11.05.17
A first of type level crossing
Source: RTM Apr/May 17
Peter Barber, principal engineer (Track) in the Capital Projects Directorate at London Underground (LU), explains how a first of type level crossing, intersecting the A28 next to Rolvenden station on the Kent & East Sussex Railway (KESR), was successfully installed in mid-March.
The edilon)(sedra precast concrete modular-unit crossing, intersecting the A28 next to Rolvenden station on the KESR, is the ‘first of type’ to be used on roads anywhere in the UK, although it has been extensively used in previous design configurations in mainland Europe for the last 30 years.
This type of installation was chosen as it provides a low-maintenance solution with a very positive whole-life cost payback. The crossing on the A28 is at the bottom of a dip, with fast heavy road traffic causing regular failure issues in the traditional set-in Tarmac-type crossing. For a number of years, the track in this area has been a significant maintenance and cost liability to the railway. However, this new type of crossing will remove a weak point in the system that has caused problems in the past, and increase the time between maintenance interventions from 10 years to a proven and manageable 40 years.
The system has a low ground pressure due to the surface area of the units making the formation preparation a simple compacted granular type 1 layer, with a thin sharp sand blinding layer. The units are placed on this layer to an accuracy to design of ±5mm, and the rails are then installed to design position in the slab channels on pads and aligned using permanent elastomeric wedges. When the track design was achieved, the FB rails were bonded into the channel troughs using a Corkelast material, which is a pourable elastomer. Fast-setting concrete was then used to fill the 200mm base section of the trench either side of the crossing and this was topped with 150mm of highways-approved tarmac. Once the road was excavated, the operation to get the five 3m units, weighing 5.8 tonnes each, down and the rail bonded prior to concreting was five hours.
The project was conceived following a discussion with the supplier wanting a UK showcase for its products. Dutch company edilon)(sedra provided the concrete units at cost, and the site team to bond the rail into the concrete trough for free. Delkor from Australia, with partner Tiflex, provided the bonded resilient baseplates and CEMEX the large transition concrete sleepers that are derived from a LU check sleeper design. Baker Rail provided free support in setting up the road closure and the safe method of working. LU engineers, working as volunteers, undertook the design, site survey and also provided additional personnel on the day.
The track/crossing design was undertaken as a training exercise by LU. This included managing the stiffness transitions running onto the crossing to create a smooth controlled deflection change from the ballasted track to the crossing. The Delkor rubber-bonded baseplates were installed on the transition concrete sleepers on well-compacted track ballast. The deflection of the Corkelast was calculated and Delkor-bonded resilient baseplates were provided to manage a smooth transition between the different stiffnesses. The use of the bonded baseplates keeps the deflection on the top of the sleeper, thereby not degrading the ballast that is a regular maintenance liability.
The KESR now has a state-of-the-art durable crossing and has removed a maintenance/economic liability. This may not be seen as ‘heritage’ in the eyes of some, but removing these financial liabilities is the only way the railway can remain sustainable. Based on the success of this, the railway is looking to roll this system out to other crossings on the line.