Unsteady Seepage Behavior of an Earthfill Dam During Drought-Flood Cycles

Abstract

Climate change with extreme hydrological conditions, such as drought and flood, bring new challenges to seepage behavior and the stability of earthfill dams. Taking a drought-stricken earthfill dam of China as an example, the influence of drought-flood cycles on dam seepage behavior is analyzed. This paper includes a clay sample laboratory experiment and an unsteady finite element method seepage simulation of the mentioned dam. Results show that severe drought causes cracks on the surface of the clay soil sample. Long-term drought causes deeper cracks and induces a sharp increase of suction pressure, indicating that the cracks would become channels for rain infiltration into the dam during subsequent rainfall, increasing the potential for internal erosion and decreasing dam stability. Measures to prevent infiltration on the dam slope surface are investigated, for the prevention of deep crack formation during long lasting droughts. Unsteady seepage indicators including instantaneous phreatic lines, equipotential lines and pore pressure gradient in the dam, are calculated and analyzed under two assumed conditions with different reservoir water level fluctuations. Results show that when the water level changes rapidly, the phreatic line is curved and constantly changing. As water level rises, equipotential lines shift upstream, and the pore pressure gradient in the dam’s main body is larger than that of steady seepage. Furthermore, the faster the water level rises, the larger the pore pressure gradient is. This may cause internal erosion. Furthermore, the case of a cracked upstream slope is modelled via an equivalent permeability coefficient, which shows that the pore pressure gradient in the zone beneath the cracks increases by 5.9% at the maximum water level; this could exacerbate internal erosion. In addition, results are in agreement with prior literature that rapid drawdown of the reservoir water level is detrimental to the stability of the upstream slope based on embankment slope stability as calculated by the Simplified Bishop Method. It is concluded that fluctuations of reservoir water level should be strictly controlled during drought-flood cycles; both the drawdown rate and the fill rate must be regulated to avoid the internal erosion of earthfill dams.

Application of a Viscoelastic Model to Creep Settlement of High‐Fill Embankments

“…Advances in Civil Engineering e agreement between the measured and calculated settlements is excellent, although the measured settlement values are more irregular because this area is in a soil region that is seasonally frozen, and during the winter, soil freezing leads to the ground heave [31,32].…”

More floods, fires and cyclones — plan for domino effects on sustainability goals

“…Another example is a wet winter in which there is a lot of plant growth -this can be a big fire risk if a hot and dry summer follows, because of the build-up of forest fuel 7 . Protections against river floods need to consider droughts as well as high water flows, because dry material in dykes can shrink, crack and become unstable 8 .…”

Reliability-based design of an earth and concrete dam.

“…The frequency, intensity, and uncertainty of drought and flood disasters have increased significantly. For instance, dry season rainfall and river discharges are decreasing, while wet season flows are intensifying (Li et al, 2018;Yan et al, 2015). Rainfall-induced landslides are common in many regions under tropical or subtropical climates, such as Hong Kong, Taiwan, Singapore, Japan and Brazil (Brand, 1984;Fourie, 1996;Glade et al, 2005;Lumb, 1962;Zhang et al, 2018Zhang et al, , 2011.…”

“…Then, the geotechnical structure fails. A relationship between rainfall, reservoir water level, and stability was developed in a deterministic approach to verify the safety of the dam (Li et al, 2018).…”

“…The usual approach during normal operating conditions (NOC) analysis is a transient seepage and limit equilibrium analysis using mean soil properties, to find deterministic factors of safety (FoS) (Feng et al, 2018;Kristo et al, 2017;Li et al, 2018;Rahardjo et al, 2007a;Rahimi et al, 2011;Robinson et al, 2016;Tang et al, 2017). Equilibrium, however, depends on loading conditions (rainfall and reservoir water level) and soil parameters, which can be modeled as random variables.…”