Study On Water-Heat-Salt Transport Law Of Soil Wall Of The Terracotta Warriors Pits

The Terracotta Warriors of Emperor Qinshihuang’s Mausoleum Site Museum is a typical representative of indoor earthen sites.Compared with the outdoor earthen sites,it is free from the deterioration of wind erosion,rain erosion and sun exposure.However,due to changes in the temperature and humidity of the environment,the earthen sites still develop cracks,powdering,mildew,crystallizing and other diseases,affecting the safety and stability of the earthen sites.The water-heat-salt interaction caused by the environment is the important reason for the development of the earthen sites diseases.In order to reveal the water-heat-salt transport inside Soil wall of the Terracotta Warriors Pits,especially the water,heat and salt transport law and influence range in the shallow surface area where the material and energy exchange between the Soil wall and the outside is the most intense,In this research,the earthen sites in the No.1 pit of the Terracotta Warriors was taken as the research object.By analyzing the temperature and humidity in-situ monitoring data of the environment inside and outside the museum,the mean level and the change rule over time were researched.A mathematical model of water-heat-salt transport suitable for the Soil wall of the Terracotta Warriors Pits was established.The multi-field coupling numerical simulation method was adopted to reveal the law of water-heat-salt transport inside the earthen sites body.The research mainly obtained the following understandings:(1)Through the real-time monitoring of the temperature and moisture content of Guodong 10 and the environmental temperature and humidity of Guodong 11 in the archaeological excavation area of the No.1 pit of the Terracotta Warriors,it was found that the temperature of the earthen site is consistent with the change law of the ambient temperature,and the closer to the surface,the greater the temperature change of the soil layer,and the closer to the ambient temperature;the change of volumetric water content inside the earthen site was relatively small.In the spring,the temperature and humidity difference of the environment in the pit was large,so it is necessary to pay attention to the monitoring and control of temperature and humidity.In the autumn,the temperature difference in the pit is also large.(2)Under the assumption that the soil is continuous and isotropic,following the law of conservation of mass and energy,considering the influence of salt transport and phase transition on water transportation and the influence of temperature change on water vapor diffusion,a two-dimensional water transport control equation was established.Considering the heat transfer and heat storage of soil particles,liquid water,salt and water vapor,as well as the latent heat of phase change of salt dissolution crystallization and the latent heat of phase change of water,a two-dimensional heat conduction control equation was established.According to the theory of solute transport and water flow theory,considering the dissolution and crystallization of salt,the twodimensional solute transport control equation in soil was established.(3)In this research,COMSOL Multiphysics was used as the numerical simulation method to research the law of water-heat-salt transport in earthen sites.A coupling model was established according to the three coupling governing equations of waterheat-salt fields.The boundary conditions were determined by in-situ monitoring data,and the reliability of the model was verified.Finally,the change laws of temperature,water content and salt content of inside the earthen sites body were obtained.It was found that the temperature variation trend inside the earthen sites is consistent with that of the environment temperature,and the influence of the environment temperature on the soil layer temperature within 10 cm from the surface of the earthen sites was more intense.The closer the soil layer temperature is to the surface,the closer it was to the environment temperature,and the greater the range of change.The internal moisture content of the earthen sites was generally less affected by fluctuations in environmental temperature and humidity,but the year-on-year impact on the moisture content of the soil layer within a range of 2cm below the surface was greater,and the closer the soil layer is to the surface,the greater the change in moisture content.The moisture content of the soil layer within a range of 2cm on the surface of the earthen sites was consistent with the trend of changes in environmental boundary humidity,while the moisture content inside the earthen sites was opposite to the trend of changes in environmental humidity.Under the influence of environmental temperature and humidity,the salt distribution of the earthen site body showed a phenomenon of gradually decreasing shallow surface salt content as the distance from the surface increases.The salt content inside the model remained unchanged overall,but within a range of 1cm from the surface of the soil layer,the change in salt content was relatively significant,and the dissolution and crystallization process was repeated,causing salt damage to the earthen site body.