| This thesis is supported by“The present situation and countermeasures of well construction technology in the western region” and“The research and engineering application of freezing shaft lining design in the Western Region”,focusing on task one,“ Geological and surrounding rock characteristics of shaft shaft in western region”,taking weakly cemented sandstone as research object,the aim of this thesis is to develop a new method for preparing weakly cemented sandstone in laboratory,which is based on the principle of thin-layer stacking-selective hot-pressing sintering,the method of hot pressing sintering of granular bulk was studied by means of numerical and physical experiments,it provides theoretical guidance for the preparation of remolded sandstones with the same composition,content,intergranular porosity and cementation characteristics as the parent rocks.Firstly,based on the momentum equation and heat conduction equation,the coupled diffusion equation is established,and the coupled equations are solved by COMSOL,the joint phase-field method was used to visualize the formation and growth of the intergranular sintering neck,and the relationship between the size of the intergranular sintering neck and the sintering parameters in the Quantitative analysis two-particle contact model was investigated.Then,the physical experiment of Hot Pressing Sintering is carried out,the characteristics of intergranular porosity and cementation were analyzed and evaluated by means of XRD,NMR,Microscope and splitting test.The results show that selective sintering can keep the main material composition of particle accumulation unchanged before and after sintering.When the mixture ratio of particles or sintering pressure is fixed,the porosity of sintered samples decreases with the increase of sintering pressure or the content of molten particles.When the particle mixing ratio or the sintering pressure is fixed,with the increase of the sintering pressure or the content of the molten particles,the relative proportion of the large pores in the sintered sample gradually decreases,and the relative proportion of the small pores gradually increases,and the overall pore diameter of the sample gradually decreased.The relationship between the proportion of the fracture surface of the fused phase cementation on the fracture surface of the sintered sample and the sintering pressure and the content of the fused particles is linear,the tensile strength of sintered samples can be deduced by the ratio of the tensile strength of the fused particle cement and the breaking surface of the glass powder cement to the total breaking surface of the samples.Finally,the numerical model of particle packing is established,and the improved calculation method of sintering neck volume is studied,combined with the simulation results of thermo-mechanical-diffusion coupled phase field model,the density of sintered samples was obtained by counting the number of particles in contact,the particle size and the contact pressure on both sides of the contact point.By comparing the densification results obtained by numerical experiment,physical experiment and densification equation deduction,the reliability of the results obtained by numerical experiment and physical experiment is verified.Considering the unfavorable factors such as the formation of pores and the limitation of the applicable conditions of the densification equation,the numerical results are treated with the mean value of the physical results,then,a method for predicting the density of granular bulk after sintering under different experimental conditions was established.The preliminary results show that the sintered samples with the lowest porosity of 20% and the lowest tensile strength of 1.0 MPa can be obtained by selective hot-press sintering with high and low melting point particles by controlling the low sintering pressure and the content of molten particles.The research results will lay a theoretical foundation for further quantitative control of pore characteristics,cementation characteristics and macro-strength characteristics of samples after hot-press sintering. |
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