Influence of relative density of the granular base soil on filter performance
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Influence of relative density of the granular base soil on filter performance Peter To1
•
Daniel Agius2 • Liam Cussen2
Received: 13 August 2019 / Accepted: 21 August 2020 Ó Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract Perpendicular contact erosion due to poorly designed filters is a frequent hazard for water-retaining structures serving as lifeblood to the community. This phenomenon occurs when the fine particles of a base soil at the contact interface with a coarser material are detached and transported through pores formed by the coarse particles. Therefore, most filter design criteria focus on the gradation of coarse particles or the gradation of pore constrictions. Meanwhile, the parameters of the base soil, such as relative density, are often overlooked. On the one hand, some experts neglect the impact of relative density because perpendicular contact erosion occurs at the interface, where fine particles expose themselves to larger pores. On the other hand, it is a general belief that the more compacted a base soil is, the less susceptible it will be to erosion as the seepage is reduced. This paper discusses this dilemma from a mutual perspective which assesses the influence of relative density from experimental, numerical, and analytical standpoints. The experimental study reveals that there is an optimal relative density which will release the least eroded mass. The influence is crucial as it can change the status of stability to unstable. The physical essence of the phenomenon is expressed by a numerical study at the microscale, which investigates the redistribution of flow lines and stress resulting from a particle detachment. The discovery at the micro-scale is confirmed by an analytical evaluation at the macro-scale, which assesses the redistribution of pore constrictions. Keywords Base soil Constrictions Contact erosion Dam design Filter Non-cohesive Relative density Simulation
1 Introduction Nearly half of all dysfunctions of dams and embankments worldwide are related to internal erosion [6], where contact erosion is a major type. In terms of erosion development, contact erosion is the only incident occurring between two soils, which did not abut before. Therefore, the stability of soils depends strongly on material selection in design. In addition, because failures due to contact erosion often advance very fast once it reaches ground surface, the chance to avert the accident is slim. In the past, internal & Peter To [email protected] 1
College of Science and Engineering, James Cook University, 15-113 James Cook Drive, Douglas, Townsville, QLD 4811, Australia
2
GHD, 15 Lake Street, Cairns, QLD 4870, Australia
erosion destroyed the Teton dam within hours from the initial detection [13]. Thus, the design criteria are of vital importance. Regarding the conditions of perpendicular contact erosion, the phenomenon occurs if (i) the seepage flow is capable of transporting fine particles away and (i
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