Some Problems of Swelling in Geotechnical Practice-Influence of saturation on the behavior of argillaceous swelling rock

Argillaceous swelling rocks are generally unsaturated. Partial rock desaturation due to tunnel ventilation is a phenomenon that inevitably occurs during construction of underground structures. The characteristics of the unsaturated zone must be known in order to predict the swelling behavior of natural expansive rock. The laboratory tests described here provide information for determining the necessary parameters. The numerical model used to predict moisture distribution within the desiccating sample provides a realistic description of the process. The presented results contribute to a better understanding of the swelling rock behavior and provide a rational framework for the analysis of the desiccation process and its influence on the swelling. The influence of swelling rock desaturation on its behavior in tunneling is described. It has been demonstrated that the same rock may abide by different swelling laws, depending on the saturation level. The consequence of this is the nonlinear characteristic curve in semilogarithmic scale. The nonlinearity of the characteristic curve is of great significance in the design and construction of tunnels. This new nonlinear 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. In other words, this curve emphasizes the danger of installing resistant tunnel supports, while pointing to advantages of yielding supports.