Experimental Study on Strength Weakening of Gypsum Rock with Effect of Long-Term Overlying Strata Pressure

A long time lag is the main characteristic of gypsum mined gob collapse disasters. With the coring of a gypsum rock specimen from the supporting pillars in gob, which formed over several years, the strength weakening effect of the gypsum rock with long-term overlying strata pressure is revealed by experimentation. The results show that: uniaxial compression stress-strain curves represent major differences in different lateral depths of the same supporting pillar. With the increase in lateral depth, peak strength increases and the corresponding strain decreases, which becomes more obvious as the age increases. As a function of time, peak strength decreases and the corresponding strain increases in the shallow part of the pillar as the age increases. Peak strength fluctuates in the middle part and increases in the deep part; the corresponding strain fluctuates in the middle and deep parts, but demonstrates the opposite changing law. Finally, the reason for the above law was comprehensively and thoroughly researched and demonstrated. The maximum strength weakening rate of gypsum rock in the shallow part of a supporting pillar of 0.5 m depth was 21.06% in the year 1996. The slow strength weakening effect of gypsum rock with long-term overlying strata pressure is the essential reason why gypsum mined gob collapses occur in subsequent years or even decades.