Compaction and Strength Characteristics Related to Soil Structure of Organic Soil

Abstract

In order to understand the macroscopic behaviors, i. e., the compaction and strength charcteristics of non-ash-derived Kuroboku soil, the response of coarse (2-4mm) and fine (<1mm) aggregate to drying and compaction have been investigated. Aggregate samples were separated by sieving from both topsoil (organic) and subsoil (organic-free).
(1) Both coarse and fine aggregates from topsoil showed numerous cracks but never broke into smaller units after drying. In contrast, those form the subsoil disintegrated rather easily, indicating a weak inter-particle bond deterioration.
(2) The changes in number and configuration of the cracks formed in the coarse and fine aggregates after compaction were much greater for the subsoil than for topsoil in the earlier stage of drying, and the reverse was true in the later stages of drying. Almost the same tendency was observed for the shape of the fine aggregates.
(3) The overall macroscopic behavior of soil, in terms of compaction characteristics or compaction curves, could be understood as a consequence of the combination of several factors such as the linking aggregates, formation and growth of cracks, increase in mechanical strength of the aggregates themselves, induction of pore pressure, etc., after drying and compaction.
(4) Both topsoil and subsoil samples, attained the values of q_u, max, where fine aggregates arranged in a complex way with uneven and angular shapes and certain mechanical strength conferred by drying and compaction.