East London Line Extension
Description of Works
The scope includes the Design and Construction of demolition, drainage, restoration of listed gates, refurbishment of Viaduct Bridge, access roads and ramps, strengthening listed building and station layouts. The site extends from Vallance Road in the London Borough of Tower Hamlets across the Bishopsgate Goods Yard, over Shoreditch High Street and Continues along the Kingsland Viaduct (London Borough of Hackney), dropping in level before the Dalston Covered Way to join the North London Line (London Borough of Islington).
The contract covers the design and construction of the preliminary works to the East London Line between Vallance Road in Tower Hamlets, passing through Hackney to Dalston in Islington. In addition to access roads and extensive drainage works, the Company are responsible for the strengthening and refurbishment of Old Street Bridge and the demolition of buildings around a listed structure at 196 Shoreditch High Street. Works also include the demolition of the Bishopsgate viaduct, track drainage and preparatory works to the covered way at Dalston.
Drainage Design and Installation:
Design and installation of track drainage in the Dalston area between Middleton Road and North London Line boundary. The drainage was designed and installed to suit the footprint and track layout for the proposed new station at Dalston. The drainage discharges to two soakaways and provides for a future connection to the main Kingsland High Street sewer. A sump was designed and installed to allow for a pumped drainage system to be installed at a later date. The sump was constructed using Larssen LX25 driven sheet piles with reinforced concrete floor and roof slabs. The existing ground level had to be excavated down to an agreed formation level to suit the new track and surplus spoil disposed of. The elevated ground water levels in this area of the site (generally being within 500mm of the surface level) caused problems in excavating for the drain installation and required operation of pumps to control the water in excavations. This was also a reason for choosing the sheet-piled construction for the sump walls.
A further element within the scope of this item was to review the existing drainage from the high level viaduct along its full extent and the associated sewer connections. A desk study of the catchment area was required, as well as mapping and proving the capacity of the existing drainage system by CCTV survey. The expected run-off from the sub-catchments between existing bridge structures for a return period of 1 in 150 year storms was compared to the capacity of the existing drainage system. New drainage connections from the base of the viaduct to existing sewers were required in areas where there was insufficient capacity to deal with predicted run-off from the viaduct catchment. The existing drainage system was generally found to be adequate and only one new connection to the existing sewer was required at Arbutus Street.
The work involved liaison with Local Authorities for agreeing traffic management measures and Thames Water for carrying out CCTV surveys and obtaining discharge consents.
Road and Access Ramp Construction:
Design and construction of a new link road between Vallance Road and Pedley Street. This road will be required to provide local access later in the Project when the current road layout is altered. The road and its associated drainage were constructed to L B Tower Hamlets standards for adopted roads. The tie-in to the existing road system has been deferred until it is required at a later date. Demolition of a steel and concrete canopy was required to accommodate the new road alignment. The road construction was carried out in phases to allow access to business premises, which occupy the adjacent arches.
Design and Construction of a new emergency Access Road:
A new emergency access road was constructed at Allen Gardens between Buxton Street and Weaver Street. It was designed to accommodate emergency access for fire appliances to Weaver House and the adjacent Spitalfields Farm. The road was a reinforced grass construction to the specification provided by L B Tower Hamlets (consisting of a layer of Type 1 sub-base under a layer of Netlon ATS200 topped with turf). Ancillary work such as fencing and gate installation was also carried out.
Design and Construction of a new Access Ramp:
A new access ramp was constructed from the Pedley Street area up to track-level to facilitate access for Network Rail’s maintenance contractors. In order to construct the ramp granular, fill had to be placed and compacted adjacent to the existing viaduct brick arches. Pre-cast concrete retaining wall units were placed on a reinforced concrete slab in front of the arches to retain the fill. A reinforced concrete run-off slab was constructed at the interface between the brick arches and fill material to distribute the load evenly and prevent any load transfer onto the edge of the brick arches.
A 3.5m wide asphalt surfaced carriageway was constructed on the compacted fill ramp. The work incorporated drainage in the form of land drains and soakaways, construction of a parking area and erection of vehicle containment barriers.
The tie-in of the ramp and its alignment was modified from that shown in the Client’s brief to avoid a line of 25,000 Volt cables in troughs. This would have placed restrictions on the method of work adjacent to the cables or alternatively would have necessitated diversion of the cables. It would have involved extensive liaison with Network Rail (owners of the cables) and delayed the construction programme. The provision of the access ramp was a pre-requisite for commencement of demolition of the eastern section of Bishopsgate Goodsyard, which was used as an access by Network Rail prior to construction of the new ramp.
The scope of this work included a detailed inspection of the existing bridge with recommendations for repair and refurbishment of the steel bridge beams. A concrete slab between the two bridge sections was also to be broken out together with removal of one of the eastern edge beams and the redundant platform slab over it. A new parapet was required at the new edge beam location. The bridge is located in a conservation area and liaison with the Local Planning Authority (L B Hackney) was required to agree the construction details and obtain consent. The redundant platforms of the old Shoreditch station, which was located at the bridge, were also required to be demolished.
The Client reduced the scope of work actually carried out. This was initially due to the difficulty in obtaining consent for traffic management lane closures to carry out the demolition and refurbishment work – the Highway Authority was engaged in work lasting several months to alter the existing traffic layout from one-way to two-way operation and could not facilitate our requests for lane closures. The work carried out consisted mainly of bridge inspection, demolition of existing platforms, liaising with the Planning Authority and preparation of drawings for approval by them for the work that would eventually take place. The proposed work was later deferred until decisions could be made regarding the proposed track alignment and how this relates to the configuration of the existing bridge. A reinforced concrete slab capable of taking rail loading was designed and constructed adjacent to the bridge to span over a void between existing brick arches, which had been uncovered during the platform demolition work.
|Client||London Underground Limited 55 Broadway London SW1H 0BD|