Environmental Services will repair about 3,700 feet of the 114-year-old Taggart Outfall sewer tunnel. This large, brick sewer tunnel is a critical sewer line serving Southeast Portland. Measuring from 58 to 120 inches in diameter and from 20 to 75 feet deep, the Outfall is showing signs of significant deterioration and fractures that require repairs.
The Taggart Outfall drains a large area of Southeast Portland and conveys overflows from the combined sewer system to the Willamette River during rain events. It is located deep underground in a difficult location close to TriMet light rail tracks, Union Pacific Railroad tracks, and Highway 26/Powell Boulevard. A structural failure of the Outfall would have profound impacts on this area, potentially flooding numerous businesses and residences and resulting in many millions of dollars of property damage and disruption. This project will increase the sewer's resiliency to earthquake damage, extend its service life for another 100 years, and help prevent sewage releases to buildings and streets.
Aboveground construction activities will be concentrated at existing maintenance access holes along the Taggart Outfall and a sewer access shaft on private property. Most of the repair work will occur belowground from inside the sewer tunnel.
Pre-Construction Activities: The contractor for this project, James W. Fowler Co., conducted closed circuit television (CCTV) inspections and 3D laser profiling of the Outfall tunnel in the fall of 2018, which allowed the City to confirm existing conditions, create a profile of the sewer's interior, and then order the materials needed to repair the Outfall.
Mobilization in October 2019: During the fall of 2019, the city's contractor completed repairs to the small-diameter (58 to 84-inch diameter) pipe sections in SE 16th Avenue and in SE Tibbetts Street.
Re-mobilization in Spring of 2019: Crews mobilized again in March 2020 when weather permitted them to work safely inside the tunnel. This phase of work will include repairs to the large-diameter (118 to 120-inch diameter) pipe sections between SE 16th Avenue and the Willamette River.
Late March to late April 2020
Crews will build a deep sewer access shaft on private property at SE Powell Boulevard and SE 13th Place. The new shaft will measure 15x15 feet wide and 35-feet deep.
This shaft will reduce the need for multiple access locations along the sewer tunnel.
Crews will lay 2,725 feet of steel tracks inside the Outfall sewer tunnel.
Using a crane, crews will lower an electric, human-operated locomotive and pipe lining cart into the sewer tunnel and onto the tracks.
Crews will use the locomotive to install the fiberglass-reinforced pipe lining. Similar locomotives have been used in mining and tunneling industries since the 1860s.
June through September 2020
Crews will install the fiberglass-reinforced pipe lining inside the sewer tunnel. Using the electric, human-operated locomotive, crews will push the fiberglass-reinforced pipe lining along the track and into position inside the tunnel.
Crews will install one section of pipe lining at a time. The project will require 330 segments of 8-foot-long straight pipe, and 36 segments of joint pipe.
After every 100 feet of pipe lining installation, crews will pump grout into the space between the lining and the old brick sewer.
Crews will continue to slip line and install grout until all sections of the tunnel are completed.
September through October 2020
Crews will power new steel liner plates into the sewer tunnel, and assemble the steel liner plates in place inside the tunnel.
Crews will pump grout into the space between the liner plates and the old brick sewer.
Crews will also clean, inspect, and repair a maintenance access hole. Casting a new concrete liner inside the existing maintenance access hole will avoid digging in the street. The new concrete liner will create a watertight, corrosion-resistant interior that will reinforce the existing structure without having to replace it.
Crews will close the sewer shaft, backfill the hole, and restore the asphalt surface.
Crews will complete post-inspection of the Outfall sewer tunnel repairs.
The Portland Noise Office granted Environmental Services a noise variance to work all days and all hours (24/7) in the industrial areas of the project west of the MAX light rail tracks. The noisiest work will be done during the daytime from 7 a.m. to 6 p.m. Crews will generally work two 10-hour shifts Monday through Saturday, and Sunday if needed, to complete the project during the dry-weather season.
The primary construction methods to repair the Taggart Outfall will be Slip Lining and Tunnel Liner Plate. Of the many construction methods Environmental Services analyzed, these methods will most effectively reinforce the Outfall pipe and cause the least impact and disruption to the neighborhood.
Crews will enter the Outfall tunnel from maintenance access holes and a sewer access shaft and climb down 30 to 75 feet below the surface. Working from a locomotive on a track laid inside the tunnel, crews will essentially construct a new sewer inside the old brick sewer. They will construct some sections by inserting a fiberglass-reinforced liner inside the tunnel. They will construct other sections by assembling new steel liner plates in place inside the tunnel. They will then fill the space between the new sewer and the old brick sewer with grout. Grout pumps located aboveground near the maintenance access holes will pump the grout into the sewer.
Both of these methods – Slip Lining and Tunnel Liner Plates – will avoid digging trenches in the roadway and reduce aboveground impacts to the traveling public.
These methods also mean that, for safety, crews can only work inside the tunnel on dry days when there will be no water flowing into the tunnel. In the event of rainfall or a sudden surge of stormwater flowing into the tunnel, crews and equipment must be removed quickly from the sewer tunnel, and completion of repairs may be delayed.
Aboveground activities will include the following:
- Establish safe work zones for the traveling public and the crews;
- Set up traffic controls, which may include temporary lane closures and on-street parking removal;
- Deliver, off-load, and set up equipment and materials;
- Power up vactor trucks to remove sediment from the sewer tunnel;
- Power up generators and compressors for pumps and other equipment used during sewer repairs;
- Power up ventilation equipment for crews working inside the sewer tunnel;
- Lower equipment and materials into maintenance access holes and sewer access shaft;
- Power up grout pumps to pump grout into the sewer;
- Power up cement pumps to install cementitious material on the inside face of the liner plate.
Noise Mitigation Measures
The major sources of noise will be the vactor trucks, grout pumps, generators, and forklifts. The contractor will be required, by contract, to use quiet generators. Mitigation measures are incorporated into the construction contract. These mitigation measures are the following:
- Night and weekend work is restricted to industrial areas where there are no residences within 200 feet.
- All compressors and generators will be silenced. Noise levels for quiet generators are around 69 dBa.
- Backup alarms on all trucks will be turned off and spotters will be used instead.
- Vactor truck use and any required saw-cutting will not be allowed from 10 p.m. to 7 a.m.
- Lighting will be adjusted to the lowest levels to limit overshooting the work site and impacts to the immediate community.
- City inspectors will be on site during work hours to enforce contract restrictions on noise.
What to Expect During Construction
While there will be some equipment and materials aboveground, most of the work will be conducted belowground inside the sewer tunnel. You can expect the following activities and impacts:
- Temporary lane closures and on-street parking removal may be necessary to enable safe access to the sewer tunnel.
- Equipment that generates noise will include vactor trucks, compressors, generators, ventilation fans, forklifts, and pile-driving equipment. Night work will require light tower trucks.
- Vactor trucks will operate vacuum pumps necessary to clean the tunnel and remove materials during construction. They may operate hours at a time.
- There may be periods of inactivity between construction phases due to a variety of factors including weather, subcontractor schedules, and availability of materials.
- A city inspector will be on-site during work hours and may be able to assist you with an immediate need during construction.
- Sewer, water, and other utilities will remain in service during construction.