Skew Brick Arch Underbridge, Brown Street, Ashfield

An "Underbridge" in NSW railway parlance is a bridge which carries the railway track. An "Overbridge" carries some other service over the railway route.

The skew arch bridges at Ashfield were constructed in 1891 as part of the project to widen the main line through the station to four tracks. Available land was limited and the crossing of Bland Street, previously a level crossing, was not at right angles to the railway. The road underpass was re-named Brown Street.

By choosing to build the bridges as brick arches the railways engineers were imposing upon themselves a difficult task but the alternatives, at least in brick, were to introduce a curve into the road on each approach to make the actual crossing square, or to lengthen the arches along their axes and thus have them project into land which was not owned by the railways, but thus allowing the railway to cross obliquely.

Another bridge, over the line, of similar skew-brick-arch design but much smaller, was built at the same time at West Street Lewisham, and it remains in service. Two previous attempts had been made in 1854 to build skew arches at Erskineville and Newtown, but the bridge under Erskineville Lane had collapsed twice during construction. Both of these early bridges have been replaced as part of track amplification since.

As Ashfield was a terminus for some services there were five tracks at the station so two bridges were built for three and two tracks. The skew angles of the two bridges are not the same as they are not quite parallel. In a standard right-angled brick arch the courses of bricks are square across the arch and meet the abutments as a single course. Because of the skew, the brick courses remain square to the rail axis of the bridge, meeting the abutments at an angle, and are thus required to terminate in succession along the stone blocks which are carefully shaped to receive them.

The western abutment, viewed from the east. Note that the stone course is level and is so recorded in the photo. The streetlights and conduit are parallel to the road centreline but do not follow the brick courses. Bill Phippen 16 September 2023

The brick courses marry into the stone abutments by means of a carefully worked top surface of the masonry. Bill Phippen 16 September 2023.

The northern, two-track, bridge. The wall beyond the arch is the pier of the sixth track 1926 steel girder bridge. Bill Phippen 16 September 2023.

The section of the bridges from the original plans. There is no detail of the stepped face of the sandstone blocks. ARHS plan collection

A section of the original plans showing the skew and the divergence of the two bridges. ARHS plan collection.

Section of the bridge from the original plans. Note that there are no details of the complications caused by the skew included in the document. The arches shown behind each arch abutment are foundation structures. ARHS plan collection

Plan of the January 1891 widening of West Street Bridge by addition of a single-track brick arch on both ends of the overbridge. Parts of the span are shown as skew arches. ARHS plan collection.

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References:
Phippen, Bill, Proposal to Nominate as Item of Engineering Heritage Interest, November 2023.

Phippen, Bill, Brown Street Skew Brick Underbridge