Energy-based indicators and optimization of coal pillar width in gob-side entry driving

Area of Science:

• Mining Engineering
• Geotechnical Engineering
• Rock Mechanics

Background:

• Gob-side entry driving in deep mines causes stress redistribution, making coal pillars critical load-bearing structures.
• Roadway stability depends on the balance between elastic strain energy and dissipated energy within coal pillars.
• Current methods struggle to identify stability transition points for coal pillar width design in deep, weak rock conditions.

Purpose of the Study:

• To develop an energy analysis framework for surrounding rock response in gob-side entry driving.
• To introduce the dissipated energy ratio as a key index for evaluating coal pillar stability.
• To determine optimal coal pillar width considering energy evolution, bearing capacity, and economic factors.

Main Methods:

• Utilizing FLAC3D numerical simulations to analyze energy distribution and evolution under varying coal pillar widths.
• Investigating the spatial distribution and temporal changes of elastic strain energy, dissipated energy, and dissipated energy ratio.
• Comparing the effectiveness of the dissipated energy ratio with traditional indicators like stress and displacement.

Main Results:

• A shift in bearing mechanism from plastic dissipation to elastoplastic coordination occurs as pillar width increases from 4m to 6m, with the dissipated energy ratio decreasing from 1 to ~0.67.
• Increasing pillar width to 8-14m leads to significant elastic strain energy accumulation, forming distinct energy concentration zones.
• The dissipated energy ratio proves more effective than stress, displacement, or plastic zone indicators for characterizing stability.

Conclusions:

• A 6m coal pillar width offers the best balance between energy characteristics, bearing capacity, and engineering economy for the studied mine.
• The proposed energy-based criterion and optimization scheme are validated by field monitoring, demonstrating engineering applicability.