Adaptability analysis of four-leg hydraulic support for underhand working face with large mining height of kilometer deep mine

In order to overcome problem of poor adaptability for the four-leg chock shield hydraulic support used in the 121302 working face of the Kouzidong Coal Mine in China,the stress of the mine pressure and hydraulic support of 121302 working face are statistically analyzed. The mechanical model of the four-leg chock shield hydraulic support is established based on the plane bar system,and the analytical expression of the magnitude and distribution range of the ultimate external load of the hydraulic support is derived. It is concluded that the external load of the hydraulic support is one-to-one corresponding to the resultant force of canopy and base,the external load that the hydraulic support can balance must meet the corresponding resultant force of canopy and base within its length range,otherwise,the support will not remain stable. The ultimate external load distribution range of the hydraulic support does not completely cover the length of the canopy,according to the maximum working resistance and maximum tension of the front and rear legs,it is divided into five:the range where the front leg reaches the maximum tension,the range where the rear leg reaches the maximum working resistance,the range where the front leg reaches the maximum working resistance,the range where the rear leg reaches the maximum tension,and the range without bearing capacity. The distribution of the range without bearing capacity depends on the hydraulic support height,friction coefficient and the horizontal distance from the front of the canopy to the front of the base. The influence of different working resistance distribution ratio and friction coefficient on the adaptability of the hydraulic support is analyzed through an example,the results show that the working resistance of the front and rear legs of the hydraulic support should not be too different,which will reduce the adaptability of the hydraulic support. If the roof and bottom of the working face are soft and there is a large angle of mining,it is most reasonable when the ratio of working resistance of the front and rear legs of the hydraulic support is 6 ∶ 4. The adaptability of the hydraulic support is improved by increasing the annular area of the second-cylinder of leg to improve the tensile strength of the rear leg. In order to protect the guide sleeve and the leg connector from damage, the upper cavity of the leg is equipped with a safety valve,and the strength of the connector of the rear leg is strength- ened. When the friction coefficient is negative,the ultimate external load range of the hydraulic support is the smallest, the ultimate external load range increases with the decrease of hydraulic support height. When the friction coefficient is non-negative,the larger the friction coefficient is,the larger the bearing capacity of the front of the hydraulic support is,the ultimate external load range decreases with the decrease of hydraulic support height.