The collar is the structural framework at the very top of a shaft, slope, or drill hole where it meets the surface. In shaft mining, it consists of heavy concrete or timber curbing that prevents the surrounding loose surface material from collapsing into the excavation. It serves as the foundation for the headframe and the starting elevation for all underground depth measurements.
The surveyors are setting up at the shaft collar to drop the final plumb line.
All underground elevations are traditionally measured relative to the collar elevation.
Also heard as
- Collaring
Related terms
Headframe
The structural frame above an underground mine shaft that supports the hoisting mechanism.
Heapstead
The surface structure around a mine shaft that supports the screening and loading of coal.
Inset
A horizontal opening partway down a vertical mine shaft that provides access to intermediate levels.