Study on the Hoek-Brown Parameters under Loading and Unloading Triaxial Laboratory Tests
Based on the brittle fracture theory of composite crack, and then overlapping the stresses at the end region of a crack under tension-shear or compression-shear failure conditions, the relationships of parameters in rock macroscopic and microscopic are determined by combining the Hoek-Brown failure criterion. There are many valuable conclusions through a series of loading and unloading triaxial laboratory tests on rock samples. The tension-shear fracture under the unloading triaxial tests at pre-peak is different from the compression-shear fracture under the loading triaxial tests. The Hoek-Brown criterion for rock is applicable and validity under the condition of loading triaxial tests. Because the uniaxial compressive strength is not the fundamental characteristic of rock, the virtual uniaxial compressive strength is proposed for the first time considering the unloading problem. Comparing with the loading tests, the Hoek-Brown material parameters of rock samples change greatly under unloading at pre-peak, and the virtual uniaxial compressive strength improves and Hoek-Brown material constant m reduces.
Guangfan Li, Yong Huang and Chaohe Chen
J. Z. He et al., "Study on the Hoek-Brown Parameters under Loading and Unloading Triaxial Laboratory Tests", Advanced Materials Research, Vols. 250-253, pp. 2074-2078, 2011