Case Studies on the Application of Remote Sensing Data to Geotechnical Investigations in Ontario, Canada
Authors: Singhroy VH 
Published: February 2009

All stages of civil engineering construction projects require the systematic collection of geotechnical and environmental data. In the preliminary stages, current topographic and geological maps and reports are studied before field sampling is begun. A variety of remote sensing data can also provide valuable information for site selection, geotechnical sampling, lithological mapping, subsurface investigations, and site monitoring during and after construction. This paper reports on the contributions and limitations of remote sensing data to: (1) the planning and construction of cross-country natural gas pipelines; (2) the search for suitable near-surface construction materials; (3) the evaluation of sites for the disposal of hazardous water; and (4) the identification of conditions likely to give rise to mine roof instabilities.

Various types of remote sensing data were acquired, analyzed, and integrated with field data to plan construction activities, determine site conditions, and assess environmental effects before, during, and after pipeline construction. Large-scale color-infrared aerial photography was taken before, during, and after construction for a number of pipeline routes and river crossings in southern Ontario, Canada. Aerial video recordings were also acquired for selected sites. The digital analysis of Landsat data, as well as the interpretation of thematic mapper (TM) and Seasat SAR data, provided information on regional terrain and land cover for route selection. Conclusions were drawn as to the type of information that could be derived from each type of imagery.

Airborne thermography was used to delineate an area of near-surface aggregate in southern Ontario overlain by a layer of sand-silt till 3 to 7 m thick. The study was based on the relationship between soil moisture and texture and on the sensitivity of thermal data to differences in surface soil moisture content, determined in large part by surface drainage characteristics.

The interpretation of infrared and geophysical data provided initial data prior to the detailed mapping of a potential nuclear waste disposal site in northern Ontario. A granitic intrusive 36 km2 in area was being investigated to determine its suitability for the safe long-term disposal of nuclear waste. The terrain was covered with variable draft sustaining extensive vegetation growth. Various types of surficial materials were delineated and dikes and faults were identified from the interpretation of both predawn thermal imagery and large-scale infrared photography.

Visible infrared and thermal data were used successfully to detect areas of instability in the roof of a gypsum mine in southern Ontario. Such local instability as small-scale wedge failures, the loosening of local rock slabs at the head of support pillars and extensive ground-water seepages had reduced the number of working faces and threatened the safety of miners. Imagery obtained in spring permitted the mapping of subtle drainage and fracture patterns on the surface. These patterns reflected folds and jointing trends in the subsurface stratigraphy. The hydrogeological information derived from the remote sensing techniques thus permitted the determination of safe mining areas when integrated with local seismic refraction surveys and underground observations.

From the above investigations, it is clear that the amount of moisture retained within the soil and in fractures at the time of data acquisition is one of the main links between remote sensing and geotechnical investigations.