Study on instability mechanism of hydraulic support in downdip and updip coal face

In order to study the instability mechanism of hydraulic support in downdip and updip coal face, taking the four-leg support type hydraulic support as an example, a stability plane mechanical model of “hydraulic support-shifting ram” in both unloaded and loaded states was established. The discriminant of shifting ram's participation in the mechanical balance of the supportand the stability judgment criteria for the standard form of the critical load of the support were obtained. Theoretical analysis and numerical calculations show that the participation of the shifting ram in the mechanical balance of downdip and updip coal face greatly improves the stability of the support. The force on the shifting ram in the updip face is greater than that in the downdip face, resulting in the phenomenon of the shifting ram force reaching the rated value. The hydraulic support of the downdip coal face has an unstable interval. Building a model based on the support and the shifting ram provides a more comprehensive analytical method for the instability research of high-incline hydraulic supports. The research results can provide theoretical guidance for the stability design of hydraulic supports in inclined and inclined coal mining faces.