[3] Extensive surveys were performed, including a series of boreholes, which helped build a wider understanding of the material in general.

[7] In June 2000, breakthrough, a key milestone in the tunnel's construction, was achieved; at this point, the work was reportedly two months ahead of schedule.

[8] One of the changes made during construction was the application of the secondary tunnel lining, composed of reinforced concrete; after testing revealed the overlying chalk to be stiffer than had been predicted by earlier surveys, it was recognised that less additional strength would be required to meet the required standards, thus the thickness of this secondary lining was reduced.

[3][2] This outcome, being better than anticipated, has been attributed to a combination of technical innovation, value engineering and an integrated observational approach that was practiced during the programme.

[3] Over 100 workers working in shifts 24 hours a day made this possible, despite the site being perceived as a major risk before the project.