ERODABILITY CLASSIFICATION OF EARTH MATERIALS

A material erodibility classification system was developed to guide transportation engineers and geologists in the evaluation and design of highway bridge crossings to predict the risk of catastrophic failure during erosion events and to monitor channel erosion to maintain bridge safety. This classification defines six classes from Very High to Extremely Low erodibility. Application of the classical soil index properties to predict erodibility resulted in non-unique classifications. It was found that a more comprehensive geological description of soils (treated like uncemented sediments) combined with the index properties allowed more accurate classification. In addition, rock shear strength was found to give non-unique classifications. A more accurate classification prediction was obtained when the geological description, rock substance and rock mass properties were combined. The materials sampled in this study are taken from sites within the State of Texas. Weakly cemented sandstones fit the High erodibility class, thinly bedded shales were found to classify as Medium erodibility and massive, unweathered, unfractured granite and quartzite occupy the Extremely Low classification. This table allows the Bridge Division of Texas Department of Transportation to quickly assess the erodibility of materials in which bridge piers are set.