Field measurement and numerical simulation are performed on the distortion of a compression wave propagating through a slab-track Shinkansen tunnel of about 26 km in length, which is the longest tunnel on the ground in the world at present. The pressure of the compression wave is measured with 12 pressure transducers set along the wall inside the tunnel. In the numerical simulation, the distortion of the compression waveform is calculated by one-dimensional compressible flow analysis combined with acoustic analysis on the effect of side branches. The results show that the compression wavefront steepens in the early stage and smoothes down in the later stage of propagation.

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