Precast concrete Underground tanks in the UAE are among the most useful solutions for water storage, waste water management and fire protection reserves in the UAE construction projects.
From a villa community that requires a septic tank to an industrial facility that demands a fire water reservoir or a commercial development that calls for an underground reservoir that is invisible, precast concrete underground tanks offer a structural integrity that site cast containers can’t match.
With the growing value of land in Dubai, Abu Dhabi and Sharjah, developers are increasingly turning to sub surface areas to release surface space for landscaping, parking or for other built up areas, while precast tanks ensure durability without sacrificing space.
The Advantages of Precast Concrete for Underground Storage
Underground tanks are produced in a factory to the highest standards, transported and installed in sections or whole units. This method reduces a number of variables that can impact cast-in-place concrete, such as the curing conditions, formwork construction accuracy, and exposure to weather conditions. In a factory environment, all the concrete is mixed, vibrated and cured in the same manner, resulting in a more uniform, denser, and less voidy product, and therefore, a lower number of cracks are likely to develop when the tank is installed in service.
In addition to its inherent compressive strength, concrete is also well suited for use in underground applications due to its resistance to sustained loading from soil, groundwater, and surface traffic over the top of the tank. This natural strength is combined with reinforcement detailing, waterproofing membranes and protective coatings to deal with the risks that are unique to underground structures and especially the risks of water ingress, and in high groundwater environments along the UAE coastline, the risk of chemical attack from saline soil conditions.
Another big plus is the speed. When a precast tank is delivered to site it’s installed ready to go, allowing contractors to dig, bed the tank, backfill and proceed with the next part of the project within days of delivery, instead of weeks. This is important on UAE construction sites where projects are time-sequenced and where delays result in a significant cost. It allows contractors to immediately backfill following installation, ensuring the project can remain on schedule with quality work performed.
Site Conditions and Design Considerations in the UAE
The UAE has certain underground conditions that need to be taken into consideration when designing tanks. Concrete curing is hastened with high ambient temperatures, and can have a negative impact on long term durability if these conditions are not closely monitored and controlled during the concrete mixing process. The coastal regions around Dubai, Abu Dhabi and Sharjah are also affected and have high salinity in ground water that over time could cause damage to buried concrete due to sulfates and chlorides. Responsible manufacturers would do this by stating that the cement blends used are sulfate-resistant, they would add more concrete cover over reinforcement, and make arrangements for external waterproofing systems before the tank is filled in.
Groundwater levels vary considerably from one part of the emirates to another and in low-lying or coastal areas buoyancy is a serious engineering problem. If not properly designed with sufficient weight, anti-flotation collars, and/or anchoring, an empty or poorly filled underground tank located in a high groundwater area may be subjected to uplift pressure that will cause the tank to shift and/or crack. Another consideration of the bedding design is the type of soil: sand is found in many parts of the UAE and in such conditions it is necessary to carefully compact the bedding layers so as to spread the weight of the tank evenly and avoid differential settlement.
Project teams must take regulatory approval into account as another factor to plan for. Underground drainage and storage structures are inspected for compliance with recognised standards by municipalities throughout the UAE, including Dubai Municipality. ASTM C478 is widely referenced in the precast concrete manhole and chamber industry for precast sections for sewer, drainage and water use applications, and is recommended to satisfy municipal specifications. Underground tanks that are connected to drainage or water networks will generally be considered within the same frameworks and manufacturers that have already proven themselves with municipalities will save a significant amount of time in the approval process.
Technical Range and Configuration Options
Underground tanks are not one product but a variety of products with a variety of capacities, shapes and finishes depending on end use. The typical water storage tanks for villa communities, staff houses or even for small commercial sites begin from a few thousand litres up to several hundred thousand litres, and can be made from a number of precast sections which are joined and sealed on site, rather than cast as one large, oversized tank. The shape of the tank is determined in large part by the site size: cylindrical tanks are best for open sites because the internal pressure is distributed most evenly across the interior surface; rectangular tanks are more efficient for small or irregular sites where every square metre of buried area is important.
Interior finishes are determined by the contents of the tank. Food grade epoxy or polyurethane linings are required for potable water storage while septic and wastewater tanks are specified with corrosion resistant coatings and access chambers for maintenance and desludging. Fire water storage tanks, which are becoming more common on commercial and industrial projects, have their own sizing and outlet configuration requirements to integrate with fire pump systems and aligned fire protection design to meet the requirements of NFPA. Manufacturers are selling cylinders from approximately 5 kilolitres for small use up to 500 kilolitres for large reservoirs for municipalities; and cylindrical, rectangular and custom-profiled shapes for tight sites.
Manufacturing Process
Production starts with a mix design that considers the tank’s service environment—whether it will be used for storing saline groundwater or in a structure carrying structural loads—along with the sulfate resistance, compressive strength and other requirements once the tank is in the ground. Reinforcement cages are manufactured to drawing requirements and fitted into the formwork prior to pouring, making sure that the depth of cover over the steel is correct so that it will not corrode in the long-term. Mechanical vibrating is used to remove air voids and minimize porosity for concrete, as one of the primary sources of water intrusion and durability problems in underground structures.
It is cured in the factory environment and NOT in the exposed site environment, ensuring that the concrete is cured to the designed strength without fail prior to leaving the yard and entering the tank. Waterproofing is applied after curing, either as an integral admixture, or as an external membrane, or as a combination of the two; joint sealing details are completed to a level of quality that will meet the requirements of the backfill material and/or load. CAD and BIM modelling has become a core part of every precast facility’s workflow, with many starting to use CAD and BIM to coordinate the positioning of all tank inlets, outlets and access points with the project’s civil and MEP drawings prior to manufacturing.
Achieving Quality Assurance and Compliance
The quality control and assurance process on underground tanks is not limited to a final inspection, but is extended across the entire process of manufacturing tanks. This usually involves strict compressive strength and slump testing of each batch of concrete, and inspections of reinforcement setting and final curing. Most tanks designed for water storage have some sort of watertightness testing before they go to the customer; if a leak is found in the factory, it is much more inexpensive to fix that leak than it is after the tank is installed and backfilled.
The documentation is as important as the physical testing. Records created by the manufacturer to meet regulatory requirements and the client’s internal audit, especially for projects that need to be handed over for facilities management or municipal sign-off are maintained. The use of a manufacturer which processes quality systems that meet the internationally recognised standards, together with the ASTM references that cover the production of precast drainage and water structures in the UAE, minimises the risk of delay at inspection and approval stages.
An Overview of Applications Across UAE Projects
A large section of the UAE construction industry uses underground tanks. They are the basis of the storage of potable water and septic systems, especially in the case of residential villas which are not yet connected to municipal sewage systems. Large underground reservoirs are used to store reserves for fire, process water or effluent for pre-treatment in industrial and logistics facilities. As commercial development demands building up to the ground, with a focus on water security and drainage, the specification of underground storage is becoming more frequent. Underground tanks and chambers are components of drainage and stormwater control systems for government and infrastructure projects such as roads, airports and utility corridors.
The Time Required to Deliver and Install the Site
Precast concrete Tanks are manufactured and are transported to site on flatbed or low-loader trailers depending on the size of the tank, and larger sectional tanks are shipped on flatbeds or low loaders as separate sections to be assembled on site. Site teams dig to a depth of the tank, form a compacted level bedding layer and then place the tank on a crane that is suitable for the weight of the tank. The entire procedure is completed almost at once after the tank has been set, sealed and, as needed, anchored to prevent ground water uplift and the surrounding works can continue without a cure-up period because the concrete is already fully cured when it is poured at the factory.
Request a Tank Specified for Your Project
The size, type, material and placement of underground tanks can differ from project to project, depending on the soil and groundwater conditions, the tank size and capacity, and the end use. If they are not specified correctly before the tanks are manufactured, the project will be time-consuming and costly in the future. Whether for water tanks, septic tanks, or underground storage, Solid Rock Concrete Works collaborates with contractors and developers in Dubai, Abu Dhabi, and Sharjah to tailor designs that meet the specific requirements of the UAE’s soil and regulatory environment. Connect with our technical team to review the project’s capacity, site conditions and delivery.
