Rheological model of soft rock creep based on the tests on marl

Basic task in mathematical description of time dependent deformations of a certain material is to define deformations as a function of time, stress and temperature. In order to formulate the rheological model of time dependent deformations of soft rocks, which is presented in this paper, laboratory tests on marl creep have been carried out. Experimental research on marl creep has been carried out in the conditions of limited change of the room temperature, having in mind that changes of temperature for usual needs in building works of tunnel-construction are also limited. Thus, in further analysis, which has been presented here, creep deformation will be treated as a value independent from temperature. The suggested rheological model is possible to be applied for the correct description of time deformations even after loading and after total or partial unloading, which is specially significant for the stress-deformation condition in the rock mass around the tunnel opening.