Experiment Study On Hydrological Effect Of Vegetation Slope Protection

The effect of vegetation slope protection is mainly manifested in two aspects:hydrological effect and mechanical effect.The mechanical effects mainly include the reinforcement of the whisker root system and the anchoring of the main straight root system.Most of the previous researches and engineering practices only consider the mechanical effects of vegetation roots and ignore the more important hydrological effects of vegetation.Vegetation hydrological effects not only include rainfall interception of plant stems,branches and leaves and impaction of raindrop splashing erosion,but also vegetation roots occupy soil pores,reduce soil permeability coefficient,and then affect soil matrix suction maintenance ability and water holding capacity curve(soil-water characteristic curve).The influence of vegetation on the stability of shallow slope and soil erosion resistance can be scientifically and reasonably analyzed by studying the change of matric suction in vegetation soil and considering the curve parameters of soil water holding capacity under the action of vegetation roots.This paper takes the ecological slope geology of a highway in Zhangjiakou as the research object.The influence of soil compaction degree and vegetation roots on the characteristics of unsaturated soil was discussed.On the one hand,the indoor simulated rainfall infiltration test was carried out for vegetation soils with different compactness covered by tall fescue.Data such as rainwater infiltration rate,matric suction and volatile water content were processed to study the variation rules of matric suction maintenance and water holding capacity of vegetation soil under different compaction degrees.Then a compactness is found which can satisfy vegetation growth and meet engineering needs;On the other hand,boxwood with well-developed roots was selected as the research object.By means of laboratory model test,the vegetation soil covered by boxwood was compared with the bare soil.The difference of soil water characteristic curve and related parameters between vegetation soil and bare soil under humidification and dehumidification was analyzed.The influence of vegetation roots on soil-water characteristic curve was further studied.Based on the experimental data,the following conclusions are drawn:The fescue can still grow normally in the soil with higher compactness.When soil compaction is high,the presence of grass roots occupies the pore volume of soil,reduces the infiltration rate of rainwater,and enhances the water-holding capacity of soil.Under a given matric suction condition,the moisture content of vegetation soil is higher than that of exposed soil,and the infiltration rate of rainwater is lower than that of exposed soil.With the increase of compactness,the influence of tall fescue on matric suction becomes more and more obvious.There was no vicious competition between plants in the plants planted with spaced 50 mm apart at the maximum extension diameter of the root system.Meanwhile,root action significantly reduced the internal pore ratio of soil.Gardner's empirical model in 1958 was able to fit well the test points of vegetation soil covered by poplar,and root action and soil state had significant influences on soil water characteristic curve and relevant parameters.