Numerical Investigation On Rock Mechanical Characteristic Under Dynamic Loadings

Aiming at increase requirement of underground space and resources,the rock engineering becomes deeper and deeper.The dynamic mechanical charachteristic of rock masses have thus been attracted numerous attentions.Common dynamic distrubances,including blasting,vibration,impact and earthquake,usually propagate inside rock masses as the form of the compressive stress waves,which may transfer to the tensile one owing to the rock heterogeneous behavior and the existing of discontinuities.Therefore,it is of great theoretical and engineering significance to investigate the dynamic compressive and tensile behaviors of rocks when subject to the dynamic loadings.In this paper,based on the FEM stress-strain analysis and equivalent continuous damage mechanics,Weibull statistical distribution function and Newmark implicit integration algorithm were utilized to describe the rock heterogeneity and to solve the dynamic finite element equation,respectively,the viscoelastic artificial boundary was firstly implemented into RFPA.followed with the determination of dynamic element size effect.The contact problem in rock mechancis was detailedly analyzed,two contact models,i.e.,static and dynamic friction based dynamic contact model and damage based contact model,were implemented into RPFA to study the interface behaviors.The first contact model has ability in simulating the whole impact process between two blocks,which was further employed to investigate the fracture process of rock plate under impact loading.In addition,simulation results demonstrated that the second contact element could successfully model the damage evolution along the interface between two different materials as well as the variation of the contact statuses.Numerical split Hopkinson pressure bar(SHPB)and split Hopkinson tensile bar(SHTB)testing systems were successfully established both in two dimensional and three dimensional based on those two contact models.The rock dynamic compressive and tensile characteristics under different setups of those two testing systems were systematically investigated after comprehensive verification works.Moreover,the strain rate effect,inertial effect and friction effect were detailedly studied and distinguished.The differences of the rock tensile strength derived from direct tesnion test and indirect tension tests under both of static and dynamic loading were discussed,followed with physical mechanics lying behind.In the static analysis,the direct tension test,Brazilian test and three point bending test were compared.And in the dynamic analysis,the dynamic direct tension test and dynamic Brazilian test were taken into comparison.The developed SHPB testing system was performed to consider the combined static and dynamic loadings,including the static axial pressure,lateral confining pressure and impact loading.In addition,three different interfacial treatments were employed to address the interface behavior between rock sample and incident bar and transmitted bar.Furthermore,the findings were utilized to investigate effect of in-situ stresses on the rock dynamic compressive strength.The depth and parameter K,which is defined as the ratio between horizontal and vertical in-situ stress,were numerically studied.