When we set out to write a specification for a flexible pipe system it is important to remember that flexible pipes are composites of both the pipe and the compacted backfill around the pipe. Most specifiers do a very good job of specifying the pipe itself. They use AASHTO, ASTM, DOT, County, or Municipal specification sections or numbers to call out the pipe or pipes that are acceptable for the particular installation or bid item.
Sometimes however, the specifier will leave out the other two necessary and important specifications for flexible pipe systems. These two components of the composite system are the backfill materials and the backfill material placement procedures. Acceptable backfill materials and placement procedures go hand in hand with the selected flexible pipe system to accomplish a quality installation.
The proper specifications for the acceptable backfill materials and placement procedures can be found in industry guidelines, AASHTO, or ASTM specifications, but the particular State Department of Transportation Standard Specifications many times is the best specification to choose from. This is because they take into account the local materials that are available and are always available to the contracting community. Most contractors who install flexible pipe systems will have both a printed copy of the DOT specs on the shelf and a copy on the computer.
Not specifying the backfill materials and backfill placement procedures can lead to bad installations, change orders, and arguments so when specifying a flexible pipe system be sure to specify the acceptable pipe, the acceptable backfill materials, and the acceptable placement procedures and you will be assured to get the system that the owner has paid for.