Challenges during Micro-tunnelling by Pipe-jacking methodology - A case study
Micro-tunnelling is a trenchless technique which has several advantages in urban areas due to the compact design and modern equipment. It does however impose some challenges such as difficulties in case of MTBM breakdowns due to inadequate working space in small diameter tunnels and the need for unplanned rescue shaft excavations to carry out cutter-head repairs. In Qatar, Doha South Sewer Infrastructure Project (DSSIP) and Contract LIS-01 of ASHGHAL (Public Works Authority, Qatar) was associated with the 24 km of micro-tunnelling through 171 nos. shafts using pipe jacking methodology, with internal diameter ranging from 400mm to 2000mm. Micro Tunnel Boring Machines (MTBMs) of diameters 600mm, 800mm, 1000mm, 1200mm, 1600mm and 2000mm were used for tunnelling and installation of GRP lined RC permanent pipes. Major challenges were encountered such as cutter disc damages, MTBM shield getting stuck and tunnel alignment deviation. This paper illustrates these cases in detail along with the adopted site-specific remedial measures to successfully accomplish the works, and a brief analysis of potential causes, followed by discussions in the form of lessons learned.