ABSTRACT
Squeezing ground conditions in tunnels are often associated with rock mineralogy, strength, ductility/brittleness, excavation sequence, and magnitude of in situ stresses. Numerous methodologies and empirical correlations have been proposed in the past to determine the level of ground squeezing conditions in tunnels. Most of the correlations are problem-specific and limited in scope. In this work, a fundamental study of tunnel squeezing is carried out using an experimental approach to simulate tunnel boring machine (TBM) excavation in squeezing ground conditions. The experimental setup employs a cubical specimen of a soft rock/soil/synthetic material with each dimensions of 30 cm long. The specimen is subjected to a true triaxial state of stress with different magnitudes of principal stresses and stress levels corresponding to realistic in situ conditions. A miniature TBM is used to excavate a tunnel into the host rock (specimen) while the rock is subjected to true-triaxial state of stress. Embedded extensometers and strain gages glued on the surface of the tunnel liner are used to monitor tunnel response during construction. This paper presents the details of the experimental setup.
