| Taking the water inrush section of 3 # and 4 # inclined shaft of Guanjiao Tunnel as engineering background,aiming at the characteristics of high water pressure,large flow,poor hydraulic connection and predictability with surface water in high water-rich limestone stratum,the water inrush mechanism of Guanjiao Tunnel Ridge limestone section is deeply analyzed,and the comprehensive construction technology of water-rich section is explored.The hydrogeological characteristics of Guanjiao Tunnel are investigated,and the stratigraphic lithology and geological structure are thoroughly studied.According to the existence and circulation of groundwater in aquifer medium,five conceptual models of hydrogeology are established.They are vertical water inrush model,horizontal water inrush model,deep circulation water inrush model,seasonal water inrush model and strong runoff water inrush model.According to the hydrogeological model of the cave body and the location of the water inrush,the water inrush mode is divided into the water inrush mode of the palm face and the water inrush mode of the cave body.The water inrush from fissure-karst zone and tectonic zone are two types of water inrush from the face of the palm,and the water inrush from the cave body is a water inrush phenomenon which occurs when the excavated cave body undergoes seasonal variation.Through continuous construction practice and experience summary,the comprehensive construction technology suitable for highland water-rich limestone tunnel is explored: 1.comprehensive advanced geological prediction scheme;2.grouting technology of water inrush mode in structural zone face;3.grouting technology of water inrush mode in seasonal zone hole body;4.grouting technology of water inrush mode in fissure-dissolution fracture face face;5.drainage measures of surface water._Comprehensive treatment measures such as reverse slope pumping and drainage technology for long inclined shaft.Through numerical calculation and experience summary,it is determined that the water inrush mode of structural belt type is mainly blocking,advanced curtain grouting is implemented,and the thickness of reserved safe rock disc is 3-10 m.Seasonal water inrush mode of tunnel body reduces the difficulty of construction by adopting post-grouting and construction in dry season.In order to ensure the grouting effect,the optimum grouting parameters are selected.The ratio of permeability coefficient of surrounding rock to permeability coefficient of grouting ring is not more than 4,and the thickness of grouting ring is not more than 6 m.Through on-site monitoring,the change characteristics of lining water pressure are found.During construction,the gushing water at the foot of the wall should be paid attention to,and the measures of water plugging and drainage should be strengthened.At the same time,the stress characteristics of lining under local high water pressure are analyzed.In order to improve the safety factor of lining structure,measures such as increasing lining thickness,increasing concrete grade and increasing reinforcement quantity are adopted,and the design parameters of lining are optimized.According to the unique hydrogeological conditions and water inrush mechanism in the water-rich limestone area of the plateau,the water inrush model of Guanjiao Tunnel is established.According to different water inrush modes,corresponding water control measures and lining structure safety measures are put forward,and a set of comprehensive water inrush construction technology suitable for super-long tunnel in Qinghai-Tibet plateau karst area in China is formed.It will certainly provide a good reference for the construction of extra-long railway tunnels in high altitude areas in the future. |
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