Optimization Of Porous Materials And Application Of Salt Drainage Engineering For Regional Saline Land Treatment In Yellow River Delta

Soil salination severely restricts plant growth in the Yellow River delta,reducing food production and posing a huge impact on regional agricultural and economic development.Besides,it threatens the ecological environment in this area.Therefore,the cultivation and reasonable utilization of local saline resources are particularly important.In this paper,a typical saline soil in the Yellow River Delta is taken as the research object;the effects of highly porous materials with six diameters(1-2mm,2-4.75mm,4.75-9.5mm,9.5-13.2mm,13.2-19mm,19-26.5mm)and four thickness(0,5cm,10cm,15cm)on the desalination efficiency of upper saline soils are investigated through indoor soil column simulation tests.Besides,the effects of silt trap with six thicknesses(0,1cm,2cm,4cm,7cm,10cm)on the salt content of the upper soil under evaporation conditions are analysed.With these analyses,the optimal embedment diameter and thickness of the highly porous material as well as the embedment thickness of the silt layer are selected.The optimized highly porous materials are buried in the soil trough for artificial simulated rainfall tests to obtain the changes in water content and salt content of saline soils under different rainfall intensities and slopes.Following this,the application of optimized indicators of porous materials for salt drainage engineering is explored.The main findings are as follows:(1)The highly porous materials buried in saline soils significantly improves the desalination effect of the soil.The embedment diameter has a significant impact on the desalination effect.When the diameter was 4.75-9.5mm,the desalination effects 24h after irrigation and 168h after irrigation were higher than other test groups,and the desalination rates were greater than 80%.By observing the junction between the upper saline soil and the highly porous material,it was found that the leakage of the soil was greater when the embedment diameter was greater than 9.5mm.Therefore,the preferred embedment diameter for the burial of highly porous material is 4.75-9.5mm.(2)The embedment thickness of the highly porous material also had an effect on the desalination effect of the soil.After 24h of irrigation,the average desalination rate of the upper layer of soil was the highest when the thickness was 5cm,with a value of 80.42%.Furthermore,after 168h of irrigation,the desalination effect was more significant when the highly porous material has a thickness of 5cm.Therefore,5cm was chosen as the optimum burial thickness of highly porous material.(3)The embedment of silt in saline soils can impede the rise of salt,and the embedment thickness has different effects on the salt content of the upper saline layer.For the two groups with 7cm and 10cm embedment thickness,no significant difference between the results was observed;while the rising rate of the wetting front and the increase in the salt content of the surface saline soil for these two groups were significantly slower than groups with other embedment thickness.The average salt content of the 0-20cm layer was measured to be the lowest after 30d of evaporation.Taking site construction,cost and other factors into consideration,the best-buried thickness of silt was determined to be 7cm.(4)Rainfall intensity has an effect on the desalination effect of saline soils.As the rainfall intensity increased,the rate of transport of soil wetting fronts and the rate of increase in soil water content increased significantly;the rate of decrease in soil salinity accelerated.When the rainfall intensity increased to 50-100mm·h-1,the effect of rainfall intensity on the wetting front,water content,and salinity decreased.(5)The slope has a significant influence on the desalination effect of saline soils.When the rainfall intensity is 50 mm·h-1 and the further away from the top of the slope,the rates for the transport of wetting fronts,the increase of water content and the decrease of salt content all became faster.The greater the slope,the more unfavourable it is for salt drainage.0-5° is the most suitable slope range for salt drainage.(6)For the engineering treatment of saline soils with a relatively deep water table in the Yellow River Delta,highly porous materials with a diameter of 4.75-9.5mm and a thickness of 5cm can be embedded in the lower layer of saline soils,which is conducive to the smooth discharge of water and salt;for saline soils with a shallow water table,a silt water barrier layer with a thickness of 7cm can be added below the layer of highly porous materials,which can effectively prevent the accumulation of salt on the soil surface and reduce the impact of the rising water table on the upper layer of saline soils.It also reduces the impact of the rising water table on the upper saline layer.At the same time,the application of the pore material optimisation index for engineering salt drainage is more suitable for saline soils with a slope of 0-50 and is more efficient in restoration.