The Mechanical Properties And Constitutive Model Research Of Soft Rock Under Dynamic Load

In deep mining, rock mass is often affected by disturbances of dynamic load such as tunneling blasting, rock fracture. The dynamic disturbances often lead to slope and local instability of tunneling surrounding rock, rock-burst and gas outburst. In order to study the mechanism of rock failure under disturbances of dynamic load and how to adopt reasonable measures of antiknock design, dynamic mechanical properties and constitutive relation of rock have to be grasped, especially the constitutive relations of rock under the action of dynamic load, which is the necessary information for studying the law of stress wave propagation and the antiknock design. Therefore the research on dynamic mechanical properties and constitutive relation of soft rock material in deep well is of great significance.For studying the dynamic mechanical properties and the constitutive relation of deep soft rock under dynamic load, the experiment system of Split Hopkinson Pressure Bar is explored to experiment on the mudstone, sandy mudstone, and fine sandstone of three kinds of typical soft rock under uniaxial dynamic compression. Through experimental research and numerical simulation, it is found that dynamic modulus of elasticity, broken size and dynamic intensity of soft rock in deep well has obvious strain-rate effect. At present, there are two constitutive model including excess stress model and Zhu-Wang-tang model, which can reflect the constitutive curve characteristics of deep soft rock under dynamic load. But, both of them have some disadvantages. Therefore, they need to be made further improvement.In this paper, the stress constitutive models have been made two improvements, and then establish the damage type simplified stress constitutive equation. Firstly, according to the function relationship between strain, strain rate and1-E(t)/Eo, the current constitutive equation of modified excess stress model is simplified with dimensionless analysis. Secondly, the continuum damage theory and statistical damage theory are incorporated into the simplified constitutive equation of modified excess stress model given consideration of the influence of damage to dynamic strength. In this paper, as for Zhu-Wang-Tang model, the damage visco-elastic dynamic constitutive model, which was based on the Zhu-Wang-Tang model, was developed by using damage body to be instead of elastic unit of Zhu-Wang-Tang model. In order to prove the rationality of two modified constitutive model. Constitutive functions are fitted out respectively on the basis of the experimental data of soft rock in deep well, hard rock and concrete in SHPB experimental system. There is a good coherence between the fitting stress-strain curves and the experimental stress-strain curves. Consequently, the two modified model equations can offer references for further research on dynamic constitutive model of soft rock and concrete and engineering application in underground engineering.