| At present,China’s thermal power generation with coal as the main fuel still occupies the first place in the power generation of the whole society,which brings hundreds of millions of tons of desulfurized gypsum industrial by-products every year.If desulfurized gypsum is applied to green building materials,it will not only It can solve the problem of environmental pollution caused by the accumulation of a large amount of desulfurized gypsum,and can further increase the value of industrial solid waste,meet the needs of social development and construction,and realize the harmony and unity of environment and development.Permeability is an important attribute of material transport in porous media,so it can be used as an important indicator of durability performance.In underground engineering,structures are often faced with complex geological environments such as in-situ stress and osmotic pressure.In engineering applications,if you can grasp the evolution mechanism of permeability,it can provide a certain theoretical basis for the actual engineering scheme design.This paper takes the modified desulfurized gypsum-based concrete as the research object,explores the permeability evolution law of the specimen during confining pressure loading and unloading under different stress states,and explores the modification under hydraulic coupling through laboratory tests and particle flow discrete element numerical simulation methods.The evolution mechanism of permeability of desulfurized gypsum-based concrete,the main research contents are as follows:(1)The microstructure and physical and mechanical parameters of modified desulfurized gypsum-based concrete were obtained through laboratory tests,and the pore water pressure was 0.25 MPa,0.5MPa,1MPa,2MPa,3MPa,4MPa and the confining pressure was 5MPa,7MPa,10 MPa,14MPa,19 MPa,25MPa,and 30 MPa confining pressure loading and unloading seepage tests,the overall permeability decreases with the increase of confining pressure,showing a negative exponential relationship.According to the stress sensitivity analysis,the loading stage is divided into high sensitive area and medium sensitive area and low-sensitivity areas,where the corresponding volumetric strain and permeability change rapidly,moderately and slowly.Although the permeability recovers in the unloading stage,it is far from reaching the permeability value in the loading stage.Under the same confining pressure,because The pore water pressure can change the internal structure of the specimen and reduce the effective stress to a certain extent,and the permeability of the specimen will increase with the increase of the pore water pressure.(2)Conduct low-field nuclear magnetic resonance tests on modified desulfurized gypsum-based concrete to obtain the pore structure characteristics of the specimen,and study the relationship between the microscopic pore structure and permeability of modified desulfurized gypsum-based concrete materials,based on the Katz-Thompson model and the dual porous medium model The formula for the relationship between confining pressure,pore water pressure and pore model constants is established,and a permeability prediction model considering the effects of confining pressure and pore water pressure is deduced.(3)Using discrete element software combined with image recognition technology,a hydraulic coupling numerical model of modified desulfurized gypsum-based concrete was established.After verifying the degree of agreement between the numerical model and the laboratory test results,the changes between the stress field and the opening of the fluid channel were compared From the mesoscopic point of view,the evolution mechanism of the permeability of modified desulfurized gypsum-based concrete under the action of hydraulic coupling is analyzed.The most fundamental reason for the change of permeability caused by the effect of confining pressure and pore water pressure is that the stress field will affect the Influencing the opening of seepage channels.Figure 70 Table 15 Reference 111... |
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