Jawaharlal Nehru Technological University Hyderabad B.Tech III UNDERGROUND MINING TECHNOLOGY Previous Question Paper (October - 2020 - R16)

Horizon mining is a method of underground coal mining primarily used in steeply dipping or irregular coal seams. In this system, the coal deposit is divided into a series of horizontal levels or horizons. Main haulage roads are driven horizontally through the rock strata at fixed vertical intervals, rather than following the inclination of the seam.

Key characteristics include:

1. Main haulage levels are established in the stable rock (stone drifts) to ensure long-term stability and accommodate high-capacity transport systems.
2. Cross-measure drifts are driven from these main horizons to intersect the coal seams at various points.
3. Extraction is carried out by driving sub-levels or faces within the seam, which then transport coal via chutes or conveyors to the main horizon level.
4. This method effectively separates the haulage and ventilation systems from the active extraction zones, allowing for more efficient management of complex geological conditions.

The merits and de-merits of horizon mining are as follows:

Merits:

• Stability: Main haulage roads are driven through solid rock rather than coal, significantly reducing maintenance costs and the risk of roof collapse.
• Efficiency: Allows for the use of high-capacity rail or belt haulage systems due to the level nature of the main roads.
• Ventilation: Provides a highly organized and efficient ventilation circuit as air can be directed systematically through the horizons.
• Flexibility: Facilitates the simultaneous extraction of multiple seams from a single main haulage level.

De-merits:

• High Initial Capital: Requires significant upfront investment for driving extensive stone drifts before coal production can commence.
• Long Lead Time: The development phase is time-consuming, delaying the return on investment.
• Geological Risk: If the seam structure is highly faulted or unpredictable, the pre-planned horizon layout may become ineffective.
• Complexity: Requires precise surveying and engineering to ensure that cross-measure drifts accurately intersect the targeted coal seams.