Utility Trenches

Utility trenches are needed for a variety of different applications.  The most common applications are for compressed air, water, gas, refrigeration, or electrical needs.  We often see utility trenches in automotive shops, manufacturing facilities, car washes, aircraft hangers, schools, grocery stores, hospitals, laboratories, computer rooms, electronics stores, retail stores, mechanical rooms, etc.  All of these facilities have one common need, they need a utility in a location other than where it comes into the property or building.  Some businesses simply need a way to access utilities so that when technology changes the wires or pipes can be updated.  Others use a utility trench to allow for flexible access points to the utilities.  Still others need utilities at certain "work stations" without having cables in the way of objects moving around in the building.  For some it is simply to achieve a cleaner look.


There are a variety of systems for this purpose.  Some are precast trench units while others are forming systems.  Most offer a method of hanging pipes or conduits inside them.  Make sure that the product is suited to your application as some are designed for very different needs.



 

Sizing the trench
  • Utility Trenches are generally sized for the type, size, and quantity of pipes, lines, or conduits that will be running through them.
  • Make sure that the trench is large enough to accommodate the pipes as they make turns.  In some cases it may be necessary to enlarge utility trench intersections or make trench turns with multiple 45 degree angles in order to handle the long sweeps of larger pipes.
  • Even though the trench is for utilities, if there is any possibility of ever getting fluid in the bottom it should have some type of drain pipe.  Secondary containment trenches often utilize piping that has a valve that goes to a decontamination tank, water treatment, or neutralization system.
  • Typically a utility trench is more cost effective to go deeper than wider to accommodate multiple pipes.  Exceptions to this rule are when the depth exceeds 48" or in some cases if there is pedestrian or no traffic.

Choosing the channel
  • If highly corrosive or caustic chemicals will be piped inside the trenches it is best to select a trench body that has chemical resistance and to properly seal the joints in the trench.  For Fiberglass trench joints a two part epoxy will work, for stainless steel the joints should be fully welded, and for plastic trenches the joints should be fully welded.
  • Make sure the anchoring system for the pipes is sufficient to handle the weight of the pipes, conduits, and wires that you will be hanging from them.  Anchors along the walls are best so that you can hang the pipes vertically allowing for access to all of the different utilities.
  • Be sure that the body of the trench has a frame capable of handling the traffic that will be over the top of it.  A common mistake is to select a channel with no frame and a heavy duty cover plate.  While the cover plate may handle the traffic the channel could fail underneath it.

Selecting the grate / cover
  • Covers for utility trenches are offered in almost any material.  Forklift traffic should use either ductile iron or heavy steel plate covers.  Lighter duty traffic options include aluminum, stainless steel, fiberglass, plastic, covers that accept tiles or carpet, etc.
  • Utility trench covers are typically solid, but open grating can also be used.  Solid covers can be sealed in place if water needs to be kept out of the trench.
  • If the trench cover is in an area of changing temperatures, high humidity, or wet processes the trench covers should be embossed in some fashion.  Trench covers are notorious for being slick and are a potential hazard for the work force.  Checkered plate or coatings with grit are common ways to avoid this liability.
  • Trenches that will require frequent access should have covers that can be easily lifted and placed.  The length of the plates should be limited to keep the weight manageable.  Consideration should be given to lifting eyes or lugs when the weight will be excessive.
  • When using the trench as a secondary containment trench it is wise to use some open grating in strategic areas for visual inspection purposes.  Also, consider a sump location with an electronic detection system for monitoring the containment system.

Designing the layout
  • Turns and intersections are common place and necessary in most utility trench layouts.  Try to keep turns out of fork lift traffic isles as the concrete can easily spall at these turns.  If you do place a turn where fork truck traffic is frequent you also need to reinforce the grating underneath the intersection because the frame will have no support.  An embedded beam or tubing is typical..
  • Cost savings can be realized if trenches can be placed under large equipment where no covers or lighter duty covers can be utilized.
  • Consider "bumping out" the trench where there might be workstations or frequent access to the trench utilities.  This will give a larger area for connections and allow for a hinged cover for easy access.