Stroll down any street in Dubai or Abu Dhabi and you will be on top of an entire underground infrastructure – power cables, fibre optic lines, sewer, storm water drains and access points to allow engineers to work on them without breaking the road. Nearly every one of these subsurface utilities is precast concrete. Let’s quickly recap the major types of structures, the regulations they have to meet, and why precast has become the preferred solution for all UAE underground utility projects.
Why Precast Leads in the First Place in This Category
Let’s start by finding out why precast concrete is the industry standard for underground utility buildings and not just in the UAE! Precast concrete may offer some advantages over cast-in-place concrete, especially in the underground market where consistency and timeliness are demanded. Made in a controlled environment and ready for installation, precast concrete offers a number of benefits over cast-in-place concrete, particularly in the underground market where consistency and speed are desired.
One of the major benefits is that of quality control. The precast vaults and structures are produced in a controlled environment in a factory with trained crews, where each pour is inspected for each mix and cured, and is typically cast at a consistent strength, often ranging from 4,000 to 5,000 psi, compared to the variable strengths that may be achieved by pouring concrete at the job site, depending on the weather conditions on that day. The weather variable is also greatly minimized since cast-in-place concrete needs to be cured in ideal weather conditions, while precast units are delivered and ready to go (assuming of course that it was an ideal week in the Gulf).
1. Utility Vaults
One of the most versatile precast structures that can be addressed in this category is the utility vault and can be used for a wide range of infrastructure industries. They install enclosures for transformers, switchgear, and circuit protection devices on electrical systems; enclose fiber optic cables, pull boxes and splice connections on telecommunication systems and enclose valve assemblies, meters and flow control devices on water and wastewater systems.
Demand for this kind has increased significantly over a certain trend: Data Center Construction. In the UAE, as it strives to build digital infrastructure and traditional infrastructure, the need for strong electrical power and connectivity in these facilities has been directly felt.
2. Precast Manholes
Manholes are a specific aspect of the regulatory systems that enable access to sewer pipes, stormwater control, and general underground maintenance in Dubai. It is a local industry standard that is referenced throughout the local precast industry and is adopted to meet the requirements of Dubai Municipality, selection of the manhole is directly linked to the pipe diameter and depth, once it is cast in concrete, it is a drawing mistake and will cost.
Dubai Municipality is quite clear about the technical standards; here, it’s emphasised that the waterproof tanking membranes and epoxy coating need to be exactly as specified, grade requirements need to be adhered to, and no substitution of materials is allowed without prior approval from Dubai Municipality.
3. Pull and Splice Boxes
The smaller enclosures will let technicians pull, splice and feed conductors for electrical and telecom cabling without digging up the whole enclosure. The standard products are available in round and rectangular form and for various types of projects, they may be different sizes to allow for routing of the cable.
The only thing that can make the difference between a properly specified pull box and liability is load rating. A traffic-rated box is required for traffic areas, but not for pedestrian areas; the latter can be either traffic-rated or non-traffic-rated – one of the more common specification errors is to mix traffic-rated and non-traffic-rated boxes on an underground utility project.
4. Duct Banks
Duct banks are designed to allow multiple conduits to be grouped into a single concrete bank, and provide a protected path for power and communications wires across a project site. They are particularly helpful in large sites that need to have a lot of cabling installed, where a single duct bank run will save from having to dig several trenches.
Thermal performance is important here because the concrete that is in direct contact with the power cable acts as an insulator (insulation is required anyway), and if the concrete is not designed properly, it can become a thermal trap, thereby shortening the life of the power cable, especially in the high ground temperatures in the UAE for much of the year.
5. Precast Chambers
There are a variety of functional types, such as drainage inspection points, telecom access, electrical cable routing, valve and utility access boxes, etc. in chambers. By their nature Chambers are not off-the-shelf, each product would need to be checked against the relevant authority or consultant specification before a product was manufactured as the technical and physical dimensions would depend on the dimensions of the chamber, the depth, cover loading, wall thickness and pipe or duct openings.
6. Cable Troughs
Typically open and easily accessible cable routing area, troughs can be fitted with removable or hinged lids allowing access to the area for easier maintenance than a totally enclosed duct system. They can be found in data centres, solar farms and industrial plants, anywhere where there are a lot of cables and need to return to the area in the future for inspection or to install more cables.
7. Docking Bay, Wave Attenuators and Silt Fences
Precast equipment pads and light pole foundations are used for factory-prepared foundations for above-ground equipment and structure such as street lighting and transformers, the last in the category. They are pre-embedded with conduit routing and anchor bolts and are ready to install, requiring no curing time or formwork on site to set and install the utilities.
That’s All This and More in the Standards That Tie This All Together
In almost all these types of structures, the structure type is represented consistently in American standards repeatedly used in the specifications, overseas and more and more in the UAE market. There are four ASTM standards relating to precast concrete underground utility structures: ASTM C857 specifies minimum structural design loading requirements, ASTM C858 specifies the requirements for precast concrete utility structures, ASTM C891 prescribes the installation practices and requirements, and ASTM C1037 sets forth the requirements for the inspection of precast concrete utility structures.
In most cases, UAE-based precast suppliers would refer to a combination of these American standards, in addition to British Standards and the specific requirements of the UAE municipalities, and ultimately form a multi-layered compliance programme for projects rather than a single document. Ask any supplier and they will tell you the standards they have for the type of structure, and if they don’t tell you, it isn’t likely to meet the needs of a structure that may be in the ground for decades.
The Exception of the Concrete, Coordination Is the Real Challenge, Not the Concrete
Typical building types have logical and well documented technical conditions that are easily read and understood. The real challenge on any project in UAE is coordinating between the design consultant, the contractor and precast supplier, especially if the site has multiple utilities including drainage, telecom, electrical, water etc., and all utilities have their own set of chambers and ducting which have to fit around the others without clash.
Projects with multiple vendors working on various aspects of supply, delivery and installation can cause coordination challenges that cannot be witnessed in projects managed by a single vendor responsible for the entire project. If there are a variety of underground utilities in your project, it might be prudent to inquire at the outset about how design coordination will be achieved between the utilities.
The Bottom Line
Precast concrete is a large and varied class of underground utility structures such as vaults, manholes, pull boxes, duct banks, chambers, troughs and equipment foundations, each to which a different set of ASTM, British and municipal standards apply. The consistent speed and consistency that these structures offer are what makes them favoured for use throughout the UAE, particularly in weather conditions that have the potential to affect the construction schedule. When constructing new infrastructure or replacing existing utilities, specifications and coordination are correct; these structures do what they are supposed to do – unobtrusively, quietly, dependably and for decades.
