Due to rapid population growth and forward planning for world events, several cities in the Middle East are developing underground infrastructure to raise living standards for residents and visitors alike. In Qatar, several ongoing projects are redefining and transforming the landscape of the region. Among these projects are Doha Metro, currently underway, and the Abu Hamour Downtown Stormwater Drainage Tunnel, which is nearing completion.
Also commencing in the final quarter of 2016 is the tunneling for the Inner Doha Re-sewerage Implementation Scheme (IDRIS). AECOM is working with Bouyges, Urbacon Trading and Contracting (UCC) and Bessac to provide lead design services and support during construction for two of the three IDRIS Main Sewer Tunnels (MTS). The AECOM team comprises of both local and UK-based engineers, geologists and hydrogeologists.
The tunnels in this scheme will run beneath the southern part of the capital, extending 45 kilometers through the southwest area of Doha where a deep pumping station will take sewage to the surface for treatment and recycling via irrigation. The internal diameter of the tunnels will range between 3.0 meters and 4.5 meters.
With a maximum depth of 60 meters, the tunnels present several technical challenges that have been considered by the design and construction teams:
- Abnormally high groundwater pressure
- Karstic nature of Doha’s geology (underground caves and cavities)
- Potentially high groundwater flows into shafts and tunnels
Based on geotechnical and groundwater advice from AECOM, the design and construction team developed several different approaches to managing the ground and groundwater at the shafts by using the following methods:
- Vertical shaft machine
- Grouting followed by open excavation
- Diaphragm walls
The effectiveness of grouting needs to be tested prior to shaft excavation to ensure that groundwater flows into the shafts. Further geotechnical and hydrogeological studies will also be conducted prior to construction. These include characterizing the ground as well as assessing the geotechnical and groundwater risks and opportunities with the construction team.
The IDRIS construction is expected to be completed by the first quarter of 2019.