Study On Crack Extension And Stability Of Fractured Rock Slopes

Stability analysis of fractured rock slope is important for slope engineeringdisaster prevention and mitigation. Whether it fails or not will be largely controlled bythe crack tip. And excavation and mining in geotechnical will increase the impacteffects. Currently, the application of traditional stability analysis method in suchslopes is unsatisfactory, mainly because the cracks in the slope make the stressdistribution become complicated. Using theoretical analysis, experimental testing andnumerical simulation, the main tasks are as follows:The mode II fracture toughness of sandstone specimens is obtained through theoriginal shear box fracture model. The shortcomings of the test method are pointedout, and its improved test method is proposed, which is more suitable. In addition, thefinite element software ABAQUS modeling is used to modify mode II fracturetoughness formula, by which the crack size effect is greatly reduced.The pure mode I and II fracture tests are carried out using CSTBD (straight crackBrazilian disc) sandstone samples. Mode I and II fracture toughness values areobtained. The two types of mode II fracture toughness tests were compared and it isfound out that they actually belong to different fracture modes. The results proved thatKIICis larger than KIC,and that the conventional composite fracture criterion is notcorrect. Then, a great deal of CSTBD composite fracture tests are carried out, anddifferent loading angles including5°,10°,15°,20°,25°,30°and60°are calibrated bythe finite element method so as to obtain their dimensionless SIF.The fractured rock slope is considered as a continuous medium containing cracks,and fracture mechanics theory is employed to analyze slope stability, theoreticalsolution and numerical method of stress intensity factor are compared and proposed.Finally, the MTS (maximum circumferential tensile stress) criterion is amendedaccording to the test data and numerical results, which makes it more suitable for rockfracture problems. The analysis method of fractured rock slope stability is establishedbased on the new criterion. Any fractured rock slope can be modeled by FEM tocalculate mode I and II stress intensity factor of the crack tip, the slope stability isobtained using fracture mechanics, so that the fractured rock slope instability can be predicted.