| The use of similarity theory to simulate the rock mass engineering site is one of the major approaches to the analysis of the mechanical properties of large-scale rock masses.The physical model test has become an important method for rock mechanics scientific research.The physical and mechanical properties of similar materials in the model have a decisive effect on the model test.The mechanical strength characteristics of the physical model and the model test process are mainly affected by the model temperature and water content factors.Studying the temperature and moisture content characteristics of the physical model,and conducting the thermal-moisture coupling effect analysis of the similar materials in the model test become the key to solving similar errors caused by the physical environment in the model test.This paper aims at the evolution characteristics of the moisture and temperature fields in physical models of similar materials.Through theoretical,experimental and numerical simulations,the prediction models of thermal and moisture coupling of model materials,model moisture content test methods and spatial reconstruction techniques,model humidity diffusion coefficients and changes The study of the law of temperature and the change of the moisture field in the drying process of similar models was conducted.Through analysing the model materials in the drying process heat transfer,wet transfer and the coupling between them,the unsteady model of heat,humidity and air coupling transfer is established,and the drying index of the model is put forward through temperature test,moisture content and humidity test to study its influence on the strength of the model,and then the model test time is obtained.Combining the Fourier law,the Fick law and the Darcy Law,considering the change of pore structure in the drying process of model materials,the effect of heat release of gypsum,ventilation and gravity on the movement of water,the wet transfer is divided into two parts of vapor diffusion and liquid water transfer,the effects of water evaporation and heat transfer of solid particles on thermal exchange are considered,and the mechanism of heat and moisture coupling in the drying process of the model materials is revealed.The humidity sensor was used to measure the moisture distribution in the drying process of the model materials to obtain the moisture diffusion coefficient.The preparation method of humidity sensing unit of fiber optic humidity sensor was innovated,and the surface bonding ability of polyimide film and fiber was strengthened with N-hydroxyethyl two amine as coupling agent,and the sensitivity of humidity measurement was enhanced.A testing system of optical fiber humidity sensor was built,and the performance(humidity sensitivity and response time)of the fiber-optic humidity sensor with 6?m-336?m thickness was studied,and the coating thickness of the humidity sensitive material was optimized.The effect of surface porosity on the response time of humidity reduction was found,and the surface porosity was divided into three intervals,which indicated that the larger the face diameter is,the shorter the absorption of moisture response time will be,but the effect on the reducing of moisture response time is unapparent.According to the model material humidity measurement environment needs,with the help of 3D printing technology,the packaging structure of optical fiber humidity sensor is fabricated by laser beam point scanning with photosensitive resin as raw material,and the sensor is used to test the internal humidity distribution and humidity variation in the drying process of model material specimen.Based on the optical fiber humidity sensor,the temporal and spatial characteristics of humidity in the drying process of model materials were studied,and the change of humidity in the drying process was revealed.In the time dimension,the humidity development in the model material time drying process is characterized by two stages.The initial stage is the humidity saturation period,and the latter is the humidity decline period.In the space dimension,the humidity distribution of the model material is graded along the height.Hydration water consumption and water diffusion are the main causes of the deterioration of the internal humidity of the model materials.Under different surface conditions,the influence of humidity diffusion on the relative humidity of the near surface of the model material is different,and the critical time and the humidity drop amplitude are different.The final model material humidity distribution is the result of hydration water consumption and humidity diffusion on the basis of initial humidity distribution.A method of spatial information statistics is proposed distribution field in the drying process of model materials.With the variation function as the basic tool,the best unbiased interpolation estimation can be achieved by studying the data with randomness and structure relativity,and the variation function of the temperature distribution of the model material is deduced.Through the calculation of the experimental variation function validation of the fitting results of various models,they are lower than the common variant function models.The method of kriging interpolation model material temperature and water distribution field reconstruction is carried out by using the model,and the deviation of measured value and reconstruction prediction value is less than 2%.The variation of uniaxial compressive strength and water content of model material specimens was obtained by testing uniaxial compressive strength of specimens with different proportioning models.The results show that with the decrease of water content,the compressive strength of model materials is monotonically increasing,this function relation can be used in the drying process of physical similarity model,and the optimum water content of the model material is determined to achieve the design compressive strength.In this paper,the concept of optimum water content in the process of pavement drying is presented,according to the relation of mechanical strength of model material under different water content,the optimal moisture content of the model material in the course of paving drying is determined in order to achieve the design mechanical strength,which is used to reduce the material mechanical strength which is caused by the water content factor to not meet the design strength.Then the similarity error of entity and the model is reduced,and the simulation precision is improved.The drying index of physical similarity model is proposed,and it is used to evaluate the drying degree of physical model pavement after completion.It is also determined that when the drying index of the model is 0.8,the model excavation test is suitable.The plane model and the stereo model test are carried out by means of optical fiber and electromagnetic sensing.In this paper,the distribution of temperature field and water field of plane model in summer with wind,no wind in summer,no wind conditions in winter and three-dimensional model in spring and autumn without wind is studied,and the relationship between the water content and the time of the model material drying is revealed.The variation rule of water content obtained by derivation accords with the characteristics of Exponential function and Boltzmann function,the fitting correlation coefficient is greater than 0.97,which can be used to predict the moisture content in the drying process of model materials.According to the relationship between the mechanical strength of the model materials under different water content,the time required to reach the design mechanical strength can be estimated,in order to reduce the problem that the material mechanical strength does not conform to the design strength due to the moisture content,and then to reduce the similarity error between the real model and the model.Prediction of dryness Time(determination)provides reference and theoretical support.The change characteristics of temperature field and water field are obtained by the interpolation method,and the change rule of the model material during drying process is revealed.In summer windy and summer without wind state,temperature field is first formed Low-temperature core area,low temperature core zone down,finally become vertical gradient distribution,horizontal direction roughly the same temperature characteristics.The three-dimensional model and the winter wind-free state of the plane model,the temperature field is to form a high-temperature core,and then formation of low-temperature core area,low temperature core zone down,and finally become vertical gradient distribution,the horizontal direction of the same temperature characteristics.The characteristics of the water field are roughly the same,the vertical direction from the top down water content gradually increased,when the wind flow into the nearby area of the model,the corresponding position due to water evaporation rate increased,resulting in a local low water content zone.Based on finite element method,Comsol Multiphysics numerical simulation is used to solve the model material multiple-field coupling mathematical model.The characteristics of temperature field and water field distribution were obtained in summer without wind,wind in summer,plane model under wind-free environment in winter,and in the dry process of three-dimensional model during the spring-autumn and winter.the basic characteristics are consistent.The basic characteristic is that under different seasons,the distribution characteristic of water field is that the horizontal direction is roughly the same,the vertical direction gradually decrease from the top down,when there is ventilation,the moisture evaporation rate is higher in the ventilated position,which leads to the water content of this area less than the water content of the surrounding model material,by comparing the simulated and measured values in the curve with the change of water content over time,we can get a plane model with no wind in summer,windy in summer and no wind in winter,and the maximum deviation between the solution of the heat-moisture coupling model and the measured value is less than 23%. |
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