TABLE OF CONTENTS An unusual soil can be defined as a soil that has rare or unconventional engineering behavior. Such soils are frequent causes of damage and distress or result in construction cost overruns. This is often because of their unusual properties that were not identified during the subsurface exploration or properly evaluated during the design phase. Some unusual soils are discussed below:
Rock Flour (or Bull's Liver) This soil consists predominantly of silt-size particles, but has little or no plasticity. Nonplastic rock flour contains particles of quartz, ground to a very fine state by the abrasive action of glaciers. Terzaghi and Peck (1967) state that because of its fine particle size, this soil is often mistaken as clay.
In describing this soil, the term "bull's liver" apparently comes from its in situ appearance. It has been observed that in a saturated state, it quakes like jelly from shock or vibration and can even flow like a liquid (Sowers and Sowers, 1970).
Peat Peat is composed of partially decayed organic matter (humic and nonhumic substances), where the remains of leaves, stems, twigs, and roots can be identified. The places where peat accumulates are known as peat bogs or peat moors. Its color ranges from light brown to black. Peat is unusual because it has a very high water content which makes it extremely compressible. This almost always makes it unsuitable for supporting foundations (Terzaghi and Peck, 1967).
Nonwelded Tuff and Volcanic Ash
