The generation of tunnel lining erosion affects the overall safety performance of the tunnel lining. Therefore, prevention of tunnel lining erosion should be done well. In fact, the main reasons for the erosion of the tunnel lining are the existence of corrosive media; the existence of easily corrosive substances; the existence and mobility of groundwater. Let’s analyze the specific causes of erosion and the corresponding preventive measures.
Causes of tunnel lining erosion
The corrosive environmental water behind the lining easily seeps along the lining pores, working joints, deformation joints and other holes to the inside of the lining, which becomes tunnel leakage water, which can cause physical or chemical effects on the lining concrete, stone masonry, and mortar joints. Corrosion, causing corrosion of the lining. Where there are geographic conditions such as coal series strata, sulfide mineral strata, gypsum-bearing strata, salt strata, silt peat strata, saline soil, salt fields, sea water and infiltration ranges, etc., areas that may cause environmental erosion and damage to concrete should be treated. note.
Tunnel lining corrosion is divided into physical corrosion and chemical corrosion. There are two main types of physical erosion: frost heave cracks at the alternate freeze-thaw area and salt crystal cracks at the alternate dry-wet area. Chemical attack is a very complex physical and chemical process. Based on the research results at home and abroad, according to the main material factors and corrosion damage mechanism, it can be divided into five types: sulfate attack, magnesium salt attack, dissolution attack, carbonate attack and general attack.
Three elements that produce corrosion:
The presence of corrosive media; the presence of easily corrosive substances; the presence and mobility of groundwater.
Corrosion of the tunnel lining makes the concrete loose and its strength decreases, which reduces the load-bearing capacity of the tunnel lining. It also causes corrosion of steel rails and fasteners, shortens the service life, and endangers driving safety. In order to ensure the safe use of tunnel buildings, lining corrosion diseases should be actively prevented.
Preventive measures for tunnel lining erosion
It is necessary to start with a good survey and design, master the engineering geology and hydrogeology data of the tunnel, find out the source and composition of the corrosive medium in the environmental water, and take preventive measures according to local conditions based on the correct determination of the degree of erosion of the lining concrete . Aiming at the causes and conditions of tunnel corrosion. At present, the main prevention and control measures taken for tunnel erosion are as follows.
(1) Improve the density and integrity of the lining.
(2) The method of admixing materials.
(3) Use corrosion-resistant cement.
(4) Strengthen the external drainage measures of the lining.
(5) Use dense materials that do not chemically interact with concrete, and make an isolation and waterproof layer on the outer surface of the lining.
(6) Use natural stone that does not chemically react with corrosive environment water to build the lining.
(7) Inject anti-corrosion grout to the back of the lining.
(8) Anti-corrosion concrete.
The anti-corrosion layer is a method of treating the surface of concrete. Various corrosion-resistant materials are laid on the surface of the lining concrete to make it a layer of anti-corrosion layer. The tunnel lining generally adopts a combination of anti-corrosion layer and waterproof layer, and is laid on the outside of the lining.
Selection of anti-erosion cement materials: sulfate-resistant cement and pozzolanic cement have good resistance to sulfate and seawater corrosion; bauxite cement has strong resistance to various chemical corrosion; pozzolanic cement is resistant to various chemical corrosive media It also has good resistance, and the price is cheap. It is suitable for use in medium and low corrosive media, but its frost resistance is poor, so you need to pay attention to it when using it. For tunnels resistant to sulfate erosion, it is better to use low-alkali and high-sulfate-resistant cement when grouting and pouring concrete; for operation and maintenance, maintenance, plugging, plastering, spraying concrete or mortar, it is better to use double fast cement .