One-dimensional compression behavior of a soil with high organic matter content

This paper addresses the one-dimensional compression behavior of a highly organic sapric soil in both its natural intact and reconstituted states, based on the results of constant rate of strain and incremental loading oedometer tests. The soil investigated contains 40-60% organic matter, comprised mainly of highly processed humic substances, and represents a "transitional" material between inorganic clays and peats. The inorganic portion is entirely finer than 0.075 mm, with over 60% in the clay fraction (<2 mu m), which XRD analyses indicate contains smectite and vermiculite. Testing of the soil in its intact state relies on high quality block samples and shows that the natural intact soil displays intermediate behavior between that typical of inorganic soft clays and that observed in peats, in terms of compressibility, hydraulic conductivity, and change in hydraulic conductivity with void ratio. As in the case of peats, the coefficient of consolidation is observed to decrease with increasing stress level and the soil shows a high tendency to creep, with C-alpha/C-c at the high end of values reported in the literature. Comparison of the compression results for the natural and the reconstituted soil serves to illustrate the degree of structuring of the natural soil, which is found to be consistent with that typical of natural sedimentary inorganic clays.