AU2012212572A1

AU2012212572A1 - Precast headwall unit

Info

Publication number: AU2012212572A1
Application number: AU2012212572A
Authority: AU
Inventors: Phil Thomas
Original assignee: CM CONCRETE PRODUCTS Pty Ltd
Current assignee: Precast Civil Industries Pty Ltd
Priority date: 2011-08-18
Filing date: 2012-08-14
Publication date: 2013-03-07
Anticipated expiration: 2032-08-14
Also published as: AU2012212572B2

Abstract

The present invention is directed to a precast headwall unit for discharging water from a pipe to a waterway. The precast headwall unit has two back walls that serve to increase the integrity of the precast headwall unit and pipe coupling and 5 avoid the need for additional formwork during installation. The invention also covers retrofitting headwalls and culverts with a second back wall. Figure 1 1<7(3

Description

- 1 PRECAST HEADWALL UNIT FIELD OF INVENTION The present invention relates to culverts and drains. In particular the 5 invention relates to a precast concrete headwall units. The present invention has particular but not exclusive application as a headwall at the outlet of a stormwater drain pipe or culvert. BACKGROUND OF THE INVENTION 0 A headwall is a retaining wall typically installed in embankments along the sides of a waterway where water from a stormwater drainpipe or culvert discharges into a waterway. A headwall unit directs the water as it exits the pipe and protects the embankment from erosion and scouring. Headwalls may be formed in situ from a multi-part construction requiring on 5 site assembly. High quality, skilled labour is required in order to ensure that correct construction and installation is carried out to provide a durable headwall unit. Furthermore, the installation process can be protracted and this incurs high labour costs. One piece precast headwall units are known. The time required for 20 installation of a one piece precast headwall unit is greatly reduced, and the construction of formwork at the construction-site is also no longer needed. However during periods of high rainfall, hydrostatic pressure behind the headwall builds up and can lead to dislodgement of the headwall. As well the high volume of flow during these periods can also contribute to dislodgement of headwalls from the water 25 pipe.

-2 OBJECT OF THE INVENTION It is an object of the present invention to provide a headwall unit that overcomes at least in part one or more of the abovementioned disadvantages. 5 SUMMARY OF THE INVENTION In one aspect the present invention broadly resides in a precast second wall adaptor for a headwall unit having a wall with opposing flanges extending from each longitudinal side, said wall having an aperture for the placement of a pipe there 0 through; wherein in use the precast second wall adaptor is attached to the rear of the headwall unit with the flanges spacing the wall from a back wall of the headwall unit so that the aperture in the wall is substantially horizontally aligned with an aperture in the back wall and able to accommodate a pipe. Preferably the precast second wall adaptor is attached by means of anchor 5 bolts. The attached precast second wall adaptor preferably forms a double wall structure having a cavity there between. Preferably in use the cavity is filled in with concrete, soil or the like. In one embodiment the precast second wall adaptor has a flange extending 20 outwardly from the bottom and integral with the longitudinal side flanges. Preferably there are weep holes near the bottom of the wall. More preferably the weep holes are shaped to accommodate a pipe that can extend between the two walls. Preferably the precast second wall adaptor can be retro-fitted to installed 25 headwall or culvert units.

-3 The precast second wall adaptor can preferably be used to retro-fit to a pit or any suitable structure into which a pipe enters or passes through. Any suitable structure preferably includes drainage units, stormwater pits, stormwater drains and gullies. Preferably the precast second wall adaptor is fixed or made integral with a 5 suitable structure to provide a more stable mounting between the pipe and the structure. Preferably the precast second wall adaptor can be fixed or precast integral with a headwall or culvert unit. In another aspect the present invention broadly resides in a precast headwall 0 unit for discharging water from a pipe to a waterway including a first back wall and a second back wall spaced apart from each other and substantially parallel with each other to form a double wall structure with a cavity there between, both the first and second back walls have an aperture that is substantially horizontally aligned and able to accommodate a pipe; 5 two side walls, each of which extend outwardly from an end of the first back wall; an apron forming a floor extending between the first back wall and the side walls; wherein during installation a water pipe is positioned in the two aligned apertures and sealed in position by adding concrete to the cavity between the first 20 and second back walls. The pipe section positioned within the cavity between the first and second back walls serves as additional surface area for bonding the pipe to the headwall unit. Preferably the horizontal distance between the first back wall and the second back wall is approximately 80mm to 110mm. More preferably the distance between 25 the first and second back walls is approximately 90mm.

-4 Preferably the side walls extend outwardly at an obtuse angle from the first back wall. Preferably the side walls extend at an angle of 120 to 150 degrees from the first back wall. In one preferred embodiment, the headwall unit has a vertical flange 5 extending downwards from the underside of the apron into the subsoil below to anchor the headwall unit in position. Preferably the flange extends transversely across the underside of the apron of the headwall unit in a substantially perpendicular orientation to the flow from the water pipe. Preferably the flange is constructed in situ during installation of the headwall 0 by inserting a precast concrete member downwards into a transverse slot in the apron of the headwall and into the soil below to anchor the headwall in place. Preferably the precast concrete member is a tapered concrete wedge. The flange slot in one embodiment has tapered edges. The slot is spaced from the edge of the apron to avoid compromising the 5 integrity of the headwall unit. The width of the slot is relatively narrow to avoid adversely affecting the integrity of the headwall unit. Preferably the slot is closer to the front edge of the apron than to the back edge. The width of the slot and flange is preferably between 300mm to 450mm. Preferably the flange is fixed with an adhesive, such as an epoxy adhesive, to 20 secure it into position in the slot. When the flange is in place in the slot, preferably the upper edge of the flange is level with the apron surface. In an alternative embodiment, a portion of the precast concrete member remains above the top surface of the apron to form a baffle to dissipate energy from 25 the flow of water to minimize scouring and gouging.

-5 The baffle in one embodiment includes shoulder portions so that the baffle can extend across the top surface of the apron. The baffle can include notches, such as v-shaped or u-shaped notches, to aid the dissipation of water. Preferably the headwall unit is fitted with one or more soil outlets to allow 5 weeping of water to facilitate release of water pressure that can build up behind the headwall during heavy rainfall. A build up of water pressure can dislodge headwall units. Preferably soil outlets are located in the side walls of the headwall unit. Preferably there are one or more outlets in the first back wall. The one or more first back wall outlets are preferably connected by pipe to corresponding outlets in the 0 second back wall to thereby allow water from the soil behind the second back wall to pass through the pipe and weep from the outlet in the first back wall. BRIEF DESCRIPTION OF THE DRAWINGS In order that the present invention can be more readily understood and put 5 into practical effect, reference will now be made to the accompanying drawings wherein: Figure 1 is a diagrammatic view of a precast headwall unit according to a preferred embodiment of the present invention; Figure 2 is a diagrammatic side view of the installed precast headwall unit of 20 Figure 1; Figure 3 is a diagrammatic bottom view of the installed precast headwall inlet unit of Figure 1; Figure 4 is a diagrammatic view of an embodiment of a precast second wall adaptor; and -6 Figure 5A and 5B is a diagrammatic view of another embodiment of a precast second wall adaptor. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 5 With reference to Figures 1 to 3, there is shown a precast headwall unit 10. The headwall unit 10 has a first back wall 11 including a circular aperture 16 to accommodate a water pipe 22, a second back wall 12, an apron 14 and two side walls 13. The side walls 13 each extend outwardly from the first back wall 11 at an obtuse angle (preferably approximately 1200 angle). 0 The second back wall 12 is parallel to the first back wall 11. The second back wall 12 has a circular aperture (not shown) in horizontal alignment with the aperture 16 in the first back wall 11 to accommodate water pipe 22. The first back wall 11 is joined to the second back wall 12 by two cavity side walls 15 to form a back cavity 17. Preferably the distance between the first back wall 11 and the second back wall 5 12 is approximately 90mm. The precast headwall unit 10 is installed near a waterway with the apron 14 facing the waterway. A water pipe 22 is placed through the second aperture (not shown), the back cavity 17 and the first aperture 16. The pipe is sealed in place by pouring concrete into the back cavity 17. There is no need for additional formwork 20 for the concrete, since the walls 11, 12 and 15 of the cavity 17 provide the necessary formwork. After the concrete is set, the concrete forms a strong join between the headwall unit 10 and the pipe 22. The apron portion 14 of the headwall unit 10 has an elongated, tapered slot 18 extending across part of the width of the apron 14 to accommodate a tapered 25 wedge-shaped precast concrete curtain wall 19. During installation the curtain wall -7 19 is inserted downwards into the slot 18 in the apron 14 to project into the soil below. The curtain wall 19 is secured in position in slot 18 using an epoxy adhesive. When the curtain wall 19 is in place the top edge can be flush with the apron surface. The slot 18 is spaced from the edge of the apron to avoid compromising the 5 integrity of the headwall unit. The width of the slot 18 is relatively narrow to avoid adversely affecting the integrity of the headwall unit. The width of the curtain wall is preferably between 300mm to 450mm. The headwall unit 10 is fitted with outlets 21 on the side walls 13 and first back wall 11 to allow water to weep from the soil. The outlets 21 allow the weeping 0 of water from the soil and thus ease the water or hydrostatic pressure that can build up behind the headwall during heavy rainfall. If the hydrostatic pressure builds up, it may dislodge or destabilize the headwall unit. The outlets 21 in the first back wall 11 are each connected by a pipe to corresponding outlets in the second back wall 12. This allows water to pass from the 5 soil behind the second back wall 12 to the first back wall 11, to relieve hydrostatic pressure. In an alternative embodiment, the curtain wall can be positioned to be partly raised from the apron to form a dissipater wall. The curtain dissipater wall may have shoulder portions to allow it to extend across the whole width of the apron. The 20 curtain dissipater wall may also have one or more notches, such as v-shaped notches, to form pathways to facilitate dissipation of water and reduce gouging of the apron by constant streams of water over the same part of the apron. The preferred embodiment described above relates to a single cell headwall unit. The present invention also includes two, three, four and multiple cell headwall 25 units intended for attachment to more than one water pipe.

- 8 The precast headwall unit 10 is installed near waterways, but is prefabricated off-site. With prefabrication, the headwall unit can cure and increase in integrity before being operational. With a precast headwall unit, no formwork is required at the site of installation, and the on-site construction work is limited to connecting the 5 headwall unit 10 to the water pipe 22, sealing by pouring concrete into the cavity 17, and securing the headwall unit 10 to the installation site by inserting the curtain wall 19. Consequently the time taken to install the headwall unit and the need for workers with specialist skills is reduced. With reference to figure 4, there is shown a precast second wall adaptor 30 0 having a rear wall 31 and two opposing flanges 32 extending from the longitudinal side of the adaptor. The precast second wall adaptor 30 has an aperture 33 for the placement of a pipe, weep holes 34 for the insertion of a small diameter pipe to allow water to weep through the precast second wall adaptor 30, and a plurality of anchor holes 36 for inserting anchor bolts to fasten the precast second wall adaptor 30 to 5 retrofit an installed headwall unit. When the precast second wall adaptor 30 is fixed to the headwall unit, concrete or soil can be placed in the space between the two walls to secure the pipe to the headwall unit. With reference to figures 5A and 5B there is shown an alternative embodiment of the precast second wall adaptor 40. The precast second wall 20 adaptor 40, has a rear wall 41 and two opposing flanges 42 extending from the longitudinal side of the adaptor 40, an aperture 43 for the placement of a pipe, weep holes 44 for the insertion of a small diameter pipe to allow water to weep through the precast second wall adaptor 40, and a plurality of anchor holes 46 for inserting anchor bolts to fasten the precast second wall adaptor 40 to retrofit an installed -9 headwall unit. The precast second wall adaptor 40 also has a bottom flange 47 extending between the two flanges 42. ADVANTAGES 5 An advantage of the preferred embodiment of the present invention is that the precast headwall has the benefit of quick installation and the back cavity allows the pipe to be sealed to the headwall unit with concrete without the need for constructing formwork on site. The installation process is quick and minimal skill is required. 0 VARIATIONS It will of course be realised that while the foregoing has been given by way of illustrative example of this invention, all such and other modifications and variations thereto as would be apparent to persons skilled in the art are deemed to fall within the broad scope and ambit of this invention as is herein set forth. 5 Throughout the description and claims this specification the word "comprise" and variations of that word such as "comprises" and "comprising", are not intended to exclude other additives, components, integers or steps.

Claims

1. A precast second wall adaptor for a headwall unit having a wall with opposing flanges extending from each longitudinal side, said wall having an aperture for the 5 placement of a pipe there through; wherein in use the precast second wall adaptor is attached to the rear of the headwall unit with the flanges spacing the wall from a back wall of the headwall unit so that the aperture in the wall is substantially horizontally aligned with an aperture in the back wall and able to accommodate a pipe. 0

2. A precast second wall adaptor as claimed in claim 1 wherein precast second wall adaptor is attached by means of anchor bolts.

3. A precast second wall adaptor as claimed in claim 1 wherein the attached precast second wall adaptor forms a double wall structure having a cavity there between. 5

4. A precast second wall adaptor as claimed in claim 3 wherein in use the cavity is filled in with concrete, soil or the like.

5. A precast second wall adaptor as claimed in any one of the abovementioned claims wherein the precast second wall adaptor has a flange extending outwardly from the bottom and integral with the longitudinal side flanges. 20

6. A precast second wall adaptor as claimed in any one of the abovementioned claims wherein there are weep holes near the bottom of the wall.

7. A precast second wall adaptor as claimed in claim 6 wherein the weep holes are shaped to accommodate a pipe that can extend between the two walls. - 11

8. A precast second wall adaptor as claimed in any one of the abovementioned claims wherein the precast second wall adaptor can be retro-fitted to installed headwall or culvert units.

9. A precast second wall adaptor as claimed in any one of the abovementioned 5 claims wherein the precast second wall adaptor can be used to retro-fit to a pit or any suitable structure into which a pipe enters or passes through; suitable structures include drainage units, storm water pits, storm water drains and gullies.

10. A precast second wall adaptor as claimed in any one of the abovementioned claims wherein the precast second wall adaptor is fixed or made integral with a 0 suitable structure to provide a more stable mounting between the pipe and the structure.

11. A precast second wall adaptor as claimed in any one of the abovementioned claims wherein the precast second wall adaptor can be fixed or precast integral with a headwall or culvert unit. 5

12. A precast headwall unit for discharging water from a pipe to a waterway including a first back wall and a second back wall spaced apart from each other and substantially parallel with each other to form a double wall structure with a cavity there between, both the first and second back walls have an aperture that is 20 substantially horizontally aligned and able to accommodate a pipe; two side walls, each of which extend outwardly from an end of the first back wall; an apron forming a floor extending between the first back wall and the side walls; wherein during installation a water pipe is positioned in the two aligned -12 apertures and sealed in position by adding concrete to the cavity between the first and second back walls.

13. A precast headwall unit as claimed in claim 12 wherein the pipe section positioned within the cavity between the first and second back walls serves as 5 additional surface area for bonding the pipe to the headwall unit.

14. A precast headwall unit as claimed in claim 13 wherein the horizontal distance between the first back wall and the second back wall is approximately 80mm to 110mm.

15. A precast headwall unit as claimed in claim 14 wherein the distance between 0 the first and second back walls is approximately 90mm.

16. A precast headwall unit as claimed in claim 12 wherein the side walls extend outwardly at an obtuse angle from the first back wall.

17. A precast headwall unit as claimed in claim 16 wherein the side walls extend at an angle of 120 to 150 degrees from the first back wall. 5

18. A precast headwall unit as claimed in claim 12 wherein the headwall unit has a vertical flange extending downwards from the underside of the apron into the subsoil below to anchor the headwall unit in position.

19. A precast headwall unit as claimed in claim 18 wherein the flange extends transversely across the underside of the apron of the headwall unit in a substantially 20 perpendicular orientation to the flow from the water pipe.

20. A precast headwall unit as claimed in claim 12 wherein the flange is constructed in situ during installation of the headwall by inserting a precast concrete member downwards into a transverse slot in the apron of the headwall and into the soil below to anchor the headwall in place. - 13

21. A precast headwall unit as claimed in claim 20 wherein the precast concrete member is a tapered concrete wedge.

22. A precast headwall unit as claimed in claim 21 wherein the flange slot has tapered edges. 5

23. A precast headwall unit as claimed in any one of claims 20 to 22 wherein the slot is spaced from the edge of the apron to avoid compromising the integrity of the headwall unit.

24. A precast headwall unit as claimed in any one of claims 20 to 23 wherein the width of the slot is relatively narrow to avoid adversely affecting the integrity of the 0 headwall unit.

25. A precast headwall unit as claimed in any one of claims 20 to 24 wherein the slot is closer to the front edge of the apron than to the back edge.

26. A precast headwall unit as claimed in any one of claims 20 to 25 wherein the width of the slot and flange is between 300mm to 450mm. 5

27. A precast headwall unit as claimed in claim 20 wherein the flange is fixed with an adhesive, such as an epoxy adhesive, to secure it into position in the slot.

28. A precast headwall unit as claimed in claim 20 wherein when the flange is in place in the slot, the upper edge of the flange is level with the apron surface.

29. A precast headwall unit as claimed in claim 20 wherein a portion of the 20 precast concrete member remains above the top surface of the apron to form a baffle to dissipate energy from the flow of water to minimize scouring and gouging.

30. A precast headwall unit as claimed in claim 29 wherein the baffle includes shoulder portions so that the baffle can extend across the top surface of the apron. -14

31. A precast headwall unit as claimed in claim 29 or 30 wherein the baffle can include notches, such as v-shaped or u-shaped notches, to aid the dissipation of water.

32. A precast headwall unit as claimed in any one of claims 20 to 31 wherein the 5 headwall unit is fitted with one or more soil outlets to allow weeping of water to facilitate release of water pressure that can build up behind the headwall during heavy rainfall.

33. A precast headwall unit as claimed in claim 32 wherein there are soil outlets located in the side walls of the headwall unit. 0

34. A precast headwall unit as claimed in claim 33 wherein there are one or more outlets in the first back wall.

35. A precast headwall unit as claimed in claim 32 or 33 wherein the one or more first back wall outlets are connected by pipe to corresponding outlets in the second back wall to thereby allow water from the soil behind the second back wall to pass 5 through the pipe and weep from the outlet in the first back wall.