Study On Slope Protection By Vegetation On Red Clay Area In Southern Yunnan

As highway construction keeps growing in China, the slope protecting plants technology develops accordingly. This technology is also different from engineering protection measures in that it, characterized by environment-friendliness, makes use of plant roots to strengthen side slope. By so doing, the environment is preserved while the highway construction keeps carrying on.’The stems, leaves and branches of slope-protection plantation can intercept water flow, transpirate, osmose. Those functions are called hydrological effect, through which the soil can be consolidated, surface radial flow can be controlled, slope surface scour, erosion, splash erosion can be inhibited and the pore water pressure of slope can be lowered. The roots slope protection by vegetation is featured by mechanical effects, such as cohesion, friction, reinforcement, anchoring, etc.The main research method of this research includes information research, field investigation and the summary of the geology of the study area;testing the samples taken from study area in the laboratory;obtaining the basic physical parameters of soil and analyzing the hydrological effects、transpiration drainage effect and mechanics of the slope protection by vegetation; consulting the results of previous researcher to determine the mechanical parameters of soil and slope-protection plantation; establishing simplified slope geological model;through setting up a series of working conditions in FLAC2D software Cable element, simulating different implantation length and different implantation direction of the root upon slope;computing the slope’s plastic state, stress, shear strain, displacement on the condition of vegetation upon it and without vegetation upon it;then comparing and analyzing the mechanical effect of plant roots and their contribution to slope stability on conditions of implanted single root and implanted combined root upon it.Through the numerical calculation, vegetation slope stress field redistribution exists. And the phenomenon of shear stress distribution concentration exists as well,diffusing and transferring to the bottom of slope. The maximum value of X-displacement appears near the foot of the slope. Accordingly, the shear strain rate at the maximum X-displacement is at maximum, with the lower slope being at shear yield stress and the upper being at tension yield. The most ideal implantation direction is at a55.5°acute angle with the horizontal direction, an ideal direction for slope stability. The direction of combined root implanted is at an angle of30°, overmatching an angle of18.5°; the direction of lateral root implanted is at an angle of55.5°,overmatch an angle of60°.The pattern of assemble root which is most beneficial to the slope stability is that the main root stand vertical to the slope. The direction of root implanted is at an angle of30°and55.5°. Under the influence of assemble root, X-displacement decreases, shear stress in the lateral roots implanted diffuses and transfers to bottom of slopes and the maximum shear strain rate appears near the end of the root on the upper part of slope and its range has reduced. The mechanical effect of the root is reflected in reinforcement effect of the shallow and fine roots and the anchoring role of the deep and rough root, so that the shear stress in the soil is converted into the tensile stress of the root, e the X-displacement of slope is reduced, the range of shear yield is reduced and the slope stability is strengthened.