Airphoto Mapping of Montgomery County Soils for Engineering Purposes

J. D. M ollard Graduate Assistant, Joint Highway Research Project Purdue University Here are described the techniques and methods developed for mak­ ing a soil map of Montgomery County, Indiana, to be used for engi­ neering purposes. This work is an integral part of a current program to map the soils and drainage of the entire state from aerial photo­ graphs. These two mapping programs, which are being carried on con­ currently, are a cooperative effort between Purdue University and the State Highway Commission of Indiana. The application of airphoto interpretation to engineering work is based on the premise that construction and design problems are related to the position and physical properties of surface or near-surface mate­ rials. Since the physical properties of the near-surface materials, or soil profile, are revealed by certain elements contained in the airphoto soil pattern, the distribution of these soils can be determined on an areal basis. The modern trend toward regional design of highways based on soils has provided a stimulus for this type of soil mapping. Another important application of the soil map is locating large granular de­ posits—many of which, as yet, have not been recognized. Numerous lesser granular deposits also may be outlined on the airphoto; and since these are frequently near the construction site, when located and devel­ oped, they provide a source of granular materials for base courses, fill construction, county road surfacing, and sand and gravel for aggregate construction work. Still another purpose of the investigation was to determine the effi­ cacy of the airphoto for producing detailed soil maps in areas of rela­ tively complex glacial soils. The so-called “complex airphoto soil pat­ terns” are usually associated with complicated soil conditions, such as shallow Wisconsin till or gravel overlying dense, indurated, preWisconsin till. In some instances the Wisconsin drift is shallow on bedrock. Because these patterns contain certain elements which permit