| Earth-rock dams are the largest and most numerous dam types in China.However,due to the long history of construction and limited to the current dam construction technology,many dams have serious seepage problems.When the seepage phenomenon continues to develop and form seepage failure,the fine particles in the dam are washed into by the water flow,forming a concentrated seepage channel.When a concentrated seepage channel is formed within a dam,it will affect the safety and stability of the dam,and in serious cases,it may cause dam failure accidents.Therefore,it is very necessary to study the influence of concentrated seepage channel on the seepage flow field in dam.In this paper,the effects of concentrated seepage channel on the seepage field in dam are studied through indoor sand tank tests and numerical simulations,and the water exchange relationship between the channel and surrounding media is analyzed.A numerical model coupled with Darcy,Brinkman,and Navier-Stokes fields is established to analyze the effects of concentrated seepage channel on the flow velocity,pore water pressure,and seepage flow in dam under different operating conditions.The main research contents and results are as follows:(1)Reveal the influence of concentrated seepage channel on the seepage field of surrounding porous media.Design a sand-box model test,and analyze the influence of the existence of channel on the infiltration line,equipotential line,and permeability coefficient inside the earth-rock dam by comparing the model results with and without concentrated srrpage channel.When there is a concentrated seepage channel in an earth-rock dam,the head of the pressure measuring pipe in the channel is significantly lower than that of the surrounding porous medium,and it will cause a decrease in the head of the pressure measuring pipe in the surrounding porous medium.The larger the diameter of the channel,the more obvious this effect.Due to the effect of dominant flow in the channel,the seepage flow rate from the surrounding medium decreases.(2)Establish the water exchange relationship between the concentrated seepage channel and the surrounding porous media.By establishing a water exchange relationship between the channel and porous media through the concentration of the outlet flow rate of the leakage channel and the measured water head,the water exchange rate is directly proportional to the diameter of the leakage channel,hydraulic gradient,and permeability coefficient of the porous media.Through orthogonal experiments,it is found that the channel diameter has the greatest impact on the water exchange rate,followed by the hydraulic gradient and permeability coefficient of the porous media.The direction of water exchange is influenced by three factors:channel diameter,water head difference,and porous media.The smaller the water head difference,the smaller the channel diameter,and the lower the permeability of the porous media,making it easier for the channel to exchange water with the surrounding media.Conversely,it is easy for the surrounding media to exchange water with the channel.(3)A numerical model coupled with Darcy,Brinkman,and degenerate Brinkman equations replacing Navier Stokes was constructed.Using COMSOL Multiphysics software to establish three coupled equation models to simulate the presence of concentrated leakage channel in the sand channel.By setting the model parameters and replacing the Navier Stokes equation with the degenerate Brinkman equation,the number of equation coupling times was reduced from three to two,reducing the difficulty of solving and the amount of numerical calculation.And analyze the influence of the existence of channel on the seepage flow field inside the sand tank from the perspectives of pore water pressure,flow rate,and seepage flow rate under different working conditions.The presence of concentrated leakage channel has a smaller impact on pore water pressure.The larger the channel diameter,the smaller the flow velocity in the Darcy domain far from the channel,and the greater the flow velocity in the Brinkman domain near the channel.The biggest factor affecting the seepage flow rate is the diameter of the seepage channel,and the influence of water head difference and porous medium permeability on the seepage flow rate is equivalent.(4)A numerical model coupled with Darcy,Brinkman,and degenerate Brinkman equations is used to analyze the seepage of a dam that has experienced leakage.The maximum seepage flow rate of the dam obtained by coupling three equations is 0.839m3/s,which has a relative error of about 5%compared to the actual measured maximum seepage flow rate of 0.886m3/s.However,the traditional Darcy’s law is used to calculate the seepage flow rate of the dam body,which is 0.017m3/s,which is significantly different from the actual situation.When there is a concentrated leakage channel in an earth-rock dam,the coupling of the three equations is more accurate than traditional seepage calculation.This model is suitable for calculating the seepage field of earthrock dams with concentrated seepage channels. |
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