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  Management of unexpected swelling clay on Cairo Metro line 3 Phase 2

  During the construction of Cairo Metro Line 3 Phase 2, ground investigations highlighted the presence of unexpected swelling clay at the tunnel elevation around Cairo Fair station. In order to control this event, investigations were ordered so as to understand why an initially stable clay layer could swell in such large proportions in case of excavation below the water table. Considering the very high potential swelling behavior and the associated time dependent effect on the next 100 years, a specific design was then developed and implemented on site. On the Cut & Cover station, a fuse layer (up to 60 cm thick) made with a specific polystyrene material was installed below the raft level. On the bored tunnel section, several sections were investigated and iterative calculations were then performed so as to estimate the clay strain amount in the influenced swelling clay layer. The conclusion was that the swelling effect had no impact on the tunnel lining design.

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