Increasing demand on infrastructures has led to
increased attention to shallow soft ground tunneling
methods in urbanized areas. Especially in metro tunnel
excavations, it is important to control the surface settlements which are observed before and after excavation,
which may cause damage to surface structures. Unlike
motorway, sewage and other infrastructure tunnels, metro
tunnels generally have to be excavated as twin tunnels and
must have a larger diameter. Metro tunnels also have
shallow depth. Due to their shallow depth, metro tunnels
generally have been constructed in weak rocks or weak
soils in cities. The construction of twin tunnels will generate ground movements which have the potential to cause
damage to existing surface and subsurface structures. To
solve this settlement problem, experts have used the Earth
pressure balance machine (EPBM) and the slurry balance
machine. In such excavations, especially in twin tunnels,
the main challenges for constructers are estimating the
maximum surface settlement, controlling the interaction of
transverse surface settlement and shaping the settlement
curve. Incorrect estimation of these parameters can lead to
significant problems above the tunnels and in nearby
structures. This paper focuses on surface settlement measurements, on the interaction of twin tunnel transverse
surface settlement and on the relationship between shield
parameters and transverse surface settlement for parallel
tunnels using EPBM shields in clay and sand soils in
shallow depth. Also, a new equation is proposed for estimating the transverse settlement curve of twin tunnels. The
results from this proposed equation are compared with the
results of field observations. The transverse settlement
curve values obtained from the proposed equation have
good agreement with the actual results for the Otogar–
Kirazli metro case studies.
Keywords Twin tunnel excavation  Surface settlement 
EPBM  Twin tunnel settlement curve