Abstract
Tunnel excavation could damage adjacent structures, both above the ground surface and embedded underground, due to the associated ground movements and stress changes. To estimate ground movement caused by tunneling, simplified methods using Gaussian curve or twodimensional numerical analysis are commonly used.
However, when there is a presence of existing underground structures such as tunnels, the simplified methods may not be applicable to predict the ground displacement. A series of three-dimensional centrifuge tests in dry sand and numerical backanalyses were carried out to improve the fundamental understanding of ground movement caused by multi-tunnel interaction.
The major objective of this paper is to study the shielding effects on the interaction of multi-crossing tunnels. The diameter of each tunnel is equivalent to 6 m in the prototype scale.
The existing tunnel was instrumented and modeled as "wished-in-place". The new tunnel was excavated three-dimensionally in-flight using a device called "Donut", which simulated the effects of volume loss and weight loss.
To further analyze the ground displacement and stress distribution in the ground, three-dimensional finite element analyses using an advanced hypoplasticity constitutive model with small strain stiffness were conducted. Unlike any conventional elastic-perfectly plastic constitutive model, the hypoplasticity model can simulate soil stiffness dependency on state, strain and stress path.
The impact of the new tunnel excavation on the existing tunnels and ground displacement is reported. Interpretation of measured and backanalyzed data of crossing multi-tunnel interaction is provided.
Influences of shielding on movement of soil, stiffness mobilization and stress redistribution are discussed and explained.