Study On Water-salt Transport Law And Engineering Salt Drainage Technology Of Regional Saline-alkali Soil In The Yellow River Delta

The heavy salinization and secondary salinization of land,as a worldwide problem,have severely restricted the productivity of cultivated land and affected the sustainable development of agriculture and economy in China.Taking the regional saline-alkali soil in the Yellow River Delta as the research object,the aim of this paper is to study the characteristics of the microstructure and the law of water-salt transport of the regional saline-alkali soil in the Yellow River Delta,and to discuss the influence of engineering salt discharge on the desalination effect of the regional saline-alkali soil.It provides scientific theory and technical support for the control of the regional saline-alkali soil in the Yellow River Delta.The main results are as follows:(1)The mineral composition of the regional saline-alkali soil was mainly composed of primary minerals,accounting for about 95%,in which quartz and albite were the highest and ferro-manganese-albite was the lowest.Primary minerals were the primary source of all kinds of chemical elements in soil.Albite was characterized by low water absorption,and the content of clay minerals was relatively low,accounting for about 5%.Most of them were from illite,and the clay minerals had very fine grains.It generally presented as a small scale less than 10?m.The content of quartz and albite with low water absorption was the highest,but the content of clay mineral with better water absorption was lower,so mineral composition was not the reason for low permeability of the regional saline-alkali soil.(2)The pore size distribution of the regional saline-alkali soil in the Yellow River Delta was in the range of 0.008~400 ?m,and it was absolutely dominant in the range of 0.1~10 ?m.The area of super-micro-pore and micro-pore in the regional saline-alkali soil was mostly,and the pore area of small pores,medium pores and large pores was very small.The salt in the regional saline-alkali soil was mainly adsorbed on the surface of soil pore.The regional salinealkali soil was compact in structure,and the diameter of soil particle was mostly between 20~30?m.There were many independent units in the soil,which were plate-shaped and multi-edgeangle-shaped.There was also a small amount of sub-spherical structures distributed in soil particles.The arrangement of the skeleton particles was mainly mosaic arrangement,and the smaller subspherical particles were embedded among the larger soil particles,which reduced the pore volume and the permeability of the soil,it slowed down the rate of water and salt migration in the regional saline-alkali soil.(3)In laboratory soil column experiments with one-dimensional constant water-head vertical infiltration,the wetting front depth increased gradually.At the early stage of infiltration,the wetting front moved fast,and with the extension of time,the infiltration rate gradually slowed down.With the progress of infiltration,the soil water content increased.From the initial infiltration time to the wetting front to the bottom of the soil column,it lasted for 170 min.The process of wetting front depth changing with time was fitted,and the relationship was power function.The cumulative infiltration increased with time,and showed a trend of fast and then slow.The initial infiltration rate was larger,which became gradually stable in the later stage.At the 170 th min,the wetting front moved to the bottom of the soil column,and the cumulative infiltration was 12.57 cm.This indicated that the infiltration capacity of the regional salinealkali soil was poor and the water-salt transport capacity was limited.(4)The laying of concealed pipes can significantly improve the drainage efficiency of the regional saline-alkali soil,and the closer the horizontal distance was to the concealed pipe,the better the drainage effect was.The influence of different concealed pipe on the open porosity and diameter was obviously different.The higher open porosity of the concealed pipe was,the higher the desalination efficiency was.In this test,the desalination rate was the highest overall when the open porosity of the concealed pipe was 9%.The desalination efficiency was positively correlated with the diameter of the concealed pipe.The larger the diameter of the concealed pipe was,the higher the desalination efficiency was.In this test,the desalination rate was the highest overall when the diameter of the concealed pipe was 90 mm.In general,when the open porosity of the concealed pipe was 9% and the diameter of the concealed pipe was 90 mm,the regional saline-alkali soil had the best drainage effect,and the maximum desalination rate was 35.1%.(5)Open ditch excavation can reduce the salt content of the regional saline-alkali soil,and it had an obvious effect on the desalination of upper soil.When near the end of the open ditch,compared with the initial result,the salt content at the depth of 10 cm decreased by 58.8%,and that at the depth of 20 cm decreased by 43.2%.When it was the closest to the open ditch,the desalination efficiency of the soil was the highest.After 8 hours of leaching,the salt content of soil at 15 cm distance from open ditch was 0.13% lower than that at 55 cm.(6)The salt content of the regional saline-alkali soil can be reduced obviously by the shaft.In this experiment,the closer the distance to the shaft,the higher the desalination efficiency.At the depth of 10 cm and the distance of 5 cm from the shaft,the salt content decreased from 0.37%to 0.21%.(7)The desalination effect of the engineering measured determines the on-site layout spacing.Respectively,the maximum on-site layout spacing of the concealed pipe,open ditch and shaft salt drainage projects was 480 cm,288 cm and 218 cm.