An Experimental Damage Model and Its Application to the Evaluation of the Excavation Damage Zone: Fid-Bau Portal

An Experimental Damage Model and Its Application to the Evaluation of the Excavation Damage Zone

Chang, Soo-Ho / Lee, Chung-In / Lee, Youn-Kyou

Summary. An experimental damage model, which can simulate both post-peak and pre-peak damage characteristics of rock by assuming distinct elastic constants in each damage level, was proposed. Each damage level was identified by two successive threshold values of major principal stresses, which could be determined from uniaxial and triaxial compression tests and measurement of acoustic emissions. Elastic constants pertaining to each damage level were expressed in terms of confining pressure (minor principal stress) by regression equations of the experimental data. Post-peak behavior was simulated by selecting suitable values of the Hoek-Brown constants mr and sr for post-failure. The proposed experimental model was implemented into FLAC by writing a FISH function. The parametric studies on Hoek-Brown constants for post-peak behavior revealed that peak strength depends greatly more on sr than mr, and post-peak slopes of stress–strain curves depend mainly on mr. Together with the elastic and elasto-plastic models, the nonlinear-brittle-plastic damage model derived from experiments was applied to the evaluation of an excavation damage zone around a highly-stressed circular tunnel for the purpose of checking the performance of the model. Of the three models, the nonlinear-brittle-plastic damage model gave the largest extent of disturbed zones and displacements around the tunnel. The damage zone predicted by the nonlinear-brittle-plastic model became larger as the magnitudes and the stress differences of in-situ stresses increased. Consequently, taking the damage model into account in the stability analysis of hard rock tunnels may be appropriate for conservative design of a highly stressed tunnel.