Study On Acoustic Emission Characteristics Of Sandstone Under Uniaxial Loading

Heterogeneity,anisotropy and discontinuity are the characters of rock materials, which mostly contain many natural weaknesses, such as joints, fractures, microcracks and voids owing to having gone through long geological history as well as complex surroundings. Rock rapidly release strain energy in the form of elastic wave and produce a large number of acoustic emission(AE) signals under external or internal force. AE signals can reflect plentiful information of inoculation, initiation, propagation and coalescence of microcracks inside the rock, therefore, internal structure change of rock can be inferred. Investigation and analysis on characteristics parameters of rock AE has a great significance to further understanding the law of microcracks damage development in the loading process, the occurrence of stress and failure mechanism of rock.While conducting the experiment with sandstone sample under uniaxial compression conditions, collect AE signals produced in the loading process. Based on the study of mechanical parameters and AE characteristics parameters, the following conclusions are obtained:First, Rock materials with Kaiser effect can "memory" the biggest initial stress. The Kaiser effect point can be located through AE characteristics parameters-time curve, combined with stress-time curve. The Kaiser effect point eigenvalues are endowed with different weights according to synchronous situation of AE characteristics parameters-time curves;Second, AE process of rock material has the feature of self-similar, besides, AE sequence has the feature of fractal. Accordingly, it’s reasonable to use fractal to study on the evolution law of rock’s damage failure process. It’s concluded that the changes of correlation dimension reflect the change of the sample’s internal structure in terms of correlation dimension-stress level curve. The correlation dimension value of sandstone sample first increase and then fluctuate, it indicates that damage failure give priority to microcracks. The sudden reduction of correlation dimension value can be used as a judgement of indicating the creation of main rupture, it has a great significant meaning to engineering safety;Finally, the initiation and extension of rupture inside the rock is the inherent reflection, and it is also the direct reason for unstable failure, which can be predicted by AE quiet period. The curves of rock AE characteristic parameters with time and strain can reflect internal rupture of rock. The square root of the total number of energy has a certain relationship with time. Based on the AE number-strain curves are fitted with different functions, the critical point of sandstone failure can be derived by means of statistical analysis. The critical point can be used as a quantitative prediction of sandstone failure. It has a important theoretical value and practical significance for the operating and construction safety management of the geotechnical engineering.