ACCESSING RELATIVE IMPORTANCE OF INTERACTING DRIVING FORCES THAT HAVE CAUSED SMALL SLOPE FAILURES ON LA VETA PASS, COLORADO

In a 2.5 mile stretch of Highway 160 on the La Veta Pass in southwestern Colorado, several small slope failures have been identified. These slope failures occurred in the new section of the highway after it was built in the mid 1960’s. And thus, road construction has been identified as the main driving force behind these slope failures. This stretch of Highway 160 was constructed in the Pennsylvanian/Permian Sangre de Cristo Formation composed mainly of arkosic sandstone and conglomeratic sandstone with minor interbeds of shale and limestone. Two prominent sets of joints have also been identified in the study area, one of which is filled with calcite. The road cuts where the slope failures have occurred have been mapped at a scale of 1:5000. Here we present information on two of the slope failures. At these two locations there is considerable variation in the lithology and the attitude of the beds. Additionally, the aspect of the slope of these two road cuts vary to result in variation of the groundwater and surface flow conditions. The geology, hydrology and topography of these road cuts thus act as additional driving forces for slope failure. The objective of this study is to rank these additional driving forces in order of importance and identify how they interact with road construction to cause landslides.