Study On Variation Characteristics Of Pore Water Pressure And Water Level In Saturated Confined Sand Layer Under Vibration

The change process of pore water pressure and water level of saturated confined sand layer caused by vibration includes three links: the dynamic load causes aquifer deformation,which triggers the change of pore water pressure of aquifer,and then drives the pore water to flow into or out of the monitoring well,resulting in well water level changes.Exploring the response characteristics of pore water pressure and water level and hydrodynamic mechanism in the above processes can help to explain the co-seismic response mechanism of shallow loose aquifer deformation and well water level caused by earthquakes in the field,and provide a reference both for studying the response mechanism of deep fluid to crustal stress and solving the practical engineering problems caused by the interaction between stress field and seepage field.In consideration of the complexity of seismic load action form and field site conditions,this study is derived from shaking table tests.A confined complete well-aquifer model device is designed with quartz sand as aquifer medium.6 groups of seepage simulation tests of saturated confined sand layer under vibration are carried out,in which the coseismic inputs are composed by horizontal sinusoidal loads with amplitude(peak acceleration)range of 0.1~0.25 g(1g=9.81m/s~2)and frequency range of 0.5~2 Hz.The dynamic monitoring data of acceleration,pore water pressure and water level are obtained from the tests.The response characteristics of pore water pressure and water level to input loads of different frequencies and amplitudes(peak acceleration)in time domain,frequency domain and space scale are analyzed.Combined with the calculation of shear stress and shear strain,the aquifer deformation characteristics in different loading stages are discussed.The qualitative and semi quantitative analysis results of pore water pressure and water level variation of saturated confined sand layer caused by vibration are obtained through analysis of the response relationships between pore water pressure and shear stress and shear strain,and the correlations between pore water pressure variation and water level variation.In order to quantitatively describe the dynamic changes of groundwater in confined aquifer caused by the change of stressstrain state,the coupled stress-seepage field model in saturated two-phase porous media and the well water level response model under the pore water pressure disturbance are established.Based on the above work,the main research results are as follows:(1)In the seepage simulation tests of saturated confined sand layer based on shaking table,the pore water pressure changes in different forms under sinusoidal loads with different frequencies and amplitudes(peak acceleration),and characteristics of pore water pressure changes in time domain,frequency domain and spatial change are affected by the intensities of proposed input loads.The water level variation trends are similar to the of pore water pressure to a large extent.The response processes of pore water pressure and water level reflect the compression and expansion of the aquifer.(2)The shear stress and shear strain at different measuring points in the aquifer are calculated by acceleration data.According to the characteristics of shear stress and shear strain changes with time and their constitutive relationships,the deformation characteristics of saturated sand layer under different proposed input load intensities are further revealed.Combined with the development of residual deformation and residual pore pressure,the elastic-plastic deformation stages are divided,and the shear strain thresholds triggering pore pressure fluctuation and monotonic change,the relationship between pore water pressure increase and shear strain,the correlation between water level variation and pore water pressure variation are discussed.The energy densities triggering the change of pore water pressure and water level are compared.(3)Based on the test model,according to Terzaghi's effective stress principle,mass conservation law,classical mechanical law,Darcy's law and Navier Stokes equation,the stress-seepage field coupling model in saturated two-phase porous media and the well water level response model under the pore water pressure disturbance are established to quantitatively represent the response of pore pressure and water level to horizontal sinusoidal load in a confined complete well-aquifer system.The unsteady movement model of groundwater to confined complete well derived from Theis formula is compared with model obtained in this study.