SBD wrote: ↑Thu Feb 01, 2024 8:37 pm
dbl96 wrote: ↑Thu Feb 01, 2024 2:08 pm
rhino wrote: ↑Thu Feb 01, 2024 1:10 pm
Considering that Balhannah and Hahndorf are at very similar elevations above sea level, that is a very steep railway from Bridgewater to Hahndorf.
Bridgewater is at approximately 400m above sea level, and Hahndorf is at approximately 350m. The proposed alignment is at a minimum 5000m between the two stations, so at a constant gradient, the slope would only be 1%, which is completely workable.
Of course, this requires that the gradient is constant - which is only possible with a tunnel under Bridgewater East and a substantial viaduct to bring the railway over the Ongkaparinga Valley.
NIMBYs, environmentalists and just about everyone else would object to a high viaduct there!
I'm curious about the gradient of your proposed route from Mitcham to Aldgate, too. Presumably you propose a long tunnel under Crafers and Stirling from somewhere in Brownhill Creek?
I'm sure they would, but would a railway bridge through an already disturbed agricultural area really be any worse a scar on the landscape than the freeway is? Designed right, it could be quite beautiful.
Yeah, the route people have discussed previously would be to use the Brownhill Creek valley to ascend the hills face, because the gradient is fairly manageable. I'm honestly not really in favour of it though because that really would be a scar on the landscape. It would completely disturb the peace and natural charm of one of the loveliest areas of the hills face.
I think a better option would be a direct tunnel from Mitcham to the Aldgate area, which would probably be somewhere in the range of 10-15km. I'm no expert in tunnel engineering, so cant comment on what the most suitable route would be, but assuming a tunnel of 15km, at constant grade, you would be looking at about 2.3% gradient from Mitcham (approx. 80 m above sea level) to Aldgate (approx. 420 m). A shorter option might be possible (assuming no freight trains on the line), but the gradient would start to get unmanageable.
More complicated would be if we want to have a station at Stirling, which I think would be ideal, considering its role as the strongest town centre and transport hub in this part of the Hills. The station would need to be a considerable depth - Stirling is a bit over 2 km from Aldgate down the tunnel, but elevation there is about 80m higher. You could design the tunnel from Mitcham to Stirling in a way that gave sufficient length to allow for appropriate gradients, but it still couldn't come too close to the surface at Stirling because it would then have to descend very steeply into Aldgate. As a consequence, whatever way it is designed, Stirling would have to be a fairly deep station. Expensive no doubt, but not impossible, there are metro stations in Moscow and Chongqing at over 100m deep. I don't think a Stirling station would need to be quite as deep as that.
Again, I don't have the engineering expertise, but there might be issues tunneling through the Hills face as it is an active fault zone. Please comment if you can throw any light on this.
Apparently a base tunnel under the Mount Lofty Ranges was considered back in the 60s. The idea never went anywhere, although apparently not because of technical issues. This article is an interesting read:
https://www.ozroads.com.au/SA/New/1/Pri ... istory.htm