How high should granular backfill of a standard underdrain be placed above the top of the collector pipe?

The recommended height for granular backfill to be placed above the top of the collector pipe in a standard underdrain system is 12 inches. This specification ensures that there is adequate support and protection for the pipe while allowing for proper drainage.

Placing the backfill at this height allows the underdrain system to function effectively by ensuring that the soil above the pipe has a sufficient depth to prevent any surface loads from adversely affecting the pipe's structural integrity. Additionally, this height promotes effective water flow towards the drain, minimizing the risk of clogs and enhancing the overall performance of the drainage system.

In highway construction, it’s critical to adhere to these standards to maintain the durability and functionality of drainage installations. When applying different heights than specified, there can be negative consequences, such as insufficient drainage or stress on the underdrain, leading to potential failures in the overall system.