查看更多>>摘要：Fatigue tests under different maximum cycling stresses were performed on salt rock specimens to study the microstructural variations and damage evolvement of salt rock under cyclic loading. A nuclear magnetic resonance (NMR) instrument was utilized to record the microstructural variations in the specimens. The results indicated that with an increase in the number of cycles, the maximum pore radius in the salt rock initially increased and then remained constant, whereas the minimum pore radius initially decreased and then increased. The minimum pore size in the salt rock after 12,000 cycles was closely related to the maximum cycling stress. The porosity and permeability of the salt rock exhibited a two-stage change of "rapid increase - slow increase" and "slow increase - rapid increase", respectively, with an increase in the number of cycles. In contrast, the tortuosity presented a two-stage process of "rapid decrease - slow decrease" with an increase in the number of cycles. With an increase in the maximum cycling stress, the porosity and permeability of the salt rock after 12,000 cycles increased nonlinearly, whereas the tortuosity decreased linearly. The permeability exhibited a gradually ascending trend with an increase in the porosity. However, a critical porosity was observed. When the porosity was lower than that of the threshold, the change in porosity had a minor effect on permeability, whereas the effect of porosity on the permeability gradually increased when the porosity exceeded the threshold. The value of critical porosity of the salt rock specimens used in this paper was approximately 0.35%. The fatigue damage evolvement equation of salt rock under cyclic loading was established based on the change in porosity. The damage evolvement process of the salt rock specimens under different maximum stresses was analyzed. The results demonstrated that the fatigue damage evolvement process of salt rock consisted of three stages. However, the damage in the first two stages was relatively small, and the damage increased rapidly only when the salt rock was close to failure.
查看更多>>摘要：The measurement of in-situ stress is a critical prerequisite for the mining design and the stability analysis of surrounding rock in deep mining engineering. In this study, a novel re-oriented core acoustic emission (RCAE) method incorporating the non-oriented core ground re-orientation and AE techniques was proposed for in-situ stress measurement. First, the principle of non-oriented core ground re-orientation is established according to the spatial coupling relationship between the drilling trajectory and the core surface characteristics. Then, an innovative apparatus was designed for recovering the original spatial orientation of non-oriented cores. Furthermore, the measurement procedures of RCAE method are described in detail, involving suitability analysis, outdoor operations, core re-orientation, specimen preparation, AE test and stress calculation. Using this method, a case study for in-situ stress measurement was performed in an ultra-deep borehole (2360 m) of the Sanshandao gold mine, China. Meanwhile, the verifications of measurement accuracy were conducted based on the tectonic stress inversion and the underground overcoring method. The results show that the measurement accuracy of RCAE method is acceptable, especially the horizontal maximum principal stress and its azimuth measured are well matched with those measured by other methods. In addition, the field applications indicate that the in borehole procedure of RCAE method only requires drilling trajectory measurement without excessive complex operations, and the adequate measuring depth of this method in the case area is up to 3841 & PLUSMN; 521 m according to the damage stress threshold analysis. Therefore, the RCAE method could break through the challenges caused by the restricted measuring space and large measuring depth when no deep underground access exists. Moreover, the non-oriented cores can be rapidly re-oriented on the ground, which could expand the application value of ordinary geological boreholes in the field of deep geostress and tectonic measurement.
NSTL
Elsevier