ABSTRACT
Organic matter in soils is usually detrimental to engineering behavior and performance. In the field, organic soils can often be distinguished from inorganic soils by their characteristic odor and their dark gray to black color, but a visual assessment of organic materials may be very misleading in terms of engineering analysis. Even a small amount of organic matter in a soil can adversely affect the engineering properties and behavior. Therefore, it is important to determine the Organic Content whenever possible if the soils at a site are suspected of having organics. Some marine deposits may have high Organic Content. One of the worst organic deposits for building on is peat, a deposit consisting of decayed organic matter such as leaves, grass, twigs and other plant matter.
In general, organic soils are not considered suitable bearing material for most structures, even lightly loaded structures. Highly organic soils, such as peats, are usually first identified in the field by very dark brown to black colors, organic odor, and the presence of decaying plant matter. They are often fibrous and are often lightweight. When exposed to air they often oxidize very quickly, turning from black to brown in just a few minutes.
