Jawaharlal Nehru Technological University Hyderabad B.Tech IV ROCK SLOPE TECHNOLOGY Previous Question Paper (September - 2021 - R16)

The overall slope angle is a critical design parameter that dictates the stability and geometry of a rock slope. The primary geometrical parameters dependent on the overall slope angle include:

• Bench Height: The vertical distance between the crest and toe of a single bench, which is influenced by the operational constraints and the required overall angle.
• Bench Face Angle: The inclination of the individual bench face, which must be steeper than the overall slope angle to accommodate catch benches.
• Catch Bench Width: The horizontal distance between the toe of one bench and the crest of the bench below, essential for safety and rockfall containment.
• Overall Slope Height: The total vertical distance from the crest of the top bench to the toe of the bottom bench, which directly limits the maximum achievable overall angle for a given factor of safety.
• Inter-ramp Angle: The angle formed by the slope of multiple benches, which is constrained by the cumulative width of catch benches and the individual bench face angles.

The relationship between overall pit slope and mine economics is defined by the trade-off between excavation costs and mineral recovery. A steeper overall pit slope angle significantly improves mine economics by reducing the strip ratio, which is the volume of waste rock that must be removed to access a unit of ore. By decreasing the amount of waste excavation, the operational costs per ton of ore are lowered, thereby increasing the net present value (NPV) of the project.

Conversely, while steeper slopes reduce waste removal costs, they increase the risk of slope failure. Geotechnical instability can lead to catastrophic costs, including equipment damage, loss of life, production delays, and the potential loss of access to ore reserves. Therefore, the optimal slope angle is the one that maximizes the economic benefit while maintaining a factor of safety that keeps the probability of failure within acceptable limits. Mine planners must balance the immediate financial gain of steeper slopes against the long-term risk and the potential costs of slope stabilization measures or remediation if a failure occurs.