In February 2002, the Traylor/ Shea/Frontier Kemper/Kenny JV submitted the lowest of three bids for the 5.3 mile (8.5km) extension of the ECIS project north to Eagle Rock. Against an Engineer’s estimate of $150.8 million, the JV’s bid of $162.15 million for the North East Interceptor Sewer (NEIS) was lower than the Affholder/Elmore JV bid of $164.5 million and the top bid of $179.3 million from the Obayashi/ Schmick JV. Continuing from the Mission/Jesse site shaft on ECIS, the 13ft o.d. (4mo.d.) (8ft (2.4m) i.d.) NEIS alignment will be excavated concurrently in three headings through varying soil conditions.

Design of the NEIS project was also completed in house by the City’s Department of Public Works Bureau of Engineering and assisted by a group of 15 consultants led by Jacobs Associates. The NEIS contract is scheduled for award by May 2002 with notice to proceed expected by June. The Traylor-led JV as the apparent lowest bidder is yet to announce supplier of the three TBMs required by the contract. Suppliers of the lining systems, as nominated in the bid, are the Traylor/Shea/ Ghazi JV for the primary precast concrete segments and Ameron for the inner carrier pipe.

Construction management for the NEIS contract is awarded as an extension of the ECIS management contract to the integrated team of City employees and staff from the Parsons Brinckerhoff Management Services/Brown & Root Services JV.

Once the ECIS and NEIS projects are completed the existing sewer will be decommissioned and rehabilitated to provide additional gravity flow sewer capacity from the LA city center to the treatment plant. Francis Fong, project leader for Jacobs, describes the challenges of NEIS.

The principal geologic units along the NEIS alignment include Holocene (Recent Alluvium) and Pleistocene (Lakewood & Older Alluvium) fluvial and alluvial soil deposits which consist of unconsolidated gravel, sand, silt and clay. Underlying are Pliocene sedimentary deposits of well-stratified siltstone and claystone in the Fernando Formation and interbedded sandstone in the Puente Formation Units 1 and 2. The Fernando Formation is a soil-like material with strengths similar to a hard silt or clay. The Puente Formation Units are lithologically similar but range from extremely weak to strong rock, Unit 2 being stronger with some strongly cemented beds. The NEIS tunnel will be excavated beneath an overburden of between 24m to 46m maximum and in three reaches.

The 2.8km Lower Reach from the Richmond shaft to the Mission/Jesse site ECIS connection, runs through Older Alluvium, Fernando and Puente Formation Unit 1 strata. Since the contact between the Older Alluvium and Fernando deposits is not well defined, the contractor should expect varying tunnel conditions, from slow raveling and flowing ground to firm ground, and possibly mixed face conditions through the southern half of the alignment. The majority of the Puente Unit 1 material is also expected to exhibit slow to fast raveling behavior.

The 2.4km Middle Reach will be excavated through Older Alluvium and two units of Puente Formation. The anticipated behavior of the stronger Puente Formation Unit 2 is slow to fast raveling to firm ground behavior, depending on the degree of cementation. Raveling to flowing ground is expected elsewhere along the Middle Reach.

The 3.3km Upper Reach is excavated entirely through Puente Formation Unit 2 and in conditions similar to the upstream segment of the Middle Reach. Tunneling in Puente Unit 2 along this reach will follow the strike of the bedding which could include steeply dipping joints resulting in blocky ground. In addition, the crown is fairly close in several areas to the Puente Formation/Older Alluvium contact increasing the risk of encountering flowing ground and crown instability.

The NEIS contract documents address several technical issues by either specifying the means and methods of construction or stating the performance requirements.

  • The Lower and Middle Reach drives lie beneath the groundwater table and through fast raveling to running ground conditions. As such the use of positive face support TBMs such as EPB or slurry machines is specified. The contractor is required to supply new machines for these two reaches. For the more stable ground along the Upper Reach, the contractor may use a reconditioned shielded TBM, although provisions for face probing and grouting is required to deal with areas of low rock cover.

  • The lower two reaches are classified by Cal-OSHA as “gassy” and requiring specialized equipment . The Upper Reach is classified as “potentially gassy”. Special consideration is also required if contaminated ground or groundwater is encountered.

  • Due to the presence of groundwater contamination, the project structures are to be constructed using watertight techniques to minimize inflows. Concrete diaphragm walls are specified to support the shafts in overburden soils and gasketed precast concrete segments are specified as the primary lining with an inner 2.4m i.d. prestressed concrete cylinder carrier pipe, protected with an inner corrosion resistant lining, installed and backfilled with cellular concrete. The primary lining and the internal carrier pipe of the gravity flow sewer will be installed at maximum depths of up to 46m and will be exposed to 3 bar hydrostatic pressures maximum. Since there is little performance experience within City of Los Angeles for carrier pipes placed at such depths, the contractor is required to conduct elaborate pipe barrel and joint testing against stringent leakage criteria.

  • Due to the difficulties for controlling groundwater inflows in permeable soils, contract documents require the contractor to pre-excavate all the required manhole shafts and backfill them with a bentonite concrete prior to the arrival of the TBM. Supplementary grouting may also be needed.

  • An old abandoned tunnel found along the NEIS horizon will be backfilled and the section presenting obstruction to the TBM, will be removed before arrival of the tunnel heading.

  • In the urban setting of the project, potential ground settlement is a serious concern. The primary tool mitigating this concern is the use of positive face-control TBMs to minimize ground and groundwater losses. Contract documents also stipulate the use of an extensive pre-excavation grouting program to be carried out at critical road crossings and monitoring via an extensive array of geotechnical instrumentation is required.

  • City of Los Angeles noise ordinance imposes work hour restrictions on all construction sites and the police commissioner has the authority to shut down any construction activities if reasonable complaints are received for surface or underground works undertaken during off hours. For tunneling underneath critical structures, the City has received permission from the police commissioner to operate on a 7-day, 24-hour schedule.

    Related Files
    NEIS Project Alignment