Wet Utility

What is ductile iron pipe (DIP)?

A strong, flexible iron pipe used for force mains and water/sewer under high pressure or in difficult soil conditions. Joined with push-on or mechanical joints. Comes in pressure classes.

What is HDPE pipe?

High-Density Polyethylene pipe — a flexible, corrosion-resistant plastic pipe used for force mains and gravity sewer. Joined by butt fusion or electrofusion. Excellent for difficult alignment.

What is concrete pressure pipe (RCCP or PCCP)?

Reinforced or prestressed concrete cylinder pipe used for large-diameter pressure mains. Heavy and strong but requires careful handling and installation. Common in large transmission mains.

What is PVC pipe in sewer applications?

Polyvinyl chloride pipe used for gravity sewer. Lightweight and easy to install. Joined with gasketed bell and spigot. Must be bedded properly to maintain grade.

What is pipe bedding?

The material placed under and around a pipe in a trench to provide uniform support and protect it from point loading. Class of bedding affects load-bearing capacity.

What is a pipe zone?

The portion of the trench from the bedding up to 12 inches above the pipe crown. Bedding and pipe zone material are critical to pipe performance.

What is dewatering in excavation?

The process of removing groundwater from an excavation to allow work to proceed in dry conditions. Methods include wellpoints, deep wells, sump pumping, and cutoff walls.

What is a wellpoint system?

A shallow dewatering method using a series of small-diameter wells connected to a header pipe and vacuum pump. Effective for lowering the water table 15–20 feet. Common in wet utility excavations.

What is a sheet pile?

Interlocking steel sections driven into the ground to form a temporary wall retaining soil and water during deep excavations. Can be extracted after backfill.

What is thrust restraint?

The method of resisting hydraulic thrust forces at pipe fittings and bends. Achieved by thrust blocks (concrete) or restrained joint pipe. Required at all changes in direction and dead ends.

What is a restrained joint?

A pipe joint that mechanically locks the bell and spigot together to resist thrust forces without a thrust block. Required in unstable soils or where concrete thrust blocks cannot be used.

What is a tie-in?

The connection point where new piping connects to an existing pipe or structure. Often requires shutdown of existing service — a critical coordination point with plant operations.

What is a wet tap?

A connection made to an existing pipe while it remains in service under pressure. Requires special equipment and a corporation stop or tapping sleeve.

What is trench shoring?

A system of supports (trench box, hydraulic shores, or timber shoring) that prevents trench walls from collapsing. Required per OSHA 1926.652 for excavations deeper than 5 feet.

What is a trench box (trench shield)?

A steel or aluminum box placed in a trench to protect workers from cave-in. Does not shore the soil — moves with the work. Most common protective system for utility trenching.

What is sloping in excavation?

Cutting back trench walls at an angle to prevent cave-in. Slope angle depends on soil type per OSHA. Type C (granular/wet) requires a 1.5H:1V slope — takes significant space.

What is compaction testing?

Field testing to verify backfill has been compacted to specified density. Methods include nuclear density gauge or sand cone. Superintendent is responsible for ensuring tests are performed at required intervals.

What is a proctor test?

A lab test establishing the maximum dry density and optimum moisture content of a soil. Field compaction is specified as a percentage of Proctor maximum density (e.g., 95% Proctor).

What is a manhole drop connection?

A vertical pipe inside a manhole that drops high-elevation incoming flow down to the flow line elevation to prevent turbulence and erosion.

What is infiltration/inflow (I/I)?

Infiltration is groundwater entering sewer pipes through cracks or joints. Inflow is stormwater entering through manholes or illicit connections. Both increase plant hydraulic load.