San Diego, CA

San Vicente Pipeline Tunnel

San Diego County Water Authority (SDCWA)


The San Vicente Pipeline Tunnel is part of the SDCWA’s Emergency Storage Project, the largest element of a $1.2 billion Capital Improvement Program. This project involved the construction of a pipeline connecting San Vicente Reservoir, one of San Diego County’s major water storage facilities, and the Second Aqueduct, which delivers water from Northern California to San Diego County. The pipeline will help sustain the water supply for the region following a major earthquake.

Fast Facts
  • 11 miles (18 km) of excavated tunnel
  • 102-inch (2,590 mm) inside diameter
  • Hard rock tunnel boring machine (TBM)
  • Sequential excavation method (SEM) through mixed rock conditions

Scope of Work

As prime consultant, Delve Underground managed the design team and served as tunnel and shaft designer. We also provided construction engineering support to SDCWA in its efforts to complete the project in a cost-effective manner while balancing community and environmental concerns.

Challenges & Innovations

Various tunneling methods were used on different reaches of the tunnel: an 11.5-foot (3.5 m) hard rock TBM was used to bore through 5,255 feet (1,602 m) of granitic rocks, drill-and-blast methods were used in the western volcanic rock reach, SEM was used for a mixed face reach, and two 12-foot-diameter (3.7 m) digger shields excavated the tunnel through sedimentary formations.

Tunnel excavation was staged from three shafts and one surface portal. Various rock support methods were employed, including rock dowels, steel sets, and precast segments. The final lining consisted of butt-welded steel pipe.