Study On Freezing Pressure Of Deep Shaft In Thick Alluvium

Since the beginning of the twenty-first century, coal mining at great depth is needed to meet the coal demand in China. Great depth brings complex geological problems in mine construction. The design of frozen wall and shaft lining is important in mine construction, and the reasonable evaluation of freezing pressure is the key to the safety of the shaft lining. The existing design theory which is based on the research of shallow mine construction is not applicable to the deep mine. Based on data of newly constructed deep mines in Huang-Huai area in China, freezing pressure and its influencing factors are studied systematically through experimental exploring, numerical simulation, theoretic analysis and in-situ measurement.Conventional geotechnical test and frozen soil physics mechanics performance tests have been carried out to obtain enough data for the following study. The results have been analyzed to have a good knowledge for the physical mechanics property of the frozen soil in thick alluvium. The results show that the physical mechanics property parameters vary with the temperature of the soil, and there are three stages for the creep of the frozen soil in thick alluvium. Because the third stage of creep character can not be ignored, the modified Nishihara model has been chosen to describe the property of the frozen soil in thick alluvium.The modified Nishihara model is not included in the existing finite element software. It is needed to add it to the materials of the existing finite element software. The finite element software ABAQUS was chosen to carry out the flowing study to calculate the viscoelastic plastic deformation of the frozen wall of the deep shaft in thick alluvium, and the software secondary development has been carried out for the above purpose. The subroutine of the nonlinear viscoelastic plastic rheological model was tested by the triaxial compression test results. The calculating results show that the development of creep is mainly related to deviation stress and coefficient of viscosity.Based on the results of the secondary development, the actual conditions of the excavation of the deep shaft were calculated. Results show the frost heave stress increases in the soil during the freezing process. The freezing pressure is related with the factors such as soil depth, soil frost heave ratio, the temperature of the frozen wall. The lower temperature of the frozen wall benefits the stabilization of the frozen wall. The soil depth and the high frost heave ratio are quite the reverse.Based on the viscoelastic plastic theory and the interaction mechanism of the surrounding earth mass, the frozen wall and the shaft lining in unload state, the equations for the frozen wall stress and displacement fields were established and the analytical solution of freezing pressure of deep shaft were derived. The results show the curves of the freezing pressure from the theoretical formula similar with those measured in situ. Both the theoretical analysis and the numerical analysis come to a conclusion about the influencing factors of the freezing pressure. Meanwhile stress fields of frozen wall can be obtained according for time-space effect.Temporal and spatial variations of freezing pressure are statistically analyzed based on a large number of measured data of both clay and calcareous clay. Grey relational analysis was used to find the important influencing factors of the freezing pressure, and based on which the empirical formula was supposed. The study shows the surrounding rock strength at the measured level and the circumferential nonuniformity of the frozen wall cause the spatial variations of freezing pressure. The soil depth, soil water content, the thickness and temperature of the frozen wall and the time period are all the important influencing factors for both clay and calcareous clay, but the soil water content is more important to calcareous clay than clay. Comparison of the curves of the freezing pressure indicates the numerical analysis is the most effective way to obtain reasonable results of the freezing pressure.