22. Improvement of the effectiveness of tunnel entrance hoods by enlargement of their cross-sectional area to reduce micro-pressure waves

As Shinkansen running speeds increase, solutions have to be found to reduce micro-pressure waves emitted from tunnel portals. One approach is to install a tunnel entrance hoods on tunnel portals at the point of trains entry. As running speeds exceed 320 km/h however, the tunnel hood that would have to be added for these measures to be effective, would be longer than the 30-50m currently applied. This limitation added to the extra cost of extra work, and in certain cases, these countermeasures would not be feasible.

Consequently, model tests were carried out on new proposed designs (Figs. 1 and 2) that could be more effective unconcerned about the existing specifications (currently, the cross-sectional area ratio of the hood to the main tunnel are between 1.4-1.6, and openings are added to the side wall of these extensions).

Results of these trials showed that on hoods under 40 m in length, raising the tunnel-hood-to-extension cross-sectional area ratio to 2.5 increased the reduction effect compared to the existing design, even if side wall openings were closed (Figs. 3 and 4). For hoods of over 40 m in length, a graduated increase in this ratio over the length of the hood was even more effective (Fig. 4). The two proposed solutions with larger and graduated cross-section ratios offer the added advantage of not requiring side openings along the tunnel hoods.