit according to claim 8, wherein the remote ends of the finger portions are secured to a support ring.

10. A drain unit according to any one of the preceding claims, wherein the uppermost surface of the water collection chamber comprises a hemispherical or domed chamber.

11. A drain unit according to any one of the preceding claims arranged to be supported on or in the bore extending through the bridge deck.

12. A drain unit according to any one of the preceding claims when formed of two or less members.

13. A method of installing a subsurface bridge drain unit comprising a water drainage portion and a water collection chamber in a bridge structure comprising a bridge deck, a protection layer, and/or base and wearing courses, the method comprising the steps of forming a bore through the bridge deck, locating the water drainage portion of the unit in the bore, disposing a waterproofing layer on the upper surface of the bridge deck, disposing a blanking plug on the water drainage portion so as to cover said portion, overlaying the waterproofing layer with a protection layer, replacing the blanking plug with the water collection chamber of the unit and laying the base course and/or wearing course over the protection layer so that the water collection chamber can collect water from the base course.

14. A method according to claim 13, wherein the blanking plug dimensions are chosen so that the plug extends at least up to the level of the protection layer.

15. A method according to claims 13 or 14, wherein the apertures of the water collection chamber are located so that an opening is provided between the internal region of the chamber and the bridge deck disposed above the protection layer.

16. A method according to any one of claims 13, 14 and 15, wherein the protection layer is red sand asphalt.

17. A method according to any one of claims 13 to 16, wherein the water drainage portion comprises funnel member whose upper, and laterally enlarged, portion is arranged to receive the water collection chamber thereon.

18. A method according to any one of claims 13 to 17, wherein the mouth of the bore is stepped so as to receive the upper portion of the funnel member therein.

19. A method according to any one of claims 13 to 18, wherein the waterproofing layer is formed from a sprayapplied waterproofing membrane.

20. A method according to any one of claims 13 to 19, when used for installing a subsurface bridge drain unit according to any one of claims 1 to 12.

21. A subsurface bridge drain unit substantially as hereinbefore described with reference to Figs. 1 to 3 or Fig.

4 of the accompanying drawings.

22. A method of installing a subsurface bridge drain unit substantially as hereinbefore described with reference to Fig. 5 of. the accompanying drawings.