不同草本植物根系提高无侧限受压土体的抗剪强度
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摘要
研究草本植物根系提高无侧限受压土体的抗剪能力,为根系固土护坡计算和草种选择提供依据。采用无侧限抗压强度试验,测定了素土和3种草根土复合体的黏聚力(C),分析了黏聚力增量ΔC与根系特征值间的关系。结果表明:非洲狗尾草、鸭茅、紫花苜蓿的根系可将0～25 cm范围内土体的黏聚力提高4.75、4.04、1.39 kPa,25～50 cm范围内土体提高3.10、2.32、0.71 kPa。非洲狗尾草、鸭茅柱体破坏面根密度(RD)、根面积比(RAR)、复合体含根量(Q)与ΔC呈二次显著相关,并以Q与ΔC相关性最好;根系平均直径Tr,a与ΔC不相关;紫花苜蓿的4个量与ΔC没有相关性。非洲狗尾草根系提高土体抗剪强度能力最强,鸭茅次之,紫花苜蓿最差,紫花苜蓿提高值的变化幅度最大;上层根系提高值要大于下层。对非洲狗尾草、鸭茅等斜生根系草本,在RD、RAR、Q三个根系特征指标中,Q是计算根系提高土体抗剪强度的最优指标。对所计算植物边坡多点取样进行无侧限抗压强度试验,使得采用概率论计算其稳定性成为可能。
【Objective】The aim of this study was to explore effects and mechanism of herb roots in natural state improving shear strength of unconfined compressed solum, so as to provide a scientific basis for calculating the capacity of herb roots to reinforce slopes and selecting proper species of grasses to grow on slopes.【Method】The experiment was carried out at the experimental farm of the Yunnan Agricultural University, China. In January 2016, a total of 40 PVC tubes, 51 cm in length, 110 mm in diameter and 3.2 mm in thickness were all cut in half, and then the halves were bound together by pair with rubber bands. Upland red soil < 5 mm in particle size was packed into in these rubber band fixed tubes with the bottom sealed with plastic film up to 50 cm. The soil in the tubes was 28.31% in moisture content and 0.78 g.cm~(-3) in dry density. The tubes were divided into four groups, 10 each. Three groups were sown with seeds of Setariaanceps Stapf ex Massey L., Dactylisglomerata L. and Medicago sativa L. 12 seeds each tube, separately, in May, and the other group left unplanted as control for comparison. Besides, the three species of grasses were planted, separately, in the field, 1 m2 each in plot area for determination of tensile strength of the grass roots. In October, out of each group, 7 tubes were picked randomly, placed in water for 24 h until they were fully saturated, and then removed out of water. The tubes were split off and the soil columns inside taken out. Shoots of the plants were cut off. The soil columns were cut into two, 25 cm each, in the middle with a hacksaw. From each half of the soil columns, a section of 20 cm in the middle was taken as test samples and the section was 10.36 cm in diameter. The samples were analyzed for saturation density and saturated water content and tested for unconfined shear strength on a SJ-1 A type strain controlling triaxial apparatus(made in Nanjing Soil Instrument Factory, China). The test went on in line with the geotechnical test code(SL237-1999) of China. Before the test the pressure cell and pressure system was removed from the apparatus and then the sample was put on the platform of the triaxial compression system for pressure test with a shearing rate of 4.14 mm·min~(-1). A dial gauge was used to monitor deformation of the soil column and of the dynamometric ring and record the process of ess-strain until collapse of the sample or the total axial strain reaching 20%. For soil samples that stood the pressure even after the total axial strain reached 20%, their shear strength should be the value that corresponded to the one when the strain reached 15%. After the compression test, the soil columns were separated along the failure surface, and then the roots appearing on the failure surface were counted and measured with an electronic calipers for diameter; Biomass of the roots in the sample was measured after the samples were oven dried. In October, roots of the three species of grasses growing in the field were dug up and measured with an electronic calipers for diameter and with a Shandu SN100 tension tester and a universal testing machine for tensile resistance of each root.【Result】(1) The root systems of all the species of grasses enhanced the cohesive strength(ΔC) of the 0～25 cm soil layer by 4.75 kPa for Setariaanceps Stapf ex Massey L., by 4.40 kPa for Dactylisglomerata L. and by 1.39 kPa for Medicago sativa L., and that of the 25～50 cm soil layer by 3.10, 2.32 and 0.71 kPa, respectively;(2) ΔC(increment in tensile strength) was significantly related to root density(RD) and root area ratio(RAR) of Setariaanceps Stapf ex Massey L. and Dactylisglomerata L. roots in the failure surface and root content(Q) in the soil-root complex. The relationship between Q and ΔC was the highest. However, ΔC was not related with mean diameter of the roots(T_(r,a)). In the case of Medicago sativa L. ΔC had nothing to do with all the four root parameters.【Conclusion】Setariaanceps Stapf ex Massey L. is the highest and Medicago sativa L. the lowest in the effect of enhancing shear strength of the soil. ΔC of Medicago sativa L. varies sharply, being higher in the upper half section than in the lower half section. As Setariaanceps Stapf ex Massey L. and Dactylisglomerata L. are herbs dominated with oblique root, among the three root parameters, RD, RAR and Q, Q is the best index for calculating ΔC, which makes it feasible to use the probability theory to calcuate stability of the unconfined compression test of samples collected from a number of sampling points on a vegetated slope.
【Objective】The aim of this study was to explore effects and mechanism of herb roots in natural state improving shear strength of unconfined compressed solum, so as to provide a scientific basis for calculating the capacity of herb roots to reinforce slopes and selecting proper species of grasses to grow on slopes.【Method】The experiment was carried out at the experimental farm of the Yunnan Agricultural University, China. In January 2016, a total of 40 PVC tubes, 51 cm in length, 110 mm in diameter and 3.2 mm in thickness were all cut in half, and then the halves were bound together by pair with rubber bands. Upland red soil < 5 mm in particle size was packed into in these rubber band fixed tubes with the bottom sealed with plastic film up to 50 cm. The soil in the tubes was 28.31% in moisture content and 0.78 g.cm~(-3) in dry density. The tubes were divided into four groups, 10 each. Three groups were sown with seeds of Setariaanceps Stapf ex Massey L., Dactylisglomerata L. and Medicago sativa L. 12 seeds each tube, separately, in May, and the other group left unplanted as control for comparison. Besides, the three species of grasses were planted, separately, in the field, 1 m2 each in plot area for determination of tensile strength of the grass roots. In October, out of each group, 7 tubes were picked randomly, placed in water for 24 h until they were fully saturated, and then removed out of water. The tubes were split off and the soil columns inside taken out. Shoots of the plants were cut off. The soil columns were cut into two, 25 cm each, in the middle with a hacksaw. From each half of the soil columns, a section of 20 cm in the middle was taken as test samples and the section was 10.36 cm in diameter. The samples were analyzed for saturation density and saturated water content and tested for unconfined shear strength on a SJ-1 A type strain controlling triaxial apparatus(made in Nanjing Soil Instrument Factory, China). The test went on in line with the geotechnical test code(SL237-1999) of China. Before the test the pressure cell and pressure system was removed from the apparatus and then the sample was put on the platform of the triaxial compression system for pressure test with a shearing rate of 4.14 mm·min~(-1). A dial gauge was used to monitor deformation of the soil column and of the dynamometric ring and record the process of ess-strain until collapse of the sample or the total axial strain reaching 20%. For soil samples that stood the pressure even after the total axial strain reached 20%, their shear strength should be the value that corresponded to the one when the strain reached 15%. After the compression test, the soil columns were separated along the failure surface, and then the roots appearing on the failure surface were counted and measured with an electronic calipers for diameter; Biomass of the roots in the sample was measured after the samples were oven dried. In October, roots of the three species of grasses growing in the field were dug up and measured with an electronic calipers for diameter and with a Shandu SN100 tension tester and a universal testing machine for tensile resistance of each root.【Result】(1) The root systems of all the species of grasses enhanced the cohesive strength(ΔC) of the 0～25 cm soil layer by 4.75 kPa for Setariaanceps Stapf ex Massey L., by 4.40 kPa for Dactylisglomerata L. and by 1.39 kPa for Medicago sativa L., and that of the 25～50 cm soil layer by 3.10, 2.32 and 0.71 kPa, respectively;(2) ΔC(increment in tensile strength) was significantly related to root density(RD) and root area ratio(RAR) of Setariaanceps Stapf ex Massey L. and Dactylisglomerata L. roots in the failure surface and root content(Q) in the soil-root complex. The relationship between Q and ΔC was the highest. However, ΔC was not related with mean diameter of the roots(T_(r,a)). In the case of Medicago sativa L. ΔC had nothing to do with all the four root parameters.【Conclusion】Setariaanceps Stapf ex Massey L. is the highest and Medicago sativa L. the lowest in the effect of enhancing shear strength of the soil. ΔC of Medicago sativa L. varies sharply, being higher in the upper half section than in the lower half section. As Setariaanceps Stapf ex Massey L. and Dactylisglomerata L. are herbs dominated with oblique root, among the three root parameters, RD, RAR and Q, Q is the best index for calculating ΔC, which makes it feasible to use the probability theory to calcuate stability of the unconfined compression test of samples collected from a number of sampling points on a vegetated slope.
引文
[1]程洪,张新全.草本植物根系网固土原理的力学试验探究.水土保持通报,2002,22(5):20-23Cheng H,Zhang X Q.An experimental study on herb plant root system for strength principle of soil-fixation(In Chinese).Bulletin of Soil and Water Conservation,2002,22(5):20-23
[2]杨旸,字淑慧,余建新,等.植物根系固土机理及模型研究进展.云南农业大学学报(自然科学),2014,29(5):759-765Yang Y,Zi S H,Yu J X,et al.Advances in research on mechanism and models of plant roots reinforcement(In Chinese).Journal of Yunnan Agricultural University(Natural Science),2014,29(5):759-765
[3]Slobodan B M,Alexia S,Rens V B,et al.Simulation of direct shear tests on rooted and non-rooted soil using finite element analysis.Ecological Engineering,2011,37(10):1523-1532
[4]Zhang B,Zhao Q G,Horn R,et al.Shear strength of surface soil as affected by soil bulk density and soil water content.Soil&Tillage Research,2001,59(3):97-106
[5]Li Q,Liu G B,Zhang Z,et al.Effect of root architecture on structural stability and erodibility of topsoils during concentrated flow in hilly Loess Plateau.Chinese Geographical Science,2015,25(6):1-8
[6]周云艳,徐琨,陈建平,等.基于CT扫描与细观力学的植物侧根固土机理分析.农业工程学报,2014,30(1):1-9Zhou Y Y,Xu K,Chen J P,et al.Mechanism of plant lateral root reinforcing soil based on CT scan and mesomechanics analysis(In Chinese).Transactions of the Chinese Society of Agricultural Engineering,2014,30(1):1-9
[7]Zhang C B,Chen L H,Liu Y P,et al.Triaxial compression test of soil-root composites to evaluate influence of roots on soil shear strength.Ecological Engineering,2010,36(1):19-26
[8]Comino E,Druetta A.The effect of Poaceae,roots on the shear strength of soils in the Italian alpine environment.Soil&Tillage Research,2010,106(2):194-201
[9]Fan C C,Tsai M H.Spatial distribution of plant root forces in root-permeated soils subject to shear.Soil&Tillage Research,2016,156:1-15
[10]Rickli C,Graf F,Rickli C,et al.Effects of forests on shallow landslides-A case studies in Switzerland.Forest Snow&Landscape Research,2009,82(1):33-44
[11]宋维峰.林木根系与均质土间相互物理作用机理研究.北京:北京林业大学,2006Song W F.Study on physical mechanism of interface between root system and loess(In Chinese).Beijing:Beijing Forestry University,2006
[12]黄英,符必昌,金克盛,等.加筋红土的广义等效围压和极限平衡条件.岩土力学,2007,28(3):533-539Huang Y,Fu B C,Jin K S,et al.Generalized equivalent c onfining pressure and limited balance conditions of reinforce d laterite(In Chinese).Rock and Soil Mechanics,2007,28(3):533-539
[13]陈仲颐.土力学.北京:清华大学出版社,1994Chen Z Y.Soil mechanics(In Chinese).Beijing:Tsinghua University Press,1994
[14]De Baets S,Poesen J,Reubens B,et al.Root tensile strength and root distribution of typical Mediterranean plant species and their contribution to soil shear strength.Plant and Soil,2008,305(1/2):207-226
[15]Waldron L J.The shear resistance of root-permeated homogeneous and stratified soil.Journal of the Soil Science Society of America,1977,41(5):843-849
[16]Tengbeh G T.The effect of grass roots on shear strength variations with moisture content.Soil Technology,1993,6(3):287-295
[17]Kleinfelder D,Swanson S,Norris G,et al.Unconfined compressive strength of some streambank soils with herbaceous roots.Soil Science Society of America Journal,1992,56(6):1920-1925
[18]周成,张继宝,周荣官,等.香根草生态护坡的根系固土试验研究.第二届全国环境岩土工程与土工合成材料技术研讨会论文集(二),2008Zhou C,Zhang J B,Zhou R G,et al.Experimental study on soil-reinforcement by vetiver grass root in bioengineering stabilization of slopes(In Chinese).Proceedings of the Second National Symposium on Environmental Geotechnical Engineering and Geosynthetics(2),2008
[19]聂影,陈晓红,付征耀,等.生态护坡根系纤维土强度和变形特性实验研究.铁道工程学报,2011,28(7):6-8Nie Y,Chen X H,Fu Z Y,et al.Experimental research on strength and deformation of root fiber stabilized soil of ecology slope(In Chinese).Journal of Railway Engineering Society,2011,28(7):6-8
[20]贺长彬,尤泳,王德成,等.退化草地复合体力学特性与影响因素研究.农业机械学报,2016,47(4):79-89He C B,You Y,Wang D C,et al.Mechanical characteristics of soil-root composite and its influence factors in degenerated grassland(In Chinese).Transactions of the Chinese Society for Agricultural Machinery,2016,47(4):79-89
[21]Karizumi N.Figure that tree roots.Tokyo:Cheng Wen Tang Shinkosha,1979
[22]范茂攀,李永梅,郑毅,等.不同生育期烤烟根系固土能力特征研究.中国生态农业学报,2014,22(5):560-565Fan M P,Li Y M,Zheng Y,et al.Soil fixing ability of flue-cured tobacco roots at different growth stages(In Chinese).Chinese Journal of Eco-Agriculture,2014,22(5):560-565
[23]南京水利科学研究院.中华人民共和国行业标准:土工试验规程SL237-1999.北京:中国水利水电出版社,1999Nanjing Hydraulic Research Institute.People’s Republic of China industry standard:Geotechnical test code SL237-1999(In Chinese).Beijing:China Water Conservancy and Hydropower Press,1999
[24]Bordoni M,Meisina C,Vercesi A,et al.Quantifying the contribution of grapevine roots to soil mechanical reinforcement in an area susceptible to shallow landslides.Soil&Tillage Research,2016,163:195-206
[25]栗岳洲,付江涛,余冬梅,等.寒旱环境盐生植物根系固土护坡力学效应及其最优含根量探讨.岩石力学与工程学报,2015,34(7):1370-1383Li Y Z,Fu J T,Yu D M,et al.Mechanical effects of halophytes roots and optimal root content for slope protection in cold and arid environment(In Chinese).Chinese Journal of Rock Mechanics and Engineering,2015,34(7):1370-1383
[26]Tosi M.Root tensile strength relationships and their slope stability implications of three shrub species in the Northern Apennines(Italy).Geomorphology,2007,87(4):268-283
[27]Loades K W,Bengough A G,Bransby M F,et al.Planting density influence on fibrous root reinforcement of soils.Ecological Engineering,2010,36(3):276-284
[28]Abdi E,Majnounian B,Genet M,et al.Quantifying the effects of root reinforcement of Persian Ironwood(Parrotia persica)on slope stability,a case study:Hillslope of Hyrcanian forests,northern Iran.Ecological Engineering,2010,36(10):1409-1416
[29]胡其志,周政,肖本林,等.生态护坡中土壤含根量与抗剪强度关系试验研究.土工基础,2010,24(5):85-87Hu Q Z,Zhou Z,Xiao B L,et al.Experimental research on relationship between root weight and shearing strength in soil(In Chinese).Soil Engineering&Foundation,2010,24(5):85-87
[30]Pollen N,Simon A.Estimating the mechanical effects of riparian vegetation on stream bank stability using a fiber bundle model.Water Resources Research,2005,41(7):W07025
[31]Li Y,Zhu X M,Tian J Y.Effectiveness of plant roots to increase the anti-scourability of soil on the Loess Plateau.Chinese SciencEe Bulletin,1991,36(24):2077-2082
[2]杨旸,字淑慧,余建新,等.植物根系固土机理及模型研究进展.云南农业大学学报(自然科学),2014,29(5):759-765Yang Y,Zi S H,Yu J X,et al.Advances in research on mechanism and models of plant roots reinforcement(In Chinese).Journal of Yunnan Agricultural University(Natural Science),2014,29(5):759-765
[3]Slobodan B M,Alexia S,Rens V B,et al.Simulation of direct shear tests on rooted and non-rooted soil using finite element analysis.Ecological Engineering,2011,37(10):1523-1532
[4]Zhang B,Zhao Q G,Horn R,et al.Shear strength of surface soil as affected by soil bulk density and soil water content.Soil&Tillage Research,2001,59(3):97-106
[5]Li Q,Liu G B,Zhang Z,et al.Effect of root architecture on structural stability and erodibility of topsoils during concentrated flow in hilly Loess Plateau.Chinese Geographical Science,2015,25(6):1-8
[6]周云艳,徐琨,陈建平,等.基于CT扫描与细观力学的植物侧根固土机理分析.农业工程学报,2014,30(1):1-9Zhou Y Y,Xu K,Chen J P,et al.Mechanism of plant lateral root reinforcing soil based on CT scan and mesomechanics analysis(In Chinese).Transactions of the Chinese Society of Agricultural Engineering,2014,30(1):1-9
[7]Zhang C B,Chen L H,Liu Y P,et al.Triaxial compression test of soil-root composites to evaluate influence of roots on soil shear strength.Ecological Engineering,2010,36(1):19-26
[8]Comino E,Druetta A.The effect of Poaceae,roots on the shear strength of soils in the Italian alpine environment.Soil&Tillage Research,2010,106(2):194-201
[9]Fan C C,Tsai M H.Spatial distribution of plant root forces in root-permeated soils subject to shear.Soil&Tillage Research,2016,156:1-15
[10]Rickli C,Graf F,Rickli C,et al.Effects of forests on shallow landslides-A case studies in Switzerland.Forest Snow&Landscape Research,2009,82(1):33-44
[11]宋维峰.林木根系与均质土间相互物理作用机理研究.北京:北京林业大学,2006Song W F.Study on physical mechanism of interface between root system and loess(In Chinese).Beijing:Beijing Forestry University,2006
[12]黄英,符必昌,金克盛,等.加筋红土的广义等效围压和极限平衡条件.岩土力学,2007,28(3):533-539Huang Y,Fu B C,Jin K S,et al.Generalized equivalent c onfining pressure and limited balance conditions of reinforce d laterite(In Chinese).Rock and Soil Mechanics,2007,28(3):533-539
[13]陈仲颐.土力学.北京:清华大学出版社,1994Chen Z Y.Soil mechanics(In Chinese).Beijing:Tsinghua University Press,1994
[14]De Baets S,Poesen J,Reubens B,et al.Root tensile strength and root distribution of typical Mediterranean plant species and their contribution to soil shear strength.Plant and Soil,2008,305(1/2):207-226
[15]Waldron L J.The shear resistance of root-permeated homogeneous and stratified soil.Journal of the Soil Science Society of America,1977,41(5):843-849
[16]Tengbeh G T.The effect of grass roots on shear strength variations with moisture content.Soil Technology,1993,6(3):287-295
[17]Kleinfelder D,Swanson S,Norris G,et al.Unconfined compressive strength of some streambank soils with herbaceous roots.Soil Science Society of America Journal,1992,56(6):1920-1925
[18]周成,张继宝,周荣官,等.香根草生态护坡的根系固土试验研究.第二届全国环境岩土工程与土工合成材料技术研讨会论文集(二),2008Zhou C,Zhang J B,Zhou R G,et al.Experimental study on soil-reinforcement by vetiver grass root in bioengineering stabilization of slopes(In Chinese).Proceedings of the Second National Symposium on Environmental Geotechnical Engineering and Geosynthetics(2),2008
[19]聂影,陈晓红,付征耀,等.生态护坡根系纤维土强度和变形特性实验研究.铁道工程学报,2011,28(7):6-8Nie Y,Chen X H,Fu Z Y,et al.Experimental research on strength and deformation of root fiber stabilized soil of ecology slope(In Chinese).Journal of Railway Engineering Society,2011,28(7):6-8
[20]贺长彬,尤泳,王德成,等.退化草地复合体力学特性与影响因素研究.农业机械学报,2016,47(4):79-89He C B,You Y,Wang D C,et al.Mechanical characteristics of soil-root composite and its influence factors in degenerated grassland(In Chinese).Transactions of the Chinese Society for Agricultural Machinery,2016,47(4):79-89
[21]Karizumi N.Figure that tree roots.Tokyo:Cheng Wen Tang Shinkosha,1979
[22]范茂攀,李永梅,郑毅,等.不同生育期烤烟根系固土能力特征研究.中国生态农业学报,2014,22(5):560-565Fan M P,Li Y M,Zheng Y,et al.Soil fixing ability of flue-cured tobacco roots at different growth stages(In Chinese).Chinese Journal of Eco-Agriculture,2014,22(5):560-565
[23]南京水利科学研究院.中华人民共和国行业标准:土工试验规程SL237-1999.北京:中国水利水电出版社,1999Nanjing Hydraulic Research Institute.People’s Republic of China industry standard:Geotechnical test code SL237-1999(In Chinese).Beijing:China Water Conservancy and Hydropower Press,1999
[24]Bordoni M,Meisina C,Vercesi A,et al.Quantifying the contribution of grapevine roots to soil mechanical reinforcement in an area susceptible to shallow landslides.Soil&Tillage Research,2016,163:195-206
[25]栗岳洲,付江涛,余冬梅,等.寒旱环境盐生植物根系固土护坡力学效应及其最优含根量探讨.岩石力学与工程学报,2015,34(7):1370-1383Li Y Z,Fu J T,Yu D M,et al.Mechanical effects of halophytes roots and optimal root content for slope protection in cold and arid environment(In Chinese).Chinese Journal of Rock Mechanics and Engineering,2015,34(7):1370-1383
[26]Tosi M.Root tensile strength relationships and their slope stability implications of three shrub species in the Northern Apennines(Italy).Geomorphology,2007,87(4):268-283
[27]Loades K W,Bengough A G,Bransby M F,et al.Planting density influence on fibrous root reinforcement of soils.Ecological Engineering,2010,36(3):276-284
[28]Abdi E,Majnounian B,Genet M,et al.Quantifying the effects of root reinforcement of Persian Ironwood(Parrotia persica)on slope stability,a case study:Hillslope of Hyrcanian forests,northern Iran.Ecological Engineering,2010,36(10):1409-1416
[29]胡其志,周政,肖本林,等.生态护坡中土壤含根量与抗剪强度关系试验研究.土工基础,2010,24(5):85-87Hu Q Z,Zhou Z,Xiao B L,et al.Experimental research on relationship between root weight and shearing strength in soil(In Chinese).Soil Engineering&Foundation,2010,24(5):85-87
[30]Pollen N,Simon A.Estimating the mechanical effects of riparian vegetation on stream bank stability using a fiber bundle model.Water Resources Research,2005,41(7):W07025
[31]Li Y,Zhu X M,Tian J Y.Effectiveness of plant roots to increase the anti-scourability of soil on the Loess Plateau.Chinese SciencEe Bulletin,1991,36(24):2077-2082
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