The federal motorway A70 crosses a mass movement area of at least 1.5 km length. Several reconstruction measures could only affect a deceleration of deformation velocity. Thus, a relocation of the route is inevitable. Until completion of road work, safety of the motorway has to be guaranteed on basis of detailed measuring and monitoring concepts which follow the guidelines of Eurocode 7 for real time surveillance. This includes the definition of thresholds for risk levels with corresponding instructions.
The interpretation of the movement processes is based on the analysis of inclinometers, geodetic measuring, ground water and pore-water pressure sensors. The aim is to correlate environmental influences (e.g. heavy rainfalls) with movement magnitudes to predict potential hazards and develop an early warning system. Water is one of the crucial parameters as the slope is situated in the Germanic Trias. The geological strata are composed of inhomogeneous clay called Feuerletten, which contains minerals with a high swelling capacity. In addition, the overlying sandstone layer is disintegrated due to tectonic movement. This leads to a critical situation, where a "hard" slab is moving slowly on a "soft" layer.
An accurate interpretation of the field results is reasonable with a profound knowledge of the material behavior. Special focus is on the determination of the shear parameters by triaxial and direct shear testing. Results of both testing methods vary distinctly due to their sensitivity concerning inhomogeneous samples and weakness zones within the material. Therefore, statistical evaluation has been performed to determine representative input parameters for a slope stability analysis. Consequently, each method available for landslide interpretation (lab & field tests, deformation & ground water measurements, failure process & stability analysis) was applied to characterize the most likely ground model including its zones of weakness for a highly complex creeping slope close to a federal motorway.
The movement at the federal motorway A70 has been noticed in 1991 for the first time. Costly reconstruction measures have been conducted to remedy the caused damage. However, these measures could only affect a deceleration of the deformation velocity and up to now, the slope is still in movement causing severe damage to the motorway. A relocation of the route is therefore inevitable but the completion of road work will take several years. Until then, the safety of the motorway has to be guaranteed on basis of a detailed measuring and monitoring concept that follows the guidelines of the Eurocode 7 for real time surveillance. This includes the determination of thresholds for several risk levels with corresponding instructions.
