By Bob Moore
| Tuesday, December 01, 2015 | 3807 Views |
What sanitary sewer pipe on the market today was first installed while John Kennedy was our nation’s president? TRUSS PIPE is the answer.
After WWII and the Korean War there was an explosion of residential and commercial building along with sanitary sewer across our country. With all the new building construction, there was a desire to find a more reliable sanitary sewer product than Vitrified Clay Pipe and Reinforced Concrete Pipe.
After years of research and development, Ashland Oil Company designed TRUSS PIPE. Contech Engineered Solutions LLC (formerly ARMCO Construction Products) purchased the product line in the early 1960’s and began manufacturing and marketing the product across the USA. Since then, hundreds of millions of feet of TRUSS PIPE have been installed and are in operation.
Designed for sanitary sewer applications, Contech TRUSS PIPE is a thermoplastic composite pipe available in 8”, 10”, 12” and 15” diameters. The unique wall design consists of a double-wall system with concentric inner and outer plastic walls braced by a truss-type structure. The truss voids are filled with Mearlcrete for additional pipe stiffness and compressive strength. The 200 psi minimum pipe stiffness provides unparalleled deflection control among thermoplastic gravity sewer pipe. (TRUSS PIPE has over four times the pipe stiffness of PVC SDR 35.)
High Pipe Stiffness
A buried pipe must possess sufficient stiffness to limit pipe deflection during installation and resist pipe buckling. Generally this deflection is limited to a maximum 5% of the pipe diameter. Controlling flexible pipe deflection depends on the combined contribution of the pipe stiffness and backfill soil stiffness.
If pipe and soil stiffness together help prevent pipe deflection, why is a high pipe stiffness (as described by ASTM D2412) desirable in small diameter sanitary sewers?
Unlike large diameter sewer pipe where deflection is easier to control (with quality backfill, small backfill lifts, and wide trench widths where proper mechanical backfill compaction can be achieved); most small diameter sanitary sewer pipe is constructed under high fills using safety trench boxes where the backfill is dumped and not mechanically compacted. As shown the attached photo.
When backfill is dumped and not mechanically compacted, it does not supply as much structural support around the pipe (lower soil stiffness). In these cases, it is important to have a high pipe stiffness to prevent deflection and possible collapse of the sanitary sewer system. TRUSS PIPE, with a 200 psi pipe stiffness, provides the necessary pipe stiffness to help prevent pipe deflection in small diameter sanitary sewer construction.