| To study the damage and AE characteristics of cemented backfill; the test of cemented backfill- cement-tailings ratio 1: 4-under uniaxial cyclic loading and unloading, has been done. The regularity for change of cemented backfill parameters are analyzed. By means of the principle of energy, not only the distributions of elastic energy and dissipated energy in whole process are obtained, but also the relationship between damage energy release rate and AE energy is established. After putting forward the damage variable under uniaxial cyclic loading and unloading, the damage evolution equation and the damage threshold of backfill are determined. By calculating and analysing of B value of AE and fractal dimension D2, the AE characteristics about the damage threshold and the AE feature point and also in the whole uniaxial cyclic loading and unloading test process are studied, which reflect the evolution behavior of micro-cracks. Further more, the characteristics of B value and fractal dimension D2 under different damage status of backfill are also studied. At last, a criterion about backfill collapse is put forward. The main conclusions are:(1) The totle strain and the elastic strain, including the corresponding energy of them, are grow accompanying with the cycles, but the plastic strain and theplastic energy in second loop are smaller than the first loop and the third loop.(2) Under uniaxial cyclic loading and unloading, the mechanical properties of backfill are not always deccreasing. Each unloading enhances the elasticity of backfill.(3) In sequence, the dissipated energy is used in micro-cracks compaction→the formation of new free surface→fractional use in the mechanism for non-linear→use in the mechanism for non-linear.(4) The damage evolution equation can well reflect the backfill damage behavior , and also the damage energy release rate has a linear relationship between AE energy. The damage threshold of backfill, which locates in the valley of B value in the first loop,is about 0.2 times of peak stress, and also larger that the AE feature point, which sites at the downcomer of B value and the fractal dimension.(5) During the loading process, the B value of AE experiences four periods-trough period to oscillation period to gradual growth period to suddenly down period. Comparing with B value, the fractal dimension has four steps- high level of numerical period to stable period to fluctuation period to decreasing period.(6) During the unloading process, there is a turning point existing in B-Stress curve. When the unloading stress is greater than the turning point, the B-Stress curve of unloading is as same as in loading. To the fractal dimension D2, the value in unloading process comparing with in loading process, is greater.(7) The B value shows ups and downs, when damage variable in"linear increase"period. As damage variable locate in"non-linear increase"period, the B-Stress curve has a downfall area, while the fractal dimension displays steadily increasing and then stable at a relatively high level.(8) That both B value and the fractal dimension decrease at same time, can be used as the filling about to damage and failure criteria.(9) The evolution of micro-cracks has randomness and uncertainty, when the stress at low lever. In the middle Stress level, violent expansion may occasionally occurred in micro-cracks. As the stress increase, large-scale breakage continuing occurred in backfill, and micro cracks began to gather, and at last form a potential slip surface. |
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