Laboratory and Field Investigation on Variation of Erodibility with Dry Unit Weight of Different Soils

Better understanding the erodibility of a given type of soil can help predict scour at bridge piers more accurately. In the past, researchers have looked into erosion of soils with the ultimate objective of understanding the erodibility with respect to the other geotechnical properties. Most research has shown the difficulties associated with correlating erodibility to any one soil property. The research described in this paper is about an investigation on erodibility and dry unit weight of soil with varying fractions of fines. Soils tested using laboratory Jet Erosion Test (JET) indicated that the logarithm of erodibility makes a linear inverse relationship with the dry unit weight. In situ JETs confirmed the range of erodibilities established by the laboratory JETs. The best correlations between erodibility and dry unit weight appeared within a single category of soil as classified by the Unified Soil Classification System. Background Two of the most common causes of bridge failure in the United States are flooding and scour accounting for 165 and 78 cases of bridge failure respectively between 1989-2000, which represents over 47% of all bridge failures that occurred. In addition, the failures caused by flooding are also believed to be related to scour (Wardhana and Hadipriono 2003). As such, accurate estimation of bridge scour is essential to protect lives and property while preventing over designing piers that can be costly. Scour prediction relies on empirical or semi-empirical equations, as a means to predict scour but most equations are applied over a range of soil conditions from clean sand to clay without consideration for soil variability. Scour is the erosion of streambed or bank material due to flowing water (Richardson and Davis 2001). Therefore, better understanding the erosion potential of a given type of soil should help predict scour at bridge piers more accurately. Erodibility is the property that describes the erosion potential of a soil in terms of the energy needed for erosion to occur. If erosion is the transportation or movement of a