Penghai Zhang

Microseismicity Induced by Fault Activation During the Fracture Process of a Crown Pillar

Shirengou iron mine in Hebei Province, China is now under transition from open pit to underground mining. During this process, the unstable failure risk of crown pillar is growing as a result of underground mining, fault activation and water seepage. To monitor the stability of the crown pillar, a microseismic monitoring system was equipped in 2006. Based on temporal and spatial distribution of microseismic events and deformation mechanism, it was found that it is the propagation of the buried fault F15 that causes the failure of the crown pillar, resulting in increased water seeping into the underground drifts. By analyzing the temporal changes in multiple microseismic parameters during the fracture process of the crown pillar, it was found that several distinct abnormalities in the microseismic data such as a rapid decrease in the b value, a sharp increase in energy release, an abnormal increase in apparent stress and a low dominant frequency, could be judged as the signal of an increasing risk. Therefore, the microseismic monitoring has been proven to be a suitable method for understanding damage and fracture process of the crown pillar during the transition from open pit to underground mining.

Study of the Rock Mass Failure Process and Mechanisms During the Transformation from Open-Pit to Underground Mining Based on Microseismic Monitoring

To quantitatively understand the failure process and failure mechanism of a rock mass during the transformation from open-pit mining to underground mining, the Shirengou Iron Mine was selected as an engineering project case study. The study area was determined using the rock mass basic quality classification method and the kinematic analysis method. Based on the analysis of the variations in apparent stress and apparent volume over time, the rock mass failure process was analyzed. According to the recent research on the temporal and spatial change of microseismic events in location, energy, apparent stress, and displacement, the migration characteristics of rock mass damage were studied. A hybrid moment tensor inversion method was used to determine the rock mass fracture source mechanisms, the fracture orientations, and fracture scales. The fracture area can be divided into three zones: Zone A, Zone B, and Zone C. A statistical analysis of the orientation information of the fracture planes orientations was carried out, and four dominant fracture planes were obtained. Finally, the slip tendency analysis method was employed, and the unstable fracture planes were obtained. The results show: (1) The microseismic monitoring and hybrid moment tensor analysis can effectively analyze the failure process and failure mechanism of rock mass, (2) during the transformation from open-pit to underground mining, the failure type of rock mass is mainly shear failure and the tensile failure is mostly concentrated in the roof of goafs, and (3) the rock mass of the pit bottom and the upper of goaf No. 18 have the possibility of further damage.

Mechanical and energy release characteristics of different water-bearing sandstones under uniaxial compression:

This paper presents the experimental results of calcium argillaceous cemented sandstones with different water contents under uniaxial and cyclic loading conditions. The effects of the water content status on peak strength, deformation, and dissipated energy are discussed. Meanwhile, the acoustic emission energy is also studied based on the accelerating energy release theory and energy distribution density function. The experimental results show that the water content has remarkable effects on the peak strength and elastic modulus by a decrease of 37–58% and 15.7–21% after being saturated, respectively. Both the accumulated dissipated energy and dissipated energy generating ratio of dry specimens are higher than those of the saturated specimens. The acoustic emission energy release rate of dry specimens is higher than those of the saturated specimens, which means a high tendency of sudden failure for dry specimens. Moreover, the distributions of acoustic emission absolute energy are consistent with the normal density distribution function, and the AE energy expectations of dry specimens are higher than those of the saturated ones in the loading process and they show an obvious increasing trend on approaching failure. These conclusions will be helpful for the illumination of water-weakening effects on the mechanics parameters and failure mechanism analysis in view of the releasing energy.

Numerical Investigation of Damage Evolution and Localized Fracturing of Brittle Rock in Compression

AbstractIn the present paper, a numerical model for deformation and fracturing of brittle rocks is used to study the damage evolution and localized fracturing of brittle rocks based on statistical ...