Crack Control Of Tunnel Concrete Lining And Finite Element Analysis

Tunnel lining as a barrier against kinds of diseases, which plays an important role for the safety and durability of tunnels, has protective anti-damage ability to resist the erosion of water, salt spray and vehicle exhaust, and supports and stabilizes surrounding rock. This paper focused on the incorporation of the mechanical properties, expansion and deformation properties of the lining concrete with new material, and analyzed tunnel’s loading situation, and computed the stress distribution and cracking simulation of tunnel lining concrete structure with expansion agent under load by finite element analysis. Main contents and conclusions are as follows:(1) Mechanics and crack resistance of lining concrete with calcareous-magnesium expansive agent was studied, and the results show that in the range of 0%-5%, the compressive strength is directly proportional to the amount of expansive materials, and when the dosage is 5% to 8%, it can be seen that there exists inverse proportions between compressive strength and the amount of expansive agent. It can be seen that the concrete strength reaches the maximum with the admixture of 3.94%-4.73% and reaches the minimum with the admixture of 7.1%-7.6%; with the increase of expansive material amount, the elastic modulus of expansive concrete increases as that of amount, but the growth rate decreases with the amount. There is a linear correlation between the compressive strength and elastic modulus of concrete tunnel lining material. Compared to the reference concrete, the cracking time of expansive concrete is later with the delay time is up to 45.1%, cracking area decrease more than 50%, and the number of cracks is reduced by 43%. It shows that the crack resistance of expansive concrete is higher than that of reference concrete.(2) The deformation performance of lining concrete in different humidity and curing conditions was studied, the results shown that concrete expansion capacity of concrete in all ages was inversely proportional to the restraint quantity. The amount of reinforced concrete deformation and restrained deformation under dry conditions is less than free deformation by 80.4% and 61.4%. The expansion of concrete in water is higher than that in standard condition by 17.2%-20.3%. Dry conditions lead to shrinkage of concrete, and the deformation of concrete with expansive material can be reduced by up to 25.5%. The TSTM experiments show that the maximum pressure, stress and stress concentrates of concrete with expansive agent are lower than the concrete with expansive agent which cracking temperature is reducing more than 5℃.(3) The finite element simulation shows that principal stress is largest in the corner parts and the cross in the top of tunnel lining. The maximum axial force occurs in the wall at the bottom; the largest deformation appears in the bottom and the middle of the cross at the top. The cracking area and degree were decreased with the incorporation of expansive material.