Slaking is a specific property of sedimentary rocks. Slaking causal factors are the ionic concentration and cationic valence of in-site groundwater, dehydration of pore water and solution chemistry to contact with the rock after dehydration. Opaliuns clay (Switzerland), coarse sandstone (Kushiro coal mine, Japan) and fine sandstone (Ikeshima coal mine, Japan) are used to investigate the slaking property. The pore water of these rocks consists of high sodium chloride like seawater.
Under the brackish water environment, the interlayer cation in smectite is occupied by sodium ion. The univalent cation rich smectite normally has one water molecule layer under the low humidity environment. The divalent cation rich smctite has two water molecule layers. Sedimentary rocks including univalent cation rich smectite are more shrinkable than the divalent cation rich smectite including sedimentary rock. Strongly rapid slaking rocks are generally contained more than 1.5wt% sodium rich smectite.
The dehydrated sedimentary rocks sampled at the brackish groundwater environment easily disintegrate to contact with the low ionic concentration solution like fresh water. The other side, these rocks don t disintegrate to contact with high ionic concentration solution like seawater. Zeta potential of rock particles obviously involves in slaking properties. In the case of the underground disposal of radioactive nuclear waste in sedimentary rocks, an unsaturated zone is possibly formed around the waste pit due to ventilation and additional heat from waste. To keep the waste pit wall, further investigations is needed with special attention to rapid slaking properties by using a deep underground sedimentary rock site.