Abstract
In a coal mine tunnel excavated at the below the sea floor, we investigated the slaking properties of sedimentary rocks, coarse sandstone, fine sandstone and sandy mudstone. Rock samples, which were calcite-free rocks, disintegrated on steeping in distilled water, following an initial drying phase. On the other hand, samples maintained their integrity in contact with brackish water (NaCl: 3.3wt%).
Strongly slaking rocks were generally collected in the excavated tunnel below the sea-floor. These rocks contained more than 1.5wt% Na-type smectite.
Non-slaking rocks were collected at ground surface exposures of the coal-bearing formation and in an oxidization zone associated with a fault in the tunnel. These rocks contained less than 5wt% mixed ion-type smectite. The uniaxial compressive and tensile strength of coarse sandstone saturated with brackish water was significantly larger than that of the rock saturated with distilled water. Coarse sandstone showed a higher permeability for brackish water (with higher viscosity) than for distilled water. Coarse sandstone saturated with distilled water in rock permeability tests disintegrated when seeped in distilled water after drying. In contrast, coarse sandstone saturated with CaCl2 solution did not disintegrate during similar contact with distilled water after drying.
The chemical composition of original porewater, thickness of the diffusion double-layer and drying process thus have a clear influence on the slaking, strength, and permeability properties of these sedimentary rocks.
