Contact Artefacts please if you have any comments or more information regarding this record.	Menu Home Upfront Now Up Books Towns Structures People Firms Lexicon		Railway Tunnel - The Spiral Komgha district, Eastern Cape CAPE GOVERNMENT RAILWAYS: Engineer

Date: c1905 Type: Tunnel Status: Extant   Click to view map Coordinates: 32°32'08.95" S 27°59'33.40" E Alt: 356m

During the construction of the Khomgha - Ndabakazi section of the Amabele - Butterworth Railway line, the CGR engineer experienced difficulties resolving line gradients down the steep southern side of the Kei River valley. The route selected meant the line had to drop in elevation more than 180 meters down to the river. The length of the line was determined by the topography and the maximum gradient the locomotives could negotiate up and down. In this case the topography did not allow sufficient length of the line – unless a steeper gradient was used. This was partly resolved by looping the line underneath itself. Called 'The Spiral', the oval loop of the railway line so formed was about 230 meters wide by 550 meters long. The travel distance from crossing overhead to passing below is a total distance of about 1 300 meters. The difference in elevation between the two lines at the crossing is about 9 meters. The crossing of the upper line over the lower line was constructed with a segmentally arched stone tunnel which was curved in plan to follow the radius of the railway line at that point. The substantial stone tunnel regularised the faces of the deep cutting and provided adequate support for the loading of the train on the overhead line. The side walls and segmental arch of the tunnel were built in fine hammer-dressed local stone formed in regular courses with tuck pointing. This form of arched stone construction was used on many of the smaller CGR culverts required beneath the railway line at crossings of minor streams. The stones forming the salient corners of the two arched openings were expressed as quoined blocks with dressed margins. The quoined corner stones project about 15mm beyond the face of the side walls, which detail helps to differentiate the quoined stones from the balance of the similarly coloured and textured stone wall surface. The radiating voussoirs of the segmental arch all have a flat top face and a vertical side face to allow easier integration into the coursed stone walling. A central keystone completed the segmental arch. The mortar joints to the voussoirs were made flush with the stone surface and struck with a half round pointing tool. The measured width of the tunnel is 5 meters and the height from the rails up to springing point of the segmental arch is 3.5 meters. The height from the rails up to the underside of the segmental arch is approximately 5 meters. These dimensions suggest that the proportions and setting out of the segmentally arched tunnel section - within a 5 x 5 meter square - were carefully considered. The tunnel is a short distance to the southeast of the Spiral Halt. The ruins of a CGR Gangers Cottage are situated a distance of about 750 meters to the northwest of the tunnel. Text adapted and extended from information provided by Denver Webb, with input from Carl Vernon and Viv Mostert, September 2015. (Submitted by William MARTINSON)