Designing a buried pipe? Be sure to avoid these common—and potentially costly—mistakes.
The design of buried pipe encompasses many of the basic civil engineering concepts we learned in college: hydraulics, soils engineering, and structural engineering. Yet, I’m willing to bet most of us didn't take a class specifically dealing with the design of buried pipe. Thus, it's easy to miss some of the finer nuances when designing buried pipe. Here are some areas where we have seen issues throughout our years in the industry.
1. Relying on the installation more than the pipe
Pipe gets built in the manufacturing plant in a controlled environment, whereas the installation surrounding the pipe gets built in whatever Mother Nature provides. So, when the going gets tough, why ask the contractor to produce miracles? (Remember the saying, "it is not nice to fool with Mother Nature.") The pipe producer can typically build a product to accommodate the environment.
#ProTip – Just because you can't find a standard class of pipe, doesn't mean our manufacturers cannot make what you need. Contact a manufacturer near your location to discuss your options.
2. Blindly using fill height tables
It sure is easy to look up what you need in a reference/fill height table, isn't it? No calculations involved! But somewhere along the way, calculations were performed to develop those fill height tables. Do you know what assumptions were made in those calculations? Do they match your site conditions?
#ProTip – Take a moment to review what assumptions were made and see if they match your site conditions. If the assumptions and your reality don't align, it's worth your time to calculate the correct value.
3. Using direct vs. indirect design
Of course, you can calculate the stress and/or strain in the pipe based upon a particular soil-structure model for the pipe and its installed condition, and then specify the required properties of the pipe based on your direct design. Or, you could determine the load on the pipe, utilize a simplified relationship between the installed condition and a test condition in the plant, and employ an indirect design method to establish proof of performance of the pipe. Both methods have their uses.
#ProTip – Generally speaking, if you can find reinforcement requirements for the pipe in the tables of ASTM C76/AASHTO M170, Standard Specification for Reinforced Concrete Culvert, Storm Drain, and Sewer Pipe, then the indirect design method is your best bet. If you can't find reinforcement values in C76/M170, then you'll be performing a direct design.
4. Overlooking Pipe Joint Requirements
5. Cut-and-Pasting Specifications
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