Experimental Investigation on Instability Characteristics of Heated Siltstone in the Coal Fire Area

Abstract

Fractures in the overlying rock is one of the main factors in the development of coal fires. Understanding the characteristics of heated overlying rock is of great significance to examine the combustion mechanism of a coal fire. In this paper, the stress-strain curves, peak stress and brittleness coefficient of siltstone specimens in the coal fire area at different temperatures were tested using an MTS810 experiment system. Meanwhile, the change in fractures caused by combustion was also explored. Results show that the peak stress of the siltstone first decreases, then increases before the secondary reduction as temperature increases. Similarly, the brittleness coefficient first increases, then decreases and increases again during this process. When the temperature is lower than 200 °C or higher than 700 °C, the decrease of the peak strength is the main factor influencing the siltstone breakage and the development of combustion fractures. As the temperature rises from 200 to 700 °C, the rock stability is dictated by compressive strength and loading structure. The higher the temperature, the greater the coal loss due to burning, and failure of the siltstone is more violent. Once the balance of rock forces is broken by the coal combustion and exceed the rock bearing capacity, severe brittle failure will occur, and a large number of combustion fractures will be generated.