Ranelagh Sewer

Effective convergence and settlement monitoring in confined, hazardous space

Real-time data allowed design verification

When designers building a massive rail tunnel underneath London’s streets encountered their biggest obstacle, a historic brick sewer, they installed ShapeArray to monitor convergence and settlement. Designers discovered the Ranelagh Sewer, a narrow brick sewer, sat just 4.5 metres over the top of the Tunnel Boring Machine’s tunnel drive.

Subsequent discussions with Thames Water determined that standard methods of measuring convergence were an unacceptable risk and not suitable for the application. Designers turned to ShapeArray to provide real-time 3D data on convergence and settlement. Additionally, ShapeArray's low profile would not obstruct the sewer’s flow and would eliminate the need for workers to enter the sewer to collect data. Convergence ShapeArrays were installed along the intrados. An additional ShapeArray installed along the crown measured settlement.


  • Conformed to Thames Water’s specifications
  • Achieved ATEX certification
  • Provided asset protection during tunnel excavation
  • Eliminated need to enter sewer to collect data
  • Did not obstruct sewer flow