Aberdeen to Inverurie redoubling inc Don Viaduct

AUTHOR ABSTRACT • Forres – new twin platform station with 1300m passing loop allowing simultaneous arrival in to the station. One new overbridge Robert McCafferty Aberdeen, population 200,000, is Scotland’s third and one new underbridge installed. Two LX’s Technical Head of largest city. Inverness is one of Europe’s fastest closed and two UWC’s upgraded. Closure Track, BAM Nuttall growing cities. Linking them is the Aberdeen to of Forres signal box and removal of token Inverness line, 107 miles of mostly single line exchange signalling system. New signalling Robert started on the railway with eight additional stations spread along system recontrolled to Inverness SC. railway in December the route, each with their own passing loop. 1995, spending his first After completion of the works on the west, six years working with Until 2019 the line carried 11 trains from attention turned to the eastern end of the line. Scott Wilson Railways Aberdeen to Inverness per day and the same on This section of line was the busiest on the whole in Glasgow. The six years were spent in a the return, with the journey averaging two hours route, allowing passengers to travel between survey and design environment and gave 18 minutes. An additional 15 commuter services Aberdeen, Dyce (Aberdeen airport) and the town Robert the foundations for the years and roles ran between Aberdeen and Inverurie and two of Inverurie. Due to a pressing need for increased to come. Six years followed with Mowlem between Inverness and Elgin per day. The journey commuter services at the eastern end of the line, Railways on the contractor side, followed by times and irregular service between Aberdeen emphasis had been placed on this section for three and a half years with Network Rail. and Inverness meant that the railway line did not the greatest extent of proposed redoubling. In offer an attractive alternative to road travel. addition a new station was proposed at the town Robert moved to Australia, spending two of Kintore. years in Brisbane with AECOM. Since As part of a strategic review carried out by returning in 2013, Robert has worked in Transport Scotland in 2008 a set of key output The existing line from Aberdeen to Inverurie was various CRE and CEM roles and is now the requirements were established for the Aberdeen 16.25 miles of single line, with a 0.75 mile section Technical Head of Track for BAM Nuttall. to Inverness line: of double track serving Dyce Station and Raiths Farm freight facility. The proposal to redouble Robert is currently working towards CEng • hourly service between Aberdeen and this section of line was made more complicated status through the PWI Experiential Learning Inverness because since the line was singled in the 1960s, Route. • half hourly service between Inverness and the existing track had gradually been renewed Elgin including a new station at Dalcross and maintained to follow the racing line in six • half hourly service between Aberdeen and areas (see image 4), removing clearance issues Inverurie including a new station at Kintore through overbridges, platforms and a tunnel (see • a circa two hour end to end journey time image 5). • maintain, as a minimum, the ability to deliver existing freight access rights on the route. In addition large sections of the existing single line had track components not suitable for a Achieving these outputs would require a series of linespeed increase. This meant that a scheme interventions to be carried out along the length of to redouble 17 miles between Aberdeen and the route. Inverurie, resulted in 60% of the existing line having to be renewed. WESTERN INTERVENTIONS Over a period of 18 months, AECOM, Jacobs Over the course of 2015, 2016 and 2017, and Siemens designed the works required for the interventions at Forres and Elgin on the western redoubling, with the output being: end of the route were designed and constructed. At completion the following works had been • 40,000 m of new track including 15 new delivered: point ends • 85,000 m3 of earthworks • Elgin – extension of existing platforms. • 4,300 m of retaining walls Extension of existing loop from 630 m to • 30 structures altered (extensions, infill, 1330 m including new F21.5 turnouts at removal, strengthening) either end allowing simultaneous arrival in • 3 level crossing removals, 3 upgrades. to the station. Upgrade of Elgin LX (level • new station at Kintore crossing) to MCB-CCTV. Closure of Elgin • plus re-signalling throughout along with signal box and removal of token exchange associated ancillary civils, resulting in signalling system. New signalling system the closure of signal boxes at Dyce and recontrolled to Inverness Signalling Centre. Inverurie

Image 1: Aberdeen to Inverness line diagram.

20 Image 2: Forres Station area - 2015. Image 3: Forres Station – December 2017.

Image 4: Aberdeen to Inverurie redoubling - existing layout.

Image 6: View towards Aberdeen from 2 m 1715 yds. Image 5: Track centred through OB51 Blackburn Road.

Image 7: Kittybrewster scheme plan extract.

21 Image 8: Don Viaduct superstructure.

Image 10: Proposed substructure works - initial option. Image 9: Don Viaduct substructure.

These works would be carried out during 2019 BLOCKADE - DON VIADUCT a series of rules of the route possessions, weekend possessions (54 or 78hrs) and a 14 As part of the 2019 blockade, Don Viaduct, week blockade in each of the summers of 2018 a 103 m long, five span viaduct was to be and 2019. upgraded to carry a second track. The viaduct carried the existing single track on waybeams 2018 BLOCKADE - ABERDEEN over the river Don and its floodplain. The rail TO DYCE bearers span between cross girders supported from 2 outer main girders on a skew angle of The 2018 blockade primarily consisted of 35 degrees. It was recently strengthened and works between Aberdeen and Dyce. During repainted but only for single track loading. the 14 weeks, all earthworks, structures work, There is no deck, apart from an open mesh drainage, ancillary civils and trackworks walkway. Therefore the deck is relatively were completed. During the initial part of the lightweight (see image 8). The superstructure blockade, all the existing track was removed is supported by eight 2.1 m diameter granite other than two short sections that only required masonry piers and two granite masonry tamping. This allowed the site to be managed abutments (see image 9). as a high street environment, reducing the need for expensive rail mounted plant and DON VIADUCT - INITIAL OPTION allowing earthworks and drainage to be WITH BALLASTED BRIDGE Image 11: Output from seismic ground completed quicker (see image 6). DECK penetration. By the end of the blockade, the existing single At early GRIP (Governance for Railway line had been lifted, slued and renewed to Investment Projects) stages it was established form the down line. Four miles of the new that the superstructure could be strengthened up line had been laid, but not connected to support a second track. Several options at either end and the Kittybrewster sidings including complete replacement and various area installed to a temporary alignment that strengthening schemes were considered. maximised the amount of the new layout that Key to this was removing the waybeams and could be installed, whilst still retaining the installing ballasted track. The existing cross existing signalling and functionality. Image 7 girders needed significant strengthening, below shows an extract from the Kittybrewster so to simplify construction these would be Scheme Plan at the end of the 2018 blockade. removed and replaced with heavier sections. Black = existing, red = new track brought in to The main girders needed some straightforward use, blue = new track not brought in to use. strengthening, and a new steel deck, ballasted Image 12: Shock transmission units. track and cantilevered walkway would be

22 Image 13: History of cross girder detail.

The group looked at ways of reducing the deadload by investigating a waybeam solution, removing the weight of ballast and steel deck plates. Using a risk-based assessment, AECOM compared historic loading against new loading to determine the reduction in factor of safety. If the factor of safety could be shown to be close to historic cases, the technical solution proposed could be shown to be feasible. For waybeams, AECOM calculated that the vertical loads only imposed a marginal reduction on the FOS (Factor of Safety). However, the longitudinal traction and braking loads meant that substructure strengthening was still required. Image 14: Typical detail of waybeam and BRC7 baseplate. Piling in the river was still the key constraint to installed. the programme so AECOM proposed the use AECOM found that we would need to install the of shock transmission units (see image 12). Proposed superstructure solution: concrete collar with piles anchored into rock The shock transmission units lock up when level for the design to work. This would have a longitudinal loading is applied transferring the • replace cross girders significant impact: load through the structure into new transition • 85 new cross girders / trimmers slabs behind the abutments. By doing this the • 164 new stiffeners • access to install piling would impede the longitudinal loading was taken out of the piers, • strengthening of main girders installation of the scaffold needed to carry and AECOM were able to demonstrate that the • new cantilever walkway out steelwork strengthening FOS were the same or better than the historic • the piling and steelwork strengthening case. This solution took the piling out of the In order to support the increased dead load of would all have to be carried out in the river clearing the way for the superstructure the deck, substructure strengthening would be blockade. Not enough time was available strengthening. The piles could be installed in required. to carry out the works advance of the blockade and the programme • piling solution would be much more could be met. No substructure strengthening From ground investigation and record expensive was needed on the piers. information available at the time, the piers were understood to be approximately 2 m deep. DON VIADUCT - REVISED By holding the focus group and including the AECOM proposed installing a concrete collar OPTION WITH WAYBEAMS fabricator in the design process we were able around the base of the piers to strengthen the to simplify details and reduce the amount of substructure (see image 10). Once these issues came to light a focus time needed in the blockade and also improve group was established involving BAM Nuttall, the safety of the design. As an example, the Following outline design some additional trial AECOM, Lanarkshire Welding and NR standard detail was to attach the new cross pits appeared to contradict the previous GI, engineers. This was an open collaborative girder to the main girder then install the and newly available record drawings seemed forum which met on a weekly basis to u-frame stiffeners. All work that would need to to show deeper foundations. This led to discuss the developing design. The aim be carried out during the blockade. specialist survey by seismic ground penetration was to integrate the requirements of design, to confirm the depth of the piers and the depth construction and fabrication to develop a By amending the detail to install a stub end and of rockbed. This found that the piers were solution that met Network Rail’s requirements stiffener in advance of the blockade using rules between 5-8 m deep (see image 11) which had in terms of scope and programme. of the route possessions, a lot of preparation a significant impact on the proposed solution. work could be carried out in advance. The A collar around the base of the piers could not The group looked at ways to avoid or reduce blockade work then became a simple drop in be installed without undermining the integrity substructure strengthening. Finding a way to and connect of the cross girder (see image of the structure and a collar around the pier at remove the need for piling in the river would 13). The focus group was a great benefit to 2 m depth would not be effective as the load go a long way to allowing the works to be the project, and a truly collaborative approach would still be transferred to the base of the pier. delivered within the required timescales and to resolving a key challenge on the project. budget. Lessons learned will be applied to future

23 Image 15: Cross Girders from east side. Image 16: Waybeam troughs span 2.

complex structure works.

DON VIADUCT - TRACK DESIGN

Having solved one problem, the focus group then had the challenge of developing details that allowed the waybeams to be installed effectively. The design of the waybeam was complicated by several factors:

• the structure was on a high skew • the track was rising at a gradient, and with differing levels of main girders • the design would need to include packer plates below the waybeams to ensure that the track sat at the correct level across the structure and also limit the variance in waybeam depth and size • the south end of the viaduct sat on a transition, with the cant varying from 49 mm to 0 mm. This required further packing plates to ensure the 1:20 rail inclination and crossfall were introduced in to the baseplate/waybeam system • a guard rail was needed as a mitigation to derailment loading as the design only Image 17: Track design - setting out - vertical. proposed a light GRP deck. This dictated the type of baseplate used and required gathering panels on approach to the viaduct • finally, the civils element of the work (waybeams and below) had to be ready for the installation of the track to commence in week eight of the blockade. The track installation had a three week window before engineering trains had to cross to access renewal works to the west

On commencement of the detailed design, AECOM proposed the use of Schwihag BCR7 baseplate. The baseplate would be fitted with CEN56E1 running rail and 33C1 guard rails. These would be mounted on a variety of tapered shims and straight shims depending on the location (see image 14).

Once the components were agreed, AECOM then had to produce a Form B design that took all the factors above into account and provided enough information to allow the installer (Babcock Rail) to install the baseplates, shims and rails in accordance with the tolerances set out in Table A.1 of NR/L2/TRK/2102 Design and Construction of Track.

Image 18: Baseplate setting out design.

24 Image 19: Extract from waybeam as built survey.

TRACK DESIGN - VERTICAL

For a normal track renewal the design is built from a series of known values, rail level, rail type, sleeper type, ballast depth. From these an engineer can calculate what the design rail level, bottom ballast level and formation level are. In the case of Don Viaduct, it wasn’t quite so simple.

Rather than a formation level, we had to work up from the top of cross girder level (see image 15), this being an anticipated level rather than fixed, the anticipated part being explained by the following note on the drawing:

“The anticipated levels to the top of each of the cross girder fixing plates shown on this drawing are derived from the proposed depth of the new cross girder construction and the bottom flange levels for the existing main girders at each of the proposed new cross girder connections obtained from the pointcloud survey completed by Plowman Craven Ltd. in September 2018. Image 20: Don Viaduct with planed waybeams on RH of picture. These levels include an allowance for the estimated additional deflection of the main girders due to the increase in dead load following.”

The design then worked up from this point - anticipated level of cross girder fixing plate, anticipated depth of bottom packing plates, target level to underside of steel troughing fixing plate then the waybeam itself.

For the waybeams we needed circa 100 m3 of FSC Greenheart and FSC Ekki timbers, 350- 380 mm x 530 mm of D70 strength (as defined in BS EN 338). Due to these being non stock sizes, the timbers were either imported from a source country (Guyana, Gabon or Cameroon) or sawn from stock in Europe.

The supplier for the timbers, Gilmour & Aitken Timber Merchants, advised the tolerance of the timbers would be -0/+10 mm however with additional planning in Europe this could be Image 21: ITP for individual baseplates.

25 reduced to +/-1.5 mm. Adding more uncertainty To enable the baseplates to be installed to TRACK INSTALLATION to the steps needed to get from cross girder the required accuracy, we asked that AECOM The first eight weeks of the blockade passed level to rail level. The output from the vertical produce a table showing the co-ordinate for all without incident, eventually reaching the element of the design is shown in image 17. three holes on every baseplate, a total of 2112 point where the waybeams were installed and setting out points (see image 18). ready for the track to be installed. Firstly an TRACK DESIGN - HORIZONTAL as built survey was completed of the top of TRACK DESIGN - MATERIALS waybeam level. As explained earlier, getting As well as the factors noted above for the to this point required a build up from the vertical alignment, the design and installation Once the design had sufficiently progressed cross girder, including packing plates and the also had to take in to account the following we were able to order the PWay materials inherent variability of the waybeam itself, so it requirements from NR-L2-TRK-3038 required for Don Viaduct, these consisted of: was no surprise that in some areas the survey (longitudinal timbers) when positioning the was slightly outside the required tolerance. baseplates: • 800 BCR7 baseplates As can be seen from image 19, the majority • 2 x gathering panel of the survey points were within the target • baseplate centres (max 650 mm) • 2 x run off panel tolerance (green), some were outside the • Centre of baseplate fixing hole to edge of • 28 x 18.288 m 33C1 guard rails with target tolerance but still within 2102 tolerances waybeam (minimum 75 mm) fishplates and screws (orange) and a small number were outside the • centre of baseplate fixing hole to end of • 800 straight packing plates in range of allowable installation tolerance (red). waybeam (minimum 150mm) sizes from 10 mm to 2 mm • max shim depth (30 mm) • 220 tapered shims All the areas identified as being outside • baseplate rotation (+/-2 mm) • plus AS screws, LS screws and other tolerance were high to design, so the solution • baseplate pair squareness (+/-5 mm) smalls required proposed was to plane the affected areas of waybeam, reducing the height locally to the affected baseplates (see the RH side of image 20). Once the waybeams were within the required tolerance, the baseplates and tapered shims were laid out and a small piece of slave rail inserted to check the resultant rail level. The Babcock engineers were then able to calculate the depth of packing shim required.

Babcock then installed 30 ft slave rails on the down line and clamped them up using temporary plates and clamps. The down line was then used as a service road to pull long welded rails across the viaduct for installation on the up line. This process required a series of rail rollers to be mounted on cross timbers supported by the waybeams. Once installed and clamped up, the process was reversed and the long welded rails installed on the down line. Once in place, the rails were clipped up and a final check carried out on the rail level, cant and twist. Height adjusting shims were then installed as required to ensure that the installation was in accordance with NR/L2/ TRK/3038, NR/L2/TRK/2102 and the AFC (Approved for Construction) design. The Image 22: ITP for pairs of baseplates. viaduct is 115 m long, so the rails extended beyond the bridge meaning no welds were required on the bridge.

Given the bespoke nature of the installation it was necessary to create a bespoke inspection and test plan (ITP) to check and record that everything had been installed within tolerance. In image 21 you will see the ITP used to check the baseplates centres, offsets from the side and end of waybeams, depth of shims used, pilot hole depths and horizontal and vertical alignment. Image 22 shows the ITP used to record the relationship between pairs of baseplates – gauge, cant and baseplate pair squareness.

The works on the viaduct, both track and civils, were completed as per programme, meeting the reduced tolerances for horizontal and vertical alignment and with minimal snagging work required post blockade. Image 23 shows the track in its final arrangement.

Image 23: Track in final arrangement.

26 of new track at the new linespeed of 75 mph Inverurie and other locations on the Aberdeen 2019 BLOCKADE – OTHER with no requirement for a TSR. Due to the to Inverness line. By the end the following WORKS amount of earthworks, structures, drainage and works had been completed: new track installed, we agreed with Network As well as Don Viaduct, other major works Rail that an amber trolley would be run nightly • 45,000 m of new track including 20 new were undertaken during the 2019 blockade. for the first two weeks. Using two trolleys point ends These included the closure of Pitmedden LX, per night we surveyed 11 miles x 2 lines x 14 • 90,000 m3 of earthworks upgrade of Boat of Kintore LX to MCB-OD, nights, a total of 308 miles of recording. No • 4,300 m of retaining walls removal of three overbridges, upgrade of six issues were detected in those two weeks or • 33 Structures altered (extensions, infill, underbridges, renewal of 8,000 m of existing since. Image 24 below shows an extract of the removal, strengthening) track, installation of 15,000 m of new track and spreadsheet used to compare runs over Don • four Level Crossing removals, six introduction of the new signalling system. The Viaduct. upgrades. line opened for driver training on Saturday 17 • new station at Forres and Kintore August, with the first passenger trains running A2I SUMMARY • closure of four signal boxes as planned on Monday 19 August. • removal of token exchange signalling and Over the course of four years, BAM in recontrol to Inverness and Aberdeen SC. POST BLOCKADE MONITORING partnership with Siemens, Babcock, AECOM and Jacobs designed and installed a series The journey from the 2008 Transport Scotland At the end of the blockade we opened 11 miles of upgrades at Forres, Elgin, Aberdeen to output requirements to now has taken 12 years, but isn’t yet finished. Further works are ongoing and planned on the Aberdeen to Inverness line. A new station is almost complete at Kintore (see image 25) and design has commenced for a new loop and station at Inverness Airport.

ACKNOWLEDGEMENTS

I’d like to thank David Herron, Associate Director with AECOM. David and I gave a presentation to the Winter Track Conference in December 2019 and his contribution to that forms part of this paper, particularly the Don Viaduct Civils elements.

REFERENCES

NR/L2/TRK/3038 - Longitudinal Timbers – Design, Installation and Maintenance NR/L2/TRK/2102 - Design and Construction of Track

Image 24: Comparison of amber trolley runs.

Image 25: Kintore Station.

27 TECHNICAL ARTICLE

AS PUBLISHED IN The PWI Journal April 2020

VOLUME 138 PART 2

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