Challenges during shaft excavations in urban areas - A case study from Doha South
Deep shaft excavation in urban areas can be challenging due to several factors such as adverse geological conditions, ground water pressure and existing utilities or backfilled trenches near the shaft. In Qatar, Doha South Sewer Infrastructure Project (DSSIP) and contract LIS-01 of ASHGHAL (Public Works Authority, Qatar) has been associated with the excavation of 171 shafts with diameters ranging from 6.5m to 11m with maximum depth of 27m along busy roads and in congested locations throughout the city. This paper illustrates the methodology adopted for shaft excavations and challenges encountered during excavation. Typical ground loss or face collapse incidents and potential reasons of failure are discussed in detail along with remedial measures taken for ground stability. Post construction geophysical (MASW) surveys were also conducted in specific zones after site reinstatements to ensure no excavation induced voids or cavity remained outside the shafts’ footprint.