火烧迹地土壤根系特征及其对抗剪强度的影响

Root characteristics and its influences on shear strength in burned areas

作为火后泥石流典型起动物源,火烧迹地浅表层滑坡的发生与其所在部位根系特征改变密不可分。为了研究林火过后火烧迹地根系变化对土壤力学性质的影响,本文以四川省乡城县正斗乡仁额拥沟泥石流火烧区和未火烧区的土壤根系特征和抗剪强度进行对比研究,通过室内单根抗拉试验和根-土复合体直剪试验,旨在探究火烧迹地土壤根系特征的变化及其对土壤抗剪强度的影响。结果表明:火烧区浅表层土壤中根系的数量、根径、根质量密度和根长密度相较于未火烧区都有所降低,分别降低了23.15%,51.35%,62.98%,29.10%;单根抗拉力随着根系直径的增加而增大,抗拉强度随着根系直径的增加而减小,但在根径相同的条件下,火烧区土壤的抗拉力和抗拉强度均有所减小;火烧区根-土复合体的抗剪强度明显小于未火烧区根-土复合体,主要体现在根系抗拉力减小造成土壤黏聚力下降,而内摩擦角则变化不大,所得结果为火烧迹地浅表层滑坡形成机理剖析提供了依据。

As a typical source of debris flow after fire,the start of shallow surface landslides is inseparable from the change in root characteristics of fired land.In order to study the effect of root system changes on soil mechanical properties after forest fire,this paper mainly compares the soil root characteristics and shear strength of the burned areas with those of the non-burned areas in Zhengdou Township in Xiangcheng County of Sichuan Province,and conducts indoor single-strength tensile test and root-soil composite direct shear test.The purpose of this work is to investigate the deterioration of soil root characteristics and its effect on soil shear strength in the burned areas.The experimental results show that the forest fire reduced the number of roots,root diameter,root mass density and root length density in the superficial soil by 23.15%,51.35%,62.98%and 29.10%,respectively.The tensile strength of single root increased with the increasing root diameter,while the tensile strength decreased with the increasing root diameter.Under the condition of the same root diameter,the soil tensile strength and tensile strength decreased after fire.The shear strength of the soil in the burned area is obviously lower than that in the unburned area.The cohesion decrease derived from root weakening should account for this phenomenon.The obtained results may be useful in the study of the formation mechanism of shallow surface landslide in burned areas.