Mechanical response and impact tendency index correction of gangue-coal combined structure

• Uniaxial compression tests on nine gangue-coal combined structures reveal that increasing gangue thickness decreases compressive strength and pre-peak energy but increases elastic modulus. • Gangue position significantly governs failure mode: lower-middle gangue yields the lowest strength/modulus yet highest pre-peak energy; mid-position shifts failure from complete crushing to incomplete point-type. • A new comprehensive impact instability index (Kcrc) is proposed, showing positive correlation with compressive strength and impact energy index, better reflecting rockburst tendency than residual energy index. • The index provides a more accurate evaluation of impact tendency for gangue-containing coal seams, with broad engineering applicability for deep-mining rockburst prevention.