Monitoring of natural thermal strains using hollow cylinder strain cells : the case of a large rock slope prone to rockfalls

Abstract : Natural daily and seasonal temperature variations are thought to play a role in rockfall triggering on fractured rock slopes. To quantify this effect, a monitoring network, based on the CSIRO Hi 12 strain cell installed in boreholes at shallow depths, has been deployed on a large slab of the ''Rochers de Valabres'' Pilot Site Laboratory in France. This paper will present the results of in situ temperature and strain measurements performed at this site and focuses on the use of thermoelastic analytical solutions and laboratory testing for results interpretation. We will demonstrate that several corrections are required to avoid artefacts linked to the thermal effect on the sensor and to obtain accurate and realistic data sets. Rectified measurements remain complex and heterogeneous yet may be correlated with the thermal boundary condition on the free surface of the slope. These results offer a quantitative contribution to the discussion regarding possible impacts of surface temperature changes on rockfall triggering