Abstract
Rock instabilities can represent major risks for local populations depending on their geographical location. Even if different mechanisms are known to trigger rockfalls such as precipitation, seismic activity and freezing, many rockfalls occur during periods when such trigger mechanisms are absent. Some recent studies have pointed out the role of thermal cycling in crack initiation or propagation. Here we use data from nearly five years of field monitoring of a French limestone cliff. Evolution of the aperture of joints were followed as well as displacements and temperature deep in the rock mass. We show that seasonal thermal variation affects the rock at depths of up to 6 m and subcritical cracking can probably appear even at this depth.
Highlights
Rockfall is one of the major risks that can occur in steep mountain terrain and in plains when the rivers have dug hard rock and left cliffs
Various factors can explain rockfalls: in the Alps Gunzburger, Merrien-Soukatchoff, and Guglielmi (2005) cite sharp topographic contrasts, intensive previous tectonic deformations leading to a high degree of fracturing, seismic activity and precipitation profiles with rainfall concentration over time
Studies focussing on thermal stress weathering were realised on different rock types: alluvial fans, boulders (Eppes, McFadden, Wegmann, and Scuderi, 2010; Eppes and Griffing, 2010), outcrops (Holzhausen, 1989) or quarry (Marmoni, Fiorucci, Grechi, and Martino, 2020), dome rock (Collins et al, 2018) or rock slopes (Gunzburger, Merrien-Soukatchoff, and Guglielmi, 2005; Vargas, Chavez, Gusmao, and Amaral, 2009) and different mineralogy: gneiss, granite, marble
Summary
Rockfall is one of the major risks that can occur in steep mountain terrain and in plains when the rivers have dug hard rock and left cliffs. Techniques for 4 years, to achieve sufficient spatial and temporal resolutions to characterise the displacements of the rockslide (Cloutier, Locat, Charbonneau, and Couture, 2015) Both papers study the role of thermal stress weathering based on surface monitoring (crackmeters, surface extensometers, strain gauges, ...) but thermal variation affects the rock in depth. There were no measurements on the site at the time of the event (08/01/2010), but afterwards the cliff was monitored to survey the remaining hazard and design the reinforcement This allows to have a long chronicle of monitoring during almost 5 The temperatures and strains were recorded, along open fractures inside the rock mass, at depths of 2 m, 4 m and 6 m from the face of the cliff.
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