Nonlinear Analysis of Tunnel Deformation and Mechanisms of Stress Transfer Caused by Basement Excavation

Many new excavations are planned and constructed near or parallel to existing tunnels. Adjacent excavations may significantly impact the stress and deformation of existing tunnels. To evaluate deformation and the mechanisms of stress transfer, well-instrumented centrifuge model tests are back-analyzed using an advanced nonlinear constitutive model, known as a hypoplasticity model. Three-dimensional stress transfer mechanisms along the tunnel axis are demonstrated by changes in normal stresses in the soil around the tunnel. It is found that, for an existing tunnel located directly beneath the basement, the maximum reduction of earth pressure around the tunnel is about 50% at the crown and 20% at the springline of its initial earth pressure. As a result, the tunnel is vertically elongated and horizontally compressed. A tunnel, located at the side of a basement, is elongated along the connection between the right shoulder and left knee and compressed between the left shoulder and right knee. It is expected that this study will help improve the fundamental understanding of three-dimensional stress transfer during basement excavation around existing tunnels.