ABSTRACT:

The temporal characterization of the failure risk in rock masses can be better known by tracking progression of cracks due to weathering. So this study aims at using a non-destructive method, the resonant frequency measurement, to estimate the failure scenario of a rock sample. The experiments focus on determining resonant frequency values of two limestone rocks at different known states of uniaxial stress which are linked to states of cracking. Then the resonant frequency is measured on the same limestone rocks submitted to a global mechanical stress: freeze-thaw cycles. First this study shows that the resonant frequency can give a model of the failure scenario of a rock sample submitted to local mechanical stresses. Besides the resonant frequency variations with global stresses are similar to the trend previously observed with uniaxial stresses. So this study enables to predict its failure scenario considering the trend of the resonant frequency values.

1 INTRODUCTION
1.1 Rock falls prevention

Rock falls prevention in mountainous area requires risk management and also infrastructure maintenance. The estimation of potentially unstable rock masses can be obtained by a probabilistic approach (Chau et al. 2003; Hantz et al. 2003). But, with this method, it is not possible to determine when a particular rock will fall. Another approach to define the failure risk in rock masses as a function of time is to study the weathering phenomena (Matsuoka&Sakai 1999; Prick 2003). This method is more deterministic and thus more adapted to the prediction of the failure scenario of a rock. Besides, the failure scenario is related to the kinetic of cracking (Frayssines & Hantz 2006). 1.2 Weathering phenomena The problem when studying rock weathering in laboratory is that it is difficult to follow the rock state progression on the same rock sample.

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