| 68.65%of the cultivated land in the Hetao Irrigation Area has different degrees of salinization,which seriously restricts the sustainable development of modern agriculture in the irrigation area.Reasonable construction of drainage system can effectively reduce the groundwater level and control soil salinization.In recent years,the underground pipe drainage technology has been widely used in the saline-alkali areas of our country,and the selection of the outer material is a very important link in the design and application of the underground pipe drainage project.Therefore,according to the characteristics of high soil silt content in the study area,it is of great significance for the promotion of the underground drainage project in the local area to select the outer material of the drainage hidden pipe suitable for the local soil quality.Aiming at the characteristics of more silt content and poor stability in the downstream soil of Hetao Irrigation Area,this thesis studies the filtering effect and anti-clogging performance of different outer materials through the combination of indoor infiltration simulation experiment and field plot experiment,so as to select suitable drainage dark The outsourcing materials of the pipes were explored,and the corresponding backwashing measures were explored,so as to provide theoretical and technical support for the selection of suitable outsourcing materials for the hidden drainage pipes of the Hetao Irrigation Area.The main results are as follows:(1)Using a self-made hydraulic permeameter,an indoor primary screening experiment was carried out to analyze and compare the permeability,soil retention and anti-clogging properties of 5 groups of outer geotextiles and local sand filter materials under 3 soil textures.The results show that the 68 g/m~2and 90 g/m~2geotextiles have relatively stable permeability for different soil textures.The soil loss of the six treatments was less than 1.0 g,meet the requirements of soil retention performance.The 400 g/m~2geotextile treatment had the highest amount of clogging,which was 3.6 times and 2.4times that of the 68 g/m~2and 90 g/m~2geotextile treatments,and the clogging rate was the68 g/m~2and 90 g/m~2geotextile treatments.31%and 27%.According to the three soil types in the study area,the 68 g/m~2geotextile,90 g/m~2geotextile and local sand filter material selected in this thesis can not only ensure the water permeability stability of the system,but also effectively slow down the clogging.(2)On the basis of the preliminary screening results,through the in-depth study of the new infiltration tank,it was found that the stable value of the permeability coefficient of the outer material of the 68 g/m~2,90 g/m~2and 68 g/m~2geotextiles with sand filter material is 18.8 times that of the treatment without the outer material.21.2 times and 20.6times,all of which can meet the water permeability requirements.By stopping water and draining,the permeability coefficient of the outer material of each treatment did not decrease,and all had good water permeability stability.The 90 g/m~2geotextile treatment had the least total soil loss(75.32 g),and the thicker 90 g/m~2geotextile treatment had a stronger ability to intercept soil.The 68 g/m~2geotextile with sand filter material has the lowest clogging amount(5.62 g),and the law of clogging rate is the same as the trend of clogging amount,which has a significant effect on anti-clogging.The permeability coefficients of the 68 g/m~2geotextile,90 g/m~2geotextile and the outer material of the local sand filter material selected in this thesis can all form a stable state.The best performance and anti-clogging performance.(3)Indoor mechanical and chemical fouling experiments show that 3～5 min water injection flushing under the condition of 0.4 Mpa water pressure has a significant effect on relieving the fouling of the outer material and restoring its permeability.At the same time,for ferric hydroxide colloid,citric acid and EDTA solution were added to dissolve and rinse,and it was found that the permeability coefficient change rate of citric acid solution was higher than that of EDTA dissolution by 2.46%(68 g/m~2geotextile)and4.54%(90 g/m~2geotextile)respectively,90 g/m~2geotextile treatment has a more significant effect on washing after dissolution.The geotextile after the citric acid is dissolved has a quicker permeability recovery,is relatively cheap,and has a strong ability to complex with iron ions,and the resulting complex has high acid-base stability,and can be used as a reagent for dissolving iron compounds.(4)The field adaptability test results show that the flow attenuation rate of 68 g/m~2geotextile with sand filter material is only 4.47%,and the acting water head and drainage flow are relatively stable.The particle size of the lost soil after each treatment experiment was different from the maximum particle size(166.55μm)of the silt loam before the experiment,and each treatment had the effect of intercepting soil particles.The soil loss attenuation rate of the 68 g/m~2geotextile treated with sand filter material is only 28%,and the amount of silt is only 7.0 g,which is significantly lower than other treatments.The stability effect is better.Therefore,the outer material of 68 g/m~2geotextile and sand filter material can meet the requirements of water permeability stability,soil retention and anti-clogging performance in the actual operation of the field under the silty loam soil in the study area. |
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