Study On Stress Characteristics Of Inclined Shaft In The Process Of Saturated Sand Thawing

In order to exploit coal resources in Jurassic coalfields in Northern Shaanxi Province,the shafts often need to cross the thick and saturated fine sand layer of quaternary.In order to find out the causes of cracking of shaft wall and water bursting sand in the thawing stage of the stratum,to ensure smooth construction of follow up inclined shaft in this area,the deformation characteristics of the inclined shaft in the thawing process of frozen saturated sand are studied in this paper.Based on the characteristics of freezing and excavation support in inclined shaft freezing construction and the freezing project of the main inclined shaft of Yuandatan Coal Mine in Northern Shaanxi,the temperature field of the freezing wall and the stress field and strain field of the inclined shaft during the process of thawing are studied by establishing the prediction model of temperature field and carrying out the indoor physical test and numerical simulation and so on.The main contents are as follows:(1)Study on the thawing temperature field of frozen wall is the premise of the study of mechanics and deformation.The main sources of heat needed during the thawing process of the frozen wall are analyzed.According to basic theoretical knowledge related to heat transmission science,by simplifying and modifying the hot sink model of the infinite long line and considering the heat exchange between wind and wellbore,the prediction model of freezing wall temperature field of inclined shaft in the stage of thawing is deduced.(2)According to the method of dimensional analysis and related phase transition temperature field theory,by simplifying some conditions of the freezing engineering of the actual inclined shaft,the physical model of the stress and deformation characteristics of the inclined shaft in the process of the thawing of saturated sand is established and the changes in the external load and the temperature field of the frozen wall during different stages of the freezing process is simulated.The results show that the temperature change trend in the early phase of phase transformation can be roughly divided into three phases: fast growth,slow growth,stable.The change trend is basically consistent with the results of the temperature field prediction model.With the progress of thawing,the external pressure in the different directions of shaft lining are increasing.In the same section,the pressure at the bottom is the largest,the pressure at the right side is the smallest,and the pressures at the top and the left are close.(3)Based on the order of the thawing of two freezing units during the freezing construction of inclined shaft,a numerical simulation model of inclined shaft crossing saturated sand with two adjacent frozen sections is established.The variation of temperature field and stress field with time when the last freezing unit has been thawing and the next freezing unit is maintaining is simulated.According to the results of numerical simulation,the external load of the shaft wall increases gradually and the pressure of the bottom is the largest during the thawing process.Tensile stress appears on the inside of the bottom and top of the plate and the outside of the lateral wall.The tensile stress range does not expand outward during the thaw process,and the tensile stress value increases significantly.According to the results of this study,the external load of the shaft wall increases gradually and tensile stress may occur in the top and bottom and the side wall of the shaft.The results of theoretical calculation and numerical simulation basically agree with the measured data of model test.Therefore,the research results in this paper have certain guiding significance for the future design and construction of inclined shafts using artificial freezing method in saturated sand layers and similar areas.