The Ministry of Transportation of Ontario (MTO) trialled the use of cellular concrete to control the ongoing settlements of approach embankments at a bridge located in northern Ontario. The bridge carries Highway 535 over the Nepewassi River, 3.5 km south of Highway 17, in the Township of Dunnet.
Historical and recent monitoring data confirmed the approach fill embankments had been settling for over 60 years. Since 2000, the south and north approaches settled 275 and 240 mm respectively.
The site is underlain by some 15 to 20 m of soft, compressible clay deposits which overlay more competent soil comprised of compact to dense sands. It was postulated that the continuing settlement of the embankments was due to the primary consolidation of the soft clay deposits.
To remediate the grade of the embankment and mitigate the continuing settlement, the existing embankment fill was removed and replaced with a lightweight fill of cellular concrete. This was carried out with the intent of reducing the effective vertical stresses on the soft clay deposits, so that the resulting ground movement would be more tolerable.
Cellular concrete is a lightweight fill material that is listed on the MTO’s Designated Sources of Material List and satisfies MTO’s prequalification requirements. Environmental approvals comprised a substantial component of the acceptance of cellular concrete.
As part of this trial, extensive instrumentation and monitoring programs were incorporated to assess the geotechnical and environmental performance of the embankment.
This paper presents the results of the foundation investigation, the design methodology, the environmental monitoring and post construction settlement monitoring after unloading the approach fills by using cellular concrete.
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