Study On Friction Characteristics Between Roots Of Pinus Tabuliformis And Soil Of The Loess Plateau Of Western Shanxi Province

Pinus tabulaeformis,as the main afforestation species in the Loess Plateau,plays an active role in the prevention of water loss and soil erosion.While root system,as the nutrient and supporting organ of P.tabulaeformis,plays an important role in the process of soil fixation.In this study,single root and multi-bifurcated root of P.tabulaeformis in the Loess Plateau of western Shanxi province were pulled out by a root pulling machine which was independently developed.Root sampling time is in July 2018.The failure modes and mechanisms of single root and multi-bifurcated root during the pulling process were explored,and the factors affecting the friction characteristics of single root were also studied.Based on the single root friction estimation formula:F=0.5pd(1+?)gL2,the influence factors of friction coefficient of the interface between root and soil were deduced and analyzed quantificationally.Based on the comparison of the results of two repeated pulling-out tests of single root,the influence factors of soil fixation ability of branch in multi-bifurcated root are studied.The results show that:(1)There are three failure modes of single root:pullout failure mode,breakage failure mode and slippage failure mode.There are four failure modes of multi-bifurcated root:pullout failure mode,breakage failure mode of branch,slippage failure mode of branch and splitting failure mode of branch(2)The maximum friction is positively correlated with the diameter of single root,the buried depth,the loading rate and the dry density of soil.With the increase of soil moisture content,the maximum friction and the initial friction increase first and then decrease;the diameter of single root,the loading rate,the soil moisture content and the dry density of soil have no effect on the displacement of main peak value,but the buried depth is positively correlated with the displacement of main peak value.the loading rate and the dry density of soil have no effect on the initial friction,and the diameter and the buried depth of single root are positively correlated with the initial friction.(3)The dry density of soil is positively correlated with the friction coefficient of the interface between root and soil which increased from 1.59g/cm3 to 1.68g/cm3,with the dry density of soil increased by 42.55%and increased by 33.74%from 1.68g/cm3 to 1.78g/cm3.With the increase of single root diameter,the friction coefficient of root soil interface decreases by 24.92%and 10.62%.With the increase of embedding depth from 50mm to 100mm and from 50mm to 100mm,the friction coefficient of root soil interface decreases by 49.72%and 33.16%.With the soil moisture content increase from 13.18%to 15.1 8%and 17.18%,the friction coefficient of the interface between root and soil first increases and then decreases.And The rate of increase and decrease was+34.57%and-34.50%.With the increase of loading rate,the friction coefficient of the interface between root and soil first increases,then remains unchanged or slightly decreases(4)The maximum friction and the displacement of main peak value which is from the results of two repeated pulling-out tests of single root are approximately unchanged,and the initial friction which is from the results of two repeated pulling-out tests of single root has greater and greater change with the increase of the diameter.The sum of diameter and angle of branch have great influence on the difference of maximum friction force,meanwhile the sum of diameter and angle of branch is positively correlated with the maximum friction which acts on the branch.The sum of diameter and angle of branch have little influence on the difference value of the displacement of main peak value,and there is no obvious regularity.For the single root with one branch and two branch,the influence of the sum of angle of branch on the difference of the maximum friction was greater than that of the sum of diameter,but for the single root with there branch,the sum of angle of branch has greater influence on the difference of the maximum friction than that of the sum of diameter.The failure modes of single root and multi-bifurcated root were obtained,and the factors affecting the friction properties of root system were analyzed,which further deepened the understanding of the mechanism of soil fixation of P.tabulaeformis root system in the Loess Plateau.All those provided theoretical basis for the construction of P.tabulaeformis vegetation restoration.