Tunnel with embedded liner holes through Nov 2009
Paula Wallis, TunnelTalk
Robbins EPBM in receiving shaft
- Excavation is complete on the first segmental tunneling project to use a corrosion protective liner embedded into the concrete segments. The Robbins EPB TBM broke through on the Upper Northwest Interceptor 1&2 (UNWI 1&2) project in Sacramento, California last Wednesday, November 18, 2009. Traylor/Shea JV completed the excavation more than two months ahead of the February 2010 program schedule.
- The project has received international interest as the first tunnel to use a protective PVC liner applied to the segments during the casting pocess. The innovation allows The Sacramento Regional County Sanitation District (SRCSD) to use the segmental tunnel as the final carrier pipe.
- The project consists of 3.6 miles of 12ft i.d. (5.7km x 3.6m) segmental pipeline, 20 manholes and the connection of three existing trunk sewer lines.
Heat welding of the PVC segment joints
- Traylor/Shea Precast set up a segment casting plant about an hours drive south of the project in Stockton, California. To provide protection against corrosion from sewer gases, the concrete segments, made of concrete containing calcareous aggregate, were cast with a proprietary material called T-Lock by Ameron on the inside of the segments to provide an impermeable protective layer.
- As the segments are installed workers heat weld the joints for a permanent seal. The SRCSD adopted the innovative system based on cost and a shorter construction schedule.
UNWI 1 & 2 is aligned within the habitat of a rare species of owl and the Giant Garter Snake, which resulted in several environmental restrictions. Construction activities had to maintain a 250ft (76m) buffer from any Burrowing Owl nesting site and one manhole location was moved to comply. To mitigate for the rare Giant Garter Snake, no excavation, other than tunneling activities, could take place between October 1 and April 30 each year.
Alignment of the UNWI 1&2 contract
- URS designed the tunnel and Hatch Mott MacDonald is providing Construction Management services. Halcrow of the UK designed the segmental lining for Traylor/Shea and CBE of France manufactured and supplied the casting molds. The TBM was designed and supplied by Robbins with specialized EPB technology by Mitsubishi of Japan and was built by Robbins in China.
- SRCSD awarded the $97.3 million construction contract to Traylor/Shea on August 22, 2007 and tunneling activities began in January 2009. The EPBM was launched on its one long drive from the main shaft, located within the New Natomas Pump Station. The alignment ran below the groundwater table in ground that consisted mostly of sands and clay. The TBM reached its receiving shaft last week and from here, the UNWI 1 & 2 will connect to the existing UNWI 3 & 4 project.
- Once the TBM and it trailing gear is removed, and the conveyor belt, grout and foam lines and rail tracks stripped out, final repairs to the T-lock liner will be completed and a spark test performed. The transition structure connecting UNWI 1 & 2 and 3 & 4 will also be constructed as well as a transition structure at the New Natomas Pump Station that will connect UNWI 1&2 to the pump station. UNWI 1 & 2 is the final segment of the 18-mile (near 30km) Upper Northwest Interceptor System. Once UNWI 1 & 2 is completed in November 2010, the entire UNWI system will be put into service.
First use of embedded liner (video) - TunnelCast, Oct 2009
Sacramento Regional County Sanitation District
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