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The AAPG/Datapages Combined Publications Database

Utah Geological Association

Abstract


Engineering and Environmental Geology of Southwestern Utah, 1992
Pages 145-158

Identification, Characterization, and Mapping of Collapsible Soils in Southwestern Utah

Kyle M. Rollins, Tonya Williams, Robert Bleazard, Russell L. Owens

Abstract

Collapsible soils have considerable strength and stiffness in their dry natural state but settle dramatically when they become wet. Settlements associated with the wetting of these materials result in significant damage to structures and roadways. Geological and environmental factors which increase the potential for collapsible soils are detailed. These factors include: semi-arid climate, location in Holocene alluvial fans from intermittent streams, drainage basin lithology with significant shale and siltstone formations, and deep water table. Correlations between basic soil properties and collapse potential are presented based on a data base of 300 soil samples. Sandy silts and silty sands constitute the majority of problem soils. Collapse strains increase as dry density decreases and degree of saturation decreases. The Gibbs and Bara collapse criteria is extended to provide estimates of dry density and liquid limit which result in collapse strains of 5 percent and 10 percent. A collapsible soil hazard map is presented for Nephi, Utah based on geological factors and soil conditions. This map rates the potential of collapsible soils being found in a zone on a scale of 1 to 5. A collapsible soil hazard map is also presented for Cedar City, Utah which divides the city into zones exhibiting various degrees of collapse strains on wetting. The map is based on geological factors, geotechnical data from 49 sites and visual damage observations. A map of Richfield, Utah is presented which indicates where collapsible soils have and have not been found in geotechnical studies. Problem soils are associated with recent alluvial fan deposits and colluvium. It is hoped that the maps will serve to (1) heighten awareness of the hazard posed by collapsible soils, (2) provide general information of value to planners and developers and (3) alert individuals to situations where additional site-specific investigation by an engineer or geologist would be appropriate.


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