Yamate vs Zhongnanshan: length, opening date and class compared

• 5entries listed

Side by side

Yamate is recorded on data/tun10.html and Zhongnanshan on data/tun10.html, compiled to the same convention, which is what makes the two figures comparable at all.

How this archive measures: lengths, bores, dates and ordering

How this table is compiled

Yamate and Zhongnanshan are compared here on the figures this archive records for each, taken from the same sources and the same measurement convention. Yamate belongs to the 2010s and Zhongnanshan to the 2000s, two decades in which what a tunnel had to provide by way of escape and ventilation was not the same thing.

Yamate is the longer of the two at 18.2 km, ahead of Zhongnanshan at 18.04 km, a difference of 0.16 km. Driven end to end the two would run 36.24 km, which is the figure to hold against the 24.51 km of the longest single road tunnel in the record.

That gap is about 1 per cent of the longer bore, which is the figure worth holding on to rather than the raw metres. Both rows are reachable from the road tunnel table they were taken from, where the note column carries the tube count, the gradient and any reconstruction Yamate or Zhongnanshan has had.

Across every class this archive records, Yamate stands 42nd by length and Zhongnanshan 44th, so the pair sits inside the top 44 of 244 structures. 32 other structures in this record opened within two years of Yamate, which is the cohort it was designed alongside and the fairer comparison for how it was built.

Counting every class, 1 recorded structures fall between these two by length; the comparison is a window on that part of the record rather than a gap in it. Both pass ten kilometres, which 161 of the 244 structures recorded here manage, so this is a comparison inside a small group rather than across the field.

Reading the figures

The 2000s account for 53 entries in this archive, and Zhongnanshan is one of them, which is the context a single opening date does not carry on its own. Subaqueous tunnels are governed by rock cover above the bore rather than by the depth of water above that, which is why depth and length are separate records.

An immersed tube is built on land and sunk into a dredged trench, so its length is fixed before it reaches the water. The longer bore is not the harder job. Ventilation shafts allow a longer bore to be driven, and their absence is often what caps a tunnel's length rather than money or ambition.

Both are recorded in this archive as road tunnels, so the measurement convention is identical and the comparison is direct. Yamate was designed under the modern regime, with cross-passage spacing and emergency ventilation specified from the outset. Toll revenue is usually pledged against the debt that built the crossing, and the toll ends when the debt does.

Among the road tunnels this archive records, Yamate stands 3rd by length and Zhongnanshan 4th, adjacent in the ranking. 41 recorded structures are longer than Yamate, the nearest of them Qinling I-II at 18.46 km. Pumps run for the life of a subaqueous crossing and are the one system that is never switched off.

A pilot bore driven ahead of the main tunnel is usually kept afterwards as the escape route. Length is measured portal to portal. Gradient limits are the main reason a railway crossing runs longer than a road crossing of the same range. Salt water attacks reinforcement differently from fresh, and subsea linings are specified accordingly.