17��1 The Supports for Sub-Level Caving

Characteristics of the supports for sub-level caving:

Shield or chock shield supports are designed for use in the mining of thick seams by the sub-level caving longwall method. The supports are also suitable for conventional longwall operation in areas where the seam thickness does not warrant sub-level caving or where a top slice is to be extracted to prepare the seam for sub-level caving.

The support configuration gives stability to thick seam mining conditions including working on gradients.

The support has an integral coal-loading door [2], which is hydraulically controlled from a safe position within the support, and can be closed at any time during coal entry. The support also protects the rear conveyor from falling debris [3].

A hydraulically operated agitator arm [4] is fitted to the rear shield to assist the flow of coal should the coal not fracture readily. The roof canopy and caving shield have apertures to enable the coal roof to be drilled for the purpose of shot firing [5] into the coal in extreme cases. The lemniscate��s linkage between the base and the rear shield enables the support to operate as a conventional shield and maintains a nearly constant canopy tip to face distance.

The power set cantilever [6] gives immediate to the newly exposed roof, whilst a face sprag is design to protect the face operators from spalling coal [7] from the coalface. Hydraulically operated canopy side flaps [8] effectively seal the gabs between supports and further exclude dirt and dust from entering the working area.

The support provides a clear traveling way in a protected position in front of the legs from which all major operations can be controlled.

The support is of simple construction, which will allow for easy dismantling and reassembly [9] for transportation.

17��2 Sub-Level Caving Systems

The longwall sub-level caving mining system is a method of extracting coal deposits with a seam thickness of six meters or more. This method is being recognized as an economical method of mining seams such thickness, as the conventional longwall method become impractical due to equipment size and cost, safety and operational problems.

Three types of sub-level caving systems:

A. Basic system of sub-level caving: On support advance, coal falls onto rear shield, door opens and coal self loads onto rear conveyor. Typical seam thickness is up to 10 m.

B. Top slicing system of sub-level caving: A top slice is worked in advance by conventional longwalling (using the same sub-level caving supports as for the operation below, but without the rear conveyor ) mainly to de-stress [10] the overburden strata. Bottom section is mainly by sub-level caving causing the coal to cave onto rear shield and then through the door opening itself loads onto rear conveyor. Typical seam thickness is up to 14m.

C. Top slicing syst

[1][2][3]��һҳ