| China is one of the countries most seriously affected by desertification in the world.China needs to implement feasible and effective sand-fixing technologies to stop the desertification process.This is of great significance for the protection of ecological environment and economic development.Based on the climatic characteristics of the high-altitude areas in Qinghai-Tibet lateau and the environmental characteristics of the sandy land around the Brahmaputra,this thesis proposes a new blown sand hazards prevention and management concept of organic fixing-bio-barrier for wind-sandified slopes.This new concept uses the organic materials to fix the original sandy soil,and at the same time adopts shrub and grass planting techniques to make a transition of sandification management from the initial fixing supported by organic materials to the fixing enabled by ecological plants,so as to achieve long-term effective sand hazards control.The creation and application of the new concept and new technology has laid a sound foundation for the sand hazards control in the sandy areas in Qinghai-Tibet Plateau.Afterthe specific mix proportion of organic materials was selected out indoors(the admixture amount of organic materials was 1.745%),theconstruction optimization study was carried out on the admixture amount(17.5%,19%,20.5%,19%,all of which werethe mass ratio with dry soil)and sand-fixation density(1.55g/cm~3,1.60g/cm~3,1.65g/cm~3)of organic materials provided with this specific mix proportion in this paper,so as to provide the indoor theoretical parameters and basis for the field application of organic materials;then the mechanism of this new sand-fixation concept was probed into and revealed by virtue of micro means(XRD and SEM).The durability(anti-ultraviolet performance,anti-freezing and thawing performance)test was conducted upon the organic materials,and the sensitivity of materials to the environment was also analyzed,which was of practical significance to the practical application of organic materials.Then,the effects of field application of organic sand-fixation materials were analyzed by field experiment,and the germination and growth situation of sand-fixing plants was observed,so as to provide a basis for the further screening of sand-fixing plants.In the end,a comparisonwas made between organic materials and natural sand bed(sand dune vegetation)as well as other sand-fixation technology(engineering sand-fixation,soil-spraying)to analyzethe applicability and cost performance of organic materials-biological barrier,a new sand-fixation technology.For the aeolian sand,after the four kinds of non-toxic and harmless sand were selected as the sand-fixation raw materials,the indoor preparation experiment was conducted based on the effect of the four kinds of materials on the sand-fixation slurry performance,and the anti-disintegration test and elymusdahuricus mixed planting compatibility test were carried out upon the screened sand-fixation slurry,so as to finally determine the optimal mix proportion of each kind of material.The test results showed:when the admixture amount of organic materials was 1.745%(including A:0.015%,B:0.07%,C:1.5%,D:0.16%,all of which were the mass ratio with dry soil),the sandy soil fixed by organic materialswas provided with good structural stability,and good biocompatibility.On the basis of that the organic materials with specific mix proportion were selected,it was found in the experiment that,within a certain range,the increase in admixture amount of organic materialscould effectively improve the mechanical properties of fixed sand sample,but when it wasbeyond a certain range,the mechanical properties of fixed sand sample would decreasealong with the increase inadmixture amount.When the admixture amount of organic materials was 20.5%,the fixation effect was most significant;meanwhile,in order to ensure that the fixation layer was provided with water permeability and shear strength,the fixation density of sandy soil should be 1.6g/cm~3,which was the optimal combination constructionapplication mode.The physical and chemical sand-binding mechanism between organic materials and sand particles was probed into based on the inspection results of XRD(X-Ray Diffraction)and SEM(Scanning Electron Microscope).The test results showed that the organic sand-fixation materialswould hardly react chemically with the sand mineral composition to produce other new substance,but make the mutuallyindependent particles link together through molecular chains by virtue of the three-dimensional mesh cementation between soil particles,so as to make the loose sandy soilbecome an integral whole,and greatly improve the water-physical properties and mechanical parameters of sandy soil after fixation.Meanwhile,this unique network structure could also significantlydecrease the rate of water evaporation,keep sand moisture,control the internal temperature of sand bed through oxygen,so as to nourish the growth of psammophyte,and provide a favorable environment for plants.Therefore,organic materials also have good plant compatibility,and the organic materials and plants could be jointlyused to control the sand damage.The quality and shear strength of organicallyfixed sand sample gradually decreased underthe continuous irradiation of UV,but the color and appearance of sand sample showed no change basically after continuous radiation for 1080h,the mass retention rate was still 98.98%,and the cohesion retention rate was 68.6%,so the sand could still be fixed.Meanwhile,the organic materials showed a strong ability to resist cold temperature when the freezing-thawing moisture content was lower than12%.The specific performance was that:after 11 freezing-thawing cycles,the mass loss rate was less than 1%,and the volume change was not obvious;at the end of the cycle,there was no fracture in the sand sample,the overall structure of fixed sand sample was stable,and the cohesion loss rate was less than 26%.In addition,organic materials also strengthened the water-holding capacity of sandy soil;in the process of freezing-thawing cycle,the moisture content of sandy soil would continue to increase as the cycling times increased.After the windy-sandyside slope is reinforced by organic materials,the using effect is obvious,so it proves that it is a newtechnology that can be popularized and utilized in frigid and arid regions.Compared withsimple plant sand-fixation,organic materials can effectively improve the original"microenvironment",effectively promote the growth of plant,and guarantee the plant survival rate,so as to make the plant germination rate and later cover degree significantly higher than sand-fixation plants;in addition,compared with engineering sand-fixation technology and sand spraying technology,organicsand-fixation technology can provide the plantswith better growth situation in later stage,and stronger erosion resistibility.Moreover,organic materials also have many advantages,such as better eco-friendliness to native plant,as well as lower cost,higher cost performance and etc.The early effective results obtained from the organic sand-fixation test in high-altitude areaslay a substantial foundation for the wind-sand control projects in the surroundingdesertification areasof Yarlung Zangbo River,Qinghai-tibet Plateau. |
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