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Gesteinsfeuchtemessung an natürlichen Felswänden und an Bauwerken und ihr Einfluss auf die Verwitterung

Rock moisture measurements in natural and built environments and their impact on weathering

Projektleitung: Dr. O. Sass,
Dr. H.A. Viles
(University of Oxford)
Projektträger:
School of Geography and the Environment (Oxford)
 
Fördergeber: various, e.g. British Royal Society Projektzeitraum: 2003 - (open)  

Rock moisture is one of the most important determining factors for the intensity and distribution of weathering processes. However, quantitative measurements are scarce, which is partly due to the lack of reliable measurement techniques. In our studies we apply 2D-resistivity profiling adapted to the requirements of small-scale rock / stonework investigation. We use a GeoTom 2D system with individually manufactured shielded cables for 50 electrodes, connected with crocodile clips to an array of screws drilled in rockwalls or, respectively, medical ECG electrodes stuck to built walls to avoid damage. The spacing between electrodes is 4-8 cm depending on the individual wall geometry, leading to total profile length of 2-4 m. Medical ECG electrodes have been found to provide good electrical contact with the wall surface, without causing any damage and to be robust over several days or even weeks. The overall aim of the sampling campaigns is to investigate the variability of moisture contents over space and time and their relation to weathering features observed.

To date, sample campaigns have been carried out...

  • at natural rockwalls in southern Bavaria (Sass 2003),
  • at alpine rockwalls under frost conditions in the Alps (Sass 2004) and in Wales (unpublished),
  • at ruined Abbey walls (Hailes and Byland Abbey) in England (Sass & Viles 2006) and
  • at a series of walls at Worcester College, Oxford (Sass & Viles 2009a+b).

geoelektrik_fig01

Fig. 1: 2D-geoelectric measurement at a rock outcrop in Snowdonia / Wales


geoelektrik_fig02

Fig. 2: 2D-geoelectric measurement using ECG electrodes at Byland Abbey, England (left), resulting resistivity profile (right)


geoelektrik_fig03

Fig. 3: Driving rain experiment at New College Lane, Oxford


geoelektrik_fig04

Fig. 4: Cross section of Worcester College boundary wall showing the level of capillary rise



Publications related to the subject:
  • Sass, O. (2003): Moisture distribution in rockwalls derived from 2D-resistivity measurements. In: Geophysical applications in geomorphology, Zeitschrift für Geomorphologie Suppl.Vol. 132: 51- 69.
  • Sass, O. (2004): Rock moisture fluctuations during freeze-thaw cycles - preliminary results derived from electrical resistivity measurements. Polar Geography 28 (1): 13-31.
  • Sass, O. (2005): Rock moisture measurements: techniques, results, and implications for weathering. Earth Surface Processes and Landforms 30: 359-347.
  • Sass, O. & Viles, H. (2006): How wet are these walls? Testing a novel technique for measuring moisture in ruined walls. Journal of Cultural Heritage 7: 257-263.
  • Sass, O. & Viles, H.A. (2010): Wetting and drying of masonry walls: 2D-resistivity monitoring of driving rain experiments on historic stonework in Oxford, UK. Journal of Applied Geophysics 70: 72-83.
  • Sass, O. & Viles, H.A. (2010): 2D resistivity surveys of the moisture contents of historic limestone walls in Oxford, UK: Implications for understanding catastrophic stone deterioration. In: Smith, BJ, Gomez Heras, M., Viles, HA and Cassar, J (eds) Limestone in the built environment: Present day challenges for preservation of the past. Geological Society of London Special Publication 331, p. 237-249.

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