Above ground storage tanks are commonly used for petroleum and refinery. They are also used in industrial plants as storage for crude oil, liquid fertilizer, molasses, and other chemicals. Most of these chemicals can cause potential health and environmental hazards, so thorough planning is put into the design and construction of these tanks.
The strength and stability of an above ground liquid storage tank depends on many considerations and one of them is the tank’s foundation. The strongest, most expensive materials can be used to construct an above ground tank, but if it is built on a weak foundation, it may soon encounter problems during its operation.
Choosing the right foundation is crucial to ensure not only an above ground storage tank’s structural integrity but also the safety of the workers involved in its construction, operation and maintenance. The most common types of materials used in constructing a tank’s foundation are earthen, pile and concrete.
While the materials used in building an above ground storage tank is important, the design of its foundation is also as significant. Below are some foundation designs for above ground storage tanks.
Earthen Foundation without a Ring Wall
This foundation design is frequently used in the construction of small tanks and when the subsurface conditions are tested to have adequate load bearing capacity. For additional stability, compacted crushed stone, fine gravel, clean sand or similar materials may be placed directly on the soil bedding.
Earthen Foundation with Crushed Stone and Gravel Ring Wall
This type of design is recommended for large diameter tanks. The crushed ring wall makes the foundation more capable of supporting the heavy load imposed by the tank’s shell especially during construction. The ring wall also evenly distributes load concentration at the bottom of the tank in a granular pattern. Another advantage of this foundation design is that it retains the fill under the tank, preventing materials from eroding.
Earthen Foundation with Concrete Ring Wall
Foundations with concrete ring walls, like those with crushed stone ring walls, are also common in building large tanks. In addition, an earthen foundation with a concrete ring wall is also used in smaller tanks, tanks with heavy or tall shells and/or tanks with self-supported roofs. This type of design allows better uniform load-bearing capacity and also minimizes moisture under the tank. Like crushed stone and gravel ring walls, concrete ring walls also prevent material loss during erosion.
Reinforced Concrete Slab Foundation
This type of foundation is suitable for all kinds of storage tanks, especially those that are constructed in areas where a significant amount of underground water is present or the soil bedding is weak. Compared to other foundation types, reinforced concrete slab foundations are more expensive to construct.
Hiring experts in geology, architecture and engineering is also imperative when designing above ground storage tanks. Factors such as soil composition, seismic activity and weather disturbance need to be properly assessed as they can also affect the structure’s performance and longevity. Safety professionals also need to be consulted to make sure that the storage tank’s construction complies with workplace health and safety regulations.