Full knowledge of the current tectonic stress state is crucial for assessing open-pit mine slope stability and regional tectonic evolution and geodynamic processes. Overcoring, hydraulic fracturing, and acoustic emission in situ stress measurement techniques were adopted to determine the 3D stress tensor in an iron mine district, North China, and 25 sets of stress data ranging from 56 to 490 m were measured. Accordingly, the current tectonic stress state and its relationship to regional geological tectonics were investigated. The results indicated that the stress condition seemed to favor thrust and strike-slip faulting, and the stress field was particularly controlled by the horizontal tectonic stress. A high horizontal tectonic stress considerably influenced the stability of high and steep slopes in this mine district, which requires great attention. The stress directions derived from different methods were almost similar, indicating a dominant NEE–SWW stress field direction or near-E–W direction, comparable to the direction revealed by focal mechanism solutions and other stress indicators around the mine district. According to geological structure analysis, the present-day stress field in this district generally inherited the third-stage tectonic stress field while partially retaining the characteristics of the second-stage tectonic stress field, which is the result of dynamic action and tectonic movement during different geological periods, and the maximum principal stress direction of the tectonic stress field that affects the modern tectonic activity in this area is the NEE–EW direction.

Uniaxial compression experiments were performed in cross-jointed granite samples with a hole, together with acoustic emission (AE) observations, to investigate AE variability and precursory information during sample failure. The variability characteristics of multiple AE time-series parameters (including AE counts, accumulated counts, energy, accumulated energy, and b-value) and frequency domain parameters (including AE frequency and amplitude) were systematically analyzed, the variations in different parameters and precursor characteristics were compared, and the AE parameters suitable for rock failure prediction in a cavern were discussed. The results indicate that the variability characteristics of different AE parameters are different, and each parameter has a precursor phenomenon of specimen fracture. The peak value of specimen AE counts does not necessarily appear at the peak stress, but the AE counts decrease significantly when the samples are damaged. The accumulated AE count curve makes it easier to identify the precursors of sample failure. The AE energy is released at an accelerated speed when the samples are near complete failure, and a critical energy release exists in the samples. The abrupt increase in AE energy has potential as a precursor to sample failure. The b-value shows a fluctuating decline during the whole loading process and a rapid decline before sample failure. The low-frequency with high-amplitude and the high-frequency with low-amplitude signals exhibit distinct characteristics at different specimen deformation stages and are sensitive to the change in specimen stress state, so they can be used as the crucial signal source for predicting specimen failure. The joint analysis of these AE parameters can better capture the precursory information of rock failure.