Mitigating tunnel launch and reception challenges.

Appropriate seals, portal ground improvement and compatible shaft construction techniques are vital elements for launching and receiving tunnels effectively in urban areas where adjacent property requires protection from excess ground movements. The seals, ground improvement and shaft wall types are discussed that are required to launch or receive tunnel boring machines within wet, permeable ground at the portal zone. The use of probing is considered to verify suitability before the tunnel eye is cut. Methods described include rubber gasket seals, soft eyes, double walls, top hats for reception and portal zone ground improvement including permeation grouting, jet grouting, unreinforced slurry diaphragm wall panels, ground freezing, deep soil mixing, dewatering and over-excavation and backfilling. The launch and reception of pressurised- face TBMs with precast concrete segment linings are also described.
Appropriate seals, portal ground improvement and compatible shaft construction techniques are vital elements for launching and receiving tunnels effectively in urban areas where adjacent property requires protection from excess ground movements. The seals, ground improvement and shaft wall types are discussed that are required to launch or receive tunnel boring machines within wet, permeable ground at the portal zone. The use of probing is considered to verify suitability before the tunnel eye is cut. Methods described include rubber gasket seals, soft eyes, double walls, top hats for reception and portal zone ground improvement including permeation grouting, jet grouting, unreinforced slurry diaphragm wall panels, ground freezing, deep soil mixing, dewatering and over-excavation and backfilling. The launch and reception of pressurised- face TBMs with precast concrete segment linings are also described.