Study On Ventilation Capacity And Cooling Effect Of Permafrost Slope Support Structure With Frame Ventilation And Cooling Anchor Pipe

With the rapid economic development in the cold regions,more and more disturbances in permafrost have been caused by human engineering activities.In addition,the global greenhouse effect has intensified,and the slopes in the permafrost regions have become increasingly unstable.The problem of destruction of freeze-thaw cycle is particularly serious,which has brought great harm to the construction and operation of the cold area project.At present,the commonly used engineering remediation measures for permafrost slopes are mostly passive governance methods,and do not comply with the principle of active protection of frozen soils in the context of climate warming.In order to better solve the problem of thermal melting and slumping of permafrost slopes,the permafrost slope support structure with frame ventilation and cooling anchor pipe is proposed.In this paper,the ventilation capacity and cooling effect of the permafrost slope support structure with frame ventilation and cooling anchor pipe are analyzed by the method of combination of theory and numerical simulation.The specific research contents and conclusions are as follows:(1)Based on the concept of "active protection of frozen soil",and combined with ventilation and cooling advantages of the pipe and anchorage advantage of the framework system,the permafrost slope support structure with frame ventilation and cooling anchor pipe is proposed,which has the functions of ventilation cooling,anchorage and reducing inflation and back to in situ,and it’s structure,construction technology and structural characteristics are introduced.(2)According to the Bernoulli principle,the loss of wind speed resistance of the ventilation and cooling anchor pipe is calculated,and the formula of wind speed inside the structure is deduced according to the equal relation between the driving force of ventilation and the differential pressure of wind field.And the formula of the wind is verified by the finite element software.Example analysis shows that the ventilation and cooling anchor pipe has good ventilation capacity.Wind pressure difference is the main driving force of structural ventilation and loss of resistance along the way is the main wind speed loss of the structure.The optimal diameter ratio between internal and external pipe of the structure is about 0.4~0.7.the setting of the drafting bend significantly improves the ventilation capacity.And the setting of the induced-draft elbow pipe improves the ventilation capacity significantly.(3)Based on the above wind speed calculation formula,the heat transfer mechanism of the wall of the ventilation cooling anchor pipe is studied,and the formula for calculating the heat transfer quantity of the ventilation cooling anchor pipe wall is deduced considering the influence of the wind speed.And then,the radial heat transfer model of ventilation anchor pipe is established,and the evaluation index of cooling effect of radial frozen front expansion is obtained by perturbation method,with the heat flux density of the pipe wall as the anchor pipe boundary conditions.Meanwhile,another evaluation index of cooling effect of thawed depth variation on axial slope for ventilation anchor pipe is obtained based on energy conservation law.The example analysis shows that the heat exchange effect of the pipe wall mainly includes convective heat transfer and evaporative heat dissipation.The total heat flux of the pipe wall is the superposition of the convective heat transfer flux and the evaporative heat dissipation flux.In addition,the slope melting depth of the permafrost slope under the ventilation cooling anchor pipe has a more prominent uplift,and the radius of the freezing front of the anchor pipe also increases with time,which shows that the structure has better cooling effect.(4)In order to further analyze the cooling effect of the ventilation and cooling anchor pipe,and verify the rationality of the two cooling effect evaluation indicators in(3),the temperature field model of permafrost slope supported by ventilation and cooling anchor pipe is established and solved by the finite element method,which is written as a calculation program.And the accuracy of program is verified by the experiment.The permafrost slopes under the support of ventilation and cooling anchor pipe and ordinary anchor is calculated using the programmed procedures.The comparative analysis shows that the temperature field distribution of ordinary permafrost slopes is changed by the ventilation anchor pipe,and the straight thawing line of overland on ordinary slopes is transformed into wavy type,the thawing depth also has a more significant elevation than the normal slope,and the degradation of the permafrost slope is restrained to a certain extent,which shows good ventilation cooling effect...