Study On The Technology Of Limited Discharge In Subject To Deep Buried And Water-Rich Tunnel

As the main battleground of infrastructure transfers to the central and western regions of China, the complex geography and landform make the proportion of bridges and tunnels in the whole line jump sharply, the length of tunnel longer and the phenomenon that tunnels encounter geological hazards such as big water inrush and high pressure when they pass through karst and water-rich regions becomes more common, which it more important to tackle water-proof and water drainage. The drainage principle "limted discharge" is usually used to ensure the safety of tunnel structure and reduce the external water pressure on the lining structure exerted by the groundwater in the past, but the mass water treatment not only wastes water but also disturbs the balance of water resource in the region where the tunnel passes through, which makes the level of groundwater drop in different degrees and affects water supply on people life and production nearby, so the principle "limted discharge" in becoming more and more popular and technology of limited drainage need to be improved further with the lapse of time.Relying on the Taihang mountain tunnel-the control project of south-central railway (line only for coal transportation), the functional relations between the variances such as external water load, the flow of water, permeability coefficient of grouting circle, the thickness of grout, hydrostatic head are deduced by establishing flow mode of deep buried and water-rich tunnel and techniqueflow of limited water drainage is enacted through debates about the relationships of variances combining with the hydrogeological parameter of the tunnel. From the design of water drainage value to permeability coefficient of grouting circle and thickness of grout enacted through acceptable external water load on the structure gained by numerical simulation by ANSYS software and put forth considering durability in operating period, the results are applied to Taihang mountain tunnel successfully and the techniqueflow of limited water drainage is displayed perfectly. Through field monitoring and measurement of structural section, external water pressure and flow of water to test the effect of limited drainage measurement, the conclusions are derived as follows:(1) The research of the relationship between flow of water and grouting circle finds that if the thickness of grouting circle is thicker or the permeability coefficient of the grouting circle is smaller, the water flow of tunnel will be smaller. The thickness of grouting circle and the permeability coefficient of the grouting circle can be control to control water flow, but institution of the parameters of grouting circle should combine with the geological parameters in specific engineering. Taking the Taihang mountain tunnel as an example, the increase in the thickness of grouting circle contribute little to the decrease of water flow when the thickness is more than 6 meter; Decrease in the permeability coefficient of the grouting circle contribute to the decrease in water flow significantly when the thickness is no more than 3 meter, but the contribution is not significant any more when the ratio of permeability coefficient of surrounding rock to grouting circle is bigger than 40. So the thickness of grouting circle and permeability coefficient have a reasonable range and the variance of grouting parameters should be considered in combination with the project cost.(2) The research of the relationship between external water load and grouting circle finds that the external water pressure on the lining will be smaller when the coefficient of the grouting circle is smaller and the thickness of grouting circle is thicker if the capacity of drainage is constant, so grout curtain can not only plug the water but also decrease the water pressure.(3) The research of the relationship between external water load and drainage capacity finds that the external load behind the lining is linearly with drainage capacity when the permeability coefficient of grouting circle is constant, that is, the drainage capacity is bigger while the external water pressure is smaller. All the accumulated water behind the lining can be drained when the drainage capacity Q is big enough, making the external water load drop to zero; the coefficient of the grouting circle is smaller while the external water pressure is smaller when the drainage capacity is constant. But when the drainage capacity is zero-not any drainage system the water pressure H1 behind the lining will drop to the original hydrostatic head H no matter how small the coefficient of the grouting circle. The combination of drainage and coefficient of the grouting circle is a must to control the external water pressure behind the lining for the external water pressure cannot be dropped just by the control of coefficient of the grouting circle.(4) Considering effect of lifecycle and duration of tunnel, the accumulated water behind the lining caused by the blockage of drainage system can generate water pressure. Water pressure withstanding lining should be constructed as safety reserve in case of the invalidation of drainage system. The constitution of specific hydraulic load should combine with cross-sectional structure.