粘土矿物与斜坡失稳

CLAY MINERALS AND FAILURE OF SLOPES

作为微米级材料,粘土矿物的单晶尺寸及特殊晶体结构使其集合体–粘土呈现低渗透性、分散–凝絮性及粘滞性等重要工程特性。除沉积岩斜坡含粘土矿物外,76%以上的斜坡岩石造岩矿物还可形成次生粘土矿物。粘土矿物广泛分布于原生沉积岩、三大岩类风化带及第四系松散堆积物构成的斜坡中。泥屑岩因含粘土矿物而易于失稳,且水稳定性差。次生粘土矿物的形成将引起源矿物、矿物集合体及岩块的强度与变形特性的显著变化,诱发岩石向松散介质转化。宏观结构面是粘土矿物最主要的形成和聚集场所,结构面及其内侧一定范围内不同成因粘土矿物的淀积将导致结构面及岩体强度的衰减。粘土矿物是滑坡滑带的常见矿物组分;粘土滑带可以在滑体与滑床之间起到润滑作用。滑带中粘土矿物的含量越多,其润滑效应越显著。粘土型滑带还具有隔水边界之功效,可将滑体与周围介质隔离,使之成为独立水文地质单元,提高坡体拦截、吸收渗入水的能力及斜坡稳定对降雨过程的敏感度。粘土矿物可以促进斜坡时效变形,甚至成为斜坡破坏的关键因素,对斜坡演化及失稳的贡献是显著的。

As a microcrystalline material, the fine crystal and special structure of clay minerals make the aggregation-clay present several important properties, such as low permeability, high viscosity, high cation exchange capacity, dispersion-flocculation and so on. Many sedimentary rocks contain clay minerals and 76% of forming-rock minerals of slope rocks can produce clay minerals during the weathering processes. Clay minerals distribute extensively in various slopes made of sedimentary rock, weathering profiles of igneous rock, metamorphic rock and sedimentary rock and colluvial deposits. Because of clay minerals, lutites fail easily, and the sensitivity of their strength and deformability to change in water content is high. Secondary clay minerals in rock may bring about marked changes in strength and deformability of parent minerals, mineral aggregation and rock and promote rock to evolve toward loose medium. Macro discontinuities are the main forming and assembling places of clay minerals, and the illuviation of secondary clay minerals in fracture surface and the rock inside fracture surface will cause the strength of discontinuities and rock mass to decrease. Clay minerals are key components of slipping zones of landslides. Slipping zones have a lubrication effect between landslide masses and bedrock. The higher the content of clay minerals in slipping zones is, the more remarkable the lubrication effect is. Slipping zones may act as impervious boundaries and separate landslide masses from the surrounding media. Thus landslide masses are changed into independent hydrogeological units, and the ability of retaining infiltrated water and sensitivity of slope stability to raining processes are raised correspondingly. To sum up, clay minerals may accelerate time-dependent deformation of slopes, and their contribution to slope evolution and failure of slopes is notable.