Study On Sand Tank Physical Simulation Of Water Exchange Between The Well-pipe And The Aquifer

China is a country with severe drought and water shortage.The lack of water resources has become an important factor restricting the development of regional economy.Therefore,the rational exploitation and utilization of water resources are very important for ensuring residents’life and promoting economic development.In recent years,non-casting-well groundwater-collecting structures,such as seepage wells and radiation wells,have been widely used in arid and semi-arid areas such as Northern Shaanxi because of large water yield,little affected by season,convenient management and relatively low cost,and there have been no lack of successful examples.The water intake projects such as seepage wells and radiation wells provided a guarantee for residential water,urban water and agricultural water,which can alleviate the problem of water shortage in some arid areas and create good economic benefits for the local area.Although there have been many successful examples in the non-casting-well groundwater-collecting engineering,because of its complex structure and lack of experimental research on the exchange yield between the non-casting-well structures and the aquifers,which leads to lacking the reasonable theoretical guide in the early design and later construction,some water intake projects cannot reach the design requirements.Therefore,in this study,the well-pipe（which is composed of a vertical shaft,drift and radiant tube）water intake is simulated through the sand tank physical simulation test.The influencing factors of water yield are summarized and the calculation formula of the well-pipe permeability performance C₁（the exchange yield between the well-pipe and the aquifers under the unit head difference）is derived,and the calculation formula’s correctness is verified.In this study,111 kinds of sand tank test plans were designed to analyze the influence by the different elevation angles of radiant tube,the different lengths of radiant tube,different river leakage capacity,the different drawdown of vertical well and turbid river（The simulation of aquifer siltation）on the water yield of the well-pipe.The main conclusions are as follows:the water yield of the well-pipe increase with increase of the drawdown in vertical well,the elevation angle of the radiant tube,the leakage capacity of the river and the length of the radiant tube.With the time of turbid river test continues,the water yield of the well-pipe decreases.With making a reasonable generalization of the boundary conditions,the whole seepage sand tank is taken as the research area.Using the exchange flow between the aquifer and the well-pipe as the couple key,the coupled seepage-pipe flow model is set up.The calculation formula of the well-pipe permeability performance is applied to the model and the experimental data are fitted with the results of the model calculation.The simulation results show that the steady flow and transient flow are well fitted,which illustrates that the model is reasonable and reliable.The results also show that the calculation formula of the well-pipe permeability performance（C₁）is correct.On the basis of the reliable model,the other influencing factors of water intake in the well-pipe are further analyzed.The main conclusions are as follows:（1）the influence of model parameters on the water intake of the well-pipe from large to small are K_z,K_y,permeability performance of the well-pipe（C₁）,the river’s leakage capacity（C₂ which is the yield of river leakage under the unit head difference）,K_x,so the well-pipe should be set in a position with greater conductivity of the aquifer and stronger leakage capacity of the river.（2）Adding reasonable filtering measures outside the radiant tube can guarantee the water intake efficiency and service life of the well-pipe.（3）The elevation angle of the radiant tube should not be too large,it is suggested that the elevation angle of the radiant tube is less than 30 degrees.（4）The aquitard has a great influence on the water yield of the well-pipe,so it should be avoided or far away from the aquitard when the well-pipe is set up.The water flowing channels can be constructed artificially to increase the water yield of the well-pipe when the aquitard cannot be avoided.（5）The reasonable position of drift can increase the water yield of the well-pipe.In this simulation research,the drift from the bottom of the seepage sand tank is 60cm,the water yield of the well-pipe is the largest and the water intake efficiency is the highest.