An experimental study of fault slips under unloading condition in coal mines

To investigate the mechanism of fault slips in coal mines, a biaxial shear experiment was carried out under unloading condition based on the fault F16 in Yima city, China. Two rock samples were used in the experiment and each sample was composed of two triangular sandstone blocks which were put together to simulate the fault. One rock sample was used to do fault slip tests and it was called slip-test sample. The other sample for comparison with the slip-test one was untested, and it was named non-slip-test sample. During the biaxial shear experiment of the slip-test sample, normal and shear strains near the fault, acoustic emission (AE) signals, and the sliding displacement were measured. After the experiment, microscopic profiles of fault surfaces of both rock samples were examined by scanning electron microscope (SEM). In addition, a numerical simulation was conducted to model the slip of the fault F16. The results indicate that: (1) three fault slips occurred during the biaxial shear experiment, and the shear stress, normal and shear strains in the first slip showed the maximum variation among three slips; (2) Shear strains near the two ends of the fault had a more significate variation than that in the middle part, and the typical trend of shear strains was first dropping, then increasing rapidly, and then falling slowly to a specific value during the first slip; (3) The first slip had the largest sliding displacement of 29.89 mu m , and in the first slip three phases including slow slip, main shock and aftershock occurred based on AE monitoring results. (4) On the fault surface of nonslip-test sample, microstructures such as bulges, voids and veins were ubiquitous and notable, making the fault surface much rough, while similar microstructures were few and the fault surface of the slip-test sample was flattened after fault slips; (5) The slipping direction in the shallow part and deep part of the fault F16 were opposite during mining.

Automated summary

In order to investigate the fault slips mechanism in coal mines in China, a biaxial shear experiment was conducted on fault F16 in Yima city. The experiment included slip tests on a rock sample and a non-slip-test sample for comparison. The results showed that three fault slips occurred during the experiment, with the first slip showing the greatest variation in shear stress and strains. Shear strains near the ends of the fault had more significant variations than in the middle part, and the sliding displacement during the first slip was 29.89 mu m. The microstructures on the fault surface also differed between the slip-test sample and the non-slip-test sample.