| The use of thermal insulation in tunnels in cold regions is a commonly used method to stabilize the surrounding rock temperature field and prevent frost heave in surrounding rocks.Thermal conductivity of insulation material is an important parameter to judge its insulation effect.In practical engineering,due to the influence of various factors,phenomenon of tunnel leakage is common.Tunnel leakage will lead to a decrease in the insulation effect of tunnel insulation materials in cold regions.At present,the research on the properties of insulating materials is basically carried out under the ideal condition of not leaking water in the tunnel of cold regions,without considering the adverse effect of tunnel seepage on the insulation effect of the tunnel insulation material.Therefore,it is of great significance to study the heat preservation effect of tunnel in combination with the actual seepage water in cold region.Combined with the types of insulation materials used in cold regions tunnels,this paper chooses three kinds of insulating materials,such as phenolic insulating board,polyurethane insulation board and foliquet insulation board,and then combines the laying mode of insulation material,and then analyzes and determined two methods: natural active water absorption and passive pressure water absorption.In order to realize the above water absorption method,an absorbent device was developed.Based on this,a water absorption test was conducted on the above-mentioned insulation material,and the law of moisture content of the insulation material changing with time was obtained.Under the condition of water content,the pore water distribution of the insulating material also has an important influence on the heat preservation effect.In order to analyze the water distribution of water-containing insulating material,CT scan images were firstly obtained by computer tomography technology.Then,according to the concept of gray value of image,the concept and formula of grayscale volumetric moisture content,saturation degree of the absorbent part of the material,average water absorption height and volume ratio of water distribution are proposed.The relationship between the water content and the gray value of the insulation material,the water distribution characteristics of the insulation boards with different water contents,and variation of water content along the thickness of the insulation plateThe water content of the insulation material is related to the change of the thermal conductivity of the insulation material.According to the principle of quasi-steady-state heat conduction,a self-made quasi-steady-state plate test apparatus was used to test the thermal conductivity of the water-containing insulation material,and the thermal conductivity was changed with the water content.The law established the corresponding formula between water content and thermal conductivity.Combined with the change of temperature field of tunnel in a cold region,based on the theory of heat transfer calculation of multilayer cylinder wall,the maximum freezing depth of surrounding rock is given by Stephen Formula,and the calculation formula of thickness and thermal conductivity of water insulating layer is established based on the two different laying modes of internal and external type.The proposed value of the thickness setting of the water insulating layer in the cold region tunnel is given. |
