“It is not the beauty of a building you should look at; it’s the construction of the foundation that will stand the test of time.” – David Allen Coe
The importance of the foundation for an aboveground liquid storage tank is often overlooked or minimized. A tank’s foundation, however, is one of the main factors that determine the quality and longevity of a storage tank. A soil and seismic appropriate foundation creates a more stable tank that usually has a longer service life. A poor, weak foundation will give in inch by inch to the structural and capacity load it bears as well as the natural forces of wind, water, and earthquakes. Impact from these forces can result in excessive or uneven settlement; water pockets causing corrosion on the underside of the tank; tank floor breakover, bulges, or buckling; additional stresses on the tank shell based on tank floor movement; and in extreme cases, tank failure.
The three main types of foundations for aboveground liquid fertilizer storage tanks are earthen, pile, and concrete foundations.
So what is the correct foundation for an aboveground storage tank?
The answer is it depends. The two major factors involved in the determination of the appropriate foundation are soil composition and whether the area is subject to seismic activity. The soil composition and what is underneath the site is usually the most critical determination when choosing the correct foundation. Below are suggested steps to take to discover the conditions of the future tank site in order to build the best foundation for the tank.
First, hire a good engineer. Yes, this costs money. However, it will be worth every penny over the life of the tank. Particularly engineers who frequently work with tank projects know the areas that are subject to earthquake requirements, how to read soil composition reports, and the best methods on constructing a solid foundation. A solid foundation will prevent all of the issues listed above and permit the tank to keep a higher maximum fill level over the liquid storage tank’s lifetime. A higher maximum fill level means more product, resulting in more revenue.
Second, have geological evaluation and soil borings conducted on the site. Such critical tests reveal whether the soil contains troublesome materials, such as peat, soft clay, loose silt, or fine sand. Other issues that can be discovered are whether the site has “leftovers” in the subsurface from prior use, such as filled in basements, underground storage tanks, underground bomb shelters, etc.
If any soil or foundation support issues are discovered, the engineer will suggest remedies to improve the site. These remedies can range from addressing any old subsurface structures, performing soil improvement by using soil additives to improve the existing soil, and moving and compacting a suitable soil mixture to create a solid earthen foundation. If soil amendments can be added and then compacted with the current soil, an earthen foundation is usually the best, economical type of foundation.
If soil amendments are not enough, there are other options. Piling is an option when tank sites that have extremely poor soil conditions and the aboveground storage tank site cannot be moved. Piling involves drilling or driving columns into the soil in the foundation area made of concrete, steel, or stone. These underground pillars create additional support for the tank to prevent extreme and uneven settling. Piling tends to be a much more expensive solution, so it may be more cost effective to find a different location for the liquid storage tank if a particular site requires piling.
The final choice is using a concrete foundation. Because this requires large quantities of material and labor to form the foundation, a concrete foundation is also a more expensive foundation choice. Earthquake zones, however, usually call for concrete foundations to assist in anchoring the tank to the foundation to prevent significant movement. Again, having an engineer is key in building a tank to ensure that a foundation is built properly to withstand the forces of nature to which a tank is subjected in seismic region.
Choosing the proper foundation for an aboveground liquid fertilizer storage tank is one of the critical decisions that significantly impact the overall quality of the end tank. Rely on the experts in engineering and geological science to get the hard facts on which foundation is best for your future storage tank.
If you have questions about engineering the best foundation for your tank, contact the engineers that Heartland Tank Services partners with: W Design Associates at (308) 345-2370.
Have general aboveground storage tank questions? Contact us.