Design and Construction of a Multitude of Trenchless Technologies of the Basin 2/3 Project in San Mateo, California

摘要

The City of San Mateo Basin 2/3 Project includes new and rehabilitated pipelines and uses both open-cut methods and trenchless technologies. The project scope included the upsizing of existing sewers and new sewer construction adjacent to existing infrastructure. The overall project increases flow equalization capability during storm events to reduce flooding. Completion of an alternatives analysis identified advantages associated with utilizing traditional trenchless methods for the new and rehabilitated pipelines, including cost and schedule benefits and reduced impacts to the community.The project includes several trenchless methods namely: microtunneling, horizontal directional drilling (HDD), and rehabilitation using cured-in-place pipe (CIPP) for gravity and pressure applications. The project, some portions which have been completed and other portions that are currently being bid or designed, includes nearly 14,000-ft of trenchless installation consisting of 6-in to 36-in sanitary sewer pipe.Microtunneling is planned to connect existing sanitary sewer flows through residential areas and provide gravity conveyance through an urban commercial and residential area. The microtunneling portion of the project was a value engineering proposal developed to save budget and schedule for the designed open-cut portion of the sewer conveyance. Due to high-groundwater level with the potential for significant inflow and drawdown potential during the open-cut portion of the project, trenchless methods were proposed to ease the construction installation. Other trenchless methods used on the project include horizontal directional drilling for installation of 200-ft of 6-in gravity sewer, over 3,100-ft of 14-in HDPE force main, and a short installation of 18-in FPVC force main. Many of the HDD installations were designed to have horizontal curves to avoid exiting utilities and mitigate public easement and right-of-way restrictions, whilst also allowing for connection to existing infrastructure.This paper summarizes project constraints, design challenges, and construction issues associated with completing the trenchless components of the sanitary sewer project.