JNTU B.Tech IV ROCK SLOPE TECHNOLOGY Previous Question Paper (March 2021 - R16)

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

1. Bench Height: The vertical distance between the crest and the toe of a bench, which must be optimized relative to the overall slope angle to ensure structural integrity.
2. Bench Face Angle: The inclination of the individual bench face, which is typically steeper than the overall slope angle.
3. Catch Bench Width: The horizontal width of the bench surface designed to catch falling debris; as the overall slope angle decreases, the required catch bench width often increases to maintain safety.
4. Inter-ramp Angle: The angle formed by the slope of the rock mass between two major haulage ramps, which is constrained by the overall slope design.
5. Slope Height: The total vertical distance from the crest of the uppermost bench to the toe of the lowest bench, which directly influences the required overall slope angle for stability.

The relationship between the overall pit slope and mine economics is defined by the trade-off between safety and the volume of waste rock removal. A steeper overall pit slope significantly improves the economics of a mining project through the following mechanisms:

1. Stripping Ratio Reduction: A steeper slope reduces the amount of overburden or waste rock that must be excavated to access the ore body. This directly lowers the stripping ratio, leading to substantial savings in drilling, blasting, and haulage costs.
2. Increased Ore Recovery: By steepening the walls, more ore that would otherwise be locked under a shallow slope can be recovered, thereby increasing the total mineable reserves and the net present value (NPV) of the project.
3. Capital Expenditure: Steeper slopes allow for a smaller surface footprint, which can reduce the costs associated with land acquisition, environmental mitigation, and infrastructure development.
4. Risk and Stability Costs: Conversely, there is an economic limit; if the slope is made too steep, the probability of slope failure increases. The cost of potential failures—including equipment loss, production delays, and remediation expenses—must be weighed against the gains from reduced waste removal.

In summary, the optimal overall slope angle is the one that maximizes the project's profit by balancing the cost of waste removal against the geotechnical risk of failure.