CFD-DEM simulations of the effect of fines content on suffusion characteristics in gap-graded sandy gravels
LIU Leilei1，2，DENG Gang3，LI Weichao3，CHEN Rui1，2，ZHOU Chao4，ZHANG Liangliang1，2
(1. School of Civil and Environmental Engineering，Harbin Institute of Technology，Shenzhen，Guangdong 518055，China；
2. Guangdong Provincial Key Laboratory of Intelligent and Resilient Structures for Civil Engineering，Shenzhen，Guangdong 518055，China；3. State Key Laboratory of Simulation and Regulation of Water Cycle in River Basin，China Institute of Water Resources and Hydropower Research，Beijing 100038，China；4. Department of Civil and Environmental Engineering，
Hong Kong Polytechnic University，Hong Kong 999077，China)
Fines content(FC) is one of the geometric conditions determining whether suffusion occurs and has a complex influence on suffusion characteristics. Based on the computational fluid dynamics-discrete element method(CFD-DEM) coupling approach，numerical simulation tests for suffusion were conducted on gap-graded sandy gravels with two hydraulic gradients and seven FCs. The mechanism of fines content?s effect on suffusion was investigated from both macroscopic and microscopic perspectives. The results show that the pore states of the soil can be classified into four types according to the FC：underfilled，filled，partially overfilled(where coarse particles are partially separated by fines)，and completely overfilled(where coarse particles are completely separated by fines). In the underfilled state(i.e.，FC≤25%)，the erosion rate of fines increases with rising FC，but decreases during the transition from underfilled to filled states(i.e.，FC = 30%). This is primarily because the void ratio of filled soil reaches its minimum，making it hard for fine particles to migrate. Subsequently，as the FC continues to increase，the erosion rate rises again. However，the erosion type gradually shifts from suffusion to backward erosion. The erosion mechanism can be determined through a comprehensive analysis of particle migration distribution and the composition of eroded particles. Specifically，in the case of partially overfilled soil(i.e.，FC = 35%)，it displays a transitional internal stability and exhibits suffusion. Conversely，for samples in a completely overfilled state(i.e.，FC = 40%)，fines cannot migrate through the pores，leading to backward erosion during testing.
Abstract：Fines content(FC) is one of the geometric conditions determining whether suffusion occurs and has a complex influence on suffusion characteristics. Based on the computational fluid dynamics-discrete element method(CFD-DEM) coupling approach，numerical simulation tests for suffusion were conducted on gap-graded sandy gravels with two hydraulic gradients and seven FCs. The mechanism of fines content?s effect on suffusion was investigated from both macroscopic and microscopic perspectives. The results show that the pore states of the soil can be classified into four types according to the FC：underfilled，filled，partially overfilled(where coarse particles are partially separated by fines)，and completely overfilled(where coarse particles are completely separated by fines). In the underfilled state(i.e.，FC≤25%)，the erosion rate of fines increases with rising FC，but decreases during the transition from underfilled to filled states(i.e.，FC = 30%). This is primarily because the void ratio of filled soil reaches its minimum，making it hard for fine particles to migrate. Subsequently，as the FC continues to increase，the erosion rate rises again. However，the erosion type gradually shifts from suffusion to backward erosion. The erosion mechanism can be determined through a comprehensive analysis of particle migration distribution and the composition of eroded particles. Specifically，in the case of partially overfilled soil(i.e.，FC = 35%)，it displays a transitional internal stability and exhibits suffusion. Conversely，for samples in a completely overfilled state(i.e.，FC = 40%)，fines cannot migrate through the pores，leading to backward erosion during testing.
刘垒雷1，2，邓 刚3，李维朝3，陈 锐1，2，周 超4，张亮亮1，2. 细颗粒含量影响不连续级配砂砾土渗蚀特性的计算流体动力学–离散元耦合模拟[J]. 岩石力学与工程学报, 2024, 43(S2): 4009-4021.
LIU Leilei1，2，DENG Gang3，LI Weichao3，CHEN Rui1，2，ZHOU Chao4，ZHANG Liangliang1，2. CFD-DEM simulations of the effect of fines content on suffusion characteristics in gap-graded sandy gravels. , 2024, 43(S2): 4009-4021.
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