Out of Sight, Out of Mind

The proverb “Out of sight, out of mind” all too often pertains to buried pipelines. You’ve likely seen references to “Call Before You Dig”, or “DigAlert”, which are services to have underground utility lines located and marked.  But on an active construction project, that service is not usually available.  The pipe installation contractor has a responsibility to protect what they have built, so it’s incumbent on the pipe installation contractor to locate and mark the pipe location once it’s been buried and is “out of sight”.

Frequently, it is necessary for heavy construction equipment to travel or operate over installed pipelines during completion of grading, paving, or activities by other trades involved in the project.  But construction equipment loading can often be much greater than what the pipe was designed to carry (i.e., AASHTO vehicle).

Protecting the pipe from heavy construction equipment may require more cover to be placed over the pipe than the finished design cover height.  The amount of additional cover needed depends upon the specific equipment that will travel or operate over the pipe.

There are three types of equipment that are commonly used on construction projects: Rubber-tired equipment, tracked equipment, and equipment employing outriggers.  We have generated cover-height tables for these types of equipment for all our pipe types.  The contractor will need the following information about their equipment to utilize the construction equipment cover-height tables:

·         For rubber-tired equipment – identify the maximum axle load when fully loaded (gross vehicle weight is not needed to use the tables).

·         For tracked equipment – identify the track ground pressure and the track shoe width.

·         For vehicles employing outriggers – identify the maximum outrigger load and the size of the outrigger (diameter or width x length).

If the tables indicate additional cover is required over the top of the pipe than currently exists, then place that fill over the pipe where the equipment will travel or operate.  For travel lanes, the width should be roughly twice the pipe span.  For operation pads the width should be twice the width of the equipment or twice the outrigger spacing.  For multiple-barrel pipe installations, the additional fill should be placed evenly across all barrels.

The additional cover required over the pipe can be temporary if final design grade is less than that needed for construction equipment loading.  However, the temporary cover must be maintained such that rutting, or surface grading does not reduce its effect.  If the temporary cover needs to be reduced for final grading and paving, the equipment used to lower grade should be verified for safe operation at the reduced cover.

“Out of sight” is a common state for buried pipelines, but “Out of mind” can result in problems.  Protect what you have built by heeding our construction equipment cover-height tables and ensuring that the other trades involved with your project are made aware of the pipe location and cover requirements for their construction equipment.