Stress generated by the freeze-thaw process in open cracks of rock walls: empirical model for tight limestone

In mountainous areas, freezing is a prominent phenomenon for weathering processes in rock walls. A freezing front penetrates rock crack networks and causes its propagation. To study the evolution of rock mass stability, a suitable model of stress generated by freezing in open rock cracks is needed. This stress evaluated by the simple volume expansion model in a closed crack is too high to be realistic. In this paper, we present an assessment method for this stress and some results. Different experiments on notched limestone specimens submitted to freeze-thaw cycles were performed. Three different tight limestones (Larrys, Chamesson, Pierre de Lens) were tested. Actually, the stress generated by freezing begins to grow at the top of the notch where an ice plug is created and makes it possible for higher stresses to develop in deeper parts of the notch. Consequently, the stress induced by freezing depends on the geometry of the open crack represented by the notch. This value is, however, limited by the permeability of the surrounding rock matrix. A model of the stress evolution generated by freezing along an open crack was established and its envelope curve, named maximum stress, was parameterized. This maximum stress generated by freezing along the crack is completely defined by knowledge of the pore network of the limestone matrix and the geometry of the crack.