Tidenham (Denhill) Tunnel

Tunnelling through rivers and limestone ridges

S H Yockney & Son of Westminster, the appointed engineers, received Parliamentary approval in August 1866, but to no avail. Due to banks collapsing, this, among many other railway proposals were put on the back burner.

In 1872, a revised route was agreed that crossed the river Wye east of Tintern and ran south on a ledge that cut into the steep slope on the English east bank.

However, the Duke of Beaufort insisted on a line that passed through Tintern village and the construction of a goods branch to serve the wireworks there. This was authorised in June 1875 by means of the Wye Valley Railway Amendment Act.

Construction work on the main line got underway at Tintern on 26 May 1874, with Messrs Reed Bros & Co appointed as the contractor.

The greatest engineering feat - a lengthy single-track tunnel - would be driven beneath the historic Offa’s Dyke and a ridge mostly comprising limestone. Originally two tunnels, they were subsequently joined together to obtain a total length of 1086m.

The full route was officially opened on 19 October 1876, but the public service was not inaugurated until 1 November.

Construction cost a little over £318,000.

The tunnel closed to public service in 1964 but was re-opened on 1 April 2020 as a cycle and walking route.

Difference the tunnel has made

Tidenham Tunnel connected the towns of Chepstow and Monmouth, allowing the safe passage of the public and goods between these two towns and elsewhere, beyond the junction to the South Wales Railway.

After it became unsafe due to years of deterioration, the tunnel was refurbished as a walking and cycling route, providing a valuable local resource for safe and sustainable travel for people of all ages.

Furthermore, the southern section has been opened with safe travel to Wyedean School in mind.

Constructing Tidenham Tunnel

In driving the tunnel’s heading (digging a smaller tunnel before the main tunnel), miners benefited from the use of Ingersoll rock drills, powered by compressed air.

These significantly increased productivity, achieving a rate of six feet per day, allowing construction to be completed in just under 20 months.

As built, the tunnel extended for approximately 1,129 yards (1km) and was separated from a second tunnel of 26 yards (24m) at its south end by a short cutting.

This was subsequently arched over and infilled to create a single tunnel of 1,188 yards (1086m), probably between 1900 and 1920.

The tunnel curves at both ends, to the west at the south end on a radius of approximately 35 chains, and to the east at the north end on a 25-chain radius. Its gradient is 1:100, falling to the north.

It’s believed that, on opening, the tunnel was substantially unlined - the limestone being self-supporting - apart from short sections at both ends where the depth of cover was reduced.

An arch was subsequently constructed through much of the southern half, supported by stone piers and brick arches.

Discrete collars of brickwork have also been inserted at various locations, presumably after inspections identified fractures in the rock and the possibility of material falling onto the track.