Meine Dissertation






Landslide research in the Bonn region have led to many new scientific discoveries in the last 10 years. The susceptibility to landslides should now be judged from to the HARDEN-BICKER maps (1994), which are first used to assess all of the slope positions in Bonn for existing landslides, and the subsequent analysis of local slide objects.
Initial opinions on the danger assessment were made possible by creating landslide susceptibility maps, which are based on disposition models. The advantage of this method is the extensive amount of available information on potential landsliding risks. Extremely varied depending on the location, parameters that determine landslide susceptibility like the inclusion of pore pressure or the depth of the slip plane are not included in this method. For this reason, no definite statement can be made about the stability of the slope. Nonetheless, the use of landslide susceptibility maps is still justified, for example when identifying slope positions that have not yet been affected by a landslide.
Two disposition models, which have different structures, scale and meanings, were supposed to identify the landslide susceptibility for certain slope positions in Bonn. The susceptibilities that were identified correlated well with the frequency of landslides in the study area. However, geological data sets, which offered a low data rate due to its scale, led to faulty surface analyses in certain cases. In addition, the overrating of the slope in both models pushed important parameters that are relevant to landslides into the background. Nonetheless, satisfactory results could be achieved for the main study areas like Katzenlochbach-Valley, Melb-Valley, the Venusberg slope and the slopes in the Friesdorf area.
A completely different way was investigated with the help of process models that are based on mathematical-physical laws. These models apply to individual slopes and should give us information on the stability of the slope. A lot of time with considerable analyses and measurements was needed to calculate the safety factor, like at the recent landslide on the weathered Trachyttuff in the Pleiser Hügelland. This landslide occurred in the lower region of a considerably older landslide. Calculations with the aid of empirical-mathematical models showed a stable slide state. However, movements could be identified with the aid of an inclinometer that led us to suspect that another slip plane that was non-localized for the time being could be the reason for the direction of movement. Determining the slip planes in the area of the slide proved to be extremely problematic. Numerous analyses led to a delimination of the depth of the slip plane, but the exact location could only be identified with the use of a soil pit. It turns out that the slip plane was very irregular and at different depths.
Hydrological analyses identified an aquifer in the sandy Trachyttuff of the recent slide. He rises upwards very weak and could no longer be identified in the higher positions of the old landslide.
The state of activity of a landslide in the Melb-Valley near Bonn could also be recorded using movement measurements. The geological subsoil of this landslide consists of interstratification of waterproof, sedimentary tertiary clay and water-permeable fine sand with interposed brown coal planes. Optical signs such as recent spalling and mass deficiencies in the area of the sliding lobe led us to assume at the beginning of the study that there was a high grade of landslide activity; however, movement measurements using wooden pegs did not support this assumption. With regard to the original assump-tion, the low rainfall between 1995 - 1997 may be the cause for the low activity; however, we have no proof for this theory.
Close-meshed bore probes on a landslide area in Katzenlochbach-Valley should be able to offer evidence on the dynamics and age of the more or less natural landslides. Due to the dense drilling network, the landslides could be subdivided in the three parts. In contrast to the landslides analyzed in the Melb-Valley and the Pleiser Hügelland, Devon's sandy weathered bag caused the sliding phenomenon. Stability estimates were not possible due to the complexity of the landslide body.
Overall, we found that the landslide problematic in the Bonn area is considerably more difficult to model than originally assumed. Heterogeneous rock strata and substratum impede the extensive calculations of the landslide susceptibility as well as the complexity of the landslides in regards to morphological and hydrological composition. In addition, data on the exact temporal classification of many landslides in Bonn are also missing.


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letzte Modifizierung: 14.01.2008