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Proceedings of the 18
th
International Conference on Soil Mechanics and Geotechnical Engineering, Paris 2013
Figure 9. Calculated spring stiffness along immersed tunnel alignment centre line and lines at 25 m distance from centreline.
9 CONCLUSION
The design of the 6 km world record long immersed tunnel with
highly variable soil and loading conditions poses significant
challenges to both the geotechnical site characterization and the
soil-tunnel interaction.
The structural tunnel design is very sensitive to differential
settlements and rotations of individual tunnel elements and
segments and thus to variation is soil stiffness along and across
the tunnel alignment. Rather than resolving to empirical rules
for handling the soil stiffness variation (Monte Carlo simulation
or additional sinusoidal variation around the mean stiffness) the
variation was handled directly by the tight mesh of CPTU prob-
ing points along and across the alignment.
Thus, the CPTUs provided a strong tool for clear geological
unit delineation and allowed for very detailed settlement and
soil stiffness assessment along the entire tunnel. The CPTU data
were correlated with results from oedometer and CAU triaxial
test results to provide site specific correlations regarding stiff-
ness and undrained shear strength.
The geotechnical site characterization thus facilitated the
tool for interaction between geotechnical and structural design
of the tunnel elements and allowed for a robust and safe design.
10 ACKNOWLEDGEMENTS
The authors gratefully acknowledge the permission by COWI to
publish the paper.
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