Large Diameter Sewer Rehabilitation in The City of Los Angeles

The City of Los Angeles operates and maintains more than 6,500 miles of sewers ranging in size from 6-inch to 150-inch in diameter. Many of the larger diameter sewers constructed in the early 1900's were constructed of un-reinforced concrete with clay tile liners or of brick. Approximately 64 miles of sewers were constructed using non-circular pipes. Sewers in Los Angeles have typically been constructed within the public right-of-way however a few sewers constructed in the early 1900's are in easements and requires rehabilitation methods that will minimize the impact on the community and access the sewer only in locations that are in the public right-of-way. After 80 to 100 years of service, these sewers have experienced severe corrosion, loss of the clay tile liners and bricks and are approaching the end of their service life.The City of Los Angeles has rehabilitated several miles of large diameter sewers and has utilized several construction methods as well as materials. Beginning in the early 1990's the City began rehabilitation of the circular portions of the North Outfall Sewer (NOS). Recently the City has begun rehabilitating non-circular sewers using newly developed and approved materials. Rehabilitation methods have included sliplining, cured-in-place liners, cast-in-place concrete with PVC liners, and man-entry installation of new sewer pipes. Materials used for installation have also included recently approved Reinforced Polymer Mortar Pipes (RPMP) specifically designed for non-circular pipes.The rehabilitation of 3 miles of the 60-inch by 73-inch oval brick Central Outfall Sewer (COS), 1.5 miles of the 60-inch semi-elliptical tile-lined concrete North Outfall Sewer (NOS), and 1,000 feet of 66-inch semi-elliptical concrete brick sewer has used man-entry installation of a new pipe, non man-entry sliplining and man-entry cast-in-place-lining construction techniques. Sliplining is utilizing recently approved materials that maintain the non-circular shape of the sewer and minimizes the reduction of capacity of the existing sewers. The cast-in-place option is constructing a new PVC lined concrete pipe inside the existing sewer. These methods will provide a long-term structural repair of these 80 – 100 year old sewers.Historical sewer construction and rehabilitation has impacted the current methods used for rehabilitation of sewers in Los Angeles. The COS was originally constructed in 1904 and subsequently rehabilitated in the 1940's. During the construction phase of this project it was determined that the 1940 rehabilitation project did not maintain the original size and dimensions. This has resulted in the need to remove a large number of bricks in order to install the cast-inplace liner with the required thickness of concrete.Rehabilitation of sewers in Los Angeles has required many techniques and materials in order to renew these pipes for their continued use for the next 100 years. Having numerous methods and materials available for rehabilitation allows the City and the contractors to select options that will meet the unique demands of each individual project and at the lowest cost.