| Up to now, the drainage and waterproof system design of most railway tunnels in China didn't consider the action of external water load, based on the principle of unlimited drainage, so a great number of railway tunnels have the problem of leakage water, some of which are very serious. Especially at the zone which has abundant water and carbonate rock in West China, owing to an inappropriate principle of the drainage and waterproof, water resource is running out and environment is worsening. With the development of tunneling technique, and in view of environment (especially water environment) protection, a principle of limited drainage on the basis of blocking water has been putting forward. The stability of lining structure and rock of tunnels should consider the action of external load. However, there is no theoritical basis for all this at present time.Taking Yuanliangshan tunnel on the newly built Yu-huai Railway for example, this thesis tries to solve the problem about design and external water load of railway tunnel lining structure at abundant water and karst zone. Firstly in the paper the research of external water load on tunnel lining structure in China, is summarized. Secondly, on the basis of seepage theory about ground water, the research way of tunnel rock seepage is investigated. Based on continuous porous medium seepage model, it is assumed that if waterproofing board of complex lining is perfect, the secondary lining is leakproof, thus the formula of external water load on secondary lining with a grouting loop is deduced. Through tunnel model test, the action law of external water load on secondary lining with a grouting loop is obtained. In accordance with Railway Tunnel Design Criteria, by using ANSYS FEM program, a comparative analysis of lining structure static behavior is carried out, which is considered both with external water load and without it. The main results of the paper are as follows:(1) The permeability coefficient of surrounding rock and drainage quantity of tunnel are two decisive factors of external water load of tunnel lining.(2) When tunnel water is blocked up fully behind the lining, water pressure on the lining will reach maximum at last so long as surrounding rock near the lining is infiltrative no mattter how much the permeability coefficient of surrounding rock is.(3) When the permeability coefficient of surrounding rock is over 10-4cm/s, water pressure on the lining will inevitably decrease until drainage quantity is large enough, having a large difference at every part of lining, which is minimum at the drainage part.(4) When the permeability coefficient of surrounding rock is under 10-4cm/s, water pressure on the lining will evidently decrease so long as drainage quantity is enough, having a little difference at every part of lining.(5) When the permeability coefficient of surrounding rock is under 10-4cm/s, water pressure near the lining is lower while it is higher far from the lining if the drainage system is open fully, the gradient of which is large in the surrounding rock.(6)According to test result and data, combined with water and geological feature of railway tunnel surrounding rock, a suggested table of decrease coefficient about external water load on railway tunnel lining structure is put forward.(7)As for the tunnel which is located at a karst zone with a complicated water environment, considering the safety of the tunnel structure and the result of test and calculation, the design of tunnels should be carried out with external water load.(8) As for the runnel which is located at a karst zone with a high water level, external water load is the main one, and rock pressure is secondary. The design of tunnel lining structure is related with the drainage and waterproofing system, lining structure shape, the permeability coefficient of grouting loop and so on, which should be carried out through special research and calculation. It is inappropriate by adopting present standard drawing briefly.(9)With the action of external...
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