Internal instability or suffusion is one of the mechanisms of internal erosion in cohesionless soils, which is described by the loss of integrity of soil by seepage flow and is associated with the migration of finer particles. The contribution of the non-plastic finer fraction in a material is a key factor governing internal instability susceptibility. This study presents the experimental investigation of the influence of the fines content on the onset of internal instability of gap-graded sands using a pressure-controlled triaxial erosion device. The results indicate that the finer fraction in the soil has a significant influence on the hydraulic gradient at the onset of erosion. The underfilled soil with fines content less than 30% is vulnerable to suffusion at a relatively small hydraulic gradient. The transitional soil, whose fines content is between 30 and 35%, also exhibits suffusion, but the erosion onset hydraulic gradient significantly increases with increasing fines content. The overfilled soil with fines content larger than 35% exhibits suffosion or internal stability at a larger hydraulic gradient. The results also highlight the necessity of the multiple indices, such as mass loss, volumetric change and change in permeability, in evaluating the onset of various instability phenomena.

中文翻译：

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细粒含量对砂混合物内部不稳定性和扩散开始的影响

内部不稳定性或泛滥是无粘性土壤内部侵蚀的机制之一，表现为渗流导致土壤完整性丧失，并与细颗粒的迁移有关。材料中非塑性细粒部分的贡献是控制内部不稳定性敏感性的关键因素。本研究使用压力控制的三轴侵蚀装置对细粒含量对间隙级配砂内部不稳定开始的影响进行了实验研究。结果表明，土壤中较细的部分对侵蚀开始时的水力梯度有显着影响。细粒含量低于 30% 的未充填土壤在相对较小的水力梯度下容易发生溢流。过渡土，其细粒含量在 30% 到 35% 之间，也表现出扩散，但侵蚀起始水力梯度随着细粒含量的增加而显着增加。细粒含量大于 35% 的过满土壤在较大的水力梯度下表现出窒息或内部稳定性。结果还强调了多个指标的必要性，例如质量损失、体积变化和渗透率变化，在评估各种不稳定现象的发生时。