Shear Mechanical Properties Of Alfalfa And Vetiver Roots

Plant slope protection has greater advantages than engineering slope protection,but the randomness and complexity of the distribution of the root system,and the shear resistance of the root-soil complex is also relatively lacking.A large number of slopes are not scientifically analyzed when plant slope protection is carried out,so that the benefits of plant slope protection cannot be fully utilized.Based on the research results at home and abroad,it can be seen that for the research on the mechanical properties of plant roots,most of the existing studies focus on the tensile mechanical properties of the roots of shrubs or arbores,and there are few studies on the mechanical mechanisms of the roots of herbaceous plants.Therefore,it is of great significance to study the morphological distribution and shear resistance properties of herb roots.In order to study the morphological distribution of alfalfa and vetiver root system and the mechanical properties of root system-loess shear resistance in loess area,this paper conducted a survey test of alfalfa and vetiver root system and a root-soil composite shear test to study the different periods and different soil bulk densities.The variation of root length,root surface area,root volume and root cross-sectional area of alfalfa and vetiver root morphological parameters;discussed the destruction process of the root-soil complex;analyzed the root growth time(1 week,2 weeks,3 weeks and 4 weeks)),different planting methods(single plant planting,double plant planting),different soil bulk density(1.1 g/cm~3,1.2 g/cm~3,1.3g/cm~3and 1.4 g/cm~3),different shearing speed(1mm/min,3mm/min and 5mm/min)and different water content(W1,W2 and W3)and other factors on the shear mechanical properties of the root-soil composite.The main results are as follows:(1)Growth time is an important factor affecting the morphology of plant roots.The root length,root surface area,root volume,root cross-sectional area and root biomass of alfalfa and vetiver all increased with the increase of growth time.Among them,root length,root surface area,root biomass and root volume increased in power function with growth time,while cross-sectional area increased exponentially with growth time.(2)Soil bulk density also affects the morphology of plant roots.With the increase of soil bulk density,the root length,root surface area,root volume and cross-sectional area all decrease.The root length,root surface area,and root volume of the two plants decrease with the increase of time,and the cross-sectional area decreases with time.The increase shows an exponential decrease.The morphological distribution parameters of vetiver at each bulk density are greater than that of alfalfa(3)Different planting methods have a significant impact on the shear resistance of the root-soil complex.The shear strength of alfalfa and vetiver planted in two plants during the growth period from 1 to 4 weeks increased by 0.17%,3.18%,9.26%and 16.43%,respectively;0.38%,4.14%compared with single plant alfalfa and vetiver planting.,11.46%and 18.93%.Therefore,compared with single planting,double planting alfalfa and vetiver can better play the role of soil consolidation,and the effect of vetiver soil consolidation is better.(4)The bulk density of soil has a little effect on the shear strength of the root-soil complex.In the same growth period,with the increase of bulk density,the shear displacement and shear strength of the rootless soil and the root-soil complex both increase.During the growth period,the shear strength increases with an exponential function relationship with the increase of the bulk density;the shear displacement increases with a power function relationship with the increase of the bulk density.(5)The soil moisture content affects the shear resistance of the root-soil complex.Under the condition of different moisture content,the shear strength is in the dry state>wet state>alternate dry and wet state.With the increase of time,the shear strength and shear displacement of the root-soil complex in the dry state increased compared with the wet state and the alternate dry-wet state.Alfalfa and vetiver had the largest increase in shear strength and shear displacement in the fourth week of the root-soil complex,which were 21.30%and19.72;29.41%and 24.63%,respectively.It shows that the two plants have better effect on soil consolidation and slope protection in relatively dry land.(6)The shear rate will also affect the root-soil complex.The law of shear displacement and shear strength is:vetiver root-soil complex>alfalfa root-soil complex>rootless soil.Under the same growth time,with the increase of the shear rate,the shear displacement decreases in a power function relationship,and the shear strength decreases in an exponential function relationship.It shows that the roots of vetiver and alfalfa are more effective in resisting relatively slow soil shear damage.