A Prediction method on the post-failure properties of rock and its application to tunnels

Öge, İbrahim Ferid
Due to special testing system requirements, data related to the post-peak region of the intact rock laboratory parameters are not as commonly available as pre-peak and peak- state parameters of stress-strain behavior. For geotechnical problems involving rock mass in failed state around the rock structures, proper choice of plastic constitutive laws and post-failure input parameters is important for a realistic modeling and simulation of the failed state of the rock mass. A total of seventy-three post-failure uniaxial compression tests were conducted. Rock samples included in the testing program are chosen to represent rock types of different origin. Intact rock testing data provide parameters like modulus of elasticity and unconfined compressive strength. These results that are readily available from a regular testing program are processed and compared to the post-failure state stress-strain parameters defined as drop modulus, residual strength and post failure state dilatancy. Results are organized and processed based on the origin of rock types used in the investigation. For the estimation of post-failure state parameters in terms of pre-peak and peak state parameters, functional relations are provided based on regression analyses and fitting parametric. In order to utilize the post-failure parameters in a practical rock engineering case, extension of intact rock parameters to the rock mass is required. Estimation of rock mass parameters based on intact rock testing will lead engineers to make meaningful entries for numerical modeling programs such as FLAC3D. Relating the post-failure parameters to the rock mass behavior is another aim. Involving a calibration work here, stability analysis of an underground excavation model is presented. Hence, the post-failure deformability and strength parameters of the rock mass which are generally assigned by engineering judgment and experience can be estimated by the proposed relations. These will assist engineer to conduct more accurate and realistic numerical modeling in using programs like FLAC3D. Proposed empirical equations enable the user to conduct detailed post-failure analyses. Considerable differences in results regarding the plastic zone extent and deformations are observed between the typical assumptions of post-failure modes like brittle, perfectly plastic, softening with Hoek-Brown and Mohr-Coulomb yield and plastic potential functions. Right choice of applicable post-failure mode and its related parameters improves the accuracy of the estimation of tunnel deformations and support selection.


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Citation Formats
İ. F. Öge, “A Prediction method on the post-failure properties of rock and its application to tunnels,” Ph.D. - Doctoral Program, Middle East Technical University, 2013.