Stabilität und Verwitterungsverhalten natürlicher und künstlicher Böschungen in Kalk-Mergelwechselfolgen

Summary

The aim of this project was to quantify the influence of lithology and dip on the inclination of natural and artificial slopes in limestonemarlstone sequences. In order to compare the results, the distinction must be made between slopes with and those without active basal erosion by a watercourse. Such erosion will lead to a limit equilibrium profile of the slope. Where basal erosion is not present, the inclination of the slope will be controlled by different weathering mechanisms (slaking in marlstones, leaching in limestones). Thus the resulting inclination reaches a critical gradient, which is controlled by weathering mechanisms.

The lithology of the slope was classified by means of a limestone to marlstone ratio. This was done by dividing the slope into sections of overall uniform lithology. For each section the average thicknesses of the limestone and marlstone beds were determined. The quotient of these two parameters is the limestone-marlstone ratio.

In order to have a better understanding of the influence of lithology on the inclination, only slopes lying within a quasi-homogeneous area (that is, identical dip and joint sets) were compared. In doing so, only slopes with beds dipping against the inclination of the slopes were used. Within the different quasi-homogeneous areas an exponential relationship exists between the slope gradient and the limestone-marlstone ratio(figs. 2 & 3). For equilibrium profiles not limited by basal erosion, the inclinations have been estimated mathematically by a simple model (secondary toppling) and compared to field measurements (fig. 7).

Furthermore the rate of retreat of vertical walls due to weathering has been determined in abandoned quarries in limestone-marlstone sequences (fig. 9). The amount of talus accumulated at the bases of step slopes during a certain time interval can be calculated from these rates of retreat.