Pore Scale Simulation Of Water Migration In Unsaturated Soil

As an important water resource,groundwater has attracted much attention.The pollution of groundwater is reflected in all aspects of daily life.As the main channel for pollutants to enter groundwater,unsaturated zone has important research significance for agricultural and engineering problems.The two-phase flow method has attracted extensive attention from researchers at home and abroad as a tool for studying two-phase immiscible solution and unsaturated problems.However,scholars at home and abroad focus more on reservoir research.In this paper,the finite element method is used to simulate the two-phase seepage.The characteristics of water absorption process and dehydration process under different static contact angles and different particle gradations are studied by two-dimensional pore-scale unsaturated soil water migration simulation.This paper mainly draws the following conclusions :(1)The contact angle changes with the process of water migration.The larger the static contact angle is,the smaller the range of contact angle is.The water holding capacity of the soil is related to the size of the contact angle.In the simulation of the water absorption process,the static contact angle of 120 ° or 30 ° has a strong water holding capacity,and the residual water content in the soil moisture characteristic fitting curve is larger.In the simulation of the dehydration process,the pore part of the water phase is wrapped and retained in the pores.The water phase in the soil with a static contact angle of 60 ° is more likely to gather into a group and be retained in the pores,and the water holding capacity is stronger.The static contact angle is 60 °.The minimum dynamic contact angle of the water absorption process is 66.22 °,which is equal to the maximum dynamic contact angle of the dehydration process of 66.22 °.The static contact angle is 30 °.The minimum dynamic contact angle of the water absorption process is 44.66 °,which is greater than the maximum dynamic contact angle of the dehydration process of 41.48 °.Through the comparative analysis of microscopic contact angle characteristics,in the same situation,the larger the contact angle,the smaller the negative pressure value of the soil dehydration process,and the smaller the contact angle,the longer the dehydration time.Through the simulation and comparison of the water absorption process,the three-phase water migration process with a static contact angle of 60 ° is relatively stable.(2)In the simulation process of water absorption process,the water phase saturation degree of poor gradation soil is higher,and it has stronger water holding capacity.The soil moisture characteristic curves of the three particle gradation dehydration processes were analyzed,and it was concluded that the water characteristic fitting curve of the equal particle size soil was more gentle and the soil was more difficult to dehydrate.The maximum width between the water absorption curve and the dehydration curve of the well gradation is the highest among the three gradations,reaching 0.2554,indicating that the water hysteresis of the soil with well gradation is more significant.Among the two main factors affecting the hysteresis effect,the influence of the ’ ink bottle ’ effect is more significant than that of the contact angle.Comparing well-graded and poor-graded soils,the more uneven the particle size,the more irregular the pore distribution,and the more obvious the ’ ink bottle ’ effect.However,according to the results of the wet and dry simulation fitting curve of the soil with the same particle size,it can be concluded that whether the ’ ink bottle ’ effect is obvious by considering the uniformity of the pore distribution through the uniformity of the particle size and then inferring whether the ’ ink bottle ’ effect is obvious or not needs to be judged by combining the factors such as the particle size distribution and particle position distribution of the soil.(3)In the process of water absorption,the gas phase can be displaced by the water phase through the pore channel,while in the process of dehydration,the gas phase is difficult to pass through the pore channel,so that the water phase cannot be discharged from the pore channel,and the water phase exists in the pore channel in the form of capillary retention water.With the increase of the number of dry and wet processes,the water lag phenomenon in the later stage of the dehydration process is more obvious,and the water phase of the gas phase displacement pore channel is more difficult,which is more conducive to the retention of water in the pore channel.