| Since the 21st century,the mining depth of newly built coal mines in Western China has been increasing,and most of the coal mines pass through the Cretaceous-Jurassic deep coal measures.Because the geosphere is mostly sandstone,conglomerate and sandy mudstone,with the characteristics of muddy cementation,water and desertification mudsification,and poor pourability.The rockshaft of vertical shaft in aquifer bedrock section is mostly constructed in the freezing method.Since there lacks the in-depth studies on the bedrock freezing in this area in China,the design of the freezing shaft still refers to that in the eastern region,The design external load on the shaft wall results in the unreasonable selection of the structure form of the shaft wall.The thickness of the shaft wall is not thick or thin,and the contradiction between safety and economy is prominent.Therefore,it has important theoretical significance and application value to study on the forming mechanism of external load on freezing shaft in the aquifer bedrock section of western area,not only for the scientific design of the shaft wall of freezing shaft in this area,but also for the coordination and unification of security and economy.We selected the medium-coarse sandstone samples of the Jurassic main aquifer zhiluo formation in the western region,and analyzed the mineral composition and microscopic pore structure through XRD,NMR,SEM and testing and observation of casting thin-sections of rocks.We conducted uniaxial and triaxial compression tests with the help of MTS 816 electro-hydraulic servo rock mechanics test system,and obtained the mechanical properties.And based on results of triaxial compression test,we revealed the deformation mechanism of weak cementation sandstone.We also deeply analyzed the hydrological and engineering geological characteristics of the Baiji-Jurassic strata,and gave the range of the parameters such as permeability,elastic modulus and Poisson's ratio.We deeply analyzed the loading characteristics of the inner and outer wall of the freezing shaft before and after the freezing of the freezing wall of aquifer bedrock,based on the principle of interaction,established the external load evolution model of the shaft wall,and obtained the evolution theoretical solution of the stress between shaft wall and surrounding rock and the external load on shaft wall,and based on which we calculated and analyzed the formation process of the external load onfreezing shaft in the aquifer bedrock.We established a seepage-stress coupling model,and numerically simulated the stress between the shaft wall and surrounding rockduring the construction process of the freezing shaft and the evolution process of theexternal load on shaft wall,which was verified by the model test.Based on the generalized effective stress principle and the seepage theory,weconstructed the analysis model of the external load on single-layer shaft wall under theaction of surrounding rock and shaft wall,and gave the analytical solution of theexternal load on shaft wall.And we had verified the correctness by comparing with theclassical solution and engineering measurement.Combined with the characteristics ofthe water-rich surrounding rock in the Northwest,we discussed the range of externalload on shaft wall in the actual project.The research showed that,in the close-attachstate,the hydraulic pressure reduction coefficient in the outside of shaft wall ? areclosely related the permeability ratio of surrounding rock to shaft wall Kr/Kc,and thatthey are proportional to each other;and that when is in the range of 100 to 10,in thewall-mounted state,the calculated value of ? is between 0.422 and 0.879,and thatthe common value of ? is between 0.5 and 0.9;and that in the off-wall state,the limitvalue of ? is 1.0.In the wall-mounted state,the external load reduction coefficient?of shaft wall ranges from 0.496 to 0.963,and the common value of that is 0.5 to0.9.In the off-wall state,? ranges from 0.520 to 1.0,and the common value of thatis 0.5 to 1.0.Based on the analysis of the external load on the single-layer shaft wall,weestablished an analytical model for the external load on the double-layer shaft wall,gave the stress conditions of the wall-mounted and off-wall shaft wall,and obtainedthe analytical solution of the external load on the double-layer shaft wall,and based onwhich,we discussed the formation mechanism of the external load on the double-layershaft wall through the analysis of influencing factors.The analysis results showed thatwhen the permeability of the inner wall is consistent with that of the concrete material,the common range of the water pressure reduction coefficient of the inner wall is0.233-0.6138;and that the external load reduction coefficient of the inner wall rangesfrom 0.46 to 0.79,when the outer wall and the surrounding rock are in close-attachstate;and that the common values of external water pressure and external load on the inner wall of double-layer shaft wall are smaller than that of single-layer shaft wall.Figure[70]Table[18]Reference[170]... |
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