Southborough Viaduct
Powder Mill Viaduct
The Tonbridge to Tunbridge Wells branch has the distinction of opening within
weeks of Royal Assent being granted for the line. The SER had commenced building
the branch, initially 4 miles and 7 chains in length, in July 1844. Earthworks
for cuttings and embankments were extensive, and a notable feat of engineering
was a 270-yard-long 26-arch red-brick viaduct, which crossed ''Jackwood Spring Valley'' near
the former site of a powder mill. Thus, it was known from the outset as ''Powder
Mill Viaduct'', and its construction was not without incident.
The structure was the product of Peter Barlow, brother of St Pancras trainshed
engineer William Barlow, who specialised in bridge and tunnel construction. The
line was initially to be a single-track affair, but at an advanced stage of
construction in April 1845, the decision was taken to make the route
double-track throughout. By this time, the viaduct had already been completed,
thus an extension of the piers and arches was made to one side, taking the
structure to an absolute width of 28-foot, with 23-foot 2-inches between parapets. On the afternoon of 31st May 1845, during widening works, the
six arches at the Tonbridge end of the viaduct collapsed. The piers which had
been supporting them, however, remained standing, and avoided damage. It was
noted that at the time of the collapse, the arches had already been secured in
place by keystones. The construction of the arches had taken place in prolonged
and heavy rain, and it was reported that these conditions were partly to blame
for the mortar not setting properly. The lime mortar itself was a local product,
made of grey chalk sourced from the cliffs between Dover and Folkestone. The
other twenty arches were robust and remained standing; although built using the
same mortar, these arches had been constructed in much better weather. The
collapsed arches were subsequently rebuilt with brick and cement, and on 19th
September 1845, the viaduct was declared fit for use by Major-General Pasley of
the Board of Trade; the line opened to traffic the following day. The arches are
of 24-foot span and the viaduct rises to a height of 40-foot.
17th January 2010
The viaduct is now Grade II Listed and spans a picturesque valley. The original Board of Trade report, published
the day the line opened, notes that this viaduct was built with 26-arches, but much later publications suggest that
there are thirty! David Glasspool
17th January 2010
A number of the arches which collapsed during construction were rebuilt with supporting brick jacks, as seen
here. David Glasspool
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