LU Future Station Project – Elephant & Castle Feasibility Studies
Project Details
Project Description
LBA Role
Project Highlights
Location
Elephant & Castle Station
Client
C344: London Underground via Tony Meadows Associates D401: Mott MacDonald
Date
C344: Feb – Dec 2013 D401: Apr 2014 – Dec 2015
Project Type
RIBA B Option Development
Skills
Constructability
Option Development
Option Programming
Option Costing
Project Description
Elephant & Castle Station is on the Northern Line and is the current southern terminus of the Bakerloo Line. These two lines cross beneath the Elephant and Castle roundabout and form a significant interchange and destination station, serving residential and commercial traffic. The location is a major hub for bus services and has a Network Rail station.
The Bakerloo platforms are deeper and lie to the north-east, the Northern Line platforms are to the south. Stairs link the platforms, giving rise to passenger flows along each platform. Both platforms are serviced by lifts and stairs, there are no escalators; in addition to the station, this site supplies traction power to both LU lines. The overlying roundabout has a complex of pedestrian underpasses and there are circuits of gas, electrical and communications utilities. The local sewers are deep, combining beneath the road flow to the south.
The project sought to solve non-compliance issues regarding projected passenger congestion levels, the use of platforms for access, the absence of PRM provision and unacceptable escape times for passengers in the event of a fire. This was to be achieved by the “penninsularization” which removed the roundabout and returned the traffic flow to two way working, with light-controlled junctions. This closed off the road between the island and the shopping centre to the south-east, forming a potential worksite. The road revision was a TfL initiative, also proposed on other LU station sites, presenting LU with opportunities for development.
The works were undertaken in two packages imposed by budgetary constraints; the second package developed options that addressed deficiencies identified in the earlier schemes.
LBA Role
LBA undertook a desk study of BGS data to determine the site geology which could then contribute to the development of scheme options. We also developed our understanding of the utilities and buried assets that could be affected, as these posed key constraints to the feasibility of options. Once options were developed, we determined the most feasible methods for their construction considering all the site constraints, including access and utility clashes requiring diversions. The sequencing of these and their duration estimates formed the construction programme. By identifying the critical path activities, the schemes could be optimised by prioritising resources and access. For speed and economy, the stages were explained in annotated hand-drawn sketches and the options were then costed.
Three options were developed during the first commission (C344) and five further options were developed during the second commission (D401).
Project Highlights
It was shown that the levels and construction methods of the historical LU tunnels had been dictated by a thin layer of London Clay. All the upgrade options had to address construction issues posed by the variable materials found in overlying and underlying strata along with their attendant groundwater issues.
Clashes with utilities were unavoidable in all the options and the enabling works that these implied added considerably to both the cost and programme, especially where multiple utilities were affected in one location. Doing this effectively was a delicate balance.
The constraints posed by the sensitivity of the Faraday Memorial Sub-station (pictured) and its equipment became apparent and the mitigation of ground movements arising from excavations was a driving constraint on the selection of the construction methods and sequencing.
The site traffic impacts of each option were required to inform TfL restrictions on both traffic times and numbers. This constrained the site logistics and dictated both construction methods and programme durations – resolving these conflicts was a challenge in each option.
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