GB2373530A

GB2373530A - Preformed Modular Sub-surface Drainage System

Info

Publication number: GB2373530A
Application number: GB0107407A
Authority: GB
Inventors: Peter Alexander Jennings; Robert James King; Martin Fairley; Walter Summerhill Mcintyre; Andrew William Young
Original assignee: Aco Technologies PLC
Current assignee: Aco Technologies PLC
Priority date: 2001-03-23
Filing date: 2001-03-23
Publication date: 2002-09-25
Anticipated expiration: 2021-03-23
Also published as: GB2373530B; GB0107407D0

Abstract

A drainage channel system is constructed from one-piece plastics channel liner sections 2. Each section 2 defines a pipe portion 4 and upstanding projections 6 which terminate in a common horizontal plane. The projections 6 are sized and spaced such that conventional concrete reinforcing mesh 60 may be installed. Internal shaping (50, figs. 8 and 9) may be employed to induce swirl in the drainage water and thereby facilitate the channel's self-cleaning tendencies. Crack inducer boards 30 are fitted around the channel liner section 2 in order to encourage the concrete slab surrounding the channel liner section 2 to crack at controlled intervals. Steel bar formed into hoops (22, fig 1) act as crack-stopping members. These are supported on longitudinal bars (24, fig 1). The liner 2 is installed in a trench, with the reinforcing mesh 60. The trench is then back-filled with concrete. After curing, the tops of the projections 6 are opened by cutting out their closed-off tops.

Description

Wide Channel Drainage System Background of the Invention The present invention relates to channel drainage systems, and more specifically to high capacity channels typically referred to as wide channel drainage systems.

Technical Background Robust drainage channels with a high hydraulic capacity are required for surface drainage in large areas such as distribution centres, car parks and airports.

One such drainage system is provided by Hodkin & Jones Sheffield Ltd and is described in GB-A-2229 212. This provides an open channel member made of glass fibre reinforced concrete, which is anchored into a concrete backfill surrounding the channel in use by means of a framework of reinforcing bars. This type of channel member is intended to be used with a separate lid. As described in GB-A-2316428, the lid provides a number of projections that terminate in slots extending transverse to the direction of the channel in the surface. Water enters the channel through the slots.

Installation problems A number of technical problems are encountered in the installation of such a system.

These are created by the need to align the lids on the channels and ensure that the top of the lid is aligned with the finished surface level. GB-A-2316428 suggests that by forming the lid and the channel in a single unit, the problems of locating the lid relative to the channel in situ are avoided. However, apart from suggesting that the separate concrete lid and channel are bonded together, there is no teaching of how such a single unit might be achieved.

This type of drainage channel is intended for use in areas where there is a heavy surface

loading from vehicles. It is therefore necessary to provide for reinforcement of the concrete slab covering the channel. In the system proposed by Hodkin & Jones Sheffield Ltd, the slab reinforcement is provided by a specially designed manufacturer supplied reinforcing bars, which is shaped to co-operate with the projections in the lid. This is a relatively expensive solution.

Levelling of the lid so that the openings to the projections are aligned with the surface also presents a significant technical problem.

The crack problem Another problem associated with the setting of a long channel in a concrete backfill is the tendency of the concrete to shrink during the curing phase creating cracks in the resulting slab. Traditionally, this has been dealt with by attempting to induce cracks at controlled spacings along the channel of every 5 to 6 m. This can be done, for example, by placing triangular sections of wood in the bottom of the trench prior to the pouring of the concrete. The sharp point creates stress concentrations and promotes a controlled crack to effectively partition the slab. Cuts are then made with a diamond saw at approximately the same locations as the triangular sections of wood. The cuts are then filled with a proprietary joint sealant. Site problems exist when the contractors omit the necessary triangular pieces of wood and the cracks are not controlled.

Drainage efficiency problems The hydraulic efficiency of wide, transverse slots in collecting water from the surface is not great.

Further technical problems are related to the efficient collection of water from the surface and the encouragement of its rapid flow away down the channel. Typically a certain amount of mud and debris will be entrained with the drained water. It is desirable that the channel should, as far as possible, be self cleaning to prevent such mud and debris being accumulated in the base of the channel to interfere with subsequent efficient drainage.

Solution of the Invention The present invention provides a unitary plastics channel section defining a pipe portion having a plurality of projections communicating with the pipe portion and adapted to terminate in a common horizontal plane, the size and spacing of the projections being such as to allow concrete reinforcing means to be seated over and between the projections during an installation process.

Preferably the reinforcing means is a conventional reinforcing mesh with grid sizes of, for example, 200 by 200 mm or 200 mm by 100 mm. Arranging the projections so that instead of a single wide slot there are two spaced projections, which will be accommodated in adjacent grids, it is possible to use standard meshes or other reinforcing bars to reinforce the concrete slab. Other arrangements of projections may allow for a plurality of smaller projections to be fitted within each grid. Preferably each projection has a closed upper end adapted to be opened after installation to define a water entry slot.

This prevents entry of debris into the channel section during installation. The slots may be aligned parallel to the longitudinal axis of the channel or the slots in adjacent grids may be oriented in different directions so as to improve the water intake efficiency.

In another aspect, the present invention provides a unitary plastics channel section defining a pipe portion having a plurality of projections communicating with the pipe portion and adapted to terminate in a common horizontal plane, at least one crack inducer board fitted externally of the channel section in a plane transverse to a longitudinal axis of the pipe portion, and a plurality of crack stopping hoops at least partially surrounding the channel section externally in spaced planes parallel to the crack inducer board, and means for supporting the crack stopping hoops and holding them in position relative to the channel section.

A plurality of such channel sections can be fitted together end-to-end in order to define the required channel lengths. When fitted together, the crack inducer boards will be at spacings of 5 to 6 m. The supporting means for the hoops may be longitudinal bars which extend along the outside of the hoops and crack inducer boards and hold the whole external assembly in position relative to the channel section. These longitudinal bars are preferably welded to the hoops in order to form a rigid trellis. The supporting means may further comprise ribs moulded into the external wall of the channel to act as a support for the trellis.

The trellis of hoops and bars may be constructed of metal, such as steel, or a glass reinforced polyester resin.

In a third aspect, the present invention provides a unitary plastics channel section defining a pipe portion having a plurality of projections communicating with the pipe portion and adapted to terminate in a common horizontal plane, wherein each projection comprises a first portion integral with the plastics channel section and a second portion slideable relative to the first portion so that the height of the projections can be adjusted.

Preferably the second portions for use with at least two adjacent projections are fixed together. Such extension units can then be conveniently fitted over the projections and adjusted to the appropriate height once the reinforcing mesh or reinforcing bars has been placed over the projections. This allows for differing depths of concrete slab.

In a fourth aspect, the present invention provides a unitary plastics channel section defining a pipe portion having a plurality of projections communicating with the pipe portion and adapted to terminate in a common horizontal plane, wherein an internal surface of the pipe portion adjacent an entry point of each projection is shaped to define a flow path that induces rotational motion in the water flow.

Such rotational motion causes the water stream to accelerate enhancing its ability to keep

mud and debris entrained and in suspension as the water flows down the channel. This enhances the self cleaning process in much the same manner as the vortex created at the plughole of a domestic bath accelerates the water exiting the bath and encourages the retention of entrained materials.

Brief Description of the Drawings In order that the invention may be well understood, some embodiments thereof will now be described, by way of example only, with reference to the accompanying diagrammatic drawings, in which: Figure 1 shows a perspective view of a first embodiment of a channel section in accordance with the invention; Figure 2 shows a perspective view of a second embodiment of the channel section in accordance with the invention shown ready for installation with a reinforcement mesh positioned over its projections; Figure 3 shows a top plan view of the channel section of Figure 2; Figure 4 shows a side view of the channel section of Figure 2; Figure 5 shows an end view of the channel section of Figure 2; Figures 6 A-G show various possible patterns of projection arrays for use with the channel sections of Figures 1 or 2; Figure 7 shows a section through an extension unit in use; Figure 8 shows a diagrammatic perspective view of a channel section to illustrate shaping of an internal surface of the pipe portion to create water guiding "vectors" ;

Figure 9 shows a section through the channel section of Figure 8 ; Figure 10 show a section through a trench during the installation process for a channel section as shown in Figure 1 ; and Figure 11 shows a third angle projection of the channel section of Figure 1 in an installed condition showing the use of a grating top to cover the tops of the projections.

Description of a Preferred Embodiment Two different designs of channel section are shown in Figures 1 and 2. Each design shares the common principle of providing sections of a unitary plastics moulding 2 that can be placed end-to-end in use to define an elongate drainage channel.

The sections 2 can be moulded in one piece from for example, polypropylene using a rotational moulding technique. The polypropylene channel sections 2 act as a liner and forms the drainage channel when the sections are surrounded with a concrete backfill during the installation process. The channel sections have no significant structural strength and are therefore lightweight and easy to handle.

Male/female watertight connection details may be formed on opposing ends of each channel section 2 to allow the sections to interlock in a conventional manner.

The channel sections 2 define a pipe portion 4 and a plurality of upstanding projections 6 that communicate with the pipe portion 4. Each projection 6 terminates in a common horizontal plane adapted to lie at ground level in the finished installation. As moulded the projections 6 are capped to prevent entry of mud and other debris into the pipe portion 4 during the installation process. These caps can be simply cut off after installation. A cutting ridge may be moulded in as a guide to cutting and to prevent concrete flaking around the inlet detail. Alternatively the projections may be moulded with open ends and

fitted with removable caps to protect them during installation.

In Figure 1 the cross section of the pipe portion 4 is hexagonal and in Figure 2 the cross section of the pipe portion 4 is ovoid. Alternatively, pipe sections with circular or polygonal cross sections can be used. A major consideration in the design of the pipe portion 4 is the need to encourage good hydraulic flow within the resulting drainage channel.

The channel section 2 may have an integrally moulded side inlet connection 8. The connection 8 is moulded with a series of steps corresponding to various standard pipe sizes. The connection 8 can be cut at the required level using a hand saw to provide an opening of the required size.

Ribs (not shown) or projecting webs 10 are formed externally of the channel section 2 as best seen in Figures 2 and 4. Ribs can be provided to stiffen the structure. These webs 10 support a trellis 20 of steel reinforcing bars (rebars). The trellis comprises hoops 22, which act to prevent cracks in the surrounding concrete, and longitudinal rebars 24, which hold the hoops at the correct spacing and support the trellis externally of the channel section 2 on the webs 10 as best shown in Figure 4. The trellis 20 stops short of the projections 6.

A crack inducer board 30 may be clipped to the channel section 2 such that when the channel sections 2 are connected together the boards 30 will be spaced by approximately 5 to 6m. The crack inducer board 30 has a T shaped profile. It may be made of any suitable material such as fibre board. The board 30 is shaped to surround the channel section 2 and is held in position by a suitable clip arrangement. A top edge 32 of the crack inducer board 30 is aligned in the common plane of the ends of the projections 6 to assist in the levelling of the channel section 2 during installation.

If the channel sections 2 have lengths of 2. 5 m, then in order to provide crack inducer boards 30 at the desired 5 to 6m spacing only alternate sections need to be fitted with crack inducer boards 30.

The projections 6 are arranged in an array 40. The depth of the concrete slab that is to be formed over the pipe portion 4 determines the height of the projections 6. The slab is reinforced by a standard steel reinforcing mesh or reinforcing rods 60, which can be simply placed over the array of projections 6 as shown in Figure 2,3 and 4. Use of a standard mesh avoids the need for cutting on site. The reinforcing mesh or rods 60 also extends into and is supported by the slab surrounding a trench into which the drainage channel is installed. The grid size of such a mesh is typically 200 x 200mm or 200 x 100mm. The size of individual rods will be from 16mm to 25mm diameter.

Slab reinforcement is critical to this type of design, otherwise the bending stresses will crack the concrete slab. When the concrete is cured, the mesh or rods act as a structural reinforcement to take the loads and the slab acts like a reinforced beam over the channel.

The concrete has to run as a continuum over the channel for this to work, otherwise cantilever beams arise and the concrete will shear. The projections 6 provide a means for locating the mesh or rods correctly and reduce the opportunity for installation errors.

The design of the array of projections 6 is determined by the need for the projections 6 to pass through grids within a mesh. Various possible patterns are shown in Figures 6A to G. Each projection 6 has a slot shaped opening 42 into the surface. Orienting these slots 42 parallel to the longitudinal axis of the drainage channel is found to be efficient at collecting surface water directed to the line of the channel by a surface camber, as the slots 42 are transverse to the direction of the water flow. Longer slots can be used for the same mesh size if they are oriented at an angle to the sides of the mesh. Preferably slots in adjacent meshes are oriented in different directions so as to improve the water intake efficiency and ensure that the slots intercept water flow in any direction.

An extension unit 44 is shown in Figure 7. The unit comprises a set of hollow tubes 46 shaped and spaced to slide over the projections 6. The extension unit allows the height of the projections to be varied to cope with deep concrete slabs. The unit is placed in position once the reinforcing mesh 60 has been positioned. With the extension unit 44 in place each projection is defined by a first portion 6 integral with the channel and a second relatively slideable portion that is one of the hollow tubes 46. Extension units 44 can be provided in a range of heights. The tops of the tubes 46 may be provided with a removable top to close them during the installation process. Where an extension unit is to be used the tops of the first portions of the projections 6 integral with the unit must be open or opened prior to fitting of the extension unit.

As shown in Figures 8 and 9 recesses 50 are formed in an internal surface of the pipe portion 4. These recesses 50 act as"vectors"to guide the water flow. Each vector starts from an internal mouth 52 of a projection 6 where it merges into the pipe portion 4. The vectors are designed to accelerate the water by forcing it to follow a curved path. The use of the vectors enhances the self-cleaning of the pipe portion 4 by keeping mud and debris entrained within the faster flowing liquid stream.

As shown in Figure 8, the drainage channel section can be moulded with integral feet 54.

The integral feet 54 are lateral projections which extend along the length of the plastics channel section 2 at either side of the bottom of the pipe portion 4. The integral feet 54 provide handling stability and also provide an anchor for the concrete that surrounds the drainage channel section.

Installation The installation of the above drainage system will now be described by reference to Figures 10 and 11. The width of the channel sections 2 is designed to suit standard digger bucket widths to minimise site work, cost and spoils volume. The trenches are dug and the channel sections 2 assembled end-to-end to provide the required drainage channel assemblies. In order to position the assembly correctly during the pouring of the concrete backfill, a support frame 70 is provided. The frame has a datum plate 72, which clips to the tops of the projections 6 in order to suspend the assembly in the trench. This leaves a space between the frame and the tops of the crack inducer boards 30 over which concrete can flow.

Fixing means 74 are provided at the outer edges of the frame to connect it to the concrete slab at the sides of the trench. Inner fixing means 76 are provided to connect to the reinforcing mesh 60. These fixing means may be screws or clamps.

Once the channel assembly has been assembled and the reinforcing mesh 60 and any required extension unit 44 placed over and between the projections 6, the support frame is positioned and the fixing means 74 and 76 engaged. The concrete backfill is then poured along the length of the trench so that it completely fills the space around the channel sections 2 up to the level of the tops of the projections 6 and the tops of the crack inducer boards 30. The reinforcing mesh 60 and the trellis 20 become embedded in the concrete.

The support frame 70 is removed once the concrete has cured. The tops of the projections 6 are then removed to leave open slots.

Figure 11 shows a system in which a grid 80 is seated over the open tops of the projections 6. The grid 80 may be cast from a composite material with openings corresponding to any of the slot array patterns illustrated in Figures 6A-G. The grid 80 rests on top of the concrete slab and may be provided with means 82 for anchoring it to the concrete. An asphalt wearing course 84 is applied to the surface of the concrete slab and is brought up flush with an upper surface of the grid.

Claims

1. A unitary plastics channel section defining a pipe portion having a plurality of projections communicating with the pipe portion and adapted to terminate in a common horizontal plane, wherein the size and spacing of the projections is such as to allow concrete reinforcing means to be seated over and between the projections during an installation process.

2. A unitary plastics channel section as claimed in claim 1, wherein the reinforcing means is a conventional reinforcing mesh.

3. A unitary plastics channel section as claimed in claim 2, wherein the projections are sized and/or grouped to fit within a mesh having a grid size of 200 by 200 mm or 200 mm by 100 mm.

4. A unitary plastics channel section as claimed in claim 1, wherein each projection has an upper end adapted to be opened after installation to define a water entry slot.

5. A unitary plastics channel section as claimed in claim 3 or 4, wherein the trellis of hoops and bars is constructed of metal, such as steel, or a glass reinforced polyester resin.

5. A unitary plastics channel section as claimed in claim 4, wherein at least some of the slots are oriented parallel to the longitudinal axis of the channel section.

6. A unitary plastics channel section as claimed in claim 4, wherein the slots in adjacent grids of the reinforcing mesh are oriented in different directions.

7. A unitary plastics channel section defining a pipe portion having a plurality of projections communicating with the pipe portion and adapted to terminate in a common horizontal plane, at least one crack inducer board fitted externally of the channel section in a plane transverse to a longitudinal axis of the pipe portion,

and a plurality of crack st (ling hoops at least partially surrounding the channel section externally in spaced planes parallel to the crack inducer board, and means for supporting the crack stopping hoops and holding them in position relative to the channel section.

8. A unitary plastics channel section as claimed in claim 7, wherein the supporting means for the hoops are longitudinal bars which extend along the outside of the hoops and crack inducer boards and hold the whole external assembly in position relative to the channel section.

9. A unitary plastics channel section as claimed in claim 8, wherein the longitudinal bars are welded or otherwise fixed to the hoops in order to form a rigid trellis.

10. A unitary plastics channel section as claimed in claim 9, wherein the supporting means further compromise ribs or projecting webs moulded into an external wall of the channel section to act as a support for the trellis.

11. A unitary plastics channel section as claimed in claim 9 or 10, wherein the trellis of hoops and bars is constructed of metal, such as steel, or a glass reinforced polyester resin.

12. A unitary plastics channel section defining a pipe portion having a plurality of projections communicating with the pipe portion and adapted to terminate in a common horizontal plane, wherein an internal surface of the pipe portion adjacent an entry point of each projection is shaped to define a flow path that induces rotational motion in the water flow.

13. A unitary plastics channel section defining a pipe portion having a plurality of projections communicating with the pipe portion and adapted to terminate in a common horizontal plane, wherein each projection comprises a first portion

integral with the plastics channel section and a second portion slideable relative to the first portion so that the height of the projections can be adjusted.

14. A unitary plastics channel section as claimed in claim 13, wherein the second portions for use with at least two adjacent projections are fixed together as an extension unit.

15. A unitary plastics channel section as claimed in any one of the preceding claims, having means at each end for enabling the channel sections to be fitted together end-to-end in order to define the required channel lengths.

16. A unitary plastics channel section as claimed in any one of the preceding claims, made of polypropylene, polythene or other suitable material.

17. A unitary plastics channel section as claimed in any one of the preceding claims, wherein the pipe portion has at least one lateral projection to provide a foot.

18. A unitary plastics channel section as claimed in any one of the preceding claims, wherein the pipe portion has a cross section which is circular, oval or polygonal.

19. A unitary plastics channel section substantially as herein described with reference to Figures 1 and 10 or Figures 2 to 6 of the accompanying drawings.

20. A support frame for use in the installation of a channel assembly comprising a plurality of unitary plastics channel sections as claimed in claim 1 together with concrete reinforcing means, the frame comprising first fixing means for connecting the frame to a concrete slab at the sides of a trench in which the assembly is to be installed, second fixing means for connecting the frame to the reinforcing means, and means for holding the assembly by the projections suspended at the correct level within the trench while concrete is poured to backfill the trench.

Amendments to the claims have been filed as follows 1. A unitary plastics channel section defining a pipe portion having a plurality of hollow projections communicating with the pipe portion and adapted to terminate in a common horizontal plane, at least one crack inducer board fitted externally of the channel section in a plane transverse to a longitudinal axis of the pipe portion, and a plurality of crack stopping hoops at least partially surrounding the channel section externally in spaced planes parallel to the crack inducer board, and means for supporting the crack stopping hoops and holding them in position relative to the channel section.

2. A unitary plastics channel section as claimed in claim 1, wherein the supporting means for the hoops are longitudinal bars which extend along the outside of the hoops and crack inducer boards and hold the whole external assembly in position relative to the channel section.

3. A unitary plastics channel section as claimed in claim 2, wherein the longitudinal bars are welded or otherwise fixed to the hoops in order to form a rigid trellis.

4. A unitary plastics channel section as claimed in claim 3, wherein the supporting means further compromise ribs or projecting webs moulded into an external wall of the channel section to act as a support for the trellis.