火烧迹地土壤根系特征及其对抗剪强度的影响
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摘要
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.
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.
引文
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[18]李建兴,何丙辉,谌芸,等.不同护坡草本植物的根系分布特征及其对土壤抗剪强度的影响[J].农业工程学报,2013,29(10):144-152.[LI J X,HE B H,S Y,et al. Root distribution features of typical herb plants for slope protection and their effects on soil shear strength[J]. Transactions of the Chinese Society of Agricultural Engineering,2018,40(4):792-801.(in Chinese)]
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[2] PARISE M,CANNON S H. Wildfire impacts on the processes that generate debris flows in burned watersheds[J]. Natural Hazards,2012,61(1):217-227.
[3]胡卸文,王严,杨瀛.火后泥石流成灾特点及研究现状[J].工程地质学报,2018,26(6):1562-1573.[HU X W, WANG Y, YANG Y. Disaster characteristics and research status of post-fire debris flow[J]. Journal of Engineering Geology,2018,26(6):1562-1573.(in Chinese)]
[4]杨亚川,莫永京,王芝芳,等.土壤-草本植被根系复合体抗水蚀强度与抗剪强度的试验研究[J].中国农业大学学报,1996(2):31-38.[YANG Y C,MO Y J,WANG Z F,et al. Experimental study on anti-water erosion and shear strength of soil-root composite[J]. Journal of China Agricultural University,1996(2):31-38.(in Chinese)]
[5]封金财,王建华.乔木根系固坡作用机理的研究进展[J].铁道建筑,2004(3):29-31.[FENG J C,WANG J H. Advances in research on slope fixation mechanism of tree roots[J]. Railway Engineering,2004(3):29-31.(in Chinese)]
[6]封金财,王建华.植物根的存在对边坡稳定性的作用[J].华东交通大学学报,2003(5):42-45.[FENG J C,WANG J H. Influence of the roots on the slope stability[J]. Journal of East China Jiaotong University,2003(5):42-45.(in Chinese)]
[7]李国荣,胡夏嵩,毛小青,等.寒旱环境黄土区灌木根系护坡力学效应研究[J].水文地质工程地质,2008,35(1):94-97.[LI G R,HU X S,MAO X Q,et al. A Study of the mechanical effects of shrub roots for slope protection in frigid and arid-semiarid loess area[J]. Hydrogeology&Engineering Geology,2008,35(1):94-97.(in Chinese)]
[8]张兴玲,胡夏嵩,李国荣,等.寒旱环境草本植物根系护坡的时间尺度效应[J].水文地质工程地质,2009,36(4):117-120.[ZHANG X L,HU X S,LI G R,et al. Time scale effect of herb roots on slope protection in a cold,arid and semi-arid environment[J]. Hydrogeology&Engineering Geology,2009,36(4):117-120.(in Chinese)]
[9]杨幼清,胡夏嵩,李希来,等.高寒矿区草本植物根系增强排土场边坡土体抗剪强度试验研究[J].水文地质工程地质,2018,45(6):105-113.[YANG Y Q,HU X S,LI X L,et al. An experimental study of the soil shear strength reinforcement of a mine dump slope by herbaceous root systems in alpine regions[J]. Hydrogeology&Engineering Geology,2018,45(6):105-113.(in Chinese)]
[10] HU X S,BRIERLEY G,ZHU H L,et al. An exploratory analysis of vegetation strategies to reduce shallow landslide activity on loess hillslopes,Northeast Qinghai-Tibet Plateau,China[J]. Journal of Mountain Science,2013,10(4):668-686.
[11]张惠忍,李法虎,张心平.天然草本植被根系对表层土壤抗剪强度的影响[J].中国农业大学学报,2015,20(4):189-195.[ZHANG H R,LI F H,ZHANG X P. Effect of wild herbaceous vegetation roots on undisturbed surface soil shear strength[J].Journal of China Agricultural University,2015,20(4):189-195.(in Chinese)]
[12]陈雨彤,李法虎.一年野生草本植物根系力学性能动态变化特征[J].人民长江,2018,49(9):19-25.[CHEN Y T,LI F H,WANG Z Fl. Dynamic variation of root mechanical properties for annual wild herbaceous vegetations[J]. Yangtze River,2018,49(9):19-25.(in Chinese)]
[13]王桂尧,胡圣辉,张永杰,等.小乔木根系根土间作用力的室外拉拔试验研究[J].水文地质工程地质,2017,44(6):64-69.[WANG G R,HU S H,ZHANG Y J,et al. An outdoor drawing test study of the root soil interaction force for a small tree root system[J]. Hydrogeology&Engineering Geology,2017,44(6):64-69.(in Chinese)]
[14]冯国建,沈凡,王世通.护坡植物根系分布特征及抗拉强度研究[J].重庆师范大学学报(自然科学版),2013,30(2):115-118.[FENG G J,SHEN F,WANG S T. Study on distribution characteristic and tensile strength of slope eco-engineering plant root[J]. Journal of Chongqing Normal University(Natural Science),2013,30(2):115-118.(in Chinese)]
[15]陆桂红,欧国强,杨顺,等.泥石流源区典型草本植物根系抗拉试验[J].山地学报,2014,32(6):725-731.[LU G H,OU G Q,YANG S,et al. Root tensile test of typical grass in debris flow triggering area[J]. Mountain Research,2014,32(6):725-731.(in Chinese)]
[16]王晓梅,陈建平,周云艳.植物根系抗拉试验研究[J].安徽农业科学,2009,37(32):15688-15691.[WANG X M,CHEN J P,ZHOU Y Y. Study on tensile test of plant roots[J]. Journal of Anhui Agricultural Sciences, 2009,37(32):15688-15691.(in Chinese)]
[17]王恒星,杨林.冻融作用下草本植物根系加固土体试验研究[J].冰川冻土,2018,40(4):792-801.[WANG H X,YANG L. Experimental study on the reinforcement of herbaceous plant roots under freezingthawing cycles[J]. Journal of Glaciology and Geocryology,2018,40(4):792-801.(in Chinese)]
[18]李建兴,何丙辉,谌芸,等.不同护坡草本植物的根系分布特征及其对土壤抗剪强度的影响[J].农业工程学报,2013,29(10):144-152.[LI J X,HE B H,S Y,et al. Root distribution features of typical herb plants for slope protection and their effects on soil shear strength[J]. Transactions of the Chinese Society of Agricultural Engineering,2018,40(4):792-801.(in Chinese)]
[19] MATTEW R,DUMLAO,SOPHIE,et al. The role of root development of Avena fatua in conferring soil strength[J]. American Journal of Botany,2015,102(7):150-160.