Study On The Features Of Concrete Structure Of Tunnel Lining Under High Hydraulic Pressure

Various degrees of damages appear in the operation of tunnels, including the deterioration of concrete, steel bar corrosion, serious seepage of water and so on,prevent them from working normally. The tunnel lining in the high water pressure sections is under the pressure of surrounding rock and external water. Because of the permeability of concrete, the seepage of groundwater in the cracks and pores of concrete brings pore pressure. In addition, the complicated environment of the tunnel and large amount of corrosive ions in groundwater will cause corrosion to the concrete lining.Tunnel lining concrete carbonization and steel bar corrosion which cause the reduction of concrete strength and increasing of concrete porosity may help seepage of water under the water pressure. And the interaction of seepage field and stress field of concrete affect the damage development. This dissertation analyzes the influence of the complicated environment of the tunnel on the concrete lining durability damage and the impact on the development of damage of the lining crack depth under the tensile stress and compression stress according to the theory of fracture mechanics. Besides an research of the coupling between the seepage field and stress field of the internal lining concrete under the action of water pressure and the finite element software ABAQUS is applied to analyze the influence on the damage of concrete of the coupling effect of seepage and stress. Main work and achievements of this dissertation are as follows:â‘  In the operation of tunnels in China, highway tunnels attracts much attention.With the growing of traffic volume, the acid gas accumulation in the tunnel increases,which accelerates the carbonization of lining concrete and reduces the working performance of concrete. When a tunnel locates a district with rich water, the steel bar in the reinforced concrete may rust because the numerous erosion ion in the water. And the rust of steel bar will lead the reduction of the effective bearing area between concrete and steel bars and the increase of damage. Besides the damage model of concrete carbonation and steel bar corrosion are established.â‘¡ Based on the principle of fracture mechanics, the analysis of impact on the damage of the lining structure of the crack depth according to the stress intensity factor.The stress intensity factor is an important factor to judge the instability of the lining structure and its value is proportional to the axial force and bending moment of lining in tension and bending moment. During the early development of the crack, the influenceon the concrete damage of the crack depth is weak and slowly growing, but to a certain extent the stress intensity factor mutates, a very small expansion of depth will exacerbate the damage of concrete lining until penetrated cracks arise and cut down the carrying capacity of the lining sharply.â‘¢ The initial damage of concrete such as micro cracks and micro pores gradually expand in the environment and the surrounding pressure. The high water pressure promotes permeability. Tunnel lining concrete seepage field and stress field interact affecting the development of damage. In this dissertation, the coupling between the seepage field under the high water pressure and the stress field of the lining concrete is established as well as the relationship between the seepage coefficient, the stress and the damage. With the help of the finite element software ABAQUS the tunnel lining concrete under high water pressure was simulated, and the conclusion that damage of the lining concrete appears in arch waist under the coupling between the seepage field and the stress field is obtained. And the results show that the injury on regions of the medial tunnel lining develops first and the damage, the equivalent plastic stress and the seepage coefficient are related to some extent.The research of this dissertation can provide evidence for where and when put the devices for the damage detection in a tunnel to take effective measures to prevent the lining from damage.