泥石流物源土体标度分布参数与粘聚力的关系

Relationship between Soil Scale Distribution Parameters of Debris Flow Source Soils and Cohesive Strength

颗粒级配影响土体力学性质(如粘聚力)。细颗粒(尤其是粘粒)含量对粘聚力起着决定性作用。颗粒级配可用土体特殊粒径(如D50等)来表征,但并不能避免同参异效等问题。采用土体标度分布μ和Dc两个参数,可准确地描述土体颗粒组成特征,但该分布参数的物理意义,以及特征参数与土体力学参数之间的关系尚不明确。本文实施室内试验测试,采用标度分布表征土体颗粒组成,研究在不同含水率和标度参数条件下土体粘聚力的变化特征,探讨土体颗粒组成、含水率和粘聚力之间的关系。结果表明:(1)标度分布参数μ随着细颗粒含量的增加而增大,并呈现指数函数关系;(2)随着细颗粒含量的增加,粘聚力先迅速增大后缓慢增加并趋于稳定,且粘聚力c与标度分布参数μ呈现对数函数关系;(3)粘聚力随着含水率的增大先增大后减小,即存在一个使得土体粘聚力达到最大值的含水率阈值,在达到此阈值之前,细颗粒含量对粘聚力的影响较为显著,达到该阈值之后,含水率成为更主要的影响因素;(4)基于试验结果,得到土体粘聚力随含水率及标度参数共同影响下的二元模型。研究可为明确标度分布参数的物理意义以及确定土体力学参数提供试验依据。

Particle gradation governs soil mechanical properties,e.g.,cohesion.The content of fine particles in soils,such as clay content,plays a decisive role in generating cohesive strength of soils.Although soil particle gradation can be characterized by specific grain sizes,e.g.,D50,it does not avoid issues in soil mechanics such as soils tagged with the same characteristic particle size but distinct geophysical properties.Antecedent research proposed a soil scale distribution model(SSDM)by two parametersμand Dc to define soil particle gradation.This model proved to be an acceptable expression of soil particle gradation characteristics,but there was unknown for its geophysical interpretation as well as its relation to soil cohesive strength.In this study,laboratory tests were conducted to characterize the soil particle graduation using SSDM;the changes in cohesive strength of soil samples were investigated under the conditions of different moisture contents and scale parameters;then geophysical relationship between granularity composition/scale distribution parameter,moisture content and cohesion was carefully concluded.(1)The scale distribution parameter(μ)increases with the increases of fine particle contents in soils,exhibiting a fine exponential function relationship.(2)As fine particle content increased,the cohesive strength in soils rapidly increased initially and then gradually stabilized.The relationship between the cohesive strength(c)and the scale parameter(μ)could be quantitatively expressed using a logarithmic function.(3)The cohesive strength increased first and then decreased with increasing moisture content.There existed a threshold moisture content that maximized the cohesive strength of the soils.Before reaching this threshold,the fine particle contents had a significant impact on the cohesive strength;however,after exceeding the threshold,soil moisture content became the dominant influencing factor.(4)Based on the experimental results,a binary model for soil cohesive strength with joint influence of moisture content and scale distribution parameters was proposed.This research can provide scientific basis for geophysical interpretation of soil scale distribution and determination of mechanical parameters for debris flow source soils.