An Infrared Thermography Approach to Evaluate the Strength of a Rock Cliff

Abstract

The mechanical strength is a fundamental characteristic of rock masses that can be empirically related to a number of properties and to the likelihood of instability phenomena. Direct field acquisition of mechanical information on tall cliffs, however, is challenging, particularly in coastal and alpine environments. Here, we propose a method to evaluate the compressive strength of rock blocks by monitoring their thermal behaviour over a 24‐h period by infrared thermography. Using a drone‐mounted thermal camera and a Schmidt (rebound) hammer, we surveyed granitoid and aphanitic blocks in a coastal cliff in south‐east Sardinia, Italy. We observed a strong correlation between a simple cooling index, evaluated in the hours succeeding the temperature peak, and strength values estimated from rebound hammer test results. We also noticed different heatingcooling patterns in relation to the nature and structure of the rock blocks and to the size of thefractures. Although further validation is warranted in different morpho‐lithological settings, we believe the proposed method may prove a valid tool for the characterisation of non‐directly accessible rock faces, and may serve as a basis for the formulation, calibration, and validation of thermo‐hydro‐mechanical constitutive models.

Evaluation of InfraRed Thermography Supported by UAV and Field Surveys for Rock Mass Characterization in Complex Settings

“…Consequently, protruding sectors of the slope facing the direction of the solar radiation gain more heat and project their shadows on the indented and inner parts, which are represented by lower temperatures in the thermograms. These outcomes are in agreement with the results reported in [17,18,21,26,32]. For instance, Figure 9f illustrates that at 13:55 the sector of the rock mass with slightly different aspect (dipping SW) are warmer compared to the other zones as an effect of the solar radiation.…”

“…The use of infrared thermography was also extended to geotechnical applications: for instance, the relation between the cooling index of rocks and the compressive strength of rock blocks was identified by coupling IRT and Schmidt Hammer tests [32]. In addition, methods to estimate the porosity of rock samples [33], to predict cracks development [34], wedge indentation [35] and to detect microstructural changes [36] at the laboratory scale were recently proposed.…”

UAV-Based Photogrammetry and Infrared Thermography Applied to Rock Mass Survey for Geomechanical Purposes

“…They found also that there is a relation between the surface temperature offered by discontinuity traces, surveyed at night, and their aperture and persistence, with the highest temperatures found at the most open/persistent cracks. The aspect related to CRI was further investigated by Loche et al [27] in the field and by Mineo and Pappalardo [28] in the laboratory, who implemented the application of such methodologies.…”

Observation of the rock slope thermal regime, coupled with crackmeter stability monitoring: initial results from three different sites in Czechia (central Europe)

“…Usually, monitoring methods using various sensors are combined. Large rockslides were monitored by Crosta et al (2017), Zangerl et al (2010), and Loew et al (2012) using a combination of remote sensing, geodetical network, and borehole inclinometers. Experimental monitoring systems aim to develop or test new sensors or approaches (Loew et al, 2017;Jaboyedoff et al, 2004Jaboyedoff et al, , 2011Chen et al, 2017;Hellmy et al, 2019) or to describe long-term processes of rock slope destabilisation (Fantini et al, 2016;Kromer et al, 2019;Du et al, 2017).…”