Northeast Interceptor Sewer
- Location: Los Angeles, CA
- Owner: The City of Los Angeles
- General Contractor: Traylor, Shea, Frontier, Kenny JV
- Technique(s) Utilized: Diaphragm Wall
- Subsurface Conditions: Alluvial Soils, Weak Sedimentary Rock
- Approximate Key Quantities: Diaphram Wall - 75,000 square feet, Shaft Depths - 62-164 feet, Shaft Diameters - 30-70 feet
The city of Los Angeles' sewer system, like the sewer systems of many cities across the country, was outdated and in need of repairs by the end of the 1990s. The main sewer system, which was approximately 70-years-old at the time, was lined with holes and cracks caused by years of typical wear and tear.
The poor condition of the main sewer line, known as the North Outfall Sewer, caused it to remain dangerously full in periods of dry weather, and to overflow through manholes and into the streets in periods of heavy rain and wet weather.
Based on the recommendation of an environmental study initiated by the California Regional Water Control Quality Board, the City of Los Angeles began a massive sewer system repair and enhancement project, which would take seven years to complete. Several new sewers would be built as part of this project, including the North Hollywood Interceptor Sewer, the Eagle Rock Relief Sewer, the North East Interceptor Sewer and the East Central Interceptor Sewer.
PROJECT BACKGROUND
Nicholson was involved in the construction of the North East Interceptor Sewer (NEIS) tunnel, which was eight feet in diameter and 5.3 miles long.
The subsurface conditions for the tunnel included alluvial soils and weak sedimentary rock with up to 100 feet of groundwater pressure. The location of the tunnel and its close proximity to the densely populated and developed neighborhoods of the City of Los Angeles further complicated construction.
THE WORK
The project involved the construction of two shafts using diaphragm walls for excavation support. The diaphragm wall panels were excavated using a Hydrofraise, which was chosen for its precise excavation control. The panel walls were excavated within a tolerance of 0.3 percent, which equates to a variance of only 0.5 inches from the designed vertical alignment, over a depth of 134 feet.
The first shaft, known as the Humboldt shaft, featured a "figure-eight" or "dual-cell" shape. One of the cells had a diameter of 70 feet and reached a depth of 135 feet. The other cell had a diameter of 41 feet a reached a depth of 62 feet. The second shaft (Richmond) measured 30 feet in diameter and reached a depth of 164 feet.
THE RESULT
The Los Angeles sewer system repair project, which was valued at $162 million, was the largest construction project ever awarded by the City of Los Angeles. The overall project was designed to improve sewer flows, reduce maintenance and potential sewer spills and minimize unpleasant odors.
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