Heavy summer rainfall induces significant soil erosion and shallow landslide activity on the loess hillslopes of the Xining Basin at the northeast margin of the Qinghai-Tibet Plateau. This study examines the mechanica...Heavy summer rainfall induces significant soil erosion and shallow landslide activity on the loess hillslopes of the Xining Basin at the northeast margin of the Qinghai-Tibet Plateau. This study examines the mechanical effects of five native shrubs that can be used to reduce shallow landslide activity. We measured single root tensile resistance and shear resistance, root anatomical structure and direct shear and triaxial shear for soil without roots and five root- soil composite systems. Results show that Atriplex canescens (Pursh) Nutt. possessed the strongest roots, followed by Caragana korshinskii Kom., Zygophyllum xanthoxylon (Bunge) Maxim., Nitraria tangutorum Bobr. and Lycium chinense Mill. Single root strength and shear resistance relationships with root diameter are characterized by power or exponential relations, consistent with the Mohr- Coulomb law. Root mechanical strength reflects their anatomical structure, especially the percentage of phloem and xylem cells, and the degree and speed of periderm lignifications. The cohesion force of root- soil composite systems is notably higher than that of soil without roots, with increasing amplitudes of cohesion force for A. canescens, C. korshinskii, Z. xanthoxylon, N. tangutorum and L. chinense of 75.9%, 75.1%, 36.2%, 24.6% and 17.0 % respectively. When subjected to shear forces, the soil without root samples show much greater lateral deformation thanthe root-soil composite systems, reflecting the restraining effects of roots. Findings from this paper indicate that efforts to reduce shallow landslides in this region by enhancing root reinforcement will be achieved most effectively using A. canescens and C. korshinskii.展开更多
To investigate the influence of root system architectural properties of three indigenous(coldadapted) shrubs on the hillslope stability of loess deposits in the Xining Basin,northeast part of Qinghai-Tibet Plateau(QTP...To investigate the influence of root system architectural properties of three indigenous(coldadapted) shrubs on the hillslope stability of loess deposits in the Xining Basin,northeast part of Qinghai-Tibet Plateau(QTP),indoor direct shear tests have been conducted on the remolded rooted soil of three shrubs.Test results show that root system architectural indices(root area ratio(RAR),root length density(RLD) and root density(RD)) of the shrubs decline with depth and the relationship between RAR,RD and depth is exponential,while a power relationship describes the relationship between RLD and depth.The cohesion force of remolded rooted soil for the shrubs initially increases withdepth,but it then demonstrates a slightly decreasing trend,which can be described with a power relationship.Power relationships also describe relationships between cohesion force and RAR,RLD and RD for the shrubs.As the growth period increases from 10 to 17 months,the incremental increase in RAR is 48.32% ~ 210.25% for Caragana korshinskii Kom and 0.56% ~ 166.85% for Zygophyllum xanthoxylon(Bunge) Maxim.This proportional increase is notably larger than that for RLD and RD.The increment in RAR is marginally greater for C.korshinskii than it is for Z.xanthoxylon.Correspondingly,the cohesion force incremental rates of remolded rooted soil for C.korshinskii and Z.xanthoxylon are 12.41% ~ 25.22% and 3.45% ~ 17.33% respectively.Meanwhile,as root content increases,the contribution by roots to cohesion force increases markedly until a threshold condition is reached.展开更多
In order to improve our knowledge of the mechanical effect of the roots of mixed-plantings on soil reinforcement and slope protection,the influence of roots of a mixed-planting with four herb species(Medicago sativa L...In order to improve our knowledge of the mechanical effect of the roots of mixed-plantings on soil reinforcement and slope protection,the influence of roots of a mixed-planting with four herb species(Medicago sativa L.,Elymus nutans Griseb.,Puccinellia distanx(L.),and Poa pratensis L.)and one shrub species(Caragana korshinskii Kom.)were investigated on the shear strength characteristics of saline loess soil.The root distribution characteristics were assessed via a survey when the plants grew for one year.The effects of the root biomass density,the root mass ratio(RMR)of the fine roots to the coarse roots,the moisture content,and the salt content on the shear strength index of the rooted soil were analyzed via a triaxial compression test,and the mechanism of these effects was discussed.The results indicate that the biomass density decreased linearly with increasing depth.The RMR initially decreased with depth and then increased,exhibiting in a quadratic relationship.The cohesion of the rooted soil increased linearly as the biomass density increased.The cohesion of the rooted soil initially increased with increasing RMR and salt content,and then it decreased.The turning point of the cohesion occurred when the RMR was 0.6 and the salt content was 1.18%.The internal friction angle of the rooted soil initially increased with biomass density and then decreased,and the turning point of the internal friction angle occurred when the biomass density was 0.015 g/cm3.The relationships between the internal friction angle of the rooted soil and the RMR and salt content were exponential incremental and linear subtractive relationship,respectively.Both the cohesion and the internal friction angle of the rooted soil linearly decreased with increasing moisture content.展开更多
基金financially supported by the National Natural Science Foundation of China(Grant No.41162010)Excellent Talents in University of New Century by Ministry of Education of the People's Republic of China(Grant No.NCET-04-G983)International Science & Technology Cooperation Program of China(Grant No.2011DFG93160)
文摘Heavy summer rainfall induces significant soil erosion and shallow landslide activity on the loess hillslopes of the Xining Basin at the northeast margin of the Qinghai-Tibet Plateau. This study examines the mechanical effects of five native shrubs that can be used to reduce shallow landslide activity. We measured single root tensile resistance and shear resistance, root anatomical structure and direct shear and triaxial shear for soil without roots and five root- soil composite systems. Results show that Atriplex canescens (Pursh) Nutt. possessed the strongest roots, followed by Caragana korshinskii Kom., Zygophyllum xanthoxylon (Bunge) Maxim., Nitraria tangutorum Bobr. and Lycium chinense Mill. Single root strength and shear resistance relationships with root diameter are characterized by power or exponential relations, consistent with the Mohr- Coulomb law. Root mechanical strength reflects their anatomical structure, especially the percentage of phloem and xylem cells, and the degree and speed of periderm lignifications. The cohesion force of root- soil composite systems is notably higher than that of soil without roots, with increasing amplitudes of cohesion force for A. canescens, C. korshinskii, Z. xanthoxylon, N. tangutorum and L. chinense of 75.9%, 75.1%, 36.2%, 24.6% and 17.0 % respectively. When subjected to shear forces, the soil without root samples show much greater lateral deformation thanthe root-soil composite systems, reflecting the restraining effects of roots. Findings from this paper indicate that efforts to reduce shallow landslides in this region by enhancing root reinforcement will be achieved most effectively using A. canescens and C. korshinskii.
基金financially supported by the National Natural Science Foundation of China(Grant Nos.41162010,41572306)provincial key project in science and technologies of Qinghai(Grant No.2003-N-134)+1 种基金Excellent Talents in University of New Century by Ministry of Education of the People’s Republic of China(Grant No.NCET–04–G983)International Science&Technology Cooperation Program of China(Grant No.2011DFG93160)
文摘To investigate the influence of root system architectural properties of three indigenous(coldadapted) shrubs on the hillslope stability of loess deposits in the Xining Basin,northeast part of Qinghai-Tibet Plateau(QTP),indoor direct shear tests have been conducted on the remolded rooted soil of three shrubs.Test results show that root system architectural indices(root area ratio(RAR),root length density(RLD) and root density(RD)) of the shrubs decline with depth and the relationship between RAR,RD and depth is exponential,while a power relationship describes the relationship between RLD and depth.The cohesion force of remolded rooted soil for the shrubs initially increases withdepth,but it then demonstrates a slightly decreasing trend,which can be described with a power relationship.Power relationships also describe relationships between cohesion force and RAR,RLD and RD for the shrubs.As the growth period increases from 10 to 17 months,the incremental increase in RAR is 48.32% ~ 210.25% for Caragana korshinskii Kom and 0.56% ~ 166.85% for Zygophyllum xanthoxylon(Bunge) Maxim.This proportional increase is notably larger than that for RLD and RD.The increment in RAR is marginally greater for C.korshinskii than it is for Z.xanthoxylon.Correspondingly,the cohesion force incremental rates of remolded rooted soil for C.korshinskii and Z.xanthoxylon are 12.41% ~ 25.22% and 3.45% ~ 17.33% respectively.Meanwhile,as root content increases,the contribution by roots to cohesion force increases markedly until a threshold condition is reached.
基金the Second Tibetan Plateau Scientific Expedition and Research(STEP)program(Grant No.2019QZKK0905)the National Natural Science Foundation of China(Grant Nos.42002283,41572306,42041006 and 42062019)+2 种基金the Project of the Qinghai Science&Technology Department(Grant Nos.2020-ZJ-906 and 2014-ZJ-906)the Key Discipline Construction Project for Geological Resources and Geological Engineering of Qinghai University(Grant No.41250103)the Ministry of Education’s‘Innovative Team Development Scheme’(IRT17R62)。
文摘In order to improve our knowledge of the mechanical effect of the roots of mixed-plantings on soil reinforcement and slope protection,the influence of roots of a mixed-planting with four herb species(Medicago sativa L.,Elymus nutans Griseb.,Puccinellia distanx(L.),and Poa pratensis L.)and one shrub species(Caragana korshinskii Kom.)were investigated on the shear strength characteristics of saline loess soil.The root distribution characteristics were assessed via a survey when the plants grew for one year.The effects of the root biomass density,the root mass ratio(RMR)of the fine roots to the coarse roots,the moisture content,and the salt content on the shear strength index of the rooted soil were analyzed via a triaxial compression test,and the mechanism of these effects was discussed.The results indicate that the biomass density decreased linearly with increasing depth.The RMR initially decreased with depth and then increased,exhibiting in a quadratic relationship.The cohesion of the rooted soil increased linearly as the biomass density increased.The cohesion of the rooted soil initially increased with increasing RMR and salt content,and then it decreased.The turning point of the cohesion occurred when the RMR was 0.6 and the salt content was 1.18%.The internal friction angle of the rooted soil initially increased with biomass density and then decreased,and the turning point of the internal friction angle occurred when the biomass density was 0.015 g/cm3.The relationships between the internal friction angle of the rooted soil and the RMR and salt content were exponential incremental and linear subtractive relationship,respectively.Both the cohesion and the internal friction angle of the rooted soil linearly decreased with increasing moisture content.
