Massenbewegungen im Saar-Nahe-Gebiet unter Berücksichtigung des Verwitterungsverhaltens der Pelite

Summary

Mass movements are geologic processes which cause a lot of damage. The object of this project was the investigation of mass movements in Rotliegendes rocks of the Saar-Nahe-region, SW-Germany. Field and laboratory work was employed to achieve a better understanding of the processes.

The field investigations showed the following results:

• Two types of mass movements occur: fall (13%) and slide (87%).

• The most important cause of mass movements are the geologic conditions, e.g. the parallel run of bedding planes and slope gradient. Additional factors can be water (precipitation, ground water, introduced water) and construction.

• Most of the mass movements are shallow, i.e. the slip plane is less than 10 m deep.

• The mass movements take place mostly in winter.

• 7,7 percent of the examined area is endangered to move, 2,6 percent is actively moving.

• A slope stability map was prepared (fig. 5).

• The drying-wetting-test, the alternate-wetting-test and the freezethaw- test were used to classify the rock samples concerning their weatherability. The results could be very well correlated (fig. 7,7).

• The drying-wetting-test is recommended for the Classification of the rocks. It is standardized, cheap and shows the clearest results. Besides, alternate Wetting and drying is the most important factor of weathering in the region in question.

• The determination of the petrographic-mineralogic and physical properties of the rocks showed, that the weatherability of the rocks is dependent on microtexture, carbonate content, clay mineralogy and water-absorbing capacity. The mean grain size and the consolidation are relatively unimportant.

Most of the mass movements occur within the weathering zone. So the weathering behaviour of the rocks was studied in the laboratory. The examinations showed the following:

• The drying-wetting-test, the alternate-wetting-test and the freezethaw- test were used to classify the rock samples concerning their weatherability. The results could be very well correlated (fig. 7,7).

• The drying-wetting-test is recommended for the Classification of the rocks. It is standardized, cheap and shows the clearest results. Besides, alternate Wetting and drying is the most important factor of weathering in the region in question.

• The determination of the petrographic-mineralogic and physical properties of the rocks showed, that the weatherability of the rocks is dependent on microtexture, carbonate content, clay mineralogy and water-absorbing capacity. The mean grain size and the consolidation are relatively unimportant.

The investigations showed, that a combination of field and laboratory examinations is a good basis for the evaluation of slope stability.