2. Secondly, during the experiment, the towel is squeezed hard and the bamboo pieces are broken hard to simulate the rock fracture.
3. Secondly, the experimental phenomenon is that the towel is deformed when it is squeezed hard, the bamboo piece is bent hard, the bamboo piece breaks and makes a "bang" sound, and the hand feels vibration.
4. Finally, the experimental conclusion is that the underground strata will be deformed under the pressure, and when the force is too great for the strata to bear, sudden and rapid fracture will occur.