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不同根系含量对山原红壤抗剪强度的影响
徐宗恒, 黄丽苹, 杨正辉, 尹李乐
云南师范大学 旅游与地理科学学院, 云南 昆明 650500
摘要:
[目的] 探讨云南省昆明市呈贡区段家营一植被覆盖的斜坡区不同含量植被根系对山原土壤抗剪强度的增强效应,为相关研究提供理论依据。[方法] 制备0(无根系空白样),0.467,0.93,1.4 mg/cm3这4种根系含量以及20%,25%,30%,35%,40%这5种含水量的根-土复合体试验样品进行抗剪强度试验。[结果] 根-土复合体中,植被根系能提供给土壤额外的抗剪能力和抵抗土体变形来增强土体的抗剪强度,植被根系对土体抗剪强度有明显的增强效应,但这种增强效应是有限的。根系含量在0.93 mg/cm3时,根系对土体的抗剪强度增强效果最好。随着根系含量的增加,黏聚力和内摩擦角总是呈现负相关性的关系,在低含水量情况下,黏聚力随根系含量增加而先降低后增加,内摩擦角随根系含量变化则相反。当含水量低且根系含量相对较少时(当含水量≤ 35%,根系含量≤ 0.93 mg/cm3时),土壤参与剪切整个过程且为被剪主体,得到的黏聚力和内摩擦角均为正值,符合库仑定律;当含水量较高且根系含量较多时(当含水量=35%,根系含量=1.4 mg/cm3时以及当含水量=45%,根系含量≥ 0.467 mg/cm3时),被剪主体为根系,得到的黏聚力为负值,不符合库仑定律。[结论] 库仑定律不适用于高含水量和高含量植被根系的根-土复合体抗剪强度的研究。在采用植被护坡时可用试验确定边坡土壤抗剪强度最高时的最佳含根量和含水量。
关键词:  山原红壤  根—土复合体  直剪实验  增强效应
DOI:10.13961/j.cnki.stbctb.2019.05.008
分类号:S157.1;TU411
基金项目:国家自然科学基金项目“典型斜坡非饱和带优先域及其降雨入渗机制研究”(41502340)
Influence of Different Root Contents on Shear Strength of Mountain Red Earth
Xu Zongheng, Huang Liping, Yang Zhenghui, Yin Lile
Department of Tourism and Geographic Science, Yunnan Normal University, Kunming, Yunnan 650500, China
Abstract:
[Objective] The effects of vegetation root content on the shear strength of mountain red earth acquired from vegetated slope in Chenggong district, Kunming City of Yunnan Province were analyzed in order to provide theoretical basis for relevant research.[Methods] The shear strength tests were carried out by preparing roots-soil complex samples with four levels of root content:0 (no root samples), 0.467, 0.93, 1.4 mg/cm3, as well as five levels of soil moisture content (20%, 25%, 30%, 35%, and 40%).[Results] The vegetation roots were found to provide soil with additional shear strength and helps soil resist deformation, which can enhance its shear strength. Vegetation roots had obvious enhancement effect on the shear strength of soil, but this enhancement effect was limited. When the root content was 0.93 mg/cm3, the root system had the best enhancement effect on the shear strength of soil. With an increase in root content, the cohesion and the angle of internal friction always presented a negative correlation. In the case of low water content, the cohesion first decreased and then increased, while the angle of internal friction changed inversely with the change of root density. When the soil moisture constant and the root content was low (water content and root content less than or equal to 35% and 0.93 mg/cm3 respectively), the soil participated in the whole process of shear and they were the main object to be sheared, and the calculated cohesion and internal friction angle were both positive, which was consistent with Coulomb's law. When the soil moisture and root content was high(water content and root content was 35% and 1.4 mg/cm3 respectively or the root content was 45% and root content was greater than or equal to 0.467 mg/cm3), the shear object was mainly the root system, and the cohesion calculated by Coulomb's law was negative, which does not conform to Coulomb's law.[Conclusion] Coulomb's law is not applicable to the study of the shear strength of the root-soil complex which has high water content and vegetation density. When using vegetation for slope protection, it is necessary to carry out experiments to determine the optimal root and water content of the slope soil to produce the highest shear strength.
Key words:  mountain red earth  roots-soil complex  direct shear tests  enhancement effect