The influence of swelling rock desaturation on its behavior in tunneling is described. The swelling potential of the desaturated rock will be more pronounced, when compared to similar rock in saturated state. A new characteristic curve for the swelling rock mass was defined based on the approach defined by Kovari et al. (1988). At that, the influence of desaturation on activation of the swelling rock potential was taken into account. The proposed curve is nonlinear on a semilogarithmic scale which emphasizes even more the observed phenomenon that a small allowed floor heave significantly reduces the swelling pressure, i.e. that a small lining resistance may significantly reduce the floor heave.
The swelling was first modeled by Wiesman (1914) using as an example the Lower Hounstein Tunnel in Switzerland. Terzaghi, who also studied the swelling phenomenon in tunneling, included swelling rocks in his classification where they are represented in category 9. The example of these authors was followed by many researches who have used various approaches in their attempts to model swelling process during tunnel construction and use. One of the approaches consisted in defining the so called characteristic curve of the swelling rock. The characteristic curve of the swelling rock identifies the relationship between the tunnel floor heave (ua) and lining resistance (Pa). The lining resistance is the pressure exerted by lining onto the surrounding rock. The swelling pressure is the pressure the rock exerts on the lining, floor slab or the invert. This approach was introduced in engineering practice by Lombardi (1979), while Kovari et al. (1988). provide some new ideas on the nature of the characteristic curve of the swelling rock. The empirical approach to tunnel design has so far provided only a modest contribution to tunneling in swelling rock.
