Numerical Analysis And Mechanism Of Fracture Spacing In Bedded Rock Materials

Fracture spacing saturation is a very important and common geological phenomenon in stratum structure componented by bedded rock. The research results on this phenomenon caused by tensile failure have been published in high-level journals like Nature and Physical Review, which indicates that the research on such phenomenon is of great importance. Fracture spacing saturation also has the characteristics of multi-scale and universality, with the small scales of fracture spacing in the composite materials at the level of millimeter, and the large scales like earthquake fault zone in plate tectonics, which is the various forms of fractures widespread in different scales of rock, concrete and other materials. The nature of deformation and failure of quasi brittle materials such as rock and concrete is the fracturing process from micro-fracture formation, propagation, coalescence to macro fractures and the final instability.Our research is carried out from the fracture spacing phenomenon in bedded rock on the basis of Realistic Failure Process Analysis, and considering the mesoscopic structure of rocks, the analysis of fracture spacing process in layered materials of various shapes, under conditions such as load, temperature and humidity, can be realized by using the statistical distribution method, heat and mass transfer theory and damage mechanics theory. Besides, combining with the physical experiments, and taking the numerical simulation as the main research method, we have discussed the fracture mechanism and evolution laws of fracture spacing caused by tensile fracture, and the main research results are as following:(1) Effectively playing the advantage of numerical analysis method, our research can present the whole process from fracture initiation, propagation, infilling and saturation from load fractures to saturated humidity diffusion fractures in layered models from2D to3D by making the temperature-stress-damage coupling layered material model and the humidity-stress-damage model from the view of mesoscopic point. It is proposed that the node displacement loading in cylindrical coordinate and spherical coordinate in Ansys models can be converted into the node displacement loading in the cartesian coordinates by program calculation, which makes the numerical simulation of fracture spacing in layered cylindrical structures and spheres come ture. Moreover, the whole process of fracutre on material surface caused by volume expansion as the temperature rises can be showed in our experiment.(2) The stress transformation mechanism of fracture spacing is studied from the stress distribution evolution with the failure process of the numerical model. The results show that the fracture spacing pattern is affected by the following factors that are the material layer thickness ratio, material properties of each layer, stress conditions of the model, model shape, and etc. The numerical results are of great reference value in the research on the laws of the fracture mechanism and rules.(3) Layered material fractures caused by the load and temperature shrinkage are with the same distance or space approximatly, the locations of initiation indeterminate, and the initiation and coalescence having obvious order. The drying shrinkage and cooling stress arising with the impact of temperature or humidity diffusion, then the surface fractures extend from the surface to the inside with the initiation and coalescence almost simultaneous, and finally, the fractures would end at the interface of different material layers,which are always perpendicular to the layers and run through the layer thickness. Thus, the final destruction is formed with the interface stripping or fracture spreading to the layer with greater strength after fracture saturation.(4) It is found from the fracture spacing evolution results of the weak layers in layered material model under uniaxial tension and vertical compression that the stress field between adjacent fractures changes from tensile to compressive stress, of which the stress is the key reason of fracture saturation. By analyzing the stress field changes in the process of fracture spacing under uniaxial tensile stress, it is showed that there are three kinds of "Self-Constraints Phenomenon" in the whole fracture process from extension to saturation, that are the constraints of the fracture itself on the stress field around the fracture, from the strong layer on the new fractures in weak layer, and from the stress field of adjacent fracture.(5) The spread of the temperature and the humidity field has great interact with the surface fractures extension in layered materials. The former may cause the surface elements damaged and the fractures extending from the surface to the internal, while the fracture existence and initiation will make the range of temperature and humidity influences more deeply and broadly, and the corresponding stress would be larger too, which is adverse to prevent temperature and dry shrinkage fracture initiation and propagation. In addition, the fracture depth is an essential factor that affects the temperature and humidity diffusion process. The fracture extension in the shrinkage process will promote the temperature and humidity diffusion, intensifying the fracture continue to expand. Therefore, repairing existing fractures will be helpful to stop the deep influence of the temperature and humidity around the fractures arm to inhibit fracture propagation, which will enhance the durability of structure.