Jens Johansson
Jens Johansson

Jens Johansson

Cell:             070-261 66 19

Research project

Impact of water-level variations on slope stability 

Waterfront-soil slopes are exposed to water-level fluctuations originating from either natural sources, e.g. extreme weather and tides, or from human activities such as watercourse regulation for irrigation, freshwater provision, hydropower production etc. Slope failures and bank erosion is potentially getting trees and other vegetation released along with bank landslides. When floating debris is reaching hydropower stations, there will be immediate risks of adverse loading on constructions, and clogging of spillways; issues directly connected to as well energy production as dam safety. 

Transient water flow within soil structures affects pore-pressure conditions, strength, and deformation behavior of the soil. This in turn does potentially lead to soil-material migration, i.e. erosion. This process is typically considered in the context of embankment dams. Despite the effects of transient water flow, the use of simple limit-equilibrium methods for slope analysis is still widely spread. Though, improved accessibility of high computer capacity allows for more and more advanced analyses to be carried out. In addition, optimized designs and constructions are increasingly demanded, meaning less conservative design approaches being desired. This is not at least linked to economic as environmental aspects. One non-conservative view of slope-stability analysis regards consideration of negative pore pressures in unsaturated soils.

In this project knowledge concerning water-level fluctuations is focused; sources, geotechnical effects on slopes, and approaches used for modelling. Moreover, different approaches used for hydro-mechanical coupling in FEM-modelling of slope stability, are evaluated.

Modelling considering unsaturated soil beahavior seems to allow for rapid changes of pore pressures and flow to be more realistically described than do classical modelling. Since such changes in turn are governing as well water-transport (i.e. the efficiency of dissipation of excess pore pressures), as soil-material transport (i.e. susceptibility to internal erosion to be initiated and/or continued), simplified modelling approaches are not suitable for analysis of processes being governed by fluctuating flows, altering hydraulic gradients, unloading/reloading etc.

Partner: SVC - Swedish Hydropower Centre