Akihiko Oshima

Concentrations of the Naturally-Derived Toxic Elements and Its Geochemical Characteristics of the Alluvial Marine Clay Layer of Osaka Plain, Japan

In this study, we compared the bulk concentrations and the water soluble fractions extracted by the simple batch leaching test of toxic elements (B, Cr, Pb, As, Cd and Se) of the alluvial marine clays taken from Osaka Plain, Japan, to assess the risk of naturally-derived toxic elements are required to promote the utilizations of excavation surplus soils. The results showed that (1) the concentrations of B, Cr and Pb of bulk sediments and the water soluble fraction leached by simple batch test were higher at the middle of marine clay layer where clay fraction is dominant, (2) the accumulation of As into the sediments and its release would be related to the change of redox condition in the sandy layers deposited in tidal zone, (3) 0.45-pm MF was not enough to remove colloidal particles, which would affect to the reproducibility of batch leaching test, especially Pb concentration, and (4) The contents of water soluble phase were small compared to the bulk concentrations, while the change of redox condition, in which the excavation surplus soils would be exposed, must be considered to evaluate the risk of toxic element dissolution.

A Newly Developed"Compacted Bulb Foundation"and Its Bearing Characteristics

A series of centrifuge model test of “Compacted Bulb Foundation Method” was carried out to investigate the effect of tamping conditions, such as ram mass, ram base area and number of blows, and foundation base area on characteristics of its bearing capacity. Main conclusions are as follows: 1) ultimate bearing capacity and coefficient of subgrade reaction of compacted bulb was hundred times or more and ten times larger than untamped ground, respectively, 2) its bearing capacity was dependent on the ram mass per unit base area, 3) compacted bulb tamped by a ram having larger base area relative to loading area had lager bearing capacity.