Numerical Simulation Of Rock Mass Unloading Damage And Its Engineering Application

Rock mass is the product of diagenetic and geologic structure movements in the long period of geologic history, in which discontinuities in rock mass of different size, different orientation and different property has been formed under loading and unloading continuously. Therefore, rock mass in the nature is a damage body which experienced these kinds of geologic structure movements. Unloading of rock mass owing to human engineering activities is a process of further damage degradation. Consequently it has very important theoretical significance to research the unloading characteristics of rock mass with damage mechanics theory.It narrates the research situation and prospect of unloading rock mass mechanics and brittle material damage mechanics, and introduces the basic theories of damage mechanics in this paper. Based on above works, a damage variable has been defined with macro approach. Using this damage variable, an unloading damage constitutive model has been derived based on Frantziskonis and Desai damage model, and the reflection of the model to unloading has been analyzed.Secondly, an unloading damage rock mass failure criterion has been educed by introducing the damage variable defined above into Drucker-Prager yield criterion based on the concept of effective stress.Thirdly, the damage evolutional process of initial microfracture in rock mass and the relationship between rock mass deformation modulus and damage virable under unloading have been studied, and the influence of two heterogeneity initial damages to rock mass unloading has been analysed comparatively.Finally, take the II profile of diversion channel of Lidi hydroelectric power station for example, computation has been carried out with finite element method, and the differences between the results of considering unloading damage and neglecting unloading damage have been compared.