Vibration Velocity, Earth Pressure, and Excess Pore Pressure Measured in Cyclic Dynamic Field Testing of Water-Rich Loess Tunnel for Passenger-Dedicated Line

Cyclic dynamic field tests simulating the high-speed train vibration effect were conducted in a water-rich loess tunnel (called Zhang Mao Tunnel) located on the Zhengzhou-Xi'an Passenger Dedicated Line with a design speed of 350 km per hour (km/h). The forced excitation tests were performed on the top of the backfill of the tunnel invert arch with 12 different vibration frequencies (5 to 27 Hz). During testing, measurements were taken at various locations below the tunnel invert for the vertical vibration velocity, the earth pressure, and the excess pore pressure. The testing results indicate that the maximum vertical vibration velocity at the excitation surface is approximately 1.55 mm/s. At the same depth, the vibration velocity increases with the vibration frequency. The increase is small when the vibration frequency is equal to or less than 21 Hz, but becomes greater when the vibration frequency is higher than 21 Hz. Under different vibration frequencies, the earth pressure versus depth remains basically unchanged. Under the constant vibration frequency, the earth pressure at the same depth remains basically unchanged for different loading numbers. Under cyclic loading, negative values for the excess pore pressure appear below the tunnel invert; but the absolute value is small.