Sabry A. Abdo*, Mohamed A.Y.**, Hassan A.A.El-Sageer***1, Mamdouh Y.H.***
The deformation and support load of the first tunnel can be changed due to the excavation of the
second tunnel, when it is in the vicinity of an existing tunnel. Severe interaction effect between
adjacent tunnels can happen, especially in poorly cemented or heavily fractured rock condition.
Severe interaction may endanger the stability of tunnel. Therefore, the traditional method of
tunnel alignment and support design based on topography in the portal area, available right of
way, simple stress analysis by elastic method and empirical rock classification method can not
properly determine the spacing between tunnels and the support required in order to avoid the
interaction effect.In this work, theoretical studies by numerical method coupled with tunnel
models were carried out to establish the criterion for judging the severeness of interaction effect
between tunnels specially when the shape of the excavated tunnels is considered.