Groundwater Level Change Caused By Land Reclamation In Yan'an And Its Prevention And Control

In recent years,large-scale Gully reclamation Projects have been carried out in the Yan'an area.In engineering practice,it has been found that cutting backfills will change the datum surface of groundwater drainage in the gully area,cause groundwater level changes in the gully area,and cause the salinization of soil and slope instability in some areas.It is of great practical significance to study the factors of water level change in the gully area and put forward prevention and control measures for the damage caused by water level changes.Taken the research area of Gully area in Gaojiahe Village of Yangjiayuanzi Town,Zichang County,Yan'an City as the research object,as well as based on hydrogeological investigation and indoor saturated penetration experiment,the paper is combined the data of hydrology and meteorology in the study area.A three-dimensional hydrogeological numerical model before and after filling the gully is established.The hazards that may be caused by the change of water level in the study area were analyzed,and the prevention and control measures to reduce the groundwater level was put forward.The main findings are as follows:(1)A hydrogeological survey was carried out in the study area.16 shallow hole water depth variations and 3 water level gauge dynamic observations indicate that the groundwater level in the study area rose by an average of 1m from July 2017 to April 2018.The salinization of soil occurs in some areas.(2)Through saturated penetration experiment with indoor variable head,the horizontal saturated permeability coefficient of the loess in the study area was concentrated in the 0.295 m/d to 0.38 m/d,and the vertical saturated permeability coefficient was concentrated in the 0.119 m/d to 0.32 m/d.Horizontal saturation permeability coefficient of hipparion red clay was concentrated in the 0.009 m/d to 0.054 m/d,and vertical saturated permeability coefficient was concentrates in the 0.01 m/d to 0.046 m/d.The saturated saturation coefficient of the horizontality of the miscellaneous fill is 0.022 m/d-0.384 m/d,and the vertical saturated permeability coefficient is 0.003 m/d-0.043 m/d.Through the well pumping test,it is calculated that the permeability coefficient of the aquifer aquifer is 0.31 m/d,and the radius of deep impact is 19.17 m.(3)By comparing the characteristics of the three-dimensional seepage field of the numerical model before and after filling the trench,the results show that the datum surface of the groundwater in the gully after filling the gully is changed,which causes the groundwater level in the gully area to rise.Through the sensitivity analysis of the hydrogeological parameters of the model after filling the trench,the results show that the recharge intensity of atmospheric precipitation in the mountainous area is positively correlated with the change of groundwater level,and is most sensitive to the change of groundwater level.(4)By analyzing the rise of groundwater level in the gully area,the pipeline precipitation measurement based on the Drain module and the precipitation measurement based on the seepage-tube-flow coupling model is designed.The results show that the influence of pipeline water flow on the pipeline's water discharge is no longer changed when the pipeline's water permeability is up to 30.The longer the pipeline,the greater the drainage of the pipeline.Based on the seepage-tube-flow coupling model,the optimal tube length is 180 m.The radiation tube with a 0.9° elevation angle can effectively reduce the groundwater level in the gully.