Effect Of Root System Regulation On Plant Performance Of Slope Stability And Protection

The ability of plants to strengthen soil and protect slope is closely related to the morphology of root system.The root system of plants growing upward through the sliding surface of slope is subjected to pulling force and plays an anchoring role on the surface soil.However,the root system growing downward to the slope is under the action of pressure and can not contribute to the sliding soil.Therefore,on the basis of the existing theory,the plant root regulation technology was introduced into the study on the mechanism to improve the ability of strengthen soil of root system,aiming at regulating the growth of plant roots to the direction conducive to the reinforcement of slope soil,so as to improve the shear resistance of plant slope and broaden the application of plant slope protection technology in engineering practice.Vetiver grass,a "deep exploration" slope protection plant with developed root system,is taken as the research object in this paper.Supported by the National Natural Science Foundation of China(NSF)Project "Research on Soil Fixation Mechanism of Plant Slope Based on Directional Regulation of Root Configuration"(No.51608545)and "Application of Ecological Slope Technology in the East Ring Project of Chongqing Railway Hub"(YF1900SD07B).The responses of vetiver root growth to spatial heterogeneity,such as water and nutrients,were studied through soil water infiltration characteristics test and different water and fertilizer combination regulation test.Secondly,based on the above response relationships,shear tests and numerical simulation analysis of unmodified soil were carried out to find out the influence law of root configuration regulation on the strength and stability of slope soil,and a root configuration regulation method was proposed to improve the stability of slope.The main research contents and innovative conclusions are as follows:(1)Under indirect subsurface drip irrigation,with the increase of initial soil moisture content,water tends to migrate vertically downward and the horizontal axis of symmetry of wet body keeps moving downward,which can be described as a logarithmic function.When the emitter flow is large,the trend of water migration to the horizontal direction is obvious.When the emitter flow rate is small,the water tends to move at vertical direction.When the root architecture of vetiver was controlled by indirect subsurface drip irrigation,the characteristic parameters of soil moisture could be controlled by adjusting the emitter flow and the initial soil moisture content,and the root architecture of vetiver could be regulated directionally.(2)Under the natural growth condition,about 65%of vetiver root tended to grow downslope.The roots growing in the downslope direction were thick,long and dense,while the roots growing in the upslope direction were thin,short and sparse.With the controlled by the combination of water and fertilizer,vetiver proliferated a large number of Grade 2 and Grade 3 roots in the uphill direction,and the proportion of root system was about 60%?66%.The results showed that the effect of water on the root growth of vetiver grass was much weaker than that of nutrient.Compared with nitrogen fertilizer,vetiver roots preferred phosphorus fertilizer,and the root in the upslope direction accounted for the largest proportion due to using the appropriate combination of water and fertilizer.(3)Through the undisturbed soil shear test,it is found that the more the number of roots in the slope soil,the smaller the root diameter,the larger the root surface area,and the greater the shear strength.When the sample is subjected to shear,the root and soil slide relative to each other,the friction force and adhesive force between the root and soil are converted into shear resistance to prevent the soil sliding.The regression analysis shows that the cohesive force of soil increases linearly with the root surface area density.The larger the number of roots,the smaller the diameter of roots,the greater the tensile strength and the stronger the cohesion ability in soil.The wider the root surface area,the greater the friction with the soil,the more resistant to shear force.(4)Based on Wu's model,the expression of the relationship between the slope root distribution angle and the slope soil strength was deduced.The increment of the soil shear strength caused by the root system of a single vetiver slope was calculated.According to this conclusion,vetiver root system growing in slope soil was regulated.The results show that there are a lot of roots of level 2 and level 3 hyperplasia in uphill after vetiver root system have been regulated.Most of the angles of growing direction of these roots with vertical direction are greater than the slope angle,which makes the shear strength of vegetated slope soil increased 17.59 kPa?33.97 kPa.(5)Through numerical simulation analysis,it is found that after regulation with the combination of water and fertilizer,the ability of root in reinforcement soil and slope protection is improved.Compared with the root system of vetiver under natural growth condition,the root system of vetiver growing uphill after regulation greatly improved the ability of the toe to withstand horizontal stress,and better constrained the slope displacement.The toe can withstand horizontal stress increased by 14.21%,and the top horizontal displacement decreased by 57.14%.Compared with the slope of vetiver plant under natural growtth condition,the safety factor of vetiver plant slope under regulation condition was increased by 7.20%.