Influence of Boundary Conditions on Centrifuge Tunnel Tests

Centrifuge experiments at the Universities of Cambridge and Nottingham were conducted to investigate shallow mechanized tunnels in cohesionless soils. In these experiments, radial stress is applied at the tunnel perimeter using a brass cylinder wrapped in a latex membrane and filled with water. The initial radial stress equaled the hydrostatic pressure on the membrane, set to match the vertical stress at the springline depth. Excavation was simulated by gradually extracting water from the space between the membrane and cylinder, thereby relieving radial stress. This study compares the centrifuge loading condition with the stress relief method through numerical modeling using the NorSand constitutive model. Both modeling approaches accurately reproduced centrifuge results for tunnel volume losses (VLt) up to 2%. Although differences on volumetric and shear strain distribution were observed near the tunnel perimeter, this study indicates that both loading conditions provide similar ground displacements for VLt up to 2%.