Abstract Manager

One of the challenging issues of highway infrastructure rehabilitation works is how to assess the conditions of the backfill behind structure abutments and how to determine whether voids are present under approach slabs which may have traffic safety implications. The presence of voids beneath approach slabs may cause roadway and structure performance problems, with such voids likely to cause loss of ground, settlement of the highway pavement, and possible drainage impediment. It is not always possible to advance enough boreholes to identify and delineate the extent of these anomalies. To develop an effective maintenance strategy, non-destructive testing such as a Ground Penetrating Radar (GPR) survey can be used to determine locations of anomalies or identify areas with changing conditions. Knowing the presence, extent, and locations of these potential anomalies can allow for a targeted approach for validation of the in-situ conditions.

As part of an initial maintenance contract at a Highway 401 structure, voids beneath the approach slabs were observed and appeared to extend across the highway platform. The Ontario Ministry of Transportation (MTO) retained the services of Thurber Engineering Ltd. to complete a GPR survey to assess the effectiveness of this technology to identify potential void development under structure approach slabs, with the information used to develop an effective maintenance repair strategy. The contents of this technical paper will present the conditions at the study locations, survey methodology, and results of the GPR surveys completed.