Shear strength attenuation law and mechanism of gravel-soil under immersion
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摘要:
水库蓄水后, 滑坡体碎石土经受长时期的浸泡, 力学性质发生改变, 从而影响滑坡整体稳定性。为探究浸泡对碎石土力学性质的影响规律, 选取三峡库区马家沟滑坡后缘未经受长期浸泡作用的碎石土进行大型直剪试验, 分析了不同浸泡天数下碎石土的剪切力学性质。试验结果表明: 浸泡40 d后, 碎石土黏聚力下降幅度达39%, 内摩擦角下降幅度为8.3%;碎石土黏聚力在浸泡前期快速下降, 下降速率随浸泡天数增加而降低, 浸泡20 d后, 黏聚力基本达到稳定。为探究碎石土抗剪强度降低的原因和机理, 对粉质黏土(碎石土细粒成分)进行了三轴剪切试验、激光粒度分析及浸出液阳离子分析等试验, 揭示了碎石土抗剪强度的衰减机理为: 浸泡作用下, 碎石土中的粉质黏土发生矿物溶解、离子交换与吸附作用, 土体中大颗粒细化, 胶结作用减弱, 进而导致碎石土整体抗剪强度降低。研究结果对库区碎石土滑坡评价与治理具有一定的指导意义。
Abstract:After a reservoir is filled with water, the gravel-soil of a slope is immersed, and the mechanical properties are changed, which affects the stability of the slope. To investigate the influence of immersion on the mechanical properties of gravel-soil, the gravel-soil at the back edge of the slope that has not been immersed was used and large-scale direct shear tests were performed to obtain the shear mechanical properties of gravel-soil after different immersion days. The test results show that after 40 days of immersion, the cohesion of gravel-soil decreases by 39% and the internal friction angle decreases by 8.3%; the cohesion of gravel-soil decreases significantly in the initial stage of immersion and the decay rate decreases with the increasing number of days of immersion.After 20 days of immersion, the cohesion does not decrease significantly with the increase of immersion days. To reveal the reason and mechanisms of shear reduction in gravel-soil, triaxial shear tests, laser particle size analysis and leachate cation analysis were performed on silty clay (fine-grained component of gravel-soil). The results indicate that the shear strength of gravel-soil is attenuated by mineral dissolution, ion exchange and adsorption of the silty clay in gravel-soil. The large particles in the soil are refined, and the cementation is reduced, which reduces the overall shear strength of the gravel-soil. This study has certain significance for the evaluation and management of gravel soil landslides in reservoir areas.
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图 6 碎石土剪应力-剪应变曲线(浸泡0 d)
Figure 6. Shear stress-shear strain curve of gravel-soil(immersed for 0 days)
图 8 粉质黏土应力-应变曲线(浸泡0 d)
Figure 8. Stress-strain curve of silty clay(immersed for 0 days)
图 9 浸泡后粉质黏土剪切强度变化曲线
Figure 9. Damage strength variation curve for silty clay after immersion
图 13 浸泡液主要离子浓度变化
Figure 13. Changes in the concentration of major ions in immersed water
表 1 碎石土中粉质黏土的物理性质
Table 1. Physical properties of the fine-grained composition of gravelly soils
天然重度/(g·cm-3) 相对密度 天然含水率/% 塑限/% 液限/% 1.92 2.72 14.2 19.25 30.46 
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