If you are walking along the edge of any UAE road, car park or industrial yard you will typically see a long narrow concrete line parallel to the road that has a slotted grate or solid concrete lid. This is a precast concrete channel with a cover, one of the most used, but least talked about products in site drainage and cable management in UAE. There doesn’t seem to be anything very complicated—it’s just a trough shaped like the letter U, with a lid. It is actually easy to see that achieving the sizing, cover rating and jointing correct is a crucial factor in whether it will perform its function gracefully for two decades or will be a constant maintenance issue.
Actually, what comes into a well-designed precast channel with cover, and why it’s become the standard approach to precasting them.
The Advantages of Precast Concrete Used in Channel Systems
If you put a cover on a channel, there are two things going on at the same time: one, there is something flowing through it (whether it be stormwater or cabling); and two, there is something driving or walking on it.
Often the cast in place channels that are poured are difficult to keep straight, level, and pre-sloped over long runs and often the pour joints fail to form a leak free, crack free seal later.
Precast channel sections are manufactured to a specific cross-section and, if necessary, a specified fall at the base to cause the water to flow to an outlet rather than stagnate.
Units are cured to design strength prior to delivery to site, eliminating the need to carefully control on-site curing conditions; a significant benefit in the UAE summer months when curing conditions on site are more difficult to control.
Simply laid end to end and jointed, sections are what would be a slow pour using formwork become a fast install in modules.
1. Channel Profile and Sizing
The channel’s width and depth must be commensurate with the material being transported.
Changing the dimensions of a channel designed to convey light surface water runoff around a walkway is a very different proposition from sizing a channel that is to carry stormwater off a large paved yard, or to serve several power and telecom cables side by side.
Undersizing is by far the most common error made—it works great until the first big rainstorm or until one more cable is added downstream than the channel was sized for.
2. Cover Load Rating
This is the key element that is often overlooked.
Covers are rated according to the traffic that they are likely to encounter, whether pedestrian load only, light vehicle access or heavy duty loading for trucks or site machinery.
A pedestrian rated cover in a site that will be used for construction traffic or delivery trucks is a quick route to a cracked or collapsing cover.
Load rating must be based on actual long-term usage of that portion of channel, not just day one after it is installed.
3. Grate vs. Solid Slab Covers
Covers are usually a slotted grate that allows water to flow in along the length of the channel, or a solid concrete cover, which is used when the channel is carrying cables or when water is only desired at certain inlet points.
It is a common practice on actual sites to combine the two in one run, for example, in grated sections where drainage capture is required, in solid slab sections where the channel crosses a walkway or where the channel is to be sealed off.
The correct mix will vary based on the location of the water and access points, which is site specific and not a default mix.
4. Channel Slope and Water Flow
When a channel is conveying water and not cable, its base should always slope towards the water outlet.
If it is not installed, water will remain in the channel and cause a buildup of debris and standing water, which will cause the line to get clogged by silt.
These precast sections are also designed to be installed so they are sloped exactly as required to ensure the channel will be self-cleaning and not require regular manual cleaning.
5. Joint Sealing Between Sections
All channel sections must be joined at some point, and this is a place where fine material can wash into the channel over time, or where it can leak.
Joints that have been properly detailed by being sealed and aligned properly during installation ensure that the channel line remains watertight and structurally continuous.
This should also take into account any small thermal expansion, especially important in the UAE where ground and surface temperatures vary significantly from summer to winter, on longer runs.
6. Cable Channel Applications
With a precast channel not for drainage but for cabling, priorities change.
The internal dimensions should include an adequate amount of space for the number of cables that will be installed, including space for future installations, and the cover should be easily removed without requiring too much effort to gain access to the channel for maintenance or installation of new cables.
This is typically the case in data center sites, industrial applications and when using a channel system is more convenient than a completely enclosed duct bank for regular access to cables with heavy power or telecom applications.
7. Certification and Approval
The following points should be considered when selecting precast channel products for use on projects in the UAE:
The manufacturer must supply a certified production process and the structural design must be submitted via the relevant municipal approval procedure.
This is related to Dubai Municipality’s Administrative Decision No. 316 of 2012, which regulates precast concrete factories, and a supplier should be able to obtain a Certificate of Conformity from the Dubai Central Laboratory’s Certification and Quality Control of Products Section (DCLD-CQPS) upon request.
It’s an easy way to prevent delays in ordering if the product should be called into question for inspection.
Standards That Tie It Together Precast Concrete Channels
In the UAE precast channel and drainage products are normally specified to British standards for structural concrete design with the relevant municipality’s specific technical guidance on drainage, cable and utility infrastructure.
A channel system may be located where you need drainage and you need to route utilities through it, so it is important to have a clear understanding of which standards and load classes will be applied to your particular application before production starts, with your supplier.
The Real Challenge is to Match the Channel to the Site Precast Concrete Channels
A channel with cover appears on the paper to be one of the easier precast products – a trough and a lid.
The difficulty arises when a single run must be used for changing loads throughout its length, for switching between drain and cable operations, or for connecting in to existing infrastructure that was not designed for the new channel.
If the load ratings, cover types and slope are determined with the original site plan, projects will proceed smoothly without resorting to one cover specification for the entire run.
The Bottom Line on Precast Concrete Channels
A precast concrete channel with cover is a simple product, but not a simple job to do – to control the flow and to protect live infrastructure, while conveying actual traffic load on top.
The key to maintaining a channel system without being a line item for repairs for decades is to get the profile sizing, cover rating, slope and jointing correct the first time.
When installing drainage or cable for a road, yard or industrial site, it may be good to begin with the actual loads and flows for each part of the site instead of applying a single standard specification to the entire site.
