Study On Hydrodynamic Model Of Response Of Shallow Unconsolidated Aquifer To Harmonic Vibration

In order to understand the mechanism of water level coseismic response and quantitatively describe the hydrodynamic process of well water level response,the experiment of well water level coseismic response of unconsolidated aquifer under sine wave input with different frequencies and amplitudes is carried out based on seismic simulation shaking table.The physical model of shaking table with medium and fine quartz sand as water bearing medium was designed.Two kinds of hydrodynamic conditions,static water and seepage,were set.The horizontal and unidirectional sine wave vibration was loaded.The loading frequency and acceleration were 0.5,1,2,5,10,15 Hz and 0.1g,0.15 g,0.25 g,respectively.The four typical water level patterns observed in the experiment are oscillation,rise,fall and step change,which are similar to the field coseismic water level patterns.At the same time,the stress and strain values in shaking table test are calculated,and the relationship between strain and pore water pressure,the relationship between cyclic loading times and strain,and the relationship between strain and void ratio are studied.The results are compared with seed's classic triaxial test and simple shear test,and the results are consistent with seed's test The correctness of the shaking table model is verified.Taking this experiment as the physical model,the fluid structure coupling model of pore water pressure response in unconsolidated aquifer under vibration and the pure hydrodynamic process mathematical model expressing the interaction between aquifer flow and well flow are established according to the principle of classical mechanics.The results show that the vibration compaction of unconsolidated aquifer leads to the decrease of porosity,and the water in the aquifer is squeezed and discharged,resulting in the rise of pore water pressure,driving water into the well and the rise of well water level.On the contrary,the aquifer expansion leads to the increase of porosity and the decrease of pore water pressure,which leads to the inflow of water into the aquifer and the decrease of water level,accompanied by the change of oscillation pattern.At the same time,it is found that the increase of vibration frequency leads to the compaction of aquifer,the decrease of amplitude and the expansion of aquifer.This study provides material for exploring the correlation between crustal stress and groundwater dynamic process and the establishment of quantitative model,and provides a reference for revealing the coseismic response mechanism of field scale well water level.