Effective Porosity,Hydraulic Tortuosity And Model Of Hydraulic Conductivity Of Quasi-saturated Porous Media

In the field of groundwater science,groundwater level will change under the influence of evaporation,rainfall and irrigation.When the water level rises,an aquifer containing entrapped air will be formed in the upper layer of the phreatic water,at this time,the groundwater is in a quasi-saturated state.The existence of entrapped air in the quasi saturated zone will reduce the hydraulic conductivity of aquifer.The study of quasi saturated hydraulic conductivity model can not only deeply understand the hydraulic properties of quasi saturated zone,but also relate to a series of problems such as air exchange,biological activity,solute transport and hydro-geochemistry in quasi saturated zone,which has important scientific significance and practical application value.In this paper,the hydraulic conductivity of air traps were measured for the three mediums of fine sand,medium sand and coarse sand,and the test results of the quasi-saturated hydraulic conductivity of eight different media were collected.A new model of quasi-saturated hydraulic conductivity based on Kozeny-Carman formula was established for the effect of quasi-saturated trap air on effective porosity and hydraulic tortuosity.The thesis achieved the following results:(1)The existence of trap air in quasi-saturation increases the hydraulic tortuosity.Using the existing tortuosity model calculation,it is shown that if the trap air is regarded as the reduction of porosity,the theoretical tortuosity can be increased by 1-2 times when the trap air saturation is 0-0.6.(2)By studying the relationship between the total invalid porosity n_0tof the medium inversion based on the Kozeny-Carman formula in the presence of entrapped air,the inherent invalid porosity n₀₁ at full saturation and the porosity n₀₂ occupied by entrapped air.It was found that the sum of n₀₁ and n₀₂ is greater or less than n_0t,which reflects the complexity of entrapped air on pores.(3)Based on the quasi-saturated displacement test data of different media(8 collecting media and 3 testing media),the quasi saturated hydraulic conductivity model of tortuosity and effective porosity affected by trap air is established based on Kozeny Carman formula.The influencing factor a of model parameter effective porosity is discussed,and its physical significance and estimation method are put forward.In addition,based on the data of trap air saturation and hydraulic conductivity of 11 samples,the quasi saturation hydraulic conductivity is proposed,which can be obtained only by effective porosity influence factor a and saturation hydraulic conductivity.This empirical model is simpler to use than the quasi saturated hydraulic conductivity model based on Kozeny Carman formula.