San Marcos Interceptor Sewer Phase 2

The San Marcos Interceptor Sewer Phase 2 project consists of replacing the existing 21” sewer interceptor with larger diameter pipelines between Twin Oaks Valley Road and Lift Station No. 1. Phase 2 is the portion from the Via Vera Cruz to Lift Station No. 1.

James W. Fowler Co.’s (JWF) scope is the microtunneling of a 2-pass drive, 120 LF long, with 60” steel casing pipe and 42” FRP carrier pipe. JWF designed and welded the casing into the carrier pipe to advance into the casing at design grade, regardless of tunnel alignment.

The tunnel alignment and orientation went through several iterations due to conflicts with existing utilities, as well as an existing box culvert that intersects the tunnel alignment with less than 12” of clearance. Furthermore, shaft locations presented a challenge to the general contractor and to JWF due to the high-density traffic on San Marcos Boulevard that required advanced engineering of the shafts to sustain traffic loads while providing required shoring for the tunneling operations.

The retrieval was more complicated than usual. The reception shaft has been installed, but the existing sewer line that our new line will tie into must be bypassed after we get to the reception shaft, but before we breakthrough. The project started on November 30th and was completed by the end of the year.