Model Tests for Plastic Response of Lined Tunnels

Static isotropic and uniaxial strain loading tests were performed on models in a rock simulant having an unconfined compressive strength of about 4,300 psi (29.7 MN/m²) and a friction angle of 33°. The liners consisted of direct-contact steel tubes of three different radius-to-thickness ratios (a/h=50, 25, 12.5). In the isotropic loading experiments, the load-deformation relationship for the liners was in good agreement with theoretical curves from an elastic-plastic analysis and showed substantial increase in strength with increasing liner thickness. At the higher loads, the a/h=50 and a/h=25 liners buckled, and the deformations became larger than predicted by the theory. The a/h=12.5 liner did not buckle, even at tunnel closures of 5%. Similar behavior was found in uniaxial strain loading experiments, but 30% to 50% less load was required to cause 5% tunnel closure than under isotropic loading.