JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech III UNDERGROUND MINING TECHNOLOGY Previous Question Paper (August - 2022 - R16)

Horizon mining is a method of underground coal mining where the deposit is divided into a series of horizontal levels or horizons. Each horizon is served by a main haulage road driven in the rock (stone drift) at a fixed elevation, which remains independent of the local dips or undulations of the coal seam.

In this system, the main haulage roads are developed in the floor or roof strata parallel to the strike of the seam. From these main horizon roads, cross-measure drifts or stone drifts are driven to intersect the coal seams at regular vertical intervals. Once the seam is intersected, the coal is extracted using methods such as longwall or room-and-pillar mining. The coal is then transported via chutes or conveyors to the horizon level below, where it is loaded onto main haulage systems, such as rail cars or high-capacity belt conveyors, for transport to the shaft bottom.

This approach is particularly suitable for multi-seam deposits, steeply dipping seams, or areas with complex geological structures where maintaining a single haulage level across the entire mine is impractical.

The advantages and disadvantages of horizon mining are as follows:

Advantages:

• Efficient Haulage: Main haulage roads are driven in stable rock, allowing for high-speed, high-capacity transport systems that are not affected by seam irregularities.
• Ventilation Control: The system allows for better control of ventilation circuits, as the horizon levels provide clear, dedicated intake and return airways.
• Multi-seam Exploitation: It is highly effective for extracting multiple seams simultaneously from a single level, reducing the need for extensive development in coal.
• Safety: Haulage roads in rock are generally more stable and less prone to roof falls compared to roads driven within the coal seam.

Disadvantages:

• High Initial Capital: The method requires significant upfront investment for driving extensive stone drifts and developing main haulage levels before production can commence.
• Long Lead Time: There is a long gestation period between the start of development and the first coal production.
• Geological Risk: If the seam geometry is not well-defined, the fixed-horizon levels may become inefficient or require additional costly development.
• Limited Flexibility: Once the horizon levels are established, it is difficult and expensive to alter the layout if mining conditions change unexpectedly.