Mainline Sewer Replacement
Open trench excavation consists of digging down to and exposing the existing pipe, removing the existing pipe or a section of it, installing a new pipe or a section of new pipe, and then backfilling the trench.
The work includes the following steps:
- Sawcut pavement and dig trench to install mainline sewer pipe.
- Sawcut pavement and dig trenches from the mainline to the curb to install sewer service laterals that connect properties to the public sewer.
- Install new mainline sewer pipes and laterals.
- Cover open trenches with steel plates at the end of each day as needed while work is in progress.
- Backfill trenches with sand or gravel and apply temporary asphalt patches.
- Conduct quality control inspections.
- Complete permanent pavement restoration of patched trenches after work passes inspections.
- Repair any curb and sidewalk panels damaged during construction.
- Restore any vegetation disturbed during construction with top soil and grass seed.
In addition to major sewer and stormwater construction activities, the following activities may require the use of Open Trench Excavation to complete:
- Sewer cleanout installations
- Spot repairs
- Sewer service lateral repair and replacement
Sewer Cleanout Installations and Vactor Excavation
A sewer cleanout is a capped opening above the sewer service lateral that connects a property or a building to the mainline public sewer. It provides access to the sewer lateral pipe for video inspection, cleaning, root removal, pipe lining, and repair of the sewer connection. Cleanouts may also be used to maintain sewer service during a mainline pipe lining process or to provide ventilation during that process.
Cleanouts are typically installed near the curb but may also be placed in the planting strip between the curb and the sidewalk, in the sidewalk near a property or building, or on private property above the sewer lateral.
Sewer cleanout installation requires digging a small-diameter hole where the cleanout will be located. Crews dig down to the service lateral, cut into the service lateral, connect a standing pipe to the surface, and add a cap at ground level. Each cleanout installation takes up to two days to complete.
Vactor Excavation
In locations with several underground utilities in close proximity to each other, crews will use a process called Vactor Excavation to install the sewer cleanout. It is a less invasive method than Open Trench Excavation, causes less surface damage, and takes less time than traditional digging methods. Most importantly, it reduces the risk of hitting other buried utility lines. Using high-flow vacuuming and high-pressure water jetting, a vacuum excavator—or vactor truck—safely vacuums the soils and water out of the ground to create a hole in a precise location for the cleanout to be installed.
Spot Repairs
A spot repair is the replacement of a short section of pipe, not the full length of pipe from manhole to manhole. A spot repair requires digging a small trench so that crews can replace the short section of broken pipe. Crews will dig a trench, remove the section of broken pipe, install a section of new pipe, backfill the trench, apply a temporary pavement patch, and then repave the patched area after the work passes inspections.
Spot repairs may be necessary to replace small sections of broken sewer pipe where it is not necessary to repair or replace the entire pipe. It may also be used to prepare the full length of a mainline pipe for replacement with trenchless construction methods such as Cured-in-Place-Pipe Lining or Pipe Bursting. To be successful, trenchless methods require an intact pipe. Replacing small portions of deteriorated or collapsed sewer pipe enable a liner or new sewer pipe to be installed without complication. It is common for spot repairs to occur a few weeks before mainline pipe repairs.
Sewer Service Lateral Repair and Replacement
A sewer service lateral is a pipe that provides a public sewer connection for a house, business, or undeveloped property. It runs from the mainline public sewer in the street to the curb and connects to the property’s private sewer line or is capped at the property line for future use, e.g., future development or resolution of a nonconforming sewer connection.
A sewer service lateral may be replaced using either the Open Trench Excavation method or a trenchless method such as Cured-in-Place-Pipe Lining or Pipe Bursting.
The City of Portland is responsible for maintaining the public portion of the lateral sewer pipe from the mainline public sewer to the curb. The private property owner is responsible for maintaining the private lateral sewer pipe from the curb to the house or building.