Experimental investigation on cohesionless sandy bank failure resulting from water level rising |
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| Authors: | Ryosuke Arai Kazuyuki Ota Takahiro Sato Yasushi Toyoda |
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| Institution: | Fluid Dynamics Sector, Central Research Institute of Electric Power Industry, 1646 Abiko, Abiko-shi, Chiba, Japan |
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| Abstract: | In the last decade, sediment replenishment forming cohesionless sandy banks below dams has become an increasingly common practice in Japan to compensate for sediment deficits downstream. The erosion process of the placed cohesionless sediment is a combination of lateral toe-erosion and the following mass failure. To explore cohesionless bank failure mechanisms, a series of experiments was done in a soil tank using a compacted sandy soil mass exposed to an increasing water level. Two types of uniform sand (D50 = 0.40 mm and 0.17 mm) and two bank heights (50 cm and 25 cm) were used under the condition of a constant bank slope of 75°. The three dimensional (3D) geometry of the bank after failure was measured using a handheld 3D scanner. The motion of bank failure was captured using the particle image velocimetry (PIV) technique, and the matric suction was measured by tensiometers. The compacted sandy soil was eroded by loss of matric suction accompanying the rise in water level which subsequently caused rotational slide and cantilever toppling failure due to destabilization of the bank. The effect of erosion protection resulting from the slumped blocks after these failures is discussed in the light of different failure mechanisms. Tensile strength is analyzed by inverse calculation of cantilever toppling failure events. The tensile strength had non-linear relation with degree of saturation and showed a peak. The findings of the study show that it is important to incorporate the non-linear relation of tensile strength into stability analysis of cantilever toppling failure and prediction of tension crack depth within unsaturated cohesionless banks. |
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| Keywords: | Riverbank erosion Matric suction Cohesionless bank Tensile strength |
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