1、翻译部分（英文原文）Numerical Simulation of Rock Burst in Circular Tunnels Under Unloading ConditionsSUN Jin-shan,ZHU Qi-hu,LU Wen-boState Key Laboratory of Water Resource and Hydropower Engineering Science,Wuhan University,Wuhan,Hubei 430072,ChinaAbstract: Rock burst in a circular tunnel under high in-situ s
2、tress conditions was investigated with a numerical method coupled the rock failure process theory(RFPA)and discontinuous deformation theory(DDA).Some numerical tests were carraied out to investigate the failuer patterns of circular tunnel under unloading conditions.Compared the results under loading
3、 conditions,the shapes of failure zones are more regular under the unloading conditions.The failure patterns in the same type of rock mass are clearly different because of non-homogeneity of the rock material.The extension of cracks shows some predictability with an increasing of in-situ stress.When
4、 the homogeneity index of rocks(m)is either relatively high or low and lateral pressure coefficients()is high,the number of regular shear slide cracks decreases and the probability of a rock burst also becomes lower.Our numerical simulation results show that the stability of surface rock and the nat
5、ural bedding stratification of rock material greatly affect rock bursts.Installing bolts with due diligence and suitably can effectively prevent rock bursts.However,it is not effective to control rock bursts by releasing the strain energy with normal pre-boreholes.Keywords: circular tunnel; unloadin
6、g; rock burst; numerical simulation; RFPA1. IntroductionRock burst is a typical geologic phenomenon caused by excavation.Many scholars have investigated the complex geological hazard from different points of view.However,the essential reasons of this phenomenon have not been understood.Rock burst ge
7、states in the rock masses and there never is any warning that it is about to happen.So files that record the entire process of rock burst are hard to find,which includes the process from gestation to burst.By model tests and investigating rock bursts records,some scholars proposed some ratiocination
8、s about rock burst processes13.Rock burst contains the emerging and extension process of cracks on the mesoscale and the macroscopic loss of stability.It is very difficult to study this phenomenon with classical theories of mechanics.As well,only one single process of it can be studied by some numer
9、ical methods.Hence,in our investigation we have analyzed rock burst with a method coupled the rock failure process analysis theory(RFPA)on ameso-scale and the discontinuous deformation analysis theory(DDA)on a macro-scale.2. Numerical Simulation Method of Rock BurstsRock burst is caused by the excav
10、ation of under-ground caves which unload the in-situ stress.It can bedivided into two basic phases.One is the gestation process of rock burst,in which rock materials crack gradually.The other is the dynamic burst of rock blocks which release vast strain energy of the surrounding rock masses.Given th
11、is classification it also can be divided into two processes when rock burst is simulated with numerical methods.In the first step,the numerical mode could be studied by RFPA that considers the non-homogeneity of rock materials.Agiven load should be specified for numerical models in order to simulate
12、 the in-situ stress in rock masses.Then,elements in a circular opening will be deleted to simulate the excavation.The processes of cracks emerging and extending can be simulated with the RFPA2D program.Based on the results of RFPA2D,the failure patterns of surrounding rock masses can be judged.If a
13、large number of failure points are distributed densely or dispersed widely and there are no long cracks,the rock mass may go into the plastic flow state(e.g.re-laxation and squeezing)and releases a mass of strain energy.However,if there are some long cracks and a small quantity of dispersed failure
14、points and the elastic module of rock blocks has not changed fundamentally,much of the strain energy may be released through rock bursts.When the surrounding rock mass is partioned into blocks it becomes a discontinuous deformation system which can be analyzed by DDA method.Based on the results of f
15、ailure analysis a DDA model of the circular tunnel can be made,in which the mechanical parameters and load conditions are equal to those of the RFPA model.When the rock mass is meshed in rock blocks and structure faces,the cracks caused by stress unloading are simplified to the structure faces.Some
16、potential crack faces are set in the model.Then the failure process of rock mass can be simulated with the DDA2D program.3. Simulation of Rock Burst GestationAccording to the slip-line theory, the surrounding rock mass will crack along the slip-line.Many rock burst records and analyses of fractured faces show,with a scanning electron microscope,that the shearing-dislocation rock burst is one of the most common patterns,especially in circular tunnels46.Hence,t
