| During operation process of subway and tunnel, there is a possibility of fire due to various reasons. The strong scent of smoke and high temperature of fire will pervade the whole tunnel and be harmful to the people‘s lives and properties while evacuating. The large amount of heat generated by the fire is harmful to the integrity and stability of the lining structure. Also, the heat can be transmitted through the lining to the outer soil layer and a certain temperature field is formed in the soil layer. Under the action of the temperature field, a part of liquid water in the soil layer appears the phenomenon of heat and moisture transfer. Thus the moisture field of soil layer is redistributed. Another part of the liquid water absorbed the heat and gasified. The water molecules exist in the void between the soil particles in the form of gas. The pressured vapor may cause burst damage to the thermal cracked concrete lining structure and further threaten the safety of tunnel concrete structure.The topic of this paper is on distribution of temperature field, moisture field and steam pressure field of losess layer in a condition of fire. Besides, this paper has a systematic study on the tunnels fire and heat transfer by means of theoretical analysis, numerical simulation and experimental investigations.The research contents include the following items.（1） Relationship between soil thermal conductivity and water content and dry density. While the dry density of soil sample is constant, the higher the water content is, the greater the coefficient of thermal conductivity is; While the water content of soil sample is constant, the higher the dry density is, the greater the coefficient of thermal conductivity is.（2） Relationship between soil thermal temperature and selftemperature. The coefficient of thermal conductivity has a linear correlation with its own temperature specific to the soil sample with a water content of 5% and a dry density of 1.50g?cm-3 which is prepared for the experiment（3） Study on the heat and moisture transfer in the soil.When heat and moisture transfer experiments were carried out, the conclusion was: there exists ―severe cooling area‖, ―slow cooling zone‖ and ―constant temperature area‖ of the temperature field. The closer the distance to the heat source, the higher the temperature of the measuring point is. The temperature of the measuring point which is close to the edge of the cylinder is close to the normal temperature. There also exists ―water diffusion area‖, ―water concentrated area‖ and ―non-distributed area‖ of the moisture field. With the increase of the distance from the heat resource to the measuring point, the water content increases gradually and roses to a peak, then gradually decreased to the initial water content.（4） The temperature field, moisture field, vapor field and vapor pressure field under various ventilation velocities and HRR（30MW and 50MW） are studied with the numerical simulation modeling.The major content of the paper can be concluded as followed:a. The heat generated by the fire diffusion along the tunnel longitudinal and transverse is affected by the fire scale and the ventilation velocity.b. The higher the temperature of a measuring point in the outer layer of the tunnel lining, the more obvious the moisture transfer of the point. When the fire is extinguished, the temperature along with the vapor mass and vapor pressure in the soil layer decreases and the water content of the point increases. The temperature field couples with the moisture field.c. The liquid water absorbs the heat and gasifies, and a continuous distribution of steam field in the soil body is formed.under the condition of constant pore volume, the higher the temperature, the greater the steam content is.besides, the kinetic energy of gas molecules increases with the increase of temperature. As a result, the steam pressure is increased.According to the research results, some suggestions are put forward in the design and construction of the tunnel lining such as joining the waterproof layer and thermal insulation layer. |
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