| The stability of landslides is closely related to the action of groundwater and is vulnerable to strong rainfall.Therefore,adopting methods such as slope drainage to reduce and control the groundwater level is a necessary technical means to manage landslides.Slope siphon drainage technology drains deeply buried groundwater from the slope by cleverly using the slope’s atmospheric pressure and topographic conditions.In response to the problems of poor long-term applicability caused by the stop-flow period during long-distance siphon drainage,the hydrodynamic characteristics of gas-liquid two-phase flow in siphons were analyzed through experimental research,theoretical analysis,and comparison of engineering data,and the calculation method applicable to long-distance siphon drainage with extended horizontal sections was derived.In addition,the flexible application of long-distance siphon drainage in engineering practice was discussed.Through the above studies,the following main results and insights were obtained.(1)In a high head siphon drainage process with a long horizontal section,the combination of the gradual decrease of air pressure in the tube with increasing height and the restriction of flow velocity due to the loss along the tube length causes the full development of the flow pattern in the tube,i.e.,the formation of a typical gas-liquid two-phase segmental slug flow.The experimental study found that the segmental slug flow is widespread in the siphon drainage process.However,because the ratio of the effect of manifest tension and gravity is closely related to the tube diameter,the different manifestations of the capillary effect cause the differences in drainage efficiency brought about by the differences in tube diameter.In the horizontal section,the slug bubbles in the larger diameter tube float up against the wall due to gravity,while the bubbles in the smaller diameter tube are intermittently disposed with the liquid and occupy the entire tube cross-section.(2)The Lagrani Mathematics model based on the conservation of mass,momentum,and energy is used to analyze the mechanism of the slug flow’s formation,development,and stabilization process.Slug flow is periodic with intermittent characteristics,and bubbles determine its stability.The stability of bubbles is related to the surface tension of the gasliquid interface,bubble shape and size,liquid viscosity and kinetic properties,pipe shape and size,and environmental conditions.(3)The gas-liquid two-phase flow in a large-diameter siphon is an incompletely developed segmental slug flow-elastic flow-formed under the dominance of gravity.The Kelvin Helmholtz instability analysis theory is used to obtain the gas-liquid interface wave disturbance equation of state and the relationship between the critical gas-liquid velocity of the segmental slug flow.The gas-liquid two-phase flow in a small-diameter siphon is a typical segmental slug flow dominated by surface tension.The analytical equations for the pressure gradient,dynamic void fraction,and relative drift velocity of bubbles are obtained using multiphase medium theory.(4)In the siphon drainage process,the slug flow facilitates the discharge of the accumulated gas in the pipe.However,the presence of the gas-liquid-solid three-phase contact line causes a significant increase in pressure drop.Therefore,the practical and engineering use of 5mm as the critical diameter of the capillary tube and large diameter tube has the advantages of forming a stable slug flow and maintaining the liquid film thickness between the bubble and the tube wall.(5)In engineering practice,the single-hole influx of water is the main factor in determining the demand for siphon drainage capacity.Through the different borehole conditions and water demand,the comparative analysis found that the long-distance siphon drainage capacity increased the efficiency of the diameter of the tube at 5.3mm to obtain the most value. |
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