Characteristics Of Solute Transport And Self-potential Response Of Filling Fracture Under Different Sizes

With the continuous deepening of human activities underground,the bedrock fissure water is increasingly polluted,which has aroused widespread concern.The law of solute transport in bedrock fissures has become a hot research topic in groundwater science..Natural rock fractures are often filled with unconsolidated loose material.Based on the self-potential(SP)method in the research of groundwater circulating heat and mass transfer in terms of advantages,for filling fracture characteristics and solute transport parameters inversion problem,design processing and filling model,carry out different gap width,the different hydraulic gradient and flow direction solute transport under the condition of experiment,filling solute migration characteristics;SP change data during solute transport were monitored in real time to reveal the law of self-potential response.The dispersion D of solute transport in the filling fissure was analyzed by using the uncoupled self-potential inversion method.The main research contents and results are as follows:(1)Solute transport characteristics under different gap widths,different hydraulic gradients,and different flow directions:(1)The penetration curves of solute transport under different test conditions are similar in shape and have a normal single-peak distribution.For the same fracture width(d),the greater the hydraulic gradient(J)and the greater the flow velocity,the shorter the peak arrival time of the penetration curve.The penetration curve is wide and slow,whereas the penetration curve is narrow and steep.At the same J,the larger d,the greater the flow velocity,the shorter the peak arrival time of the penetration curve,and the wider and narrower the penetration curve.The horizontal flow direction and the vertical flow direction are basically consistent with the penetrating curve.The horizontal flow direction has a higher peak concentration and a shorter peak arrival time.(2)In the same d,the peak concentration of the penetration curve increases first and then decreases with the increase of J,and the inflection point appears at 0.25,where J is in the range of 0.05-0.25,and the peak concentration of the penetration curve shows an increasing trend,J is in the range of 0.25-0.45,The concentration of the penetration curve shows a decreasing trend;under the same J condition,as the fracture d degree increases,the time required for the peak to continue to shorten,the peak concentration of the penetration curve gradually decreases.(2)The response law of self-potential under the corresponding conditions:(1)At the same d,with the increase of J in the test range,the corresponding time of SP peak is significantly shortened,and the absolute value of SP peak shows a trend of first increase andthen decrease,where J is within 0.05 ~ 0.25,the absolute value of SP peak showed an increasing trend;within J of 0.25 ~ 0.45,the absolute value of SP peak basically showed a downward trend;under the same J condition,as d increased,the time required for the SP peak to reach Gradually shorten,the absolute value of SP peak gradually decreases.(2)Under the same conditions of d and J,as the solute transport distance increases along the direction of water flow,the absolute value of the SP peak in real-time monitoring shows a gradually decreasing trend,and the steepness of the SP peak gradually decreases,but the SP response curve drags the tail phenomenon is more and more obvious;and from the beginning of the solute injection,the peak value of SP varies logarithmically with the solute transport distance,which basically meets the equation: SP=a-bln(L+c)?(3)Parameter inversion method and results.(1)Under the condition of the same gap width,the dispersion coefficient increases with the increase of the hydraulic gradient;and under the same hydraulic gradient condition,the dispersion coefficient increases with the increase of the fracture size;the laws of the horizontal flow direction and the vertical flow direction are basically the same,but the two kinds of reaction The calculation methods all show that the dispersion coefficient is larger in the horizontal flow direction than in the vertical flow direction.(2)Use the self-potential to invert the value of the dispersion coefficient during the solute transport.Along the direction of water flow,the dispersion coefficient value fluctuates as the solute transport distance increases,but it generally decreases.And as the monitoring points gradually approached,the value of the dispersion coefficient inversion using self-potential was significantly closer to the value of the dispersion coefficient inversion of solute transport.(3)The movement of solute in the filling fracture is blocked by the filling medium.The calculation of the solute movement speed by SP and conductivity monitoring methods shows that they are less than the actual average flow velocity calculated by flow rate,and the average relative error of SP monitoring method is used smaller and more accurate monitoring.