Cesium-adsorption capacity and hydraulic conductivity of sealing geomaterial made with marine clay,bentonite, and zeolite

Great amounts of soil and waste contaminated with radioactive cesium have been generated due to the decontamination work after the Fukushima Daiichi Nuclear Power Plant accident. The aim of this study is to develop a sealing geomaterial for use at the disposal facilities of the soil and waste constructed in the maritime environment. The geomaterial consists of marine clay, bentonite, and zeolite. The hydraulic conductivity and cesium-adsorption performance of the geomaterial were examined through laboratory tests with different proportions of bentonite and zeolite added to marine clay. It was concluded that the hydraulic conductivity could be reduced to the required level by increasing the amount of bentonite and that the cesium-adsorption capacity could be enhanced by increasing the amount of zeolite.     

Evaluation of erosion resistance capacity on compacted weathered granite soil using non-destructive tests

This paper deals with the evaluation of the erodibility of compacted weathered granite soil through non-destructive tests. A rotating erosion cylinder test (RECT) was employed to evaluate the erosion resistance capacity of weathered granite soil with various relative densities and pre-consolidation pressures. In addition, non-destructive tests, i.e., electrical resistivity and bender element tests, were conducted to investigate a correlation between erosion resistance characteristic and non-destructive property. The results indicated that the critical shear stress increased with an increase in relative density and pre-consolidation pressure, and the threshold shear stress increased with an increase in relative density, while its increase was independent of an increase in pre-consolidation pressure. Thus, the relative density of weathered granite soil has a more significant effect on erosion resistance than its pre-consolidation pressure. The electrical resistivity and shear wave velocity increased with increases in relative density and pre-consolidation pressure, and these results had a good correlation with the porosity of weathered granite soils. The empirical equations for estimating the critical shear stress and the threshold shear stress of weathered granite soils, based on the relationship between the values of erosion resistance capacity normalized by those of non-destructive tests and porosity, were proposed. It is expected that the proposed correlation might be useful in determining the erosion resistance capacity of compacted weathered granite soil by using non-destructive tests.

     

Experimental evaluation of the effect of the incidence angle and consolidation pressure on the hydraulic resistance capacity of clayey soils

The primary aim of this study is to examine the variations in erosion and hydraulic resistance capacity of clayey soils with a changing water flow under variable flow conditions. Clayey soils were artificially prepared with various kaolin-sand ratios and consolidation pressures. A laboratory flume apparatus, called an erosion function apparatus (EFA), is improved to measure the scour rate and critical shear stress of samples with changing water flow directions. A series of tests that use the improved EFA was performed for artificial clayey soils considering various directional changes in the water flow at incidence angles of 0°, 90°, 135°, and 180°. Based on the test results, the undrained shear strength indicated the highest correlation with the critical shear stress. Furthermore, the critical shear stress decreased and the scour rate increased with an increasing incidence angle. Finally, the characteristics of the hydraulic resistance capacity, the variations in critical shear stress, and the scour rate changed with the magnitude of consolidation pressure of the clayey soils.