I recently spent a day with Dr. Jim Nevels.  Jim taught me how to correctly identify soil series in the field and the “backsloping” sampling technique.  Both of these are important when conducting a pedological soil survey.

 

For a pedological survey, the proposed alignment of a roadway is plotted on county soil survey maps to determine which soil series are intersected.  Then the soil series are located and sampled in the field.  The soil series can be found along the alignment or a short distance away.  Sometimes the soil series is exposed, as with a creek bed (see picture, left) and can be sampled using the “backsloping” technique.  The samples are tested for soil classification, pH, resistivity, sulfates (as appropriate) and resilient modulus. 

 

ODOT geotechnical specifications state that pedological surveys are required for new highway alignments, new parallel construction of grade (embankment and/or cut) adjacent to existing highway alignments and the raising of grade on and above existing highway alignments.

 

This pedological survey was for Interstate 40 in Del City, Oklahoma.