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Tight timescales at Holyrood
RailEngineer
The upgrade and redevelopment of the Thameslink route continues. With one of the major stations, Blackfriars, now largely complete and open for use, the next major challenge is London Bridge station.
Situated almost under the Shard, which at 306 metres (1,004 ft) high is the tallest building in the European Union, the station will be largely rebuilt. This is a significant piece of work that includes three of the nine existing platforms being closed and replaced with three new through platforms. There will also be a programme of track layout remodelling to streamline paths so that the increased number of trains can pass through the station without hindrance.
As an early part of the programme, Network Rail contracted UKPN Services to provide a new signalling power supply substation at Holyrood, close by London Bridge. UKPN Services has a good track record in delivering power supply projects for Thameslink, but the new Holyrood substation was to be one of the most challenging yet.
Challenges for Christmas
For a start, the timescale was tight. The new substation was to be commissioned over Christmas 2012, giving the contractor just six months to deliver the project. Any slippage would have an impact on the development project as a whole as well as Network Rail's ability to continue running rail services with minimal disruption. In addition, the project was challenging in that it was to be built in existing archways that were damp. There was evidence of water seepage in the area where the high voltage electrical switchgear would be housed and the brickwork was in poor condition.
The contract covered conceptual design, detailed design, procurement, installation and commissioning for all aspects of the new electrical substation. When UKPN services broke the work down into its constituent parts, it included:
» Diversion of 11kV feeders on track and installation of a new trough route;
» Design of a water tight environment suitable for an electrical substation, installation of a new lining to the entire structure to provide increased water integrity
and provide aesthetic design together with the provision of a new drainage system;
» Repairs and upgrade to the current structure to ensure it was fit for purpose and the construction of a new floor capable of housing the transformer and rectifiers;
» A robust piling design and construction execution plan for working in a confined location and the construction of a stand-alone steel structure
to support the lining, cable management and other facilities. This frame could not be tied into the existing civil structure walls and arched ceilings;
» A complete cable management system within the archway, along the walls adjacent to neighbouring properties and finally onto and along the railway infrastructure;
» Blast proof walls to ensure robust operation in case of a catastrophic failure
» Design, procurement and installation of transformers, switchgears, battery charger and SCADA (supervisory control and data acquisition) equipment;
» Installation of low-voltage cabling from the transformers to the signal box;
» Enhance security and integrity of the final building.
Due to the complex nature of the London Bridge works, and an opportunity on Thameslink to accelerate the overall programme, UKPN Services were set a six months target to complete the project and commission the new substation during the Christmas 2012 blockade. In order to achieve this, daily progress and interface meetings were held with other inter-related project stakeholders, project teams and contractors on a regular basis to ensure everyone was working towards a common goal. Meetings were also held with the local council and associated neighbours to keep disruption and/or disturbance to a minimum.
During the later stages of the project, daily flash reports were used to ensure all the team were focused on agreed targets and, for the Christmas closure works, hour-by-hour schedules were produced and reviewed on a daily basis to ensure all work was executed effectively.
Construction complications
The team faced major challenges from the limited site access, unknown ground condition and the state of the arches and archways. The only access to the site was through entrance doors located in Holyrood Street having a dimension of 2.4 metres high by 1.9 metres wide. This necessitated close collaboration with other projects and a number of neighbouring businesses to manage site deliveries both for equipment, plant and materials.
The removal of existing cladding on the archway wall exposed the poor condition of the brickwork which then required grit blasting, removal of loose and perished mortar and re-pointing. In addition, asbestos was detected during a survey and had to be removed safely by a specialist contractor.
Following an assessment of the existing foundations, it was confirmed that piling was required to support the new equipment bases. 58 piles to a depth of nine metres had to be installed within a confined area on a challenging schedule.
The poor condition of the archways presented further challenges. The brickwork was extremely damp, the air quality wasn't good nor was the lighting, and there was limited room for construction. Drainage was inadequate and had to be redesigned and incorporated into the building design due to the complexities of the associated electrical equipment.
The new steel structure was designed and installed within the electrical switch room that would house the associated electrical switchgear, transformers and rectifiers. This frame supported the water containment by installing appropriate lining sheets on it which did not allow water penetration. The design of the structure and placement of the lining had to accommodate sub-structures to enable a cable management system to be installed and also inspection hatches for future maintenance requirements.
Despite all of the challenges, UKPN Services successfully and safely completed everything in a little under six months. The 11kV feeders were diverted, the new troughs and cables installed, and the almost-unusable arches completely refurbished to produce a water-tight and stable location. The transformers, rectifiers and associated equipment were supplied, installed, commissioned and energised on time.
In addition, despite the challenges and tight timelines, the project team remained focused on environmental issues and recycled 95% of waste with less than 5% going to landfill. During construction LED technology was used to provide temporary lighting instead of that normally found on complex construction sites, effectively reducing the electrical requirements significantly.
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