CHALLENGES OF RELOCATING LARGE WATER MAINS FOR RAIL SYSTEM EXPANSION

By Robert Card

On Feb. 7, the city of Santa Clara celebrated a major milestone when it hosted Super Bowl 50 at the state-of the-art Levi’s stadium, home of the San Francisco 49ers. Next year, the city will celebrate another milestone with the completion of the 10-mile Berryessa Extension, the first phase of Bay Area Rapid Transit’s commuter rail extension south to San Jose, thanks to Santa Clara Valley Transportation Authority’s (VTA) vision.

As part of the Berryessa Extension, several new stations were proposed. Two of the new stations impacted large diameter water pipelines owned by the Santa Clara Valley Water District (SCVWD). The existing lines had to be relocated away from the new stations.

The technical design aspects of installing new pipe and fittings into an existing 66-inch concrete pressure pipe raw water main and into an existing 42-inch steel pipe treated water main are quite challenging in order to properly relocate both lines. One key consideration in this modification to the existing lines is the thrust forces generated from the realignment. The thrust restraint of the old 66-inch line posed a number of challenges since the original pipe in this area did not have longitudinal thrust forces. Additionally, the owner, the Santa Clara Valley Water District, had its own specialized thrust restraint procedure that was based on a 1960s paper.

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