Study On Structural Analysis Methods Of Hydraulic Pressure Tunnel Linings

With the successive construction of a large number of diversion type power stations and pumped storage power stations, more and more high pressure tunnels are needed to be built. The types and analysis methods of the lining are both very important for safe operation of the pressure tunnels. Taking a hydraulic tunnel as the prototype, the lining was calculated and reinforced based on surface force theory and body force theory, respectively, and this paper studies reinforcement of reinforced concrete lining under two theories. In addition, in the case of weak rock, steel liner with reinforced concrete was chosen and analyzed through elastoplastic finite element method. The main work and conclusions are summarized as follows:(1) The research progress in hydraulic tunnels was first introduced, and the calculation methods for high pressure tunnels with reinforced, concrete lining and with steel liner were reviewed and compared. The stress and deformation of steel lining reinforced concrete pressure pipes used in Savimbi River Hydropower Station were simulated through ANSYS software. Its good numerical results showed that the finite element method can effectively simulate the entire process of concrete elastic-plastic-cracking and steel elastic-plastic-yield, until the capacity of carrying loss. Compared with the method of structural mechanics and elastic mechanics method, finite element method is more able to reflect the stress and deformation of the pipe structure.(2) Hydraulic tunnel lining of reinforcement was analyzed separately in the 62m and 200m water pressure. The results showed that: surface force theory is more suitable for the analysis of low-head pressure tunnel lining. In order to meet the design requirements of crack, a lot of steel needed to be configured when high pressure tunnel linings are reinforced by surface force theory, which does not meet the actual stress conditions of high pressure tunnel concrete linings. So, internal water pressure should be used as a volume force.(3) A high pressure tunnel concrete lining was analysis based on body force theory, the results showed that: surrounding rocks bears most of the load, while lining bears only a small portion of the load; only by increasing the area of reinforcement steel to reduce stress or crack width has little effect, while the permeability of the lining surrounding rock significantly affect the calculation results. Therefore, consolidation grouting and other measures should be the focus of our consideration of measures to enhance the integrity of the surrounding rock, elastic resistance and impermeability.(4) A underground pipe was simulated by ANSYS software using the elastoplastic finite element method. The results showed that: backfill concrete under 200m of water pressure has been completely cracked, and the concrete after cracking has been basically unable to bear the hoop tensile stress, but can transmit radial stress, most of the water load is borne by the steel liner and surrounding rock. The steel liner can effectively prevent leakage. For Class IV, V surrounding rock, steel lining is recommended in order to avoid leakage problems affecting plant operation.(5) The initial gap between steel liner, concrete and surrounding rock has a relatively large impact on the stress of steel liner, so the construction processes need to ensure the quality of backfill grouting in order to minimize the initial gap.