3D PHOTOGRAMMETRIC MODELING OF GLACIAL SAND AND GRAVEL DEPOSITS IN A METROPOLITAN AREA

Sand and gravel are vital aggregate resource for construction, and demand of near source supply is increasing due to rapidly expanding urban and metropolitan areas and high transportation cost. Aggregate quality and quantity of the resources are important determinants in mining economics, but this information is generally not available from conventional 2D geologic maps. New 3D geologic models have improved understanding of glacially-derived sediments around the metropolitan Chicago area, but 3D models are usually constructed from point data (borings) with limited surface geophysical transects. Economic data such as quantities, texture, and lithologies are usually obtained from transient exposures in pits or outcrops, which have not been incorporated into the 3D models.

Close range photogrammetry, however, could be used to take remote measurements to characterize sand and gravel deposits on high and unsafe outcrops. In this study, we used stereophotography to measure a 214 meter long, 13 meter high exposure at a pit 45 miles northwest of Chicago to demonstrate the usefulness of this methodology.

Using the remote sensing method of unsupervised classification on conventional RGB digital photography allowed discrimination of the dolomites and boulders from smaller textures of mixed lithologies. Lithostratigraphic description of a measured section showed 7 meters of matrix-supported gravel consisting of about 5% cobble or boulder on the top (with the largest one 642 mm), and 6 meters of coarse to fine sand with pebble gravels at the bottom (with the largest one 125mm). The remote sensing correlates well with the results from lithostratigraphic description.

Computer-based georeferenced stereomodels allowed measurements of dip and dip direction of imbricated cobbles on high and unstable outcrops. Our measurements showed that the deltaic sand and gravel sediments were deposited incrementally by periodic flooding from the east and sometimes from the northeast.

We concluded that the data of lithology, texture and dipping direction derived from photogrammetric technology can aid characterization of the quality and quantity of sand and gravel deposits.