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Understanding Geotechnical Embankment Washout Due to Overtopping: Insights From Physical Tests

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Dec 04, 2024

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Figure 1:

Experimental setup. I – balance tank, II – check valve (close of the overflow window), III – overflow window with Thomson’s weir, IV – energy dissipation device, V – upper tank Vmax = 14.4 m3, VI – analyzed embankment, VII – downstream channel B=2.0 m, VIII – two Thomson’s weirs, IX – free discharge channel B >> 2.0 m, X – hydrostatic pressure sensors.
Experimental setup. I – balance tank, II – check valve (close of the overflow window), III – overflow window with Thomson’s weir, IV – energy dissipation device, V – upper tank Vmax = 14.4 m3, VI – analyzed embankment, VII – downstream channel B=2.0 m, VIII – two Thomson’s weirs, IX – free discharge channel B >> 2.0 m, X – hydrostatic pressure sensors.

Figure 2:

Distribution of grain size of the soil used in the laboratory test.
Distribution of grain size of the soil used in the laboratory test.

Figure 3:

Phases of failure mode of a noncohesive homogeneous dam – photos from Test 2 and isometric schemes.
Phases of failure mode of a noncohesive homogeneous dam – photos from Test 2 and isometric schemes.

Figure 4:

Phase duration in each test
Phase duration in each test

Figure 5:

Breach width at the crest since the beginning of phase III.
Breach width at the crest since the beginning of phase III.

Figure 6:

Upstream discharge from tests 1, 2, and 3.
Upstream discharge from tests 1, 2, and 3.

Figure 7:

Discharge and water level from Test 1.
Discharge and water level from Test 1.

Figure 8:

Discharge and water level from Test 2.
Discharge and water level from Test 2.

Figure 9:

Discharge and water level from Test 3.
Discharge and water level from Test 3.

Dam breach parameters of tests 1, 2, and 3_

Test Peak discharge (l/s) Timing of the peak discharge (s) Duration of breach (s) Duration of expansion of the breach (s) Eroded material (m3) Average erosion rate (m3/s) Final width of the top of the breach (cm) Average rate of breach expansion (cm/s)
1 114.65 102 171 129 0.571 0.004 121 0.9
2 122.67 86 162 157 0.520 0.003 114 0.7
3 182.17 64 122 117 0.586 0.005 127 1.1

Comparison of breach parameters using empirical formulas_

Ashraf et al. (2018) Soliman (2015) Webby (1995) Chinnarasri et al. (2004) The present study
Test 1 Test 2 Test 3
Qp (l/s) 16.51 - 138.93 38.42/471.07* 114.65 122.67 182.17
Bavg (m) 1.30 2.41 - - 1.20 1.10 1.23
Hf (m) 0.39 0.44 - - 0.5 0.5 0.5
Tf (s) 411 654 - 75/79* 128 157 117
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