[1] The tunnel, constructed by the Rhondda and Swansea Bay Railway, was engineered by Sydney William Yockney.
Progress was restored when the original contractor, William Jones, was replaced by Lucas and Aird, who brought in more men.
[2] By the 1870s, the volume of coal being extracted threatened to exceed the capacities of the Taff Vale and Cardiff Docks Railways.
A typical return journey that took two days because of congestion and inadequate handling was a hindrance to customers, particularly the coal shipping facilities at Swansea.
Early reports by Yockney to the R&SBR's directors were positive, ground conditions were favourable and there was little water ingress.
The tunnellers who worked from shafts driven into either end of the approach cuttings were equipped with compressed air-powered rock drills and were boring into the sandstone at 240 yards (220 m) per month.
[2] The tunnellers faced dire conditions, resulting in injuries and deaths, several due to rock falls and explosions.
The headings met on 16 March 1889 and were perfectly aligned, but the delays led to William Jones being stripped of the contract in favour of Westminster-based Lucas and Aird in September 1889.
[2] Between 1938 and 1953, around 500 steel ribs were installed to resist pressure which was causing inward movement of the side walls and pushing-up of the crown particularly towards eastern end.
More problems were caused by substantial water penetration from underground springs which weakened and washed out the mortar between bricks in places.
This conveniently coincided with the Beeching cuts and stations either side of the tunnel, (Blaenrhondda and Blaengwynfi), were closed at the same time.
[citation needed] In the long term, the society aims to raise money to reopen the tunnel as a cycle path.
Highways England is responsible for the tunnel and is unwilling to reopen it but is willing to transfer ownership to the Welsh government or local authorities.