Summary and discussion on the effects of clear-distance shielding tunnels

Generally the tunnel construction in downtown area is restricted by high-density buildings, narrow site space, complicated geotechnical condition, dense underground networks and busy traffic. The double or multiple tunnels are frequently used in processing subway engineering in cities. Sometimes underground space construction must be done close to the existing tunnels with complicated mechanics behavior. With the increasing adjacent-tunnel engineering by shielding, problems of interaction induced by nearby-neighbor shielding tunnel become more and more serious. Therefore, controlling the effect of clear-distance shielding tunnels can ensure the safety of existing shield tunnels and successful construction of new shield tunnel, which is very important to the development and utilization of urban underground space. In this paper, an overall analytical study was made on the neighborhood effects during the nearby-neighbor tunnel construction with shield driving method. On the basis of summarizing the current studies, some typical practical cases and treatment methods were introduced, some key problems encountered in the present studies are put forward, and some new ways for research in future are expected.