As a subconsultant to Gannett Fleming, Inc., BTE provided trenchless design services for the microtunnel installation of 650 feet of 42-inch diameter steel casing with second pass installation of 15-inch PVC gravity sanitary sewer over two drives for the City of Vista, CA. Trenchless methods were selected due to the required depth of the crossings which exceeded 25 feet. The project was located along a heavily traveled traffic corridor with significant existing overhead and subsurface utilities. The gravity pipeline was sited within the Santiago Formation sandstone, siltstone, and claystone. The anticipated rock conditions and critical flat grade necessitated an oversize 42-inch steel casing be installed. Challenges included minimizing impacts to businesses and traffic, constrained work areas, avoiding impacts to utilities, and crossing Caltrans right-of-way.
BTE evaluated geotechnical conditions, evaluated alternative trenchless construction methods, evaluated trenchless alignment alternatives and associated work areas, conducted estimated settlement calculations and proposed mitigation measures, provided technical trenchless specifications, wrote the Geotechnical Baseline Report for the trenchless components, reviewed contractor submittals, and responded to RFIs related to the trenchless work. Construction was completed February, 2020.