| Natural loess is a porous medium composed of solid,liquid and gas phases,with developed pores and significant vertical joints.Due to the strong water sensitivity of loess,when wetted by water,it is easy to cause uneven settlement of foundation,house cracking and other engineering diseases.In order to eliminate the wetness of loess,the actual engineering often use strong ramming method to deal with loess foundation,but the effect of strong ramming method is closely related to the soil moisture content,natural loess moisture content is low,strong ramming method can not achieve good reinforcement effect.And the use of traditional pre-saturated water method to humidify unsaturated loess has a long humidification time,humidification uniformity is poor,and the scope is difficult to control and other problems.Therefore,some scholars propose a new method of using water vapor to humidify unsaturated loess.In this paper,based on the existing method of water vapor humidification and remodeling of unsaturated loess with vacuum pre-pressure technology,we propose a new method of water vapor humidification and remodeling of unsaturated loess under the condition of negative pressure applied to the surface layer of soil through a hollow cylinder with a hole only at the bottom side wall.Three different test conditions were designed according to the single variable principle to investigate the effect of negative pressure on the surface layer on the changes of moisture field and temperature field in the soil and the transfer effect of negative pressure in the soil under different water vapor pressure conditions.And the comparative analysis of water vapor humidification effect on unsaturated loess under the same water vapor pressure,surface normal pressure and negative pressure conditions was carried out.Finally,numerical simulations were carried out using Numerical simulation software in combination with indoor tests for two conditions with the same water vapor pressure and different negative surface pressure,and the results were compared with those of indoor tests,and the following conclusions were mainly drawn:(1)The negative surface pressure of the soil can be rapidly transferred within the remodeled unsaturated loess foundation,but the transfer effect is inversely proportional to the transfer path.During the test,with the diffusion of water vapor,the moisture content of the soil gradually increases,the pore liquid water content between soil particles gradually increases,the negative pressure downward transmission path is further blocked,affected by this,the deeper the value of air pressure within the soil,while the soil surface pressure is seriously affected by the negative pressure system,has been stable at about-10 k Pa,which has always maintained a large interlayer negative pressure difference with the deep soil body.(2)Water vapor through the bottom of the open-hole column humidification remodeling unsaturated loess test process,the three conditions of soil moisture content in the horizontal direction,the more distant from the humidification column soil,the moisture content of the initial change point later,the slower the rate of rise,the smaller the final moisture content value characteristics.In the vertical direction,the water content of the bottom layer under the condition of condition 2(negative pressure applied to the surface layer)was influenced by the negative pressure difference between the layers and the upward trend of water transport was increased,and the water content of each measurement point of the soil at a depth of 80 cm decreased slightly at the end of the test compared with that under the condition of condition 1(no negative pressure applied to the surface layer),and the water content of each measurement point of the soil at a depth of 20 cm increased slightly,and the water content of the soil in the model was more uniform.The diffusion pressure of water vapor increased to 100 k Pa under the condition of working condition three,and the negative pressure of the surface layer of the soil remained at-10 k Pa.The diffusion rate and the diffusion volume of water vapor outward during the test were significantly increased,and at the end of the test,the water content of each layer increased more than that under the condition of working condition two.(3)During the test,the temperature change inside the soil was closely related to the water vapor diffusion rate and soil water content.The more water vapor diffusion,the greater the water and heat transport,and the more water vapor adsorbed by the soil,the more obvious the water content and temperature rise.The greater the rise of soil water content,the more the pores between soil particles are filled with liquid water,the greater the heat transfer coefficient of temperature between soil bodies,the higher the heat transfer efficiency,and the higher the temperature of the soil body at the end of the test.The soil temperature field changes in the three working conditions are relatively similar,the more distant the soil is from the humidification column in the horizontal direction,the lower the final temperature value,and the closer the soil is to the water vapor diffusion hole in the vertical direction,the higher the final temperature value.(4)The numerical simulation results are in good agreement with the indoor test results.The simulation clouds of temperature field,moisture field and pressure field in the soil body can show that the change of temperature field is closely related to the moisture migration in the soil body.The change of pressure field is influenced by both temperature and moisture content in the soil,and the influence range of its cloud diagram lags behind that of temperature and moisture field. |
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