The Mine Safety and Health Administration (MSHA) specification for rock dust used in underground coal mines, as defined by 30 CFR 75.2, requires 70% of the material to pass through a 200 mesh sieve (<75 µm). However, in a collection of rock dusts, 47% were found to not meet the criteria. Upon further investigation, it was determined that some of the samples did meet the specification, but were ...

A literature review revealed that most of the empirical equations introduced for determination of the uniaxial compressive strength (UCS) of rocks based on the Schmidt hammer rebound number (N) are not sufficiently reliable mostly due to the relatively low coefficient of correlations. This is attributed to the fact that in most cases one formula is used for all types of rocks, altho...

A thin coal seam mined as a protective coal seam above a gas outburst coal seam plays a central role in decreasing the degree of stress placed on a protected seam, thus increasing gas permeability levels and desorption capacities to dramatically eliminate gas outburst risk for the protected seam. However, when multiple layers of coal seams are present, stress-relieved gas from adjacent coal sea...

The following article analyzes the effectiveness of directional hydraulic fracturing (DHF) as a method rock burst prevention, used in black coal mining with longwall system. In order to define changes seismic activity due DHF at “Rydułtowy” Black Coal Mine (Upper Silesia, Poland), observations were made regarding mass during system using roof layers collapse. was recorded area itself, where, on...

Response characteristics of key strata during the periodic weighting process in Dongjiahe coal mine were investigated using micro-seismic (MS) monitoring. Fracture types identified through moment tensor inversion. Finally, fracture mechanism roof was revealed from a microscopic viewpoint. The results show that there are three concentrations MS events distributed along dip direction. And two eve...

Understanding and estimating the rock stress state has become increasingly important as nowadays numerical models are mainly used as rock engineering design tool. The objective in determining rock stresses may, in many cases, be seen as an interactive process. The type of data needed may change, depending on at what stage an underground project is in. Further more, preliminary measurements may ...

In 2000 and 2003, two massive hydraulic fracturing experiments were carried out at the European Geothermal Hot Dry Rock site at Soultz-sous-Forêts, France. The objective was to create a dense network of enhanced permeability fractures, which would form the heat exchanger. The injection of water in the fractured rock generated a high level of microseismic activity: around 30,000 and 90,000 micro...

The development of most unconventional oil and gas resources relies upon subsurface injection of very large volumes of fluids, which can induce earthquakes by activating slip on a nearby fault. During the last 5 years, accelerated oilfield fluid injection has led to a sharp increase in the rate of earthquakes in some parts of North America. In the central United States, most induced seismicity ...

During the hydraulic fracturing procedure in shale-gas exploitation, the poroelastic properties of shale formation can be altered significantly. However, it is difficult to evaluate these variations using microseismic field data. In this study, we conduct a hydro-fracturing experiment using Longmaxi shale, which is a major formation for shale-gas production in China, to simulate the water injec...