| Historical notes: | The first regional railway lines in NSW were inland routes to Bathurst and Goulburn constructed in the 1870s. Coastal railway lines had to traverse large rivers so initially it was less expensive to continue using ships and boats to service coastal settlements. However when seams of good quality coal were discovered in the Illawarra escarpment near Wollongong in the 1860s, Wollongong’s small harbours and rough seas soon proved too unreliable for the loading of colliers. The Illawarra railway south from Sydney to Wollongong became the first coastal line to be built in NSW and was opened in stages progressively southward from Sydney between 1884 and 1893 (Godden Mackay, 1992).
A particularly difficult section of the Illawarra line was crossing the ‘amphitheatre’ or ‘gorge’ around Stanwell Creek because of the 300m high Bald Hill on the north, and the 350m high cliffs on the south. A report written in 1874 proposed three alternative designs, of which the cheapest was chosen - with steep grades, sharp curves, small bridges and many tunnels. The rough terrain meant that this section of line, from Waterfall to Scarborough, was finished over a year later than the line from Scarborough to Wollongong, opening on 3rd October, 1888. This section of the line passed through eight tunnels, including the 1550 m long Otford Tunnel, a notorious single-track bore on a rising grade of 1 in 40 towards Sydney. Traversing this tunnel in a steam train could be unbearably hot and sooty, and it came to be known as the 'most dreaded tunnel on the railways of Australia' (Camberlaid, n.d.) (Godden Mackay, 1992).
Passengers also complained about the transit through the Stanwell Park amphitheatre. Coal traffic was increasing, the tourist attractions of the Illawarra were becoming recognized and rail operators were calling for double lines and better grades to avoid congestion. In 1909, a survey was made to set out a ‘deviation’ from the original railway line between Coalcliff and Otford - to build a replacement line nearby with easier grades and duplicate rails. This plan was approved by NSW Parliament in 1915 and the deviation opened on 10th October, 1920. Its centrepiece was the huge masonry viaduct or railway bridge over Stanwell Creek (Godden Mackay, 1992).
The design of the viaduct at Stanwell Park is similar to others built around that time and the radius of its arches was to a standard pattern. Brick construction was chosen here largely because other materials were unavailable due to World War I - while the state brickworks at Homebush was in full production. It has been estimated that the total number of bricks used in the massive tall piers of the viaduct and its eight arches was around 3 million (SHR listing for Stanwell Park Viaduct). 1920 construction photos and contemporary site observations confirm that the viaduct was soundly constructed and well founded (Yang, 1991).
For over 60 years, the viaduct required only routine maintenance, indicating the quality of its original design and construction. In 1985 damage to the viaduct resulting from massive compressive forces was noticed, possibly generated by mine subsidence. Described as the 'most serious case' of deterioration amongst all the state’s brick railway bridges (Yang, 1991), major remedial works were undertaken in 1986 (see modifications, above). These remedial works saved the viaduct but compromised the integrity of the structure. In 1990 an engineering report identified further options for its treatment. The preferred alternative involved retaining the existing structure, replacing defective elements and widening the deck. The engineers concluded that movement of the two sides of the gorge may have been due to removal of coal pillars in nearby leases. The earth movements are regularly monitored and have reduced. Train traffic is now normal over the viaduct, although a modest restriction in train speed has been laid down (Godden Mackay, 1992).
Comparative analysis – viaducts
There were 123 brick masonry arch bridges reported extant in the NSW railway network in 1991, mostly constructed in the 1920s and 1920s (Yang, 1991). The first railway viaduct in NSW was built at Lewisham in 1855 with large sandstone blocks, which were locally available and allowed for a display of pride in this, the first railway line in the state. By the 1870s surveyors were asked to minimise the use of bridges and culverts. Larger structures built from more expensive materials like iron were only constructed when absolutely necessary (as at Como and Menangle). The Eddy administration, beginning 1891, saw a new policy of duplicating and upgrading all main rail lines out from Sydney with a preference for bridges being designed in brick especially between 1910 and 1924. Hundreds of kilometres of lines in NSW were improved at this time, with the line at Stanwell Park being one of the last to be completed (Godden Mackay, 1992).
There are a number of viaducts similar to Stanwell Park in basic form but none are as high. The brick viaduct at Knapsack Gully between Emu Plains and Glenbrook on the western line also has eight arches, battered piers and a brick parapet with stone footings and coping, and arches built on the standard 13 m diameter with brick spandrels. There are many other small viaducts of four or five arches constructed to this standard design. The Back Creek viaduct at Branxton is a typical example of a five arch viaduct with the abutments having engaged piers. On the western line, bricks were used particularly for the numerous crossings near Tarana such as the Solitary Creek viaduct between Sodwalls and Tarana - another standard design with four arches and no engaged piers which lacks the visual finesse of the larger and later structures. The Mulwaree Ponds viaduct between Marulan and Goulburn on the southern line was built in 1914 adjacent to the old iron truss / brick pier bridge constructed in 1873. The viaduct has 13 arches and is built to a standard design with parapet and engaged piers similar to those at Stanwell Park. However, the piers are insufficiently tall to require battering and the structure lacks the grace of Stanwell Park. On the western line, bricks were used particularly for the numerous crossings of Solitary Creek near Tarana. There are no significant brick bridges or viaducts on the northern lines (Godden Mackay, 1992).
Additional references
Adams, Michael 2005. Little Bulli, the Pioneering of Stanwell Park and Northern Illawarra till the 1860s, Cultural Exchange International, Russell Lea, p21.
Camberlaid, B. n.d. ‘The Notorious Otford Tunnel and the Stanwell Park Deviation,” B Camberlaid, ARHS Bulletin, no.344 6/66.
Yang, Y., Y.C. Loo and R.Best, 1988. ‘Behaviour of Stanwell Park Viaduct, a multispan brick masonry arch system on tall piers,’ Proceedings 8th International Brick/ Block Masonry Conference, Ireland, pp 1759-1767.
Yang, Yan, 1991. ‘Progressive failure analysis of Masonry Arch Bridges,’ PhD thesis, Department of Civil and mining Engineering, University of Wollongong, online at:
https://ro.uow.edu.au/cgi/viewcontent.cgi?referer=https://www.google.com.au/&httpsredir=1&article=2257&context=theses |