Blue clay slope angle in relation to some geological and geotechnical characteristics, Italy

Observation of blue clay slopes outcroppingalong the Italian peninsula (Apennine foredeepand other inland areas) promptedinvestigation into several factors whichgovern their actual slope angle. Though characterized bygood gradient, slope angle may differ from slope to slope,as well as within certain limited areas.The study attempts to connect structural order (dipstrata) and shear strength of the soil to explain slopeangle. In many cases it is possible to distinguish (i) slopeangle controlled by substratum and, thus, characterizedby shear strength higher than the residual condition,and (ii) slope angle controlled by colluvium cover,characterized by shear strength reduced to residual.Following an infinite slope stability model approach,the above conditions are connected to the half residualfriction angle value, R′/2, which splits the slopes intotwo main types: cover-controlled, characterized by≤R′/2 and completely or in part substratum-controlled,characterized by >R′/2.Slope angle distribution, deduced from slope map,can help us to understand the relative role of footsloperemoval processes and to distinguish slope type,substratum-controlled or colluvium-controlled.This study cannot embrace all the factors and processesleading to a blue clay slope angle, and localgeomorphological processes may complicate the outlineproposed, though it does provide a useful first approach.