Stepney Green Cavern Design Concepts and Performance of SCL Lining

Summary

Crossrail includes several kilometres of SCL tunnels which were designed by Contract C121, Mott MacDonald supported by Gall Zeidler Consultants. The largest of these SCL tunnels are Stepney Green turnout caverns designed to allow trains from Maidenhead in the west to travel to Shenfield and Woolwich in the east. The caverns represent the largest span underground SCL works constructed below London. This paper concentrates on the primary lining design of the largest Stepney Green sections, excavated with sidewall drift sequences. The eastbound cavern, located approximately 25m below ground surface level, was constructed predominantly within London Clay. The westbound cavern is about 5m deeper. Its upper two thirds were excavated in London Clay while its lower third was excavated in the underlying Lambeth Group stratum, which contains sandy channels with high porewater pressures. This paper discusses the analytical part of the primary lining design which was aimed to simulate the ground lining interaction considering the ground behaviour, lining parameters and excavation and support sequence and provide predictions to be checked against required standards. The design for the caverns was based on 2D and 3D numerical modelling and the paper outlines the major analytical issues and compares the predicted behaviour against the results of monitoring.