Gantry slag bucket device capable of completing automatic slag unloading through gravity effect of device and method

The invention discloses a gantry slag bucket device capable of completing automatic slag unloading through the gravity effect of the device and a method. The device comprises a triangle support (1) and a slag bucket (2), wherein the triangle support (1) comprises a rail (1-1) horizontally arranged and located at the top of the triangle support, and a limiting device body (1-2) is arranged at the end of the rail (1-1) or on the position close to the end of the rail (1-1); the two side faces of the rear half part of the slag bucket (2) are outwards provided with rotary shafts (3) protruding out of the side faces correspondingly; and the width between two rail bars of the rail (1-1) is larger than that of the slag bucket (2), the bottom of the slag bucket (2) can enter the middle of the rail, and the rotary shafts (3) can be erected on the rail and make planar motion relative to the rail. The device is suitable for vertical well fixing-type gantry slag-unloading operation of various city underground railway tunn