Cross passage construction on the Crossrail C310 Thames Tunnel

This paper provides a detailed description of the construction of the four cross passages between the main tunnel drives on the Crossrail Thames tunnel Contract, all constructed within the Seaford Chalk formation. Information is given on the methods employed for the excavation and the construction of the primary sprayed concrete and secondary cast in-situ concrete linings. The challenges encountered and how they were overcome. The paper compares the Chalk classification derived from the initial boreholes and that encountered when excavating caverns and the construction techniques used to create these 5.5m diameter excavations in the saturated Chalk, including the challenges encountered under the River Thames.