The Occurrence Mechanism Of Anomalously Low Friction-type Rockburst And Its Quantitative Prediction In Deep Caverns

Unlike the shallow rock mass, deep rock mass which characterized by the discontinuity of medium and high geostress shows entirely different behavior under the state of excavation unloading. The stress wave propagation induced by excavation disturbance can cause an anomalously low friction phenomenon and induces the pressure variation of structural surface in rock mass which may lead to a rockburst. Therefore, based on the study of anomalously low friction effect in dynamic response of the deep rock mass, this paper proposes an occurrence mechanism of anomalously low friction-type rockburst and establishes a discontinuous block rockburst prediction model. Moreover, new prediction method is applied to an engineering project. The main contents of this paper are as follows:Firstly, one dimensional discontinuous block model of deep rock mass from which displacement, velocity, acceleration of blocks and the relative displacement between two adjacent blocks can be obtained is established. By exploring the pressure variation of structural surface, this paper reveals the existence of anomalously low friction effect and illustrates its influence on block movement and rock damage.Secondly, by introducing the angle freedom, a two-dimensional discontinuous block model of deep rock mass is established. Through the interaction relationship between blocks, the translational and rotational equations are acquired. Explicit finite difference method is adopted for determining the time-history curve of strain between blocks. It is proved that the anomalously low friction phenomenon exists in two-dimensional rectangular tunnel model as well. The occurrence mechanism of anomalously low friction-type rockburst are proposed. Moreover, the influence of different geological parameter on anomalously low friction effect are studied.Thirdly, a two-dimensional rockburst prediction model is established to analyze the intensity of anomalously low friction-type rockburst including rockburst initiation process and characteristics of rockburst. The corresponding relation between the empirical rockburst intensity classification criteria and the present rockburst prediction model is established to prove the feasibility of new model. In addition, the influence of different geological mechanical parameters on the intensity of rockburst are analyzed.At last, the two-dimensional rockburst prediction model is applied to investigate the rockburst of the drainage tunnel in Jinpingâ…¡Hydropower Station. Sections of the drainage tunnel with different grade of surrounding rock are analyzed. The prediction result agrees well with the measured data and the simulation result by UDEC that verify the accuracy of the present model in predicting rockburst intensity.