Initial plans were to construct the new 7,929 m long tunnel using a single shield TBM. However Herrenknecht’s TBM S-943 was working concurrently at Rio Churubusco’s project and once it had completed its excavations there it was decided to transfer this TBM to an intermediate shaft (Chalco) to complete the final part of the Canal General del Chalco project.
To commission the second TBM at the intermediate shaft umbilical cables some 100 m length were used with the machine’s control cabin being positioned on surface.
Ultimately TBM S-944 completed 6,076 m of tunnelling with the other 1,853 m being completed by TBM S-943.
Across the full length of the Canal General del Chalco tunnel there were 5 intermediate shafts accommodating a primarily horizontal alignment which included various straight and curved sections, the curved sections having a minimum radius 200 m.
In support of the tunnelling effort of course with the requirement for curved sections as well as straight runs, the right navigation and information systems were needed to ensure accuracy at all times.
Tunnelling operations on the various sections started in December 2015 with the first TBM which ran until March 2017. TBM S-943 started in April 2017 and finally holed through in March 2018.
Using the VMT navigation systems high accuracy in the various breakthroughs was achieved across the whole project.
The contractor chose to operate with VMT equipment and software having experience of the company and its operations on previous projects.