Research On The Mechanism Of Rock Fracture And Creep Damage Failure

Abstract:Due to the effect of fissures on mechanical characteristics of rock mass, the research on fracture mechanism and creep damage failure of fractured rock mass affected by stress field or fluid-solid coupling is a hot topic in rock mechanics. It has significant theoretical value and guiding significance to the safety and efficiency of rock projects.The study on the fracture mechanism and creep damage failure of fractured rock mass affected by stress field or fluid-solid coupling is conducted systematically in this dissertation. It is different from the previous studies which are generally restricted to the developing patterns and mechanism of wing cracks. However, previous studies rarely explore the strength change laws. Consequently, previous studies ignore inevitably the scope of application of the slipping crack model theory interpreting and analyzing the developing patterns and mechanism of wing cracks. Meanwhile, previous studies of creep damage failure of rock mass mainly focus on nonlinear combination model and neglect the nonlinear feature of creep deformation of jointed rock mass, which usually make mistakes of describing the nonlinearity with linear element. Based on the difference between the theoretical solution and the experimental result of slipping crack model, it is firstly proposed that there exists limitation when applying sliding crack model theory to interpret and analyze the fracture failure mechanism of open fissures. Furthermore, combining the elasticity theory and the analytic solution of circular tensile stress of oblate ellipsoid hole under compression is put forward. According to the distribution of positive stress on the fracture surface under fluid-solid coupling, the criterion of the high or low seepage condition in jointed rock mass is presented creatively. On one hand, the general geotechnical engineering problem can be simplified into three kinds of mechanical models which are calculated and analyzed numerically. On the other hand, the damage factor is applied in the study of rheology that the damage element model is established based on basic rheological elements. Moreover, the nonlinear visco-elastoplastic mechanical model considering the impact of native joints is deduced by imbedding jointed plastic body and accelerated creep body in combined creep damage model. The work done is mainly composed of following four parts:(1) The developing mechanism of the wing cracks caused by tension at the fissure tips which are subjected to the stress composed of compression and shear is deduced excellently by the theory of slipping crack model. Combined with the Maximum Circumferential Tensile Stress theory, this slipping crack model was established based on the neglect of the mechanical effects exerted by the compression stress at the fissure tips, while only the friction resistance in the slipping process was taken into consideration in this model. However, this model is limited to investigate the law of the strength in fissured body. Combined with the morphological characteristics and the mechanical response law of fissured body, the limitation of the slipping crack model in predicting the failure mechanism was investigated. According to the analytic solution of the elliptical-hole problems in the field of elastic mechanism, the mechanical response law at the boundary of the flat elliptical hole was proposed, and then the investigation of the deformation and failure mechanism of the specimens with opening fissures which were subjected to uniaxial loading was conducted.(2) The model programs in the Fish Tank were adapted based on fish language on the PFC numerical calculation platform to improve the development of models in the Fish Tank. Then, the computation and analysis of the simulation specimens with multiple fissures or single fissure were conducted by programs contained in the Fish Tank and improved Fish Tank programs. Comparing numerical computing results with experimental results, it showed the existence of the limitation of the slipping crack model in interpreting the developing pattern and mechanism of wing cracks caused at open fissure tips.(3) The construction techniques and methods of the closed fractured rock mass model were investigated numerically. In addition, the uniaxial and biaxial compression tests of closed fracture numerical model were conducted in the2-D Particle Flow Code. Compared with the mechanical response law of open fracture model, the influence of closure forms of fissures on fracture failure modes was further confirmed.(4) The mechanical characteristics of fissured rocks in seepage field and the mechanism of actions between water and rock are the front directions in rock mechanism. And these directions are going to be hotpots which attract more theoretical and experimental studies gradually. Meanwhile, the existence and the change of the seepage field are the main factors which may lead to the instability of engineering rocks and even the geological disasters in large scale. So, it is promising in application and valuable in academic to investigate the response of the fissured body in the unloading process and conducting analysis on engineering stability in the seepage field. According to the stress distribution of the inner surface which was subjected to the action exerted by coupled seepage and stress field, the criterion of the high or low seepage condition was proposed, and the fracture mechanisms of the fissured body corresponding to the different seepage pressures were also obtained. Moreover, the general geotechnical engineering problem can be simplified into three kinds of mechanical models including vertical loading, lateral unloading and increasing the osmotic pressure, and fissured body models were calculated and analyzed numerically under corresponding mechanics conditions.(5) The study of the creep deformation which is a typical deformation in deep tunnels conducted in the loading tests in laboratory is a main technical method performed on typical rock specimens to investigate the creep law of rocks. The experimental study conducted on typical rocks of creep deformation characteristics in deep tunnels has been a hotpot in study of rock rheology, and some important engineering significances and academic value can be obtained in this study. Based on the research on creep model and combined with the developing mechanism of creep damage in rock specimens, the damage factor adopted in damage mechanism was introduced to depict the nonlinear deformation law which was caused bv the aging-damage-degradation effect in rocks. And the unified description of nonlinear parameters was proposed in the fields of physics and rheology. According to above achievements, the nonlinear description of the creep damage and deformation characteristics of classical creep models and basic creep units was conducted. The creep deformation mechanism of original fissures was depicted by introducing plastic body containing fissures. The damage model of nonlinear elastic visco-plastic creep with original fissures which was characterized by varying parameters was proposed by introducing creep body with acceleration, and then the creep state equation of the composition mode under corresponding stresses was obtained. Finally, the verification and analysis of the creep damage model were performed via conducting creep tests on the rattler obtained from Dong Xiang copper mine.