Design of the Deep Cut and Cover Crossrail Paddington Station Using Finite Element Method
Summary
The flagship Crossrail Paddington Station is generally located within London Clay and takes the shape of a deep cut and cover underground box structure approximately 264 m long, 24 m wide and 24 m deep framed with diaphragm walls and constructed top down using plunge columns connected to 1.8 m diameter bored piles. It is located at the heart of one of London’s most significant existing transport hubs, directly beneath Departures Road and Eastbourne Terrace and is adjacent to the Grade I listed Paddington mainline station.
The geotechnical design of the deep cut and cover underground box structure was undertaken using two-dimensional finite element method and in accordance with the Crossrail Civil Engineering Design Standards.
Monitoring data from inclinometers located within and behind the main box diaphragm walls has provided valuable information throughout the construction process and on completion has allowed the geotechnical approach to the design of these walls to be assessed.
The deep excavation of the station is mainly influenced by the undrained behaviour of London Clay, which can be assessed either in terms of effective (Undrained (A) and (B) analyses) or total (Undrained (C) analysis) stresses.
Three constitutive soil models have been adopted for the undrained analysis of London Clay. These are the Mohr-Coulomb model (MC), Hardening soil model (HS) and Hardening soil model with small strain stiffness (HSS), the results of which are compared to the diaphragm walls deformations measured during construction to assess the performance.
The deflections obtained from the Undrained (A) HSS model were found to match the measured wall deflections reasonably well, especially for the final excavation stages. Generally, the predictions of all FE models gave a narrow range within which the field data is enclosed.
This paper provides insight into the mechanism of soil-structure interaction of this deep excavation as well as into the appropriateness of the design approach, using advanced finite element analysis that was calibrated against field data.