Research On The Mechanisms Of Soil Stabilization And Slope Ecological Restoration During The Succession Process From Modified Organic Stabilizer To Plant Root

China's desertification area accounts for more than 27% of the country's land area,it is one of the most serious desertification countries in the world.The desertification disasters have seriously threatened the safety of human settlements,protection of regional water conservation areas,and national ecological civilization construction.Promoting desertification governance,strengthening ecological protection and restoration,and building a beautiful China have become the country's clear political deployment.Soil stabilization is the fundamental way of desertification control.However,the existing mechanical soil stabilization method cannot achieve greening;the inorganic chemical soil stabilization method destroys the soil ecology;the plant root soil stabilization method relies heavily on artificial water replenishment;the comprehensive soil stabilization method is expensive;the most important is that these methods are extremely difficult to achieve the process of succession from manual intervention to natural restoration.Based on the national requirement of "maximize the use of near-natural methods and ecological restoration techniques",environmentally friendly sustainable soil fixing methods are urgently needed to be studied.In this paper,the most widely distributed types of desertification slope is taken as the research object,and the modified organic material independently developed by the research team is used as the soil stabilizer.Three types of typical desertification slopes were selected: excavated slopes in arid and moderate desert areas in Xinjiang,aeolian desertification slopes in semi-arid and severe desert areas in the middle reaches of the Yarlung Zangbo River in Tibet,grassland desertification slopes in ruoergai alpine humid light-medium-severe desert area in upper reaches of the Yellow River.Based on series of sample block tests,potted plants tests,large-scale field site tests and physical simulation tests,the research of the mechanisms of soil stabilization and slope ecological restoration during the succession process from modified organic stabilizer to plant root is carrying out,and obtained the following results:(1)Based on the performance deterioration characteristics of the stabilized soil related to the aging of the modified stabilizer and the enhanced performance of the root soil performance with the growth of the plant root system,the basic properties of the modified stabilizer fixed soil,natural plant root soil and modified stabilizer-root fixed soil were obtained:(i)Modified stabilizers and root systems can significantly improve soil agglomeration,mechanical strength,and reduce permeability;(ii)Modified stabilizer-root fixed soil has better soil stabilization properties than simple stabilizer fixed soil or simple root fixed soil;(iii)The effect of modified stabilizer-root soil fixation is affected by root shape,soil density,and organic matter,that is,fibrous root reinforcement effect is better than straight root,low density soil root development density is better than high density soil,organic matter promotes root development.(2)Through testing the aggregation,mechanical strength and permeability of stabilizer treated soil after dry and wet cycles,freeze-thaw cycles and ultraviolet irradiation,the characteristics of the stabilizer fixed soil performance continued to deteriorate with the aging of the modified stabilizer;A quantitative mathematical description of the time-dependent deterioration of the performance index of the stabilizer fixed soil is introduced;Based on the strengthening characteristics of the stabilizer-root soil chemical-physical properties with the continuous growth of the root system,a quantitative mathematical description of the time-dependent strengthening of the performance index of the modified material root soil is given.Therefore,for the first time,a succession method from modified organic stabilizer fixed soil to plant root fixed soil was proposed,and a large-scale field test has been carried out for 3 years so far based on this method.Comprehensively obtained the field data of the multi-disciplinary(physical,chemical,mechanical,hydraulic,biological,ecological)index of the modified stabilizer-plant succession fixed soil,which revealed the dynamic time-varying characteristics of the modified stabilizer-root fixed soil index.The succession process of modified stabilizer-plant root stabilization soil function is divided to modified material initial soil fixation,material-root succession combined soil fixing,plant root stable soil fixation.Furthermore,with the solidification degree of the reinforced soil(S)as an index,the factors of material aging degree(AI)and root strengthening degree(F)were introduced to establish a quantitative evaluation system during succession process from modified stabilizer to plant root fixed soil.(3)Based on the environmental background of the selected typical desertification area,considering the dynamic effects of wind erosion,rain erosion,freezing-thawing main erosion forces within one hydrological time span,six large-scale physical model tests including a control group were designed.To simulate the erosion performance of modified stabilizer – root slope on the "development-growth-dormancy" stage corresponding to the annual process of the plant “spring sprouting – summer growth – winter wilt”.The law of erosion control of slopes mainly stabilized by modified materials,the law of erosion control of slopes mainly stabilized by modified stabilizer-roots combination during root growth maturation and during root dormancy was revealed.(4)The mechanism of modified stabilizer-plant root fixed soil and slope ecological restoration was revealed from multiple levels.(i)The mechanism of "physical reunification" and "chemical bonding" of the modified material solid soil is revealed from the microstructure level,and the matrix suction strengthening mechanism of the stabilizer fixed soil depending on the small pore capillary effect is revealed from the microstructure level.(ii)The mechanical “reinforcement” mechanism of plant roots fixing soil and matrix suction enhancement mechanism related to root physiological water absorption is revealed from macro-meso and mechanics level.(iii)On this basis,the slope erosion control mechanism of the modified material-plant root solidification is systematically revealed from the micro-fine-macro level.(iv)The soil maturation mechanism of modified stabilizer-plant root stabilized slope were clarified and demonstrated from the physical-chemical-biological level.The mechanism of ecological restoration of slopes during the long-term succession process from modified stabilizer to plant root is discussed.For the three typical desertification slopes in the selected study area,practical applications according to local conditions were carried out.The results of years of monitoring showed that the slope ecological restoration achieved good results.It was verified that the modified organic material-plant root succession soil fixing method in this paper was effectiveness and feasibility on ecological restoration of slope.