Abstract
The so-called soft grounds, characterized by peaty layers, consist mainly of lake or swamp sediments deposited in Holocene drowned valleys which had been blockaded by coastal or flood drifts at the mouth of bay or tributary valleys.
Flood plains between natural levees and deltas near the mouth of gently graded rivers pouring into calm bay are another conditions under which the soft grounds are formed.
Moreover, at some soft grounds, artesian conditions are found.
This may promote the development of soft layers.
The alluvial clays deposited in the drowned valleys surrounded by mountains consisted of mainly volcanic soils and rocks, have a tendency to possess a large void ratio in comparison with ordinary environments.
