Manufacture And Application Of Water-Air Two-Phase Apparatus For Unsaturated Soil Under Unloading Disturbance

The unsaturated zone is an important place for the exchange of material resources on the earth during the circulation process.The water-gas two-phase flow in the unsaturated zone passes through mutual displacement or escapes the surface or infiltrates into the groundwater saturation zone,so the unsaturated zone is studied.The two-phase transport of water and gas is of great significance.According to the research,the migration of water-gas two-phase in the unsaturated zone is a fluid-solid coupling process.In fact,the active factors of water-gas two-phase fluid-solid coupling in the unsaturated zone include stress field and seepage field.At present,most studies on the two-phase transport of water and gas in unsaturated soils focus on the factors affecting the change of fluids in geotechnical media,that is,from the perspective of seepage field,such as rainfall infiltration.In the actual project,the pores of the soil in the unsaturated zone are filled by the gas phase and the water phase,and the stress state of the geotechnical medium changes,which will cause the distribution of the pores in the soil to change,thereby affecting the unsaturated soil.The migration mechanism of water and gas two phases.Based on the actual engineering background,this paper aims to study the influence of stress field changes on the two-phase transport mechanism of unsaturated soil water and gas.Based on the summarization of water and gas two-phase theory and experimental equipment at home and abroad,a set of experimental instruments for studying the two-phase flow of unsaturated soil water and gas under unloading disturbance was developed independently based on the parameters of soil and various phases in the unsaturated zone.And carry out indoor simulation experiments,the main research results are as follows:(1)According to the functional requirements and force requirements of the experimental instrument,a set of experimental equipment for bearing load is designed.The structurally innovative frame structure with rigid contact between the column foot and the foundation is selected to meet the requirements of high rigidity.Steel is selected on the material to meet the requirements of strong bearing capacity and durability.Based on the ideal elastoplastic model,the mechanical properties of the beams,columns and panels of the experimental instrument were analyzed by using the ABAQUS/CAE simulation experiment under the conditions of loading and unloading.Simulating the force of the experimental instrument under different material strengths,economic evaluation of different strength schemes,selecting the steel with grade strength Q345 as the optimal solution,the maximum load that the experimental instrument can withstand during the loading process is 86 t,At this time,the maximum force is located at the intersection of the flanges at both ends of the top beam and the web,and the maximum stress is 345 MPa;the deflection curves of the beam,the column and the front panel are linearly changed and within the allowable range.(2)According to the design optimal scheme of the water-gas two-phase experimental instrument,the main frame of the experimental instrument is assembled,and the unloading system,the soil stress monitoring system,the gas phase pressure monitoring system and the water phase pressure monitoring system are installed according to the design requirements.The experimental operation procedure was designed,and the operation instructions,precautions,maintenance instructions and other operational procedures of the water-gas two-phase experimental instrument were given.(3)Using the developed water-gas two-phase experimental instrument to carry out indoor simulation experiments,the relevant parameters of the two phases of unsaturated soil water and gas under unloading disturbance are obtained,and the data analysis is carried out,and the pressure duration curve and pressure fluctuation curve are drawn respectively.Contour map of soil moisture content and soil stress duration curve.According to the characteristics of soil stress,water phase and gas phase,it is concluded that the water-gas two phases in the unsaturated soil are constantly displaced by the unloading disturbance.The distribution of pore size in the body is the main influencing factor affecting the migration of water and gas.