Evaluation of Structural Integrity of Underground Concrete Water Storage Tanks

[KHoff]

I have been contacted to evaluate the structural condition of three underground concrete water storage tanks, the largest of which containing 500,000 gallons of water. I don't believe there are any known issues, I believe this evaluation is part of a regular maintenance schedule.

I am comfortable with and have experience in evaluating concrete structures. However, I do not have experience specific to water storage tanks. I am unsure how easily I could inspect the concrete structure if it is covered by a liner. Are there any other concerns or issues specific to water storage tanks? Any references that may be of use?

I appreciate any input.

 

[ATSE]

Not a project to venture into without experience. Look to a very senior experienced engineer with water experience, and AWWA and ACI for guidance.
Usually, before an engineer gets involved, a diver documents the inside of the tank (concrete or steel) with digital photos and video, and writes a summary report.
The plant operators should have some idea of how much the tank leaks (X gallons per day).
If you are in seismic country and the tank is more than 30 years old, then it might be a candidate for a retrofit.
Otherwise, evaluating a structure - especially with a liner or high performance coating - without any known problems can be uneventful.

 

[JedClampett]

A few things:[ul][/ul]
[li]Do you have confined space training? If these meet the criteria for an OSHA confined space (they almost certainly do), you'll need a permit, attendants, gas monitoring, etc..[/li]
[li]A liner will make it very difficult. You can't evaluate what you can't see. Taking samples of the liner where it won't cause a problem is a good idea. There's labs that test them.[/li]
[li]These are small tanks. You might be able to evaluate them from the inside when they're drained. For deeper ones, most of the issues concern the roof, and that means leaving the tank somewhat full and going in with a rubber raft that gets you up close and personal.[/li]
[li]Take a lot of pictures. With a digital camera, you can practically get unlimited ones. The camera shots are better than your eyes, plus you can magnify them (the pictures, not your eyes). Water resistance is a must. Sometimes if you're illuminating an area with a flashlight the flash won't work, so it's a little tricky. Make sure your battery is charged and your memory chip is not full. It's almost impossible to take pictures and record what you're looking at at the same time, so plan on sitting down and labeling the pictures immediately when you get out. These are your legal record that the tank was good (or bad) when you went in.[/li]
[li]The rest is common sense. Cracks are bad. Spalls are bad. Bring a hammer and hit the wall (where there isn't a liner) and listen for a hollow or ringing sound. Ringing is good, hollow is bad. Plus the owners love to watch an engineer lugging a bunch of equipment into a tank and coming out looking like a wet dishrag.[/li]
[li]It might be better to go in with another engineer or assistant. Measuring, taking pictures, noticing things is pretty busy work.[/li]