Study On Working Characteristics Of The Permafrost Slope Supporting Structure With Frame Unpowered Acceleration Convection Anchor

With the continuous advancement of the Belt and Road strategy,many newly excavate slopes have appeared in the permafrost area.Under the thermal effect of engineer and mutual influence of engineering,the physical,mechanical and hydraulic properties of the excavated permafrost change significantly,leading to the frequent occurrence of the freezing and thawing problems of permafrost slopes.Especially in the context of global warming,the active layers of permafrost slopes is strongly degraded,which makes the problem of freeze-thaw collapse more serious,bringing great difficulties to engineering design,construction and operation in permafrost regions.However,passive treatment methods are mostly adopted in the engineering measures for slope treatment,which have poor service performance and cannot fundamentally solve the problem of freeze-thaw collapse.Aimed at the freezing and thawing problems of permafrost slopes,a new type of permafrost slope supporting structure with frame unpowered accelerated convection anchor is proposed.In this study,theoretical analysis and numerical simulation are combined to study the working characteristics of the new support structure.The specific research contents are as follows:(1)Combined with the unpowered ventilation,ventilation pipe cooling and geotechnical anchoring,the slope supporting structure with frame unpowered accelerated convection anchor is proposed.The structure and characteristics of the structure are discussed in details.And its design thought,construction method and working mechanism are discussed.(2)According to the principle of thermal balance,the wind speed required by the unpowered accelerated convection anchor is given.Based on the law of conservation of energy,the relative negative pressure of the unpowered hood,the average wind of unpowered accelerated convection anchor and the air intake of the anchor are derived.Based on the relationship between structural wind field and soil temperature field,a simplified calculation method for the axial lift of freeze-thaw interface in the permafrost slope is presented.Basing on Winkler foundation beam,a calculated model of the collaborative work between supporting structure with frame unpowered acceleration convection anchor and soil is established.According to the static equilibrium and deformation compatibility condition,a simplified calculation method of the frost heave effect is put forward.The results show that the suction effect of the unpowered hood and the chimney effect of the exhaust pipe are superimposed on each other,and it enhances the ventilation capability and air convection of the unpowered acceleration convection anchor,so it increases the air circulation flow rate.The unpowered hood improves the average wind speed of unpowered acceleration convection anchor.And the wind speed is greater,the stronger the convective heat transfer and evaporative heat dissipation between cold air and soil.So the more heat the air takes away from the soil,the stronger the heat transfer and the better the soil temperature is cooled.The amount of cooling brought by the unpowered accelerated convection anchor accumulates in the slope year by year,which is enough to offset the heat absorbed in the warm season to reduce the thickness of the seasonal active layer year by year.The simplified calculation method of frost heave effect can accurately describe the anchoring performance of the new supporting structure.The structure can reduce the harm of frost heave effect of slope soil and improve the stability of frozen soil slope.(3)Based on the principle of ventilation,heat transfer and permafrost mechanics,the frame and unpowered accelerated convection anchor are coupled with soil.Considering the pumping effect,a hydro-thermal coupling model of the atmosphere-structure-slope system is established.The governing equation of hydrothermal coupling of permafrost is solved by finite element method,and the hydrothermal coupling finite element formula considering the new supporting structure is given.So the analysis program is compiled by MATLAB software.The results show that the unpowered accelerated convection anchor brings the heat inside the slope to the external environment by means of convection heat transfer and evaporative heat dissipation.It is a heat dissipation channel to the interior of the slope,and the depth of the seasonal melting layer is significantly reduced.The low temperature freezing zone on the lower side of the melting layer gradually expands into the slope,and the temperature of the slope soil is also significantly reduced.Therefore,the unpowered accelerated convection anchor has good ventilation and cooling ability.Under the action of temperature gradient in the slope,the water transfer of the supporting slope is more obvious.Through the freeze-thaw cycle,the new style of supporting slope change dynamically with the seasonal freeze-thaw cycle,and the stress and displacement change range is relatively small.So the new style of supporting sturcture can improve the stress distribution in the slope and improve the stability of the slope.