When it comes to designing large storm sewer conveyance systems, did you know there are alternatives to reinforced box culverts? For years, Contech has worked with engineers and agencies across the country on finding efficient and effective ways to move stormwater. Traditionally, you may be used to defaulting to concrete when looking at larger systems, but have you ever heard of Smooth Cor™? Smooth Cor™ double wall is a hydraulically efficient (manning’s “n” = 0.012) corrugated metal pipe (CMP) product that combines the strength of a corrugated outer shell, a smooth steel liner, and the durability of a polymer coating! By combining both strength and durability, Smooth Cor™ represents a cost-effective and installation friendly alternative to concrete box culverts ranging in size from 3’ x 3’ to 7’ x 7’ or more. Because of the strength to weight ratio of steel, you are able to get longer lengths (up to 25’) at much lower weights. Even the smallest 3’ x 3’ concrete box can weigh up to 1,120 lbs/ft compared to a 42” Smooth Cor™ that can weigh 60 lbs/ft! These longer lay lengths and lower weights directly correlates to quicker and cheaper installation. It only gets better as you go up in size!
To prove this point, we had a project in Alabama where an owner was trying to find the best option to connect 2 pieces of property over an existing gorge. Initially, the owner looked at a 7’ x 4’ RCB, but after much evaluation, they decided to use a 72” Smooth Cor™ double wall due to quicker delivery (7 trucks vs. 19 trucks) and shorter project timeline, equivalent hydraulic capacity, extended durability, installation time (12 hours vs 48 hours), number of joints (14 vs 56) and the cost effectiveness of the system. Not to mention, this was being designed to handle RR loading! In addition, this system was going to handle a pretty significant height of cover. CMP’s unique ability to transfer load from the pipe to the surrounding compacted backfill allows for much greater fill heights, up to 70+ feet!
Another huge benefit of CMP vs. concrete boxes or concrete pipe is inline fittings. We had another large project at an air force base in Georgia that required over 8,000 LF of pipe with many inline fittings along that run. Inline fittings are a bear with concrete. With CMP, they can be made right into the pipe, so the installation is a breeze! On this project, the contractor was able to save time and money by going with Smooth Cor™ while not losing any hydraulic capacity or durability. The polymer-coated pipe was designed to carry stormwater and the occasional jet fuel leak! This installation was done back in 2002 and is still going strong today!
In the end, you have choices when it comes to large storm sewer systems. Not all products were created equal and there are advantages and disadvantages to all of them. Just knowing you have options puts you in the best position, and Contech is here to help you navigate them when needed.