Lafayette, CO – When the San Diego County Water Authority (SDCWA) inspected its First Aqueduct water conveyance system in Valley Center of San Diego, CA, engineers identified that rehabilitation was required. Groundwater was infiltrating three tunnels within the system, and rehabilitation was required to maintain the tunnels’ structural integrity and extend their service life.
Michels Trenchless, Inc. was chosen to develop design-build solutions for the project. The organization partnered with Stantec for engineering services with GeoTree Solutions joining the group to provide rehabilitation materials for two out of three tunnels included in the project scope – GeoTree’s GeoSpray 61 geopolymer mortar was used to rehabilitate portions of two 72-inch horseshoe-shaped tunnels – known as the Lilac Tunnel and the Red Mountain Tunnel.
The third tunnel was rehabilitated using fiberglass-reinforced polymer pipe and grout via slip lining. To carry out the required repairs, the authority identified three 10-day shutdown periods during which 204 hours of production work was possible. December 5 to 15, 2022, January 23 to February 2, 2023, and February 27 to March 9, 2023.
A 500-foot section of the Lilac Tunnel displayed minor water infiltration. A solution was developed to apply a 1.5-inch layer of geopolymer to the entire section after cleaning, filling the haunches with approximately 2 inches of GeoSpray 61.
A 3,100-foot section of the Red Mountain Tunnel also had moderate infiltration, and again a 1.5-inch layer of geopolymer was applied after cleaning to mitigate the infiltration of groundwater. Haunches were filled with approximately 2 inches of GeoSpray 61.
The Lilac Tunnel rehabilitation was completed during the first shutdown as well as the work to fully grout the Red Mountain Tunnel. Work on the Red Mountain tunnel was performed from two temporary access portal locations. The first half of the geopolymer application was completed during the second shutdown, and the second half was completed in the early portions of the third shutdown. Following the geopolymer applications, the Lilac and Red Mountain tunnel sections were completed and released back to the Water Authority on schedule.
GeoSpray 61 was chosen for the project for a range of reasons: The rehabilitation needed to meet NSF/ANSI/CAN-61 certification for drinking water contact – a standard met by GeoSpray 61. The physical properties of the material also played an important part, such as 1500 psi flexural strength (ASTM C78), fast-setting and curing, and chemistry to self-bond without cold joints when multiple layers are applied.
GeoSpray has gone through a rigorous certification program through the Water Research Centre (WRc) including the material and design approach. GeoSpray 61 has proven application in deep water heads meaning it can be pumped a long distance without setting. This meant the temporary access points were sufficient to feed the workers inside the pipe carrying out the application.
The GeoSpray 61 was applied using Michels Trenchless’ proprietary centrifugal application devices specifically designed for the 72-inch tunnel. For the Lilac tunnel alignment, GeoSpray 61 was pumped approximately 750 feet to the application device and retracted at the appropriate calculated speed. The total thickness was applied in two passes, each of ¾ of an inch. For the Red Mountain alignment, the material was mixed topside and conveyed into specially designed diesel conveyance carts and delivered to the application device for installation.
Two crews consisting of approximately 30 members total took 26 days to complete the project including preparation time.
Michels Trenchless President Matt Smith said: “Trust between the customer, contractor, engineering firm and material supplier is essential with all critical infrastructure projects. This project had a particularly challenging timeline and conditions. As a result, we only had one chance to get this right and provide safe, clean water to more than 3 million people. Our experience and the ability to work with products and teams we had confidence in allowed us to achieve the project’s goals.”
GeoTree Solutions, President John Hepfinger said: “We have partnered with Michels for several years and have complete faith in their highly-skilled application teams. Trusting that the geopolymer material will be correctly mixed and installed is key to asset owners trusting in the integrity of GeoSpray 61. We’re fortunate to have a long relationship with Michels, and we look forward to working with them on a number of other projects in the near future.”