Some Aspects of Physical Weather Related Slope Processes

Abstract

It is well-recognized that pore water has an important role on the stability of slopes. In this project the principal objective has been to examine the influence of weather on the ground water regime in a quick clay deposit in Røesgrenda, Mid-Norway, where slides have occurred frequently since 1995. A goal of the project has been to relate stability and slide activity to the ground water regime. Observations of the ground water regime at the Røesgrenda site show little fluctuations with time. The seasonal variation in pore water pressure has been related to snow loading of the deposit and has had a negligible influence on stability and slide activity. Precipitation and melt water infiltration affect only the ground water regime and stability in the crust layer above the quick clay and cause only surface slide activity. Frost has had a negligible influence on pore water pressure and stability in the deposit.

Failure in quick clay develops slowly over periods of months, and weather controls only the rate of deformation only the failure process has started. In contrast, materials such as mica-rich sand studied in Sikkim Himalaya fail in periods with a high rate of precipitation.

Seasonal snow is especially sensitive to weather processes as the material has temperatures close to the melting point where the physical and mechanical properties change rapidly. Avalanches are primarily released as a consequence of high rate of snow accumulation on a snow pack with weak layers or as a consequence of creep due to methamorpism. Retaining structures on slopes with deep snow cover are also exposed to loading from weather related snow creep processes where temperature plays a critical role.

Comparison of observed failure and flow processes in the soil and snow structures described above indicates similarities in behaviour for seemingly different materials.