Breaking New Ground Beneath Lake Ontario: How Collaboration and Innovation Delivered a Successful Microtunnel Drive

Abstract

This paper explores the design evolution and successful construction of a 1200mm diameter (1500mm OD), 190m microtunnel drive with a wet retrieval beneath Lake Ontario — a key component of the R.C. Harris Water Treatment Plant Zebra Mussel Control System for the City of Toronto. Designed by Associated Engineering and constructed by Ward & Burke in 2024, the project originally included 2.8km of 600/400mm HDPE intake pipe installed using dredging techniques within the lakebed. The alignment was to follow the existing intake pipe through traditional in-water trenching techniques and included an onshore jack and bore crossing under a storm outfall. During project re-tendering, a comprehensive marine geotechnical investigation using geophysical, sonar, magnetometer and other technologies was conducted to provide additional information for the geotechnical conditions within the lake. Ward & Burke identified and proposed an alternative approach of using microtunneling to reduce in-water and onshore disturbance as well as eliminating the jack and bore. This solution required tunneling through the existing bearing wall, beneath shoreline steel sheet piles, and executing a wet retrieval. Close collaboration between the contractor and consultant optimized the alignment and mitigated construction risks. This paper highlights the critical design decisions, innovative problem-solving, and teamwork that transformed project challenges into a groundbreaking trenchless success story under Lake Ontario.