Geotechnical Properties of Overexcavated Expansive Shale at a Steeply Dipping Bedrock Site

Infrastructure development in the Rocky Mountain Front Range piedmont near Denver, Colorado is marked by unique hazards arising from underlying beds of steeply dipping, expansive bedrock. Efforts to reduce the occurrence of damaging differential movements among adjacent strata with dissimilar swelling characteristics often include overexcavation, remolding, and recompaction of the on-site materials. This paper examines the geotechnical engineering behavior of two end member materials obtained from adjacent shale strata at a steeply dipping site where overexcavation prior to construction is warranted. The series includes index (Atterberg limits), compaction, suction, and volume change (shrinkage) testing for each end member material as well as mass controlled mixtures of the end members. Linear relationships are noted between the relative mass fraction of the end members and the engineering behavior of the mixtures, thus allowing the swelling potential, compaction characteristics, and volume change characteristics of remolded fill at the site to be predicted from characteristics of the end member soils comprising it.