Influence of saturation on the behavior of swelling soils

It has been noted that the saturated unloaded swelling rock does not swell nor disintegrate when submerged in water. Conversely, if the same rock is partly desaturated and then submerged in water, it shows swelling effects. Swelling effects become more pronounced with the increase in desaturation. The paper shows in which way this fact influences test sample preparation procedures, testing program, tunnel design practices, and measures to be undertaken during excavation in saturated rock in order to avoid negative effects of swelling. A new characteristic swelling rock curve, nonlinear on the semilogarithmic scale, can be obtained by balancing the swelling zone with the partial desaturation zone. This new nonlinar characteristic curve emphasizes, more than other curves, the known fact that small stresses significantly reduce swelling deformation, i.e. that a small allowable displacement significantly contributes to the reduction of swelling stress. On-site measurements have shown that the characteristic curve is nonlinear on the semilogarithmic scale.