Railing against Rayleigh Waves

The Sunday Telegraph reported at the weekend that research commissioned by HS2 Ltd has shown that trains on the HS2 route are at risk of derailment in places if they travel at more than 157 mph.

This came out of a research project into Rayleigh Waves: we reported on the project on some time ago – see here and here.

At the time, we were told by Heriott-Watt university that “Detailed results will be published on completion.” These results have now been classified “official-sensitive”.

According to the Telegraph, the research, completed last year, Prof Peter Woodward found that the speeds proposed by HS2 would create “critical track velocity effects” and “significant issues” with track instability.

Prof Woodward said that the ballasted track of the kind to be used by HS2 “may not be able to adequately retain the track geometry” at the speeds proposed by HS2. He said that “embankment instability, particularly over poor soils … will generate significant issues during construction and operational running”

Woodward said that speeds as high as those planned by HS2 could cause “rapid deterioration of the track, ballast and sub-ballast, including possible derailment and ground failure”.

Rayleigh Waves were first brought up a couple of days after HS2 was originally announced, in 2010, when Peter Woodward spoke to The Engineer.

“According to Woodward, it is most critical to look at the increasing forces and vibrations induced in the track as a train’s speed picks up. ‘A point can be reached whereby a ground wave starts to develop ahead of the train,’ he said. ‘The analogy is that of an aircraft going through the sound barrier.’”

According to Telegraph Prof Woodward says his simulations “clearly show the development of Rayleigh wave effects… [and] the development of critical track velocity effects.” and he recommends 

“massive ground stiffening and said that the track should be laid on a concrete slab. However, this would be more expensive and much noisier than ballast.”

This cure had previously been suggested by Prof Victor Krylov of Loughborough University who had also added “but the best or cheapest measure you can do is just to reduce the speed.”

Issues like this have delayed the decision on the route of Phase 2. But it is also  clear that these huge geotechnical issues are still ongoing with the Phase 1 third reading just days away.