Overburden failure characteristics and fracture evolution rule under repeated mining with multiple key strata control

Area of Science:

• Geotechnical Engineering
• Mining Engineering
• Rock Mechanics

Background:

• Understanding overburden structure failure and fracture evolution is critical for repeated mining in coal seams.
• Superimposed mining of closely spaced coal seams (e.g., 6# and 7#) presents complex challenges.
• Multi-key stratum control significantly influences overburden behavior during mining.

Purpose of the Study:

• To investigate the overburden structure failure and fracture evolution law under multi-key stratum control during repeated mining.
• To clarify the effects of cumulative damage and superimposed mining-induced stress fields on fracture morphology.
• To provide a theoretical basis for water hazard prevention and surface damage management in the Xinjiang mining area.

Main Methods:

• Comprehensive research integrating theoretical analysis, similarity simulation, numerical simulation, and field monitoring.
• Identification of key strata using key stratum theory.
• Field monitoring employed double-end water plugging and borehole observation joint detection.

Main Results:

• Four key strata identified; fracture zone height after initial mining of 6# seam was 40.2 m.
• Repeated mining intensified cumulative damage and stress superposition, leading to rapid fracture propagation.
• Final fracture zone and caving zone heights stabilized at 139.68 m and 42.88 m, respectively, with a 'double-trapezoidal' composite structure.

Conclusions:

• Overburden failure evolves from a single 'trapezoidal' to a 'double-trapezoidal' composite structure under repeated mining.
• Fracture evolution follows a pattern of initial slow expansion, leap increase due to cumulative damage, and gradual stabilization.
• Key strata play a crucial role in regulating fracture morphology and heights during repeated mining operations.