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SOSTANAH Soil stability and natural hazards: from knowledge to action


Heavy rainstorms with shallow landslides and soil erosion often cause substantial damage in Switzerland. This project within the framework of the National Research Programm NRP 68 "Soil as a Resource" aims to quantify the stabilysing effects of vegetation and micorrhizal fungi on slope stability.


In Switzerland, substantial damage on infrastructure and sporadically loss of lives are caused by erosion and landslides due to heavy rainstorms. The protection against as well as prevention and prediction of superficial soil failure are, however, still difficult. To improve knowledge of and action against these hazards, it is important to understand the processes at regional scale, define critical thresholds, and subsequently transfer knowledge into action at large scale. The most challenging questions are related to the interdependency of vegetation, mycorrhizal fungi and soil fabric. In this regard we want to quantify the effects of vegetation and land-use on soil resistance, in particular against superficial landslides but also against related surface erosion, triggerd by rainfall. In this context we want to consider the hitherto neglected fact that the majority of plants in mountain ecosystems live in symbiotic relationship with mycorrhizal fungi which contribute to soil aggregation and soil strength, too. This project aims, therefore, at (1) quantifying biological effects relevant to soil stability, (2) crystallising appropriate indicators for superficial soil failure, and (3) developing a concept of sustainable soil use.


Experiments with new shear-apparatus

We will take advantage of more than 700 documented landslides, restoration measures, and soil mechanical experiments, already available at WSL, SLF and IGT and analyse them in terms of thresholds for soil stability (Fig. 2). In order to bridge gaps of rhizosphere processes decisive for soil strength and facilitate the development of thresholds in respect of slope stability, we will specifically complement these existing data, with laboratory experiments (direct shear tests, soil aggregate stability analysis, rain-fall simulation) and additional field investigations on soil fabric (texture, hydrology), plant community aspects (diversity, growth forms, root types), land-use management and mycorrhiza. On this basis we will deduce appropriate indicators and, in close collaboration with projects of the NRP68 stream "land mapping/GIS", spatial models of the susceptibility to superficial soil failure. Based upon these findings, we aim at providing thresholds for information and warning systems as well as input for land management planning. Furthermore, we will negotiate strategies to reconcile protection against natural hazards, land-use, and economic aspects of agriculture, forestry and tourism as well as nature protection in collaboration with projects of the NRP68 streams "soil biology" and "land mapping/GIS".


A new shear-apparatus (Fig. 3) was developed combining the advantages of common field and laboratory methods: easily controllable and repeatable experiments on the one hand, and large soil samples that appropriately represent natural conditions on the other hand. To investigate the stability of planted and unplanted soil samples, the scientists apply well-defined forces – with the samples not only in horizontal position, but also inclined up to an angle of 45°. This allows, for the first time, to investigate soil in the laboratory under conditions that are similar to real slopes.