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Seepage
Published in Braja M. Das, Advanced Soil Mechanics, 2019
For construction of flow nets for seepage through earth dams, the phreatic line needs to be established first. This is usually done by the method proposed by Casagrande (1937) and is shown in Figure 7.39a. Note that aefb in Figure 7.39a is the actual phreatic line. The curve a′efb′c′ is a parabola with its focus at c′. The phreatic line coincides with this parabola, but with some deviations at the upstream and the downstream faces. At a point a, the phreatic line starts at an angle of 90° to the upstream face of the dam and aa′ = 0.3Δ.
Measuring stiffness of soils in situ
Published in Fusao Oka, Akira Murakami, Ryosuke Uzuoka, Sayuri Kimoto, Computer Methods and Recent Advances in Geomechanics, 2014
Fusao Oka, Akira Murakami, Ryosuke Uzuoka, Sayuri Kimoto
There are a number of reasons that cause the slope failure. Improper seepage control is one of the main reasons that results in instability of slopes. To prevent the slope failure, it is significantly important to understand and control water flow, including the evolution of the free surface (phreatic line). Therefore, the accurate phreatic line must be determined in order to assess the slope stability. A number of numerical methods have been used to find out the location of the free surface including strategies based on finite element method (FEM)
Experimental investigation of failure modes and breaching characteristics of natural dams
Published in Geomatics, Natural Hazards and Risk, 2018
Xiangang Jiang, Yunwei Wei, Lei Wu, Yu Lei
The other failure mode was caused by dam slope instability, i.e. the slope failure mode (Figure 4(b)), the appearance of which is directly related to soil permeation. As the water level gradually increased, significant seepage occurred in the dam, and the phreatic line was observed to rapidly develop towards the downstream. When the phreatic line developed at the toe of the inner slope and formed a through-going seepage channel, the soil above the phreatic line suddenly lost its stability and rushed downstream. Then, the hammed water was immediately released, overtopped the dam, and rushed downstream. Subsequently, the water flooded to the dam crest and gradually eroded the dam.