Track irregularity is an important factor of train induced ground vibration, and sometimes causes strong ground vibration. For example, track irregularity due to corrugated rail increased 16 to 31.5 Hz components of ground vibration more than ten decibels on a shallow freight train line tunnel. To estimate the influence of track irregularity, we performed a parametric study using a program for solving coupled vibration of moving-vehicle and structure. We at first confirmed the accuracy of the program by comparing measured and calculated vibration of an in-situ measurement site. In the parametric study, we calculated the acceleration of roadbed caused by sine wave form track irregularity with various wavelength and amplitude. As a result, track irregularity amplitude was found to have certain threshold value. If track irregularity amplitude is larger than the threshold, roadbed acceleration increases as the track irregularity amplitude increases. However, if track irregularity amplitude is smaller than the threshold, roadbed acceleration is almost independent to the amplitude of track irregularity. The threshold amplitude corresponds to the balance point of static axle load and inertial force excited by the track irregularity.
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