The fundamental elements of an open pit mine are the key physical and operational components that define its structure, function, and efficiency. These elements are essential for both the design and operation of the mine. The most important are:
The benches
It is a fundamental technological element of open-pit mining, representing a portion of the overburden or orebody that is removed independently and served by its own dedicated transport systems.
Each bench generally has two exposed surfaces:
- The working face
- The bench slope
Benches that retreat during open-pit mining operations are referred to as operating benches. Benches other than those in active operation are bordered by narrow platforms, typically 20% to 50% of the bench height in width. These platforms are designed to enhance slope stability and are known as safety berms.
A portion of the mined area, limited in length and worked using independent drilling and loading equipment, is called a block.
The Pit edges
The pit edges are the lateral surfaces that define the voids created by mining operations. These include the benches and slopes of the pit.
There are two types of pit edges:
- Working edges
- Non-working edges
Working edges refer to the set of benches where mining activities are progressively carried out. Non-working edges are areas where no mining operations take place; they are used for material haulage and to ensure operational safety.
The Pit outline
The upper outline of the pit is the intersection between the upper edge of the pit and the original ground surface. The lower outline is the intersection between the lower edge of the pit and its bottom.
Pit Slope (Bench Slope)
The primary position of the pit edge at any given stage of mining operations is defined by the pit slope. This slope is an imaginary surface connecting the upper and lower contours of the pit.
The pit slope angle is determined based on:
- The depth position of the operation (Hx)
- The width of the working platform and safety berm
- The geomechanical strength of the rock forming the pit walls
For active pit edges, the slope angle (γ₁) is always less than that of the inactive or unmined pit edges (γ₂).
As a general rule, lower slope angles are adopted when dealing with weak or unstable rock formations. Conversely, steeper angles are used for strong or competent rock.
The final pit slope (also known as the ultimate or liquidation slope) refers to the overall angle of the pit walls during the final stage of the mine’s life. This angle is selected based on detailed geotechnical calculations to ensure wall stability and to minimize the amount of waste material to be removed.
In practice, the final pit slope angle usually corresponds to the slope angle applied to the unmined (inactive) side of the pit. That is, γₗ = γ₂.
