Potentially swelling soil and rock in the front range urban corridor, Colorado

Abstract

Swelling is generally caused by expansion due to wetting of certain clay minerals in dry soils. Therefore, arid or semiarid areas such as Colorado with seasonal changes in soil moisture, experience a much higher frequency of swelling problems than eastern states which have higher rainfall. The Front Range Urban Corridor includes the foothills and piedmont area of Colorado from Fort Collins and Greeley on the north to Pueblo and Canon City on the south. This area includes more than 80 percent of Colorado's population. Although only half of the 30 sedimentary bedrock formations that are exposed in the Urban Corridor contain swelling clay, these swelling formations underlie all of the major cities. Swelling clays are, therefore, one of the most significant, widespread, and costly, but least publicized, geologic hazards in Colorado. The report sections include: What is swelling clay; How can one recognize swelling soil or rock; Examples of swelling clay damage; Potential hazard areas in the Urban Corridor; What can be done to minimize damage; and Suggestions for further study. Also included are four appendices containing a) Glossary, b) Sources of project data, c) Factors influencing swelling of natural clay soils, and d) Methods for estimating swell potential from soil index properties.