Study On The Dynamic Damage Constitutive Model For The Cracked Rock Mass Basing On Coupling The Macroscopic And Mesoscopic Flaws

Through a long period and complicated geological action, rock mass is a kind of natural geological body which contains not only macroscopic flaws such as joints and cracks but also mesoscopic flaws such as microcracks and microholes. Now most of the existing rock mass dynamic damage constitutive models only consider the effect of one of them, which is difficult to reflect the real mechanical property of the rock mass.Therefore, the Split Hopkinson Pressure Bar (SHPB) test is firstly adopted to study the effect of the crack on the cracked sandstone samples. Then the pendulum-type impact test is also done on the cracked samples made with similar material. Based on the test result above and the damage and fracture theory, the dynamic damage constitutive models for rock mass with the persistent and non-persistent joints are established. And their validity is verified with the calculation examples. Finally, the proposed model is preliminarily applied into the design method of the dimension of the mine pillar in the underground mine.The following research conclusions and achievements are obtained in this dissertation.1) The dynamic mechanical property of the rock mass is studied with the SHPB test. The relationship among the dynamic mechanical property of the rock mass and the crack orientation, density, the ratio of the sample’s length to its diameter, loading rate is set up. The pcndulum-typc impact test discovers the effect degree and change law of the crack length and dip angle on the cracked rock mass dynamic failure mode, absorbed work and impact toughness.2) The damages caused to the rock mass by the macroscopic and mesoscopic flaws are regarded as the macroscopic damage and mesoscopic damage, respectively. And then the calculation formula of damage variable (tensor) by coupling the macroscopic and mesoscopic flaws is deduced based on Lemaitre strain equivalent hypothesis.3) Basing on the basic principle of the damage mechanics and TCK (Taylor-Chen-Kuszmaul) constitutive model for the intact rock, the dynamic damage constitutive model for the rock mass with persistent cracks is established which can reflect the coupled effect of the macroscopic and mesoscopic flaws.4) According to the propagation mechanism of the non-persistent cracks under the uniaxial and biaxial compression, the calculation formula of the macroscopic damage variable (tensor) of the cracked rock mass which can consider the geometrical and mechanical parameters at the same time is firstly deduced based on the damage and fracture mechanics. Then effect of the deformational parameters of the crack such as the normal and tangential stiffness on the rock mass elastic modulus is considered. Finally, the dynamic constitutive model for the rock mass with the non-persistent cracks under uniaxial compression is established basing on TCK model for the intact rock and the coupled damage variable (tensor), which can consider the effect of the crack geometrical, mechanical and deformational parameters on the rock mass dynamic mechanical property at the same time.5) The design method of the dimension of the mine pillar in the underground mining engineering in Shirengou Iron Mine of Hebei Iron and Steel Group Mining Limited Corporation is preliminarily discussed with the proposed dynamic constitutive model for the rock mass. The study result can be referred for the engineering design.