A new station for a new stadium
White Hart Lane is the station for, and shares its name with, Tottenham Hotspur Stadium. It is used by 1.3 million customers each year, with a daily peak usage of 1,446, rising on match days to 7,455. This is expected to increase to 12,395 next season, now the new 62,000 seat stadium has fully opened.
Abellio Greater Anglia and London Overground, which took over some of the former’s services in 2015, both serve White Hart Lane station. The existing station and tracks are located on an embankment, with the platforms carried on narrow brick-arch viaducts built into the earthworks, a form of construction common in this area.
The High Road West Masterplan
White Hart Lane station is located on the western end of London Borough of Haringey’s ambitious ‘High Road West’ regeneration masterplan. The area between the station and Northumberland Road station to the east includes a 1950/60 development that is to be redeveloped providing 2,000 new homes, along with retail and public spaces around the rebuilt stadium.
In 2014, Haringey engaged Landolt + Brown and Arup to draft the masterplan. This envisaged creating a new public space between the stadium and the station, with ‘Moselle Square’ replacing the aged flats of the Love Lane estate. A key part of this would be an enlarged, and architecturally engaging, station at the end of this boulevard, forming a key gateway to the regenerated High Road West area.
The masterplan was generally well received in public consultation and it was agreed that the station redevelopment should go ahead.
Delivering the project
The project is being led by Transport for London (TfL), with regular engagement with representatives from London Borough of Haringey and the Greater London Authority (GLA). Funding is being provided by TfL’s Growth Fund and GLA Mayor’s Regeneration Fund.
Taylor Woodrow was awarded the £17.8 million contract to redevelop the station, delivering improvements including a new ticket hall, station entrance and step-free access from street to platform.
The existing station is of a poor standard, offering very limited passenger facilities and no step-free access. There are single staircases to each platform that struggle to cope on match days, with no alternatives in case of an emergency.
The surrounding area of lockup garages and land was in a poor state of repair and had been identified as a hotspot for anti-social behaviour and criminal activity. It was recognised that the redevelopment of the High Street West area, and of the White Hart Lane stadium, would place tremendous additional footfall pressure on the station. The footway beneath the underbridge was relatively narrow and discouraged pedestrian movement between the two sides of the line.
The White Hart Lane station upgrade aims to rectify these shortcomings by creating a new western station entrance on Penshurst Road and a new ticket hall south of the current station building on Love Lane. This would be at a more central location along the platforms, facing across the future Moselle Square with urban realm works to the station forecourt and surrounding area.
Lifts will provide step-free access from the street to platform level and two new stair accesses from the new ticket hall will reduce bottlenecks and speed up the movement of passengers on match days. The existing stairs will be retained as emergency evacuation routes.
The new station is designed to cope with and manage the heavy footfall of match days, including a control room for British Transport Police. The two sides of the station will be connected by a new underpass and a second public underpass will provide a new and better public pedestrian route from east to west.
The architectural design for the station was carried out by Fereday Pollard, building on Landolt + Brown’s concept design. The external façade of the two entrances include terracotta pot panels, reflecting the area’s history of manufacturing pots for the Lea Valley’s market gardening industry, as well as louvred glass, drawing local inspiration from its horticultural glasshouses.
The design and construction of the works was technically complex and was explained to Rail Engineer by Taylor Woodrow’s Paulo Lotter and Tony Gee’s Oliver Engleback. The structural engineering design by Tony Gee and Partners was complex for a small site but reflected the challenges of the original structures and earthworks.
The original concept for the passenger and public access through the embankment was to have been a new bridge constructed top down, however this would have required multiple weekend closures. Taylor Woodrow’s alternative design of twin underpasses, using 9m x 3.6m x 4.7m jacked boxes installed during a 52-hour possession, was instead selected by TfL.
The precast boxes would be a tight fit into the existing structures, with their formation below that of the viaducts’ piers and with only 75mm clearance to each side. There would also be only 1000mm clearance below sleepers, which could be a very great risk to track stability, resulting in a spile canopy (an array or ‘canopy’ of self-drilling rods or ‘spiles’ driven into the roof above the subway to prevent ground movement) and friction reducing measures used in driving the boxes.
The installation of the jacked boxes through two adjacent arches, and taking space for station offices, would require excavation to pier foundation level, so the six affected piers were underpinned in advance. Since the platform viaducts were built into the embankment, it was necessary to excavate the embankment toe to expose the base of the piers.
To retain the stability of the embankment and the tracks above, the excavation of the toe in each arch was undertaken in three stages, top-down, using king post walls and walings tied back to their counterpart on the opposite side. First, a concrete diaphragm wall was constructed beneath the arch below the platform wall above. Two steel walings were attached to the piers below springing level. Four short steel king posts were bolted to the diaphragm and the walings and timber laggings inserted between these. Horizontal tubes (spiles) were driven through the embankment and 40mm diameter Dywidag ties inserted between the temporary works on each side. As careful staged excavation took place, a second row of ties was inserted and, at the lowest level, extension king posts bolted to the upper were used to support the lowest section of excavation.
To ensure stability of the viaducts, further ducted tie rods were inserted through the embankment and secured to heavy steel needles inserted in sawn holes through the piers. The foundations, once they were exposed, were underpinned in a series of six bays per pier, those at the rear requiring short timber headings to complete the excavation. Using an in-concrete strength-gain sensor system from Converge, two weeks were saved on the original programme’s curing periods for each bay.
Once complete, the brickwork spread footings in the arches were trimmed to provide sufficient width to install the underpass boxes and the rafts for the station offices.
As a precautionary measure, an array of 15 spiles were installed above the positions of the two underpasses. These horizontal piles formed an arch above the boxes, with 600mm cover to the sleepers above, to prevent loss of ballast during the jacking operation. These 219 CHS steel tubes were installed in possession on 28/29 July 2018.
The construction of the complex underpinning and jacked underpasses was contracted to Joseph Gallagher, which specialises in hand tunnelling and jacking.
Four headings, each 1.6m x 1.2m, were hand excavated through the embankment by Gallagher’s miners over a two-week period. They were supported by timber framing, grouted into the embankment at the end of each shift. Within these, concrete beams were cast to support slide rails, which would ensure the accurate alignment of the boxes during installation and help to reduce friction. Jacking slabs for each were also constructed each side.
The three precast boxes for each underpass were manufactured by ABM Precast at its Newark facility. Steel formwork was manufactured to ensure precise placement of post-tensioning ducts, tunnel shield connections and installation sliders. A trial assembly ensured the accuracy of fabrication and fit of adjacent sections.
Drag reduction was minimised by grease lubrication of the slide rails via internal grease ports. The sides and roof of the box had twin layers of BASF Elastalan polymer membranes with Mudtech TK60 lubrication between them. Internal injection ports allowed additional lubrication to be injected to the lower part of the box walls, which did not have the twin membrane system.
Prior to commencement, the boxes were post tensioned together with a force of 9,720kN using Macalloy bars installed through ducts in the units. A 12-tonne raked steel shield at the front provided ground support for the excavation in advance of each jacking move as well as protection for operatives and plant.
The two underpasses were installed in a single operation on 27/28 October 2018. Gallagher’s jacking equipment comprised 3,000kN front jacks pulling, plus 1,000kN rear push-jacks as an unused contingency, a total of 4,000kN jacking force per box. The maximum jacking force required to drive these through the embankment was 2,880kN. Using a sequence of dig and pull, the boxes were installed in a continuous 34-hour operation.
Excavation within the boxes was undertaken using two three-tonne excavators standing on timber platforms, with each machine straddling a conveyor that removed the 135 cubic metres of spoil.
A real-time distance-measurement system, provided by Sixense, was implemented to ensure the forces applied did not cause movements and strains on the existing structures beyond allowable limits. Once the box was in position, grout was injected around the box from precast holes within the box to fill any voids that had formed during the jacking, however this was minimal as there was very little ground loss from above the shield and culverts. The sub-ballast was observed during this operation to ensure grout did not infiltrate the ballast and form hard spots.
Station building construction
Two of the 1950s OLE (overhead electrification) gantries were within the footprint of the development, and these have been replaced by three new gantries designed by SNC Lavalin, equally spaced, to minimise effects on catenary support. One of these was founded at ground level in the sloping side of the embankment between the viaduct and the boundary.
To install the piled foundations here, Taylor Woodrow would have installed temporary sheet piling and fill to create a piling platform for a small rig. Instead, a very versatile Menzi Muck all-terrain mobile excavator was used. This was able to independently move all four wheels to allow the machine to sit level on the side of the embankment and install steel tubular piles with a vibratory piling attachment.
The station superstructures were both founded on ground-bearing reinforced-concrete rafts, a value engineering saving from the concept of a piled slab. The lift shafts on the west side were founded on short piles, installed by a Klemm KR708 rig, through the Enfield Silt and gravels into the London Clay.
The station steelwork was installed by McNeally Brown. The building’s design called for large clear spaces without obvious bracing, so the steelwork was of portal frame design. In addition, it was architecturally important for the new to abut the old, resulting in the new steelwork and lift shaft concrete being only 75mm from the viaduct brickwork, making construction difficult.
Access to the west side of the site was very restricted, with closures of Penshurst Road being required to accommodate craneage for steelwork and cladding erection.
Small station offices and service rooms were squeezed into the arches within the new building. These were constructed with wide cavities to side and rear, enabling access for future viaduct inspection and for drainage.
The planning consent for the works required that run-off towards the nearby River Moselle should be constrained to 50 per cent of an equivalent greenfield site. To ensure that this was achieved, 140 cubic metres of crate attenuation tanks were constructed beneath the paving of the public realm areas.
The project is due to open in late summer 2019, whilst Tottenham Hotspur played its long-awaited first competitive match in its new stadium on 3 April – a 2-0 win over Crystal Palace in front of 59,215 fans. In advance of this, the London Borough of Haringey required a couple of ‘smaller’ test events (Under-18s beat Southampton 3-1 – crowd 28,987, Spurs Legends lost 4-5 against Inter Milan Forever – 45,000), giving all agencies involved the opportunity to see the effectiveness of crowd management and traffic flows, although the crowds weren’t much smaller than for a normal match day, such was the draw of the new stadium.