During construction of twin tunnels running parallel side-by-side, there are Geotechnical concerns
due to tunneling near annex structures. One of these concerns is occurred as a new tunnel is
constructed side by side to an existing tunnel. The serious damage in the existing tunnel liner is
predicted and the maximum radial displacement of the existing tunnel is also computed.
In the present study, the prediction of the tunnel system performance under the impact of the new
constructed tunnel running side by side to the existing tunnel is highlighted and a model is proposed
to study the soil structure interaction using a 2-D finite element analysis. The horizontal separation
between the twin tunnels is also studied so as to ascertain the zones of influence. The study presents
a case history along El-Azhar road tunnel to assess the accuracy of the proposed finite element
model. Based on this case history, extensive study using the finite element model is conducted to
predict the performance of the tunnel system under the twin tunnel construction. The constitutive
model for this analysis contains elasto-plastic materials. A yielding function of the Mohr-Coulomb
type and a plastic potential function of the Drucker-Prager type are employed. A linear constitutive
model is employed to represent the tunnel liners.
At the case study, the study presents comparison of the results obtained by the field measurements
and those obtained by the finite element analysis. There is a good agreement between computed and
measured values. The tunnel system performance is expressed in terms of settlement and radial
deformation in the existing tunnel under the twin tunnel construction. The study includes the
prediction of the settlement, the relative movements, and the lining stress under construction
processes. The horizontal separation between the twin tunnels is varied so as to determine the zones
of influence. The horizontal separation between the twin tunnels has a significant effect on the existing tunnel movement due to the new tunnel construction parallel side by side to the existing
tunnel.