A numerical geotechnical model for computing soil slides at banks of water reservoirs

Nils Reidar B Olsen,Stefan Haun

doi:10.1186/s40703-020-00129-w

Abstract

Soil slides can occur when the water level in a lake or a reservoir is lowered. This may take place in situations when a reservoir is flushed to remove sediments. The current study describes a three-dimensional numerical model used for the simulation of reservoir flushing that includes the slide movements. The geotechnical failure algorithms start with modelling the groundwater levels at the banks of the reservoir. A limit equilibrium approach is further used to find the location of the slides. The actual movement of the sediments is computed by assuming the soil to be a viscous liquid and by solving the Navier–Stokes equations. The resulting bed elevation changes from the slides are computed in adaptive grids that change as a function of water level, bed erosion and slide movements. The numerical model is tested on the Bodendorf reservoir in Austria, where field measurements are available of the bank elevations before and after a flushing operation. The results from the numerical simulations are compared with these observations. A parameter test shows that the results are very sensitive to the cohesion and less sensitive to the E and G modules of the soil.

Highlights

Water is a valuable resource in most parts of the world
The current study focuses on the process of bank failures during the flushing
The groundwater levels were computed by solving Eq 2, which is based on the water continuity equation and Darcy’s equation for the relationship between the water velocity and pressure head in a soil element: Fig. 1 Plan view of the 2D depth-averaged grid for the Bodendorf reservoir with 10 cells in the lateral direction and 195 cells in the longitudinal direction

Summary

Introduction

Water is a valuable resource in most parts of the world. It is stored in reservoirs and used for several purposes, such as irrigation or hydropower. The groundwater levels were computed by solving Eq 2, which is based on the water continuity equation and Darcy’s equation for the relationship between the water velocity and pressure head in a soil element: Fig. 1 Plan view of the 2D depth-averaged grid for the Bodendorf reservoir with 10 cells in the lateral direction and 195 cells in the longitudinal direction. Haun et al [4] computed bed elevation changes during the 2004 flushing of this reservoir without taking the sediment slides at the bank into account. The aspect ratio of the 2D cells was not changed, so the number of cells in the longitudinal direction was 1,560 This 2D grid was used to compute the water level in the reservoir, the groundwater level and the location of the slides. The measured average lowering of the end cross-sections of Fig. 10 was 0.48 m, which represents a 20% deviation

Findings

Discussion

Conclusions and outlook