So Kondo

Evaluation of the Effect of Soil Paticle Damage on ²²²Rn Elution

Tomoko Ohta

 This study investigates the effect of soil particle damage on the elution of radon(²²²Rn). ²²²Rn is a radioactive gas generated from radium in soil and rocks. Changes in ²²²Rn concentration in groundwater have been reported before earthquakes. Therefore, understanding the mechanism of ²²²Rn release is important in geotechnical and disaster prevention studies.
 In this research,direct shear tests were conducted using Toyoura snad and Granite gravel. After the shear tests, soil particles were observed using a scanning electron microscope(SEM) and X-ray CT to examine surface and internal cracks. Grain size distribution was also measured. The amount of ²²²Rn released from the soil was measured after strong the samples insealed containers filled pure water.
 The results showed that in Granite gravel,higher normal stress and lower void ratio led to an increase in ²²²Rn elution. Inaddition, the number of cracks, especially newly generated cracks, increased with higher ²²²Rn release. These results suggest that particle damage and crack development create more pathways for ²²²Rn to move from inside the particles to the water. On the other hand, clear relationships were not observed in Toyoura sand. 
 This study suggests that microscopic damage of soil particles plays an important role in ²²²Rn elution behavior.