Remediation of Slope Failure in the Application of Lightweight Fill and Timber Piles on Highway 17 in Ontario

ABSTRACT: The failure site is located along Highway 17 approximately 2 km West of Hagar, Ontario. As a part of a frost heave repair, the existing embankment was widened to the north of Highway 17 to allow for temporary traffic flow. During construction, approximately 50 m of the newly widened detour embankment failed. The head scarp of the failure was located at the north edge of original pavement. Following the failure, a Geotechnical Site investigation was carried out to examine the conditions and provide remedial options. The shear key option was chosen as an effective method of dealing with the likely mode of failure. However, a second failure occurred following installation of the shear key, after reinstatement of the highway embankment to the final grade. This failure was assessed to be a deeper-seated slip surface just under the constructed shear key. Several factors may contribute to the second slope failure including: (i) Shear key was not installed deep enough, (ii) Previously weakened slip surface/zone was remolded and lubricated by infiltration of the surface water during the construction; and (iii) Placement of fill materials and heavy construction equipment vibration at 1 m near the slope crest and toe area exacerbating the conditions. Remediation of the second failure involved installation of timber piles driven to bedrock to intercept the failure zone and the use of EPS lightweight fill to reduce embankment loads. A toe berm was also placed to stabilize lower riverbank area. After the second remediation, the highway embankment was stabilized and is performing well with no signs of distress to date. This paper emphasized the importance of Geotechnical Site investigation prior to embankment widening on soft soil near river banks and demonstrates the effectiveness of ground improvement using timber piles and lightweight fills.