The study looked at how coal mining affects the strength of coal-rock layers deep underground. They tested different conditions to see how fast mining and pressure changes impact the strength of the rock. The results showed that the speed of mining affects how strong the rock is, while the initial pressure affects how much energy is used during the mining process. The study found that the rock goes through different stages before breaking, and higher pressure makes the rock more elastic. The speed of mining doesn't affect how the rock stretches.