A Numerical Study On Dynamic Responses Of Rock Tunnels Subject To Blast Wave Using The Discrete Element Method

Numerical studies on transmission of blast-induced shock wave in jointed rock masses and responses of rock tunnels subject to blast-induced shock waves are performed with discrete element method (DEM) in this thesis.Firstly, a numerical study on wave transmission across jointed rock masses is performed with UDEC, where multiple intersecting joint sets exist. The capability of UDEC of studying wave transmission across rock joints is validated through comparison with analytical solutions or experimental data, where the cases of normally incident wave across a single joint, normally incident wave across a joint set, obliquely incident wave across a single joint, obliquely incident wave across multiple joint sets are modeled. Through parametric studies on wave transmission across jointed rock masses, it is found that joint mechanical and spatial parameters including joint normal and shear stiffnesses, nondimensional joint spacing, joint spacing ratio, joint intersecting angle, incident angle, and number of joint sets together determine the wave transmission. But, for P wave incidence, compared with other parameters, joint normal stiffness, nondimensional joint spacing, and joint intersecting angle have more significant effects on wave transmission. The physical reasons lying behind those phenomena are explained in detail. Engineering applications and indications of the modeling results are also mentioned.Then, numerical modeling of a large-scale decoupled underground explosion test using10tons of TNT in Alvdalen, Sweden is performed combining UDEC and AUTODYN modeling codes. AUTODYN is adopted to model explosion and blast wave generation and wave acting on the explosion chamber surface, while the UDEC modeling is focused on shock wave propagation in jointed rock mass surrounding the explosion chamber. The numerical modeling results from the hybrid AUTODYN and UDEC method are compared with empirical estimations, AUTODYN modeling results, and the test data. It is found that in terms of peak particle velocity, empirical estimations are much smaller than the test data, while AUTODYN modeling results are much larger than the test data. The UDEC-AUTODYN numerical modeling results agree very well with the test data. Therefore, the UDEC-AUTODYN method is appropriate in modeling large-scale explosive detonation in a closed space and the following wave propagation in jointed rock masses.Following these, numerical modeling on the damage of rock tunnel subject to blast-induced shock wave was carried out with hybrid UDEC and AUTODYN method. The disturbed zones including failure zones, open zones and shear zones around circular tunnel and peak particle velocities (PPVs) at tunnel surface are employed to analyze the damage of tunnel. The effects of joint angle, joint spacing, joint stiffness, initial stress of rock mass, and magnitude of shock wave amplitude to damage of rock tunnel were evaluated in this study. The difference of damage between non-supported rock tunnel and bolt-supported rock tunnel subject to the same blast-induced shock wave was also studied. It is found that the orientations of joints in rock mass around the tunnel have great effects on tunnel damage. The initial stress around tunnel has relatively small influence on tunnel damage. The bolt support could greatly increase the stability of tunnel by changing the particle vibration velocity, which occurs after the time of peak particle velocity and can be explaned by the fact that bolts could absorb blast wave energy through there deformation.Moreover,2D equivalence of3D plane wave propagation across a single joint and a joint set is proposed and verified through spatial conversion, and the corresponding conversion formulas are derived. This conclusion can be a useful method for simplify of wave transmission problems in specific3D condition, and reduce the computing cost and improve the computing efficiency. Numerical modelings of wave transmission in jointed rock mass, including normally incident wave across a single joint, normally incident wave across a joint set, obliquely incident wave across a single joint, obliquely incident wave across a joint set, obliquely incident wave across multiple joint sets, are performed with3DEC. The analytical solutions and experimental data are employed to evaluate the modeling results.Finally, the main achievements of the whole PhD work and future research works are summarized and prospected.