土体发生破坏最开始往往是从内部的土壤颗粒破坏开始，而抗剪强度是反映土体抵抗剪切破坏能力的重要指标。本文以紫色页岩发育的坡耕地土壤为研究对象，通过测定土样颗粒组成以及不同含水率和垂向压力下的抗剪强度，研究页岩发育的土壤颗粒特性及其对抗剪强度的作用机制。结果表明从坡顶至坡脚，土壤颗粒组成与其母岩颗粒组成具有显著相关性；土壤中 <0.25 mm颗粒累计含量在995.65 ~ 998.62 g/kg之间，其中以0.25 ~ 2 mm岩石碎屑存在的土壤颗粒含量为439.80 ~ 510.40 g/kg，以0.25 ~ 2 mm团聚体存在的土壤颗粒含量为6.01 ~ 80.50 g/kg，随着位置高程的降低，土壤中岩石碎屑和团聚体的含量并没有显著变化。在含水率从7% 增加到25% 的过程中，土壤水分与内摩擦角呈负相关关系且对内摩擦角的影响随着高程的降低缓慢减小，而对黏聚力的影响是随着含水率的增加单一坡位黏聚力呈现先增加后减少的趋势，但是随高程降低变化并不明显。因此，在紫色页岩发育的土壤颗粒组成中存在大量 <2 mm的岩石碎屑，这些大量致密坚硬的岩石碎屑提高土壤抗剪强度同时减弱了抗剪强度的水敏性。

The beginning of soil destruction is often from the internal destruction of soil particles, and shear strength is an important indicator to reflect soil’s resistance to shear failure. The paper takes shale-derived purple soils in sloping land as the research object and study particle characteristics of purple soil and their mechanism of shear strength by measuring soil particle compositions and shear strengths under different moisture contents and vertical pressures. The result showed that soil particle compositions from summit to footslope were significantly correlated with those of parent rocks. Soil particles <0.25 mm were about 995.65 – 998.62 g/kg, in which particles presented as 0.25 – 2 mm rock fragments were about 439.80 – 510.40 g/kg, however particles presented as 0.25 – 2 mm aggregates were about 6.01 – 80.50 g/kg. With the decrease of elevation, the contents of rock fragments and aggregates in soils did not change obviously. Within soil water content from 7% to 25%, soil water content was negatively correlated with internal friction angle and the influence of soil water content on internal friction angle decreased slowly with the decreased elevation, however cohesion was increased first and then decreased with soil water content increased on single slope, but cohesion did not change obviously with the decreased elevation. Therefore, there are a large amount of <2 mm rock fragments in soil particles in purple soil, and these rock fragments improve soil shear strength while weaken its water sensitivity.

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国家科技支撑计划项目(2012BAD05B00)资助。