Carollo was retained by King County to rehabilitate 3,700 feet of severely corroded 96-inch diameter reinforced concrete pipe in a densely populated commercial area in Renton, WA which included Boeing’s 737 airline facility. Due to potential long-term impacts to the community, the pipeline was rehabilitated using trenchless technology. To construct the project during summer 2019, Carollo expedited preliminary and final design over a 14-month period.
The team prepared a Flow Bypass Study to analyze existing flows in the interceptor and to develop a plan to bypass up to 45 mgd during summer months. The bypass plan included provision that would allow for working under the live flow conditions while also providing the capability to remove all personnel and equipment during emergency high flow conditions. The bypass plan also included preparation of a flow management plan that coordinated efforts of three treatment plants and two operations groups.
Geologic study of the project area determined the suction pit needed to be constructed within unstable, liquefiable soils. The Carollo team designed the shoring system required to protect the existing pile-supported pipeline and the adjacent BNSF railway, including the use of pressed-in shoring.
The Carollo team developed traffic control strategies using standard traffic control barriers, variable message boards, long-term detour routes, and temporary road closers to limit the impact on the local community. The Construction Footprint Study analyzed the optimal location for the bypass suction pit, alternative routes for the bypass alignment, and conducted potholing of existing utilities to determine conflicts with bypass pipes through existing intersections.
Carollo also mitigated noise impacts on the surrounding community by specifying electric bypass pumps and requiring the Contractor to meet stringent noise levels during non-normal working hours.