SPECIAL GEOTECHNICAL WORKS FOR METRO CAIRO (EGYPT)-Paper

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Bauer Egypt carried out specialist geotechnical works at 18 of the 22 underground stations on Cairo Metro Line 3, completing approximately 600,000 m of diaphragm walls and 58,000 m of silicate-gel grout plugs. The works supported station, ventilation-shaft and TBM-launch excavations, which extended as much as 32 m below groundwater level. Because suitable natural impermeable layers were generally unavailable, deep grout plugs provided groundwater cut-off and enabled excavation with limited seepage.<br /><br />Station construction typically used reinforced-concrete diaphragm walls, followed by staged top-down excavation and temporary supports. Silicate gel was injected through valves in drilled pipes to form horizontal sealing bases, generally 4.5–12 m thick. Quality controls included checks on drilling depth, slurry and gel properties, injection volumes and pressures, and pump testing before excavation.<br /><br />Several challenging operations required specialized methods. Low-headroom equipment allowed diaphragm-wall construction near and beneath existing bridges. Jet grouting strengthened the ground between an existing sewer and the planned tunnel, limiting the risk of sewer damage and settlement as the TBM passed beneath it. After a tunnel collapse buried a TBM about 30 m below ground, Bauer constructed a 95 m-deep, 18 m-diameter diaphragm-wall rescue shaft and installed horizontal freezing pipes. The frozen ground formed a temporary watertight and structural body, allowing the TBM to be dismantled and recovered.<br /><br />The project demonstrated the use of diaphragm walls, permeation grouting, jet grouting and ground freezing in complex urban conditions. Following its Line 3 work, Bauer was contracted for geotechnical works at six stations on the planned Line 4.

Keywords

Cairo Metro Line 3

geotechnical works

diaphragm walls

silicate-gel grout plugs

groundwater cut-off

top-down excavation

jet grouting

ground freezing

TBM launch shaft

urban tunneling