Reuse of existing steel pile foundations – Greenock Creek Bridge, Walkerton, Ontario, Canada

Abstract

Following a preliminary assessment of bridge replacement/rehabilitation options for the existing Greenock Creek Bridge located near Walkerton in Southwestern Ontario, Canada, the removal of the existing superstructure and the reuse of the existing foundations was selected as the preferred option. The preferred alternative was based on condition survey of the deck and superstructure and traffic mobility, economic, sustainability and environmental advantages. The decision is demonstrative of the Ministry of Transportation’s (MTO) commitment to assess new technologies and applications that support Ministry initiatives and operational needs and specifically to encourage the reuse of existing foundations. The existing structure, built in 1971, is a single span structure that carries Hwy 9 over Greenock Creek. The existing abutments are founded on H-Pile foundations that according to the original construction contract drawings are approximately 8 metres in length and installed at 1:4 and 1:8 batters. The subsurface conditions at the site consist of clayey silt to silt underlain by silty sand with gravel. The groundwater table is at or near the ground surface. The relative density of the subsoils is loose to dense in the surficial 3 to 5 metres and becoming very dense below these depths. This paper describes the process of evaluation of the capacity, integrity and durability of the existing steel HP310x79 H-piles. A comprehensive programme was planned, organized, and implemented that included exploratory boreholes to verify the subsurface conditions, retrieval of soil samples to determine the corrosivity of the soil and groundwater around the piles in order to assess the degree of corrosivity and geophysical testing including parallel seismic and borehole magnetometer testing to estimate the embedment lengths of the existing steel piles. The results of this investigation were used to assess if the existing steel pile foundations can carry the new superstructure loads for another 75 years.