Uniaxial Compression Creep Behavior Of Green Sandstone Subjected To Dynamic Disturbance Of Drop Weight Hammer

Many rock masses engineering would serve for decades or even one hundreds years.Therefore,the safety of such engineering must be ensured in the service life.Creep behavior is one of the main mechanical characteristics of rock materials.As many engineering practices have indicated,creep is an important factor that can result in the large deformation or instable failure of rock.Although a great advance have been made in experiment and theory of creep behavior,the accelerating creep failure mechanism of rock has not been fully revealed so far.In mining engineering,the dynamic disturbances such as drilling and blasting,roof failure,mechanical vibration and blasting-induced stress wave will have significant impacts on the rock creep behavior.Therefore,incorporation with experimental tests,theoretical analysis and numerical simulation,this paper study the creep properties of green sandstone under conventional uniaxial compression and dynamic disturbances.Based on the results of creep tests,a creep damage-based model was proposed by virtue of rheological mechanics and damage mechanics theory.The model was solved by programming on the basis of finite element software.And then,the time-dependent damaged zone distribution and long-term stability of surrounding rock were analyzed in detail.The main research work in this paper can be summarized as follows:(1)Uniaxial compression creep experiments on green sandstone were carried out on the rock rheology-impact test machine.The creep properties of green sandstone were well investigated.The duration of the decelerating creep stage,the stress of onset of dilatancy(?c)and the long-term strength were determined.The power-law creep equation was adopted to fit the experimental data and finally the creep parameters were obtained.(2)On the basis of classical power-law creep equation and damage mechanics principle,a creep damage-based model was presented in which the damage evolution is considered as a key factor dominating the accelerating creep.In the proposed model,the heterogeneity of rock is considered,and both the maximum tensile strain criterion and the Mohr-Coulomb criterion are utilized to evaluate the damage thresholds of rock.The model was implemented using finite element method by MATLAB programming under the environment of COMSOL Multiphysics and validated by a uniaxial compression creep experiment.In addition,the sensitivity of the parameters was analyzed in detail,which can provide references for parameter assignment when conducting other numerical simulations with this model.(3)Based on the proposed model,numerical simulations of creep induced progressive damage and failure process of green sandstone were performed under uniaxial compression and triaxial compression.The influences of differential stress on creep strain and failure time were discussed.The initiation,propagation and coalescence of cracks during creep are vividly reproduced in the numerical modelling.Numerical experiments on different sizes of specimens under uniaxial compression creep were also conducted and the size effect on long-term strength of rock was analyzed.(4)Creep tests on green sandstone specimens coupled with single and multi-cycle impacts were conducted using the rock rheology-impact test machine.The influences of dynamic disturbance on creep behavior are investigated under different creep deformation and impact energy.The impact energy utilization is also calculated.In order to clarify the mechanism of accelerating creep induced by dynamic disturbance,the damage and failure process of creep under dynamic loading was simulated.The evolution of creep damage and failure of rock was well represented under stress wave.(5)Uniaxial compression creep tests on square green sandstone specimens with precut circular hole were carried out.The variation law of deformation with time and the initiation and propagation of microcracks around the hole are analyzed.The deformation of surrounding rock of horizontal circular roadway is calculated by using viscoelastic theory,the distribution laws of stress,strain and displacement are obtained.In addition,using the proposed model,time-dependent deformation of surrounding rock was numerically simulated.The failure time and fracture mechanism of surrounding rock are analyzed under different lateral pressure coefficients.