Effects Of Morphological And Mechanical Properties Of Roots Formed From Mixed Forest And Grass On Shallow-slope Stability In Loess Region

Vegetation is the most positive factor for shallow slope stability,especially plant roots play an important role in soil shear strength reinforcement.Hence,plants are widely used in slope ecological-protection project.High stable slope protection technology of forest-grass integration could form three dimensional space structures in a short time.It would be reasonable to believe that the anchoring and supporting effects of roots of arbors and herbs in slope ecological protection.In this paper,indigenous plants community of Populus simonii and Bothriochloa ischaemum were selected as the test samples,and were to further explore the mechanical effects of the soil reinforced with mixed forest and grass in slope protection in Northern Shaanxi.The experiments as follows are done: 1)distributing characteristic of roots structures in 1m3,2)relationship between mechanical characteristics of tensile strength and root parameters,especially root diameter;3)relationship between shearing strength and root parameters,especially roots biomass,root length and roots area.To maintain the roots distribution characteristics in natural state,the field sampling method was used.Cutting ring was cube of side length with 10 cm.Firstly,slow shear tests was proceed indoor with stochastic sampling,to analyze shearing strength characteristics of root-soil composites of forest and grass.Then,the single tensile tests was proceed through selected roots of Populus simonii and Bothriochloa ischaemum respectively.And fitting function between roots diameter and single tensile strength were systematically analyzed.Finally,the fitting function between roots structures characteristics and shearing strength characteristics of root-soil composites of forest and grass were analyzed too.The main conclusions are as follows:(1)Characteristics of densities of roots biomass,root length and roots area of mixed Populus simonii and Bothriochloa ischaemum in vertical direction showed fluctuating decrease trend with the increase of soil depth.And this trend were expressed in three distinctive characteristics: roots were obviously centralized distribute in soil depth of 0-30 cm,roots in soil depth of 40-70 cm was decreasing gradually,roots below 80 cm soil depth was were kept to a minimum.In horizontal direction,Characteristics of densities of roots biomass,root length and roots area showed fluctuating decreasing or increasing trend.The growth site of Bothriochloa ischaemum was voluntary,that lead to the above phenomenon.(2)The single root tensile resistances increases with the diameter increasing,and power relations exist between them of the forest and grass respectively.Meanwhile,the single root tensile strengths and the diameter showed a negative logarithm relations of the forest and grass respectively.Especially,when root diameters were <0.6mm,the single root tensile resistances of Populus simonii was smaller than that of Bothriochloa ischaemum under the condition of same root diameter.When root diameters were >0.6mm,the single root tensile resistances of Populus simonii was gradually increased,and far greater than than that of Bothriochloa ischaemum paddy fields.When root diameters were <0.75 mm,the single root tensile strength of Bothriochloa ischaemum was great bigger than that of Populus simonii under the condition of same root diameter.When root diameters were <0.75 mm,trends of the single root tensile strength of the two plants were inverse.(3)The shear strength was increased gradually,with the increase of vertical load pressure.And,with the increase of soil moisture,the shear strength was increased firstly and then decreased.And,with the increase of root biomass density,the shear strength was increased,but the growth rate was decreased gradually.By further analysis,the internal friction angle ? was logarithmic growth and cohesion C was linear growth with the increase of root length density and root surface area density.In this paper,roots of mixed common plants of Populus simonii and Bothriochloa ischaemum were selected as the test samples to further explore the mechanical effects of the soil reinforced in slope protection in Northern Shaanxi.with mixed forest and grass forest and grass can improved the shear strength in the Loess Slope in Northern Shaanxi to enhance the slope stability and has a special significance in the further research,ecological benefit evaluation and its application of vegetation concrete base material ecological protection technology.