Study On Biomechanical Characteristic Of Five Plant Roots In Two Growth Periods

This paper aims at two natural conditions of spring soil drought and after summer rainstorm,using the soil mechanics and material mechanics principles and research methods,the test of axial tensile test,root-soil complex vertical drawing test,root-soil complex direct shear test and root-soil interface friction characteristic test were carried out.Tap root of five plants of four years old artificial plants: Medicago sativa?Astragalus adsurgens?Hedysarum mongdicum?Hippophae rhamnoides and Caragana microphylla researched object in the Heidaigou Open Pit Mine.Analyze the mechanical properties of soil reinforcement by roots difference between preliminary period and blooming period.principal component analysis was carried out on eight indexes that affect the root fixed soil of five plants,to explore the dominant mechanical factors affecting root soil consolidation.The results show that:(1)When the root diameter of five plants is within 0-6 mm,the single ultimate tensile resistance increases with the increase of the diameter in the preliminary period and blooming period,the single ultimate tensile strength decreases with the increase of diameter in the preliminary period and blooming period.The single ultimate tensile resistance and tensile strength values of Medicago sativa ? Astragalus adsurgens ?Hippophae rhamnoides and Caragana microphylla are all of preliminary period value greater than that of blooming period value.The average ultimate tensile resistance was the largest of the Hippophae rhamnoides representative root in the preliminary period(62.97±1.19 N)and blooming period(35.37±1.11 N).(2)When the root diameter of five plants is within 1-1.5mm,the stress-strain curves of the five plants representative root showed a single peak curve.The ultimate elongation values of Caragana microphylla were the highest in two growth periods and within diameter-scale ranges1-1.5mm.compared with the other three plants,the Caragana microphylla and Hedysarum mongdicum roots have better tensile deformation resistance.(3)Shear relations are subject to the Moore-coulomb theory of roots-soil complexes shear strength and residual shear strength and pure soil.Under 12.5 KPa and 25 KPa loads,both the shear strength and the residual shear strength of the five plant roots-soil complexes in the two growth periods were greater than the value of the pure soil.The value of shear strength and residual shear strength of the root-soil complex were preliminary period higher than blooming period.The shear characteristics and residual shear characteristics of the Astragalus adsurgens were stronger than the other four plants.The shear characteristics and residual shear characteristics of five plants under different loads and different growth periods were analyzed comprehensively,the existence of root system has no obvious influence on the change of internal friction Angle of soil,but the increase of cohesive force plays an important role in the improvement of shear strength of the root-soil complex.(4)Under 12.5 KPa and 25 KPa loads,both the growth rate of shear strength and the growth rate of cohesive force of the root-soil interface were higher than that of soil-soil interface.preliminary period and blooming period of between roots-soil interface shear strength growth rate and the cohesive force growth rate of growth value order size consistent is Caragana microphylla> Hippophae rhamnoides > Hedysarum mongdicum > Astragalus adsurgens > Medicago sativa.The plant root system can play a better role in soil consolidation under the loading condition of 12.5 KPa(0.8m soil layer).The angle of internal friction and friction coefficient of the root-soil interface was the largest in two growth periods of the five plants,the blooming period value(38.31°±1.63,0.79±0.14)> preliminary period value(38.04°±1.19,0.78±0.15).(5)In the spring soil drought,the main component scores were: root-soil interface friction characteristics > root-soil complex shear characteristics > root tensile resistance characteristics;After the summer rainstorm,the main component scores were: root tensile resistance characteristics > root-soil interface friction characteristics > root-soil complex shear characteristics.