Classification of organic soils for engineering geology

Abstract

This paper reviews the classifications of organic soils as applied in different countries, with particular attention drawn to those based on international and European norms. These norms propose the distinction of four groups of organic soils: peats (fibrous, pseudo-fibrous, and amorphous), gyttja and humic soils, which may be further divided into sub-groups. Organic soils are included within poor soils, because of their considerable susceptibility in relation to water, which causes their high compressibility, low strength and high shrinkage. Existing regional and international norms and plans appear not to characterise these soils sufficiently. The classification proposed in this paper will allow determination of the relationships between particular engineering geological parameters, which, to a large degree, will help planning of such objects as embankments or melioration structures. This is, however, possible only within particular genetic types. Organic soils developed in different conditions differ not only in organic matter content, but also in their chemical and physico-chemical character (i.e. degree of carbonisation, relation of humic acids to fulvic acids, bitumen content, degree of coagulation and decomposition of organic matter). The evaluation of organic soils requires firstly the determination of their origin, and then each genetic group should be subdivided based on the content of organic matter. The relationships between the physical, physico-chemical and mechanical properties should be then determined within these groups.