Ricken Tunnel

During January 1904, construction of the tunnel commenced. Its excavation proceeded at a rapid pace, to the extent that a record was set in the process.[3] During the boring process, workers encountered pockets of natural gas as well as traces of oil.[4][5] The tunnel proved to be relatively dry, with the use of cement drainage proving sufficient to handle the levels of water infiltration present.[6] On 30 March 1908, breakthrough was achieved in the Ricken Tunnel.[7]

The complete tunnel was first opened to traffic on 1 October 1910. Prior to its electrification, the line was initially operated by steam locomotives; during this period, the Ricken Tunnel acquired a negative reputation because of its relatively steep gradient and the lack of adequate ventilation, which caused smoke to accumulate and linger within it. No substantial alterations were made to the tunnel to address its apparent ventilation issues prior to a fatal incident occurring.

On 4 October 1926, a steam hauled freight train stalled while inside of the tunnel whilst attempting to ascend the gradient; this unplanned stop was a result of the use of the poor quality briquettes that were being used as fuel for the locomotive. Despite multiple attempts to rescue the train crew, a total of nine railway employees died of carbon monoxide poisoning, which included three of the rescuers.[8] As a consequence, both the line and the tunnel were promptly electrified during the following year.[9][10]

Portal of the Ricken Tunnel, note the presence of the overhead electrification apparatus

Since the tunnel's original construction, it has been subject to repeated remedial repairs over time. These have been partially attributed to the surrounding geology, which consists of a high proportion of clay minerals and anhydrite rocks, that absorbs water and swells, with the dimensional changes causing damage to the tunnel walls.[11] These repairs have sometimes necessitated temporary closures of the Ricken Tunnel; during these periods of unavailability, rail-replacement buses via the Ricken Pass have been provided for the use of the travelling public.[12]

During the 1990s, an energy capturing heat pump was installed at the southern portal of Ricken tunnel to function as a source of geothermal energy; by 2003, it was reportedly providing 501 kWt of energy to heat several public buildings in the neighbouring village of Kaltbrunn. This apparatus does not interfere with its use as an active railway tunnel.[13][14]