4 ms·
They touch on that briefly at 8:10 in the video. The rings aren't perfect cylinders; the top and bottom are angled so that each ring is slightly longer on one s
by jetrink 7y ago
They touch on that briefly at 8:10 in the video. The rings aren't perfect cylinders; the top and bottom are angled so that each ring is slightly longer on one side. (I.e. They resemble radial slices of a torus.) If each ring is rotated 180 degrees relative to its neighbors, the lengths average out and the tunnel goes straight. If the orientation is kept roughly constant, the tunnel curves in the direction of the short side of the cylinders.
- abduhl 7y agoThis is partially correct. This is how the curve is maintained with the concrete liner. Steering is also accomplished via articulation jacks at the head and controlling differential stroke of the main jacks. It should be noted that only certain types of precast segments work the way that is stated with all rings having an angled face - other types have specific concrete segments for each particular curve with the rest of the rings being planar. This approach has gone away in the industry with advances in software.
- amelius 7y agoDoes the machine itself deform while going through a curve?
- abduhl 7y agoTechnically the answer is yes (any stress state results in deformation) but for all practical purposes the answer is no. The TBM does not bend to any degree worth talking about and is considered rigid. This leads to curves in tunnels generally having a very large radius because you have to build the leading part of the curve inside a rigid cylinder. The tunnel is slightly smaller than the TBM and so some curvature can be tolerated.
- amelius 7y agoSo I suppose the curvature is much smaller than what a typical train can tolerate.