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A large-size creeping natural slope was simulated with the Finite Element (FE) method, using a visco-hypoplastic material model, which describes the mechanical behaviour of cohesive soils, allowing for viscous effects (i.e. creep, relaxation and rate-dependence of stiffness). First, the required material parameters were determined by means of standard geotechnical laboratory tests using representative soil samples taken from the slope. Then a FE mesh of a slope section was constructed and boundary conditions were established. The slope movements were simulated and compared with inclinometer measurements, which were available for a period of 16 years. The calculation results are in good agreement with the observed velocities. A parameter study was carried out in order to assess the influence of slope angle, initial void ratio, material parameters as well as their spatial distribution.

This paper presents the numerical simulation of a creeping slope in Upper Austria, using a visco-hypoplastic material law which describes the mechanical behavior of cohesive soils allowing for viscous effects, i.e. creep and relaxation. The method consists of: (1) determination of the parameters of the material law, based on laboratory tests on soil samples taken from the slope; (2) simulation of the laboratory tests with an element test program in which the used material law was implemented, in order to test whether the model holds for the soils studied; and (3) simulation of slope movements at different sections along the slope, assuming an infinite slope. The simulation results fit well with the field measurements. This demonstrates that despite strongly simplified boundary conditions and limited availability of subsurface data (e.g. density) the visco-hypoplastic law is a promising tool for predicting creep movements.

Many flood defences in The Netherlands have been disapproved for flow slides of the Holocene subsoil. Traditionally these flow slides are assumed to be induced by static liquefaction. Only in recent times it has been recognized that flow slides may also concern breach flows, which do not necessarily require loosely packed sand. For both static liquefaction and breach flow the inaccuracy of the currently applied methods to determine in situ density lead to high computed probabilities of failure, which is one of the main problems in the safety assessment of flow slides. In order to reduce this uncertainty, based on a literature study a number of methods were selected and applied on four test locations: two sites where flow slides occurred and two sites where no flow slides occurred, but for which high probabilities on flow slides were calculated based on current Dutch assessment rules for liquefaction and breach flow. For these sites CPT’s and electrical resistivity cone tests available from earlier investigations, were extended with seismic CPT’s and interpreted for relative density and state parameter. The results of this study lead to the conclusion that some of the historical flow slides in The Netherlands may have been the result of static liquefaction in loosely packed sand. For many other slopes, however, it is more reasonable to assume that the failures must have been breach flows in medium or densely packed layers.