Flexibility through maximised adjustability
Adjustment is a fundamental requirement, and there are several aspects. The range over which adjustments can be made in both the vertical and lateral directions; the accuracy with which this can be done; the ease and speed of adjustment and the number and complexity of any additional or exchange parts are all important.
Adjustment figures at least twice. Firstly, on curved track made up of short straight panels, the positions of the fastenings to achieve a smooth alignment will clearly need to be offset. This applies particularly to the lateral baseplate position and becomes more of an issue the tighter the curve. The fastenings must be positioned very accurately to achieve the tight tolerances on track gauge required on high speed track.
Our Fastclip Baseplate is infinitely adjustable in the lateral direction. It can be tightened down and held firmly in position at the exact location required. The baseplates can also be slewed slightly relative to the axis of the slab, so that each baseplate is aligned exactly towards the centre of the curve that the particular slab to which it is fixed will form a part. This means that every slab can be identical to every other slab, and every fastening is identically configured relative to every other fastening on initial track construction. Only the exact positions of the baseplates fitted to any one slab differentiate it from other slabs in the track. So ‘spare’ slabs needed for repairs are universal, and do not need to be purpose constructed with the associated difficulties and lead times. Nor are any bespoke fastening configurations required to achieve exact track alignment.
While high speed lines built in earthquake zones such as Japan and Taiwan have in the past led to a need for relatively high levels of vertical adjustment – typically +50 mm – the HS2 requirement for +70 mm is a little greater. The difference may not seem large, but the overturning moment that acts on the fastening is greater and any concrete upstands provided to react lateral loads are further distant from the top level of pre-stressing or reinforcement in the base slab. Pandrol has tested the new maximum height adjustment requirement very thoroughly. We conducted a very successful test against the relevant European CEN requirement, running 3 million load cycles with a block configured so we could test adjacent assemblies at installation heights of +0 mm and +70 mm.
On slabs with rail seats, as vertical adjustments are made, the lateral position of the gauge face of the rail changes too. In order to maintain close control of track gauge, vertical adjustments may mean that the components that determine lateral alignment need to be replaced unless, like the Pandrol baseplate, the position of the baseplate itself can simply be adjusted. A +70 mm height adjustment on a 1:20 rail inclination as is the case for HS2 results in a 7 mm change in gauge, much greater than the 2.5 mm change that results from a +50 mm maximum height adjustment on a 1:40 track, as, for example, in China.