Evolution Mechanisms Of Rock Fragmentation Under Blasting And Optimum Design Of Drilling And Blasting In Deep Tunnel

With increasing demand on resources and utilization of underground space,underground excavation has gradually extended to greater depth.When the drilling and blasting method is applied for the excavation of deep rock mass,due to rock mass under the action of high in-situ stress,the blasting load will be influenced by the high in-situ stress,which leads to the different damage mechanism of rock mass induced by blasting between deep rock mass excavation and shallow rock mass excavation.Therefore,the investigation on it will be a great help to a better understanding on fracture process of blasting excavation for deep rock mass.Additionally,the the success in blasting excavation of deep rock mass can be achieved by optimizing design of.Consequently,the drilling and blasting method can be better applied in the underground engineering construction.At present,much investigations have been done on the damage mechanism of periphery blasting,while only a little works are done for the damage mechanism of the cut blasting and stopping blasting.In the paper,the research on the damage mechanism of the cut blasting and stopping blasting are performed.In cut blasting excavation of deep tunnels,the rock mass is subjected to dynamic-static coupling load.To investigate the damage evolution mechanism of rock mass,the damage model is developed,and is further implemented into LS-DYNA software as a user-defined model.According to the research results,it is found that the fracture of rock mass is caused by shock waves,stress waves,superimposed stress waves,reflected tensile waves,while resistance of in-situ stress to the damage extent and the anisotropy of the damage zone results in the challenges in cut blasting excavation of deep tunnels.To overcome the challenges encountered during cut blasting excavation of deep tunnels,the cut blasting design needs to be optimized,the RHT model in LS-DYNA software is applied to simulate the cut blasting design.To apply the RHT model in the cut blasting design of deep tunnels,the parameters of the RHT model is determined.Based on the determined parameters,the blasting of cut holes and auxiliary cut holes with different burdens are simulated.Through the simulation,the causes of challenges encountered during cut blasting are analysed,and the cut blasting design is optimized to overcome these difficulties.After the cut blasting excavation of deep tunnels,the strain energy in rock would concentrate.When the collected strain energy is greater than the energy storage capacity of rock masses,the strain energy is released and transformed.At this time,there is a phenomenon of easy blasting for the stopping blasting excavation of deep tunnels.To investigate the damage evolution mechanism of deep tunnels under stopping blasting,it is rational to study on it from the view point of energy.In the paper,the JHR damage constitutive model is proposed based on JH2 model and it is used to research the damage evolution mechanism of deep rock mass under stopping blasting.The research results indicate that the fracture of rock mass is caused by shock waves,stress waves,superimposed stress waves,reflected tensile waves;unloading of rock mass has induction effect on rock fracture;the energy storage capacity of rock masses and the anisotropy of the damage are main reason for the easy blasting in the deep rock mass.