Research On Anti-seepage Mechanism Of Tidal Dike And Treatment Of Saline-Alkali Land Engineering In Yellow River Delta

The Yellow River Delta is an important backup base for the exploitation and utilization of soil resources in the Huang-Huai-Hai Plain.However,the soil salinization leads to the extremely low soil utilization rate in this region,which restricts the local agricultural production and economic development,and the ecological environment is also damaged due to the land salinization.This paper takes the saline-alkali soil in the Yellow River Delta as the research object,and takes the reconstruction and upgrading project of the east tidal barrier in Kenli District,Dongying City,Shandong Province as the engineering background.Through particle size distribution,X-ray diffraction,mercury intrusion analysis and other methods,quantitatively and qualitatively analyze the physicochemical properties and microscopic characteristics of the saline-alkali soil in this area and explore the types of saline-alkali soil and the reasons for the difficulty in salt drainage.At the same time,according to the characteristics of the saline-alkali soil in this area,adopt the tidal dike project to treat the coastal saline-alkali soil.In the seepage field,stress deformation field and seepage stress-deformation coupling field of Auto Bank software,study the influence of 7 kinds of dam foundation depth and 13 kinds of dam foundation width on the anti-seepage effect of the moisture-proof embankment,determine the optimal dam foundation depth and dam foundation width under the background of the project,and summarize the anti-seepage mechanism of the moisture-proof embankment.Through the laboratory simulation test,explore the salt removal effect of the tidal dike project under the working condition of concealed pipes,summarize the water and salt transport law in the soil,and discuss the on-site construction parameters of the tidal dike for saline and alkaline land treatment.The main research conclusions are as follows:（1）The saline-alkali soil in the Yellow River Delta region has a very high salt content,which is a typical coastal saline soil.The salt content of the surface soil reaches 11.39 g·kg^-1,and only a few salt-tolerant crops can grow in this soil.At the same time,the soil p H of this region is less than 8.5,which is the neutral salt soil in the coastal saline soil.The mineral composition of the soil in the extraction area contains more illite,which has strong cohesive force as a clay mineral.In addition,the surface soil in this area has small pore volume and small pore size,and the soil pores are almost always filled with the adsorbed water on the surface of soil particles,which is easy to cause the surface soil to harden,making the treatment of saline-alkali soil in the borrow area difficult.（2）The properties of saline-alkali soil in the Yellow River Delta region are related to soil depth.The salt content and ion content of the soil in the sampling area are the highest in the surface layer,and decrease with the increase of soil depth,which is consistent with the climate with high evaporation and precipitation ratio.The pore volume and pore diameter of the surface soil in the sampling area were small,and the soil pores were composed of inactive pores（pore size<2μm）and capillary pores（2μm<pore size<20μm）.With the increase of soil depth,the pore size and volume of the soil were increased.These characteristics lead to difficulties in drainage and salt drainage of saline-alkali soil in the Yellow River Delta.（3）The depth of the dam foundation has a great influence on the anti-seepage effect of the tidal dike in the treatment of the coastal saline-alkali land.When the dam foundation soil intercepts all the soil layers with high permeability coefficient,the anti-seepage effect of the moisture-proof embankment can be improved to the maximum extent,and it is not easy to make the sea water form preferential flow in the soil layers with high permeability coefficient.The width of the dam foundation has a great influence on the anti-seepage function,stability and deformation resistance of the tidal dike.With the increase of the width of the dam foundation,the anti-seepage ability of the tidal dike increases.Through the comprehensive analysis of seepage field,stress deformation field and coupled seepage-stress deformation field by Auto Bank software,it is determined that the optimal dam foundation depth is 4.7m and the optimal dam foundation width is 30m under the background of this project.（4）When seawater seeps into the tidal wall,it can prevent seawater from flowing backward on the top and seawater from seeping into the bottom.After seawater infiltration,the salt content of some saline-alkali soil behind the dam does not change significantly,indicating that the anti-seepage effect is good,laying a good foundation for the treatment of saline-alkali soil behind the dam.After several times of leaching,the maximum desalting rate of the soil under the condition of underground pipe is 82.44%,which becomes a light salinized coastal saline-alkali soil in which crops can be normally planted.The soil without hidden pipe condition has a maximum desalting rate of 64%,so it becomes the medium-salinized coastal saline-alkali soil,which will seriously affect the crop yield when planting crops.The results show that the salt removal effect can be significantly improved by burying dark pipe.（5）After repeated leaching of the soil under the embedded hidden pipe condition,the desalting rate curve presents an"inverse funnel"shape,and the desalting rate has no negative value.The soil always maintains the desalting state and the desalting effect is stable.The soil desalting rate under the condition of unburied hidden pipe is negative,the phenomenon of soil salt content rising exists in the process of leaching.The salt solution at the bottom cannot be discharged in time,and the upper soil is easy to be invaded again by the salt solution at the bottom,which is similar to the phenomenon of groundwater level rising due to precipitation in real life.In the process of site construction,the depth of the dam foundation is determined according to the distribution of soil layer,the purpose is to intercept all the soil layer with large permeability coefficient.The width of the dam foundation is the distance from the dam heel to the toe of the dam numerically.The construction parameters of the tidal dike can ensure its anti-seepage effect and stability.The horizontal spacing of the hidden pipe（bore diameter is 4mm,percentage of opening is 4%）is 0.5m.