Defining the Excavated Layerrs Height for Coal Extraction by Backhoes

Abstract

Currently, large machine building companies produce hydraulic excavators serially with a wide range of operating parameters (bucket capacity, digging radius, digging depth and height). Hydraulic excavators have found wide application in quarries all over the world (USA, France, England, Japan, Australia, Russian Federation etc.). A sufficiently wide range of backhoe capabilities for the formation of various forms of surface workings and bench slopes allows them to work without leaving various prisms of coal losses in the coal seam's bottom, at the optimum height of the excavated layer. The most efficient way is to work off the bench by hydraulic backhoe by downward digging and bottom loading. The depth of digging (the height of the face) is approximately equal to the height of the body of a dump truck. The minimum value of the excavation cycle is achieved when the dump truck is positioned at an angle of 35-60° to the axis of the excavator. To reduce the time for installing a dump truck for loading, an end-to-end truck approach scheme is recommended, but the duration of the excavation cycle is increased as a result of increasing the angle of the excavator during loading. The research shows that: (1) at the excavated layer's height of 5.0 m, additional coal losses due to nonscooping is not formed only for seam's angle of 50 or more, except when using hydraulic backhoes with large operating parameters; (2) for excavated layer's height of 4.0 m, the minimal coal losses will be achieved for dip angle of at least 40 degrees, and for long-boom excavatorsnot less than 30°; (3) the excavated layer's height of 3.0 m makes it possible to virtually eliminate coal losses, except for excavators with a short boom.