Thrall, F.G., 1981, Geotechnical significance of poorly crystalline soils derived from volcanic ash: Corvallis, Oregon, Oregon State University, Ph.D. dissertation, 445 p.
Poorly crystalline soils derived from volcanic ash under moist climatic conditions develop unique engineering properties which significantly depend on their weathering and drying histories. These soils occur in many areas of the world associated with volcanic activity. Though volcanic ash soils have been related to engineering problems in Alaska, Hawaii, and Oregon, their presence has largely been ignored by the engineering profession. Sampling of disturbed and undisturbed specimens from specific sites in Oregon and Alaska was conducted. These samples were studied using electron microscopy, infrared spectroscopy, and X-ray diffraction analysis to determine mineralogical and structural composition. Atterberg limits, moisture-density characteristics, specific gravity, grain size and strength behavior were investigated. Characterization tests were also conducted on air and oven dried soils to determine irreversible changes which occur with drying. A literature review oriented to obtain all available geotechnical data on soils derived from volcanic ash is included as an integral part of the study. Geotechnical data, from this review, gathered for volcanic ash soils from around the world, are presented in summary form. Correlations between engineering and index properties for poorly crystalline soils derived from volcanic ash are investigated for the combined literature and laboratory studies. A guide which geotechnical engineers can use to recognize these soils in the field is proposed. Results indicate that engineering and index properties can be divided into three statistically separate groups which may be distinguished by specific physical characteristics such as color, mineral content, and drying history. Correlation studies show that values for effective angle of internal friction ((phi)'), undrained shear strength (c), and compression index (Cc) can best be estimated from in situ void ratio (e(,o)) as the predictor property. The major difference in engineering behavior between crystalline soils and poorly crystalline soils derived from volcanic ash results from the presence of saturated amorphous materials within the soil matrix. These materials appear to have an unusual distribution of small pores within their structure which make them sensitive to remolding and/or drying.
Theses and Dissertations