Potentials of monitoring rock fall hazards by GPR: considering as example the results of Salzburg

Abstract

A part of the IUGS-UNESCO research project "Landslide Hazard Assessment and Cultural Heritage" includes testing the application of geophysical methods for assessing hazard risks to people and cultural assets. In this work, Austria contributed with a study on the assessment of rock-fall hazards. As the Old Town of Salzburg is a prime example of such hazards, systematic GPR-measurements were made on major rock surfaces. The aim of the exploration with GPR was to assess the potential of the method for monitoring rock walls. That is, whether structures in the rock mass which could become important when considering the risk of a rock fall, can be imaged. To manage this problem successfully, moving the antenna over the rough rock surface was made as regular as possible. The effects of vegetation lifting the antenna from the rock surface and of overhanging regions could not be avoided. Due to the loss of coupling of the antenna and the change of radiation pattern, some interference of the records occurred. Thus, only after processing could it become clear which reflections came from within the rock. A three-dimensional survey of discontinuities in the rock requires accurate mapping of the rock surface by photogrammetric methods, to get a digital terrain model for the analysis of the GPR records. The results of repeated measurements have proved to be of essential relevance. They have shown that it is possible to reveal changes with time. For the interpretation of such observations, modeling is a very useful tool.

On the use of dispersive APVO GPR curves for thin-bed properties estimation: Theory and application to fracture characterization

“…Recently, ground-penetrating radar ͑GPR͒ investigations conducted directly on various cliff faces successfully provided images of fracture continuity with a satisfying resolution ͑Jeannin et al, Roch et al, 2006; In some cases, these images were quantitatively interpreted in terms of maximum rock-bridge percentage ͑Deparis et al, 2007͒. Even if it constitutes a large projection to approach the stability factor in terms of hazard assessment, we need more quantitative information about discontinuities ͑aperture and filling properties͒ to determine the stability factor.…”

Ground reinforced embankments for rockfall protection: design and evaluation of full scale tests

“…After the definition of the risk for the areas sited below the rock slope (Evans and Hungr 1993;Cancelli and Crosta 1993;Pierson et al 1990;Duncan and Norman 1996;Roch et al 2006;Bonnard and Corominas 2005) and the forecast of the possible detachment points and of the trajectories of the falling blocks, it is possible to chose the appropriate stabilisation method for the particular conditions at each site (Peckover and Kerr 1977;Duncan and Norman 1996;Giani 1992;Pelizza et al 2004). Different types of technological solutions can be used, some of which are able to prevent the detachment of rock from the rock walls (active interventions), whereas others are designed and constructed to intercept and stop the blocks during their movement (passive interventions).…”

Dynamic response of the Chamousset rock column (Western Alps, France)

“…Rock bridge mapping is then a crucial step for rock failure assessment. In the past few years, several authors [ Jeannin et al , 2006; Roch et al , 2006; Deparis et al ., 2008a] have applied geophysical techniques for delineating and characterizing the joint pattern inside the rock mass. It turned out that ground penetrating radar (GPR) profiles conducted on the cliff face yielded the best results in terms of penetration and resolution and provided the geometry and continuity of the major open joints.…”