Pressure amplification effect of initial compression waves in circumferential cracks of high-speed railway tunnel linings

TLDR: In this paper , the authors investigated the aerodynamic amplification effect of the initial compression wave (ICW) in circumferential cracks induced by high-speed trains and found that the ICW may be the main cause of crack propagation and concrete block formation.

Abstract: Spalling of concrete blocks from tunnel linings is a severe defect in high-speed railway tunnels (HSRTs). The amplified initial compression wave (ICW) in circumferential cracks induced by high-speed trains may be the main cause of crack propagation and concrete block formation. To investigate the aerodynamic amplification effect of the ICW in circumferential cracks, tunnel-crack models are established and solved based on the unsteady viscous k–ε turbulence method. A scaled indoor experiment is carried out to verify the reliability of the calculation method. The characteristics of amplified pressure and corresponding mechanisms are analyzed and revealed. Three influential parameters, including the crack width, crack depth, and train velocity, are analyzed and discussed in detail. The main conclusions are as follows: (1) the maximum amplified pressure in a typical circumferential crack is 5.68 times that of the ICW. (2) The maximum power spectrum density (PSD) of the aerodynamic pressure at the crack tip is 91.04 times that at the crack mouth. The crack tip suffers most from the aerodynamic impact of the fluctuating component of pressure waves, whereas the crack mouth is most susceptible to the average component. (3) The train velocity is the most influential parameter on the maximum pressure at the crack tip, followed by the crack depth. The power function with an exponent of 2.3087 is applicable for evaluating the relationship between the maximum pressure and train velocities. (4) The train velocity and crack depth are most influential parameters to the maximum PSD. The relationship between the maximum PSD and the crack widths, crack depths, and train velocities can be reasonably described by the power function. (5) The mechanism of pressure amplification is as follows: first, the superposition of the internal energy possessed by air molecules near crack surfaces. Second, the increase in the internal energy of air near the crack tip because of the gradually narrowing space. The results of our research may be applicable in analyzing the cracking behavior of tunnel lining cracks and preventing the spalling of concrete blocks in HSRTs.