Geotechnical properties of ash deposits near Hilo, Hawaii

Abstract

Open-File Report 82-279This report is prelim!inary and has not been reviewed for conformity with U.S. Geological Survey editorial standards and strati graphic nomenclature.Any use of trade names is for descriptive purposes only and does not imply endorsement by the USGS. ABSTRACTTwo holes were hand augered and sampled in ash deposits near Hilo, Hawaii. Color, water content and sensitivity of the ash were measured in the field. The ash alternated between reddish brown and dark reddish brown in color and had water contents as high as 392%. A downhole vane shear device measured sensitivities as high as 6.9. A series of laboratory tests including grain size distribution, Atterberg limits, X-ray diffraction analysis, total carbon determination, vane shear, direct shear and triaxial tests were performed to determine the composition and geotechnical properties of the ash. The ash is very fine grained, highly plastic and composed mostly of gibbsite and amorphous material, presumably allophane. The ash has a high angle of internal friction ranging from 40-43° and is classified as medium to very sensitive.

Creep, strength and other characteristics of Hawaiian volcanic soils

“…The slightly granular response agrees with a relatively high frictional resistance, larger than what would be expected for most temperate sedimentary clays with equivalent plasticity. Nonetheless, the friction angles in Table 2 are comparable to those obtained in previous studies of Hawaiian ash soils by Tuncer & Lohnes (1977) and Wieczorek et al (1982). The high plasticity of this soil, in its non-dried state, can obviously not be used to estimate its strength using classical relationships such as the one by Kenney (1959) and others.…”

“…However, there was little evidence of the presence of these two minerals upon X-ray diffraction examination, as is discussed below. A complicating factor is that some of the Hilo area soils also have a significant organic content (Wieczorek et al, 1982), the drying of which is irreversible as well. In any case, all the soils in this study were kept moist at all times.…”