I’m overseeing the plans and specifications for construction of a 100,000 gallon AWWA D103 water tank with a bolted steel shell and floor that my company is purchasing. The tank is being constructed in an area with frequent significant seismic activity (Los Angeles). The current design calls for a concrete ringwall installed under the tank shell. The area inside the ringwall consists of a minimum 3” layer of sand on top of a compacted fill. The dimensions of the tank are such that no seismic anchoring is required from a design standpoint.
The contract specifications call for a shimmed 1” space between the bottom of the shell and the top of the ringwall to be completely filled with grout. However, the contractor is proposing that we dispense with this method, and instead install a ½” pad made from fiberboard expansion joint material (conforming to ASTM D1751), that would line the entire tank bottom. I suspect that the contractor wants to use this method because it is faster and cheaper than the grouting method.
It is my understanding that one of the most important aspects of tank longevity is the degree to which the shell is planar and true, and remains that way over time. Am I wrong to assume that this is best accomplished by grouting the bottom of the shell to the top of the ringwall? Substituting fiberboard, it is unclear to me what exactly the fiberboard is doing structurally. Apparently it is mentioned in API 650 as a way to minimize water infiltration underneath the tank bottom and corrosion of the portion of the tank bottom in direct contact with the concrete ringwall. It seems like this material could degrade over time.
AWWA D103 allows for both methods, as does FM 4020/4021. However, the FM spec prohibits the fiberboard method from being used in areas with significant seismic activity. The contractor claims that with the fiberboard method, if the tank bottom has a significant leak, the fiberboard will provide a leak path to the edge of the tank, where the leak will be seen. In contrast, he says that with the grouting method, you will never be able to tell if the tank bottom is leaking. I don’t know if I buy the statement about leak detection – I thought the fiberboard was supposed to prevent movement of water under the tank, not conduct it. However, I am concerned about the possibility of never being able to detect a leak in the tank bottom. Are there any methods to detect this without removing the tank from service? Would it work to place a waterproof membrane under the sand layer and include an array of weep-holes around the top of the ringwall? Or, perhaps a leak-detection pipe buried under the tank with an inlet at the center and a discharge outside of the tank footprint?
Finally, with regard to the grouting method, what becomes of the steel shims that are used to control the gap before grouting? Are they left embedded in the grout? Are they pulled out after the grout sets? If anybody can point me to information detailing this practice, I’d much appreciate it!
The contract specifications call for a shimmed 1” space between the bottom of the shell and the top of the ringwall to be completely filled with grout. However, the contractor is proposing that we dispense with this method, and instead install a ½” pad made from fiberboard expansion joint material (conforming to ASTM D1751), that would line the entire tank bottom. I suspect that the contractor wants to use this method because it is faster and cheaper than the grouting method.
It is my understanding that one of the most important aspects of tank longevity is the degree to which the shell is planar and true, and remains that way over time. Am I wrong to assume that this is best accomplished by grouting the bottom of the shell to the top of the ringwall? Substituting fiberboard, it is unclear to me what exactly the fiberboard is doing structurally. Apparently it is mentioned in API 650 as a way to minimize water infiltration underneath the tank bottom and corrosion of the portion of the tank bottom in direct contact with the concrete ringwall. It seems like this material could degrade over time.
AWWA D103 allows for both methods, as does FM 4020/4021. However, the FM spec prohibits the fiberboard method from being used in areas with significant seismic activity. The contractor claims that with the fiberboard method, if the tank bottom has a significant leak, the fiberboard will provide a leak path to the edge of the tank, where the leak will be seen. In contrast, he says that with the grouting method, you will never be able to tell if the tank bottom is leaking. I don’t know if I buy the statement about leak detection – I thought the fiberboard was supposed to prevent movement of water under the tank, not conduct it. However, I am concerned about the possibility of never being able to detect a leak in the tank bottom. Are there any methods to detect this without removing the tank from service? Would it work to place a waterproof membrane under the sand layer and include an array of weep-holes around the top of the ringwall? Or, perhaps a leak-detection pipe buried under the tank with an inlet at the center and a discharge outside of the tank footprint?
Finally, with regard to the grouting method, what becomes of the steel shims that are used to control the gap before grouting? Are they left embedded in the grout? Are they pulled out after the grout sets? If anybody can point me to information detailing this practice, I’d much appreciate it!
