Every deep underground mine begins the same way: someone has to dig a hole straight down. That hole, the shaft, becomes the mine's main doorway. Workers, equipment and fresh air go down through it, while rock, coal or ore and foul air come back up. Digging it is called shaft sinking, and it is one of the hardest, slowest and most expensive jobs in all of mining.
In this post we explain what shaft sinking is, why shafts are usually circular, how a shaft is sunk step by step, what special methods are used in difficult ground, what the main hazards are and what factors decide whether a shaft is worth building. It is written for mining students and anyone curious about how mines are opened up.
- Shaft sinking means excavating a vertical or near-vertical opening from the surface to reach deposits at depth
- It is costly, slow and risky, so planning and skilled people are essential
- Mine shafts are mostly circular because the shape is strong and stable
- In water-bearing or weak ground, special methods such as freezing or grouting are used
What Is Shaft Sinking?
Shaft sinking is the process of excavating a vertical or near-vertical opening from the surface down to the level of a deposit, where there is no other way to reach it. The opening serves as the main route for people, machines and materials, and also for ventilation, power and communication. Because the work is done in confined conditions, often with water, gas and unstable rock, it is dangerous and demanding. It also takes a long time, and a mine cannot start producing until the shaft is complete.
The surface structure above a shaft is the headframe, a tall frame that carries the sheave wheel over which the hoisting rope runs. The hoist in the winding house raises and lowers the cage or skip. At the bottom is the sump, where water collects before it is pumped out, and at different depths stations connect the shaft to horizontal roadways (levels).
Uses of Shafts
- Mining: to reach and extract a deposit and to hoist people, material, coal or ore
- Ventilation: to bring fresh air in or take foul air out. See our post on mine ventilation formulas
- Underground storage: shafts can lead to chambers used for temporary storage
- Foundations: deep shafts are also used for the foundations of bridges and heavy structures
In this post we focus on shafts for mining.
Why Are Mine Shafts Mostly Circular?
Shafts can be rectangular, square or elliptical, but in mining the circular shaft is preferred. A circular section spreads the pressure of the surrounding rock evenly around the wall, so it is stronger and more stable than shapes with corners. It also needs less lining material for the same area and gives smooth airflow for ventilation. Rectangular shafts are sometimes used in smaller mines and shallow workings, where timber or steel sets are easier to fit.
Steps in Sinking a Shaft
The details depend on the ground and the method, but the main stages are as follows.
1. Site selection and planning
Before any digging, geologists and engineers study the rock, the water table and the hazards. They decide the location, diameter, depth and lining type. Boreholes drilled from the surface give a picture of the strata, and any water-bearing layers or gas zones are noted so that the right sinking method can be chosen.
2. Pre-sinking preparations
The site is cleared, and the headframe, sinking winches, power supply, pumps and ventilation fans are installed. A temporary arrangement is built to lower men and equipment into the shaft during sinking, along with a sinking stage, a working platform that hangs in the shaft and protects workers below it.
3. The sinking cycle
- Drilling: holes are drilled in the shaft bottom in a planned pattern.
- Charging and blasting: explosives are placed in the holes and fired, with everyone moved to a safe place.
- Ventilation: blasting fumes and dust are cleared before anyone returns, usually with fans and ducting. Gas safety matters here. Read about the main gases in our mine gases posts.
- Mucking: the broken rock is loaded into a bucket called a kibble, often with a mechanical grab, and hoisted to the surface.
- Support and lining: the freshly exposed walls are supported with bolts, mesh or shotcrete, and the permanent lining is built.
4. Lining the shaft
The permanent lining keeps the shaft open, stops loose rock from falling and controls water. It is usually concrete, sometimes steel, brick or a combination. In sound rock a thin lining may be enough, while weak or water-bearing ground may need a heavy lining designed to resist pressure.
5. Equipping the shaft
After sinking, the shaft is fitted with guides for the cages or skips, pipes for water and compressed air, electrical cables, communication lines, ladders or an emergency escape arrangement, and the permanent hoisting and ventilation systems. Stations are cut at the required levels so that roadways can be driven from the shaft.
Special Sinking Methods
In normal, dry rock, conventional sinking works well. But if the shaft has to pass through water-bearing sand, fractured rock or other weak ground, special methods are needed.
| Method | How it works | Used when |
|---|---|---|
| Ground freezing | Pipes are drilled around the shaft and cold brine is circulated to freeze the ground into a wall of ice | Water-bearing, loose or running ground |
| Cementation (grouting) | Cement or chemical grout is injected into the rock to seal fissures and reduce water inflow | Fissured or water-bearing rock |
| Dewatering | Water is pumped out ahead of or during sinking to lower the water level | Moderate water inflow |
| Tubbing | Watertight rings (segments) of cast iron or steel are fitted to hold back water pressure | Strong water pressure that a normal lining cannot resist |
| Shaft boring or raise boring | Machines drill the shaft, either downward or by reaming upward from an existing level | Suitable rock and where mechanisation is preferred |
Choosing between these methods depends on the geology, the water inflow, the depth, the cost and the time available. Often more than one method is combined.
Hazards and Safety in Shaft Sinking
| Hazard | What can happen | Main controls |
|---|---|---|
| Falling objects | Tools, rock or equipment dropping from above onto workers below | Sinking stage with a protective deck, secure tools, no overloading of kibbles |
| Water inrush | Sudden inflow of water from strata | Advance probing, pumping, grouting, freezing |
| Rock falls and instability | Walls collapsing before they are supported | Timely support and lining, regular examination |
| Blasting fumes and dust | Harmful gases and poor visibility | Strong ventilation and waiting for fumes to clear |
| Methane or other gases | Gas collecting in the shaft bottom in gassy strata | Gas monitoring, ventilation, approved equipment |
| Hoisting accidents | Cage or kibble falling, overwinding, rope failure | Examined ropes, safety devices, trained signallers, strict signalling code |
For basic safety practice, test yourself with our Mining Safety MCQ Series and learn how rescue is organised in our post on advanced mine rescue training.
Factors Influencing Shaft Sinking
- Depth and diameter of the shaft
- Rock and ground conditions, including water and gas
- Material to be handled through the shaft, which decides the size and type of hoisting
- Manpower and skills available
- Machinery and level of mechanisation
- Ventilation needs of the mine
- Capital cost and operating cost, and the value of the mineral that must pay for the shaft
A shaft is a long-term investment, so mine planners compare it with alternatives such as inclines or opencast methods before deciding.
Why Shaft Sinking Matters
The shaft is the backbone of a deep underground mine. It gives access to deep reserves, supports the mine's life, allows safe movement of people and material and provides the airways that keep the mine breathable. A well-planned and well-built shaft can serve a mine for decades.
From Manual to Mechanised Sinking
Shaft sinking has changed a great deal. Early shafts were dug by hand with simple tools. Later, drilling and blasting with hoisted buckets became standard. Today, mechanised mucking, mechanical shaft lining, remote monitoring and shaft boring machines are making sinking faster and safer in suitable ground, though conventional methods are still widely used.
Check Your Knowledge
1. What is the bucket used to hoist broken rock during shaft sinking called?
A. Skip
B. Cage
C. Kibble
D. Sump
Show Answer
C. Kibble
2. Why are mine shafts usually circular?
A. It looks better
B. The shape distributes rock pressure evenly and is strong and stable
C. It is the cheapest to blast
D. It needs more lining
Show Answer
B. The shape distributes rock pressure evenly and is strong and stable
3. Which method freezes the ground around a shaft to hold back water?
A. Ground freezing
B. Cementation
C. Tubbing
D. Raise boring
Show Answer
A. Ground freezing
4. Where does water collect at the bottom of a shaft before being pumped out?
A. Station
B. Headframe
C. Kibble
D. Sump
Show Answer
D. Sump
5. Which structure at the surface carries the sheave wheel for the hoisting rope?
A. Hoist house
B. Headframe
C. Lamp room
D. Fan house
Show Answer
B. Headframe
Frequently Asked Questions
What is shaft sinking in mining?
It is the excavation of a vertical or near-vertical opening from the surface to reach a deposit deep underground.
Why is shaft sinking so expensive?
It needs heavy surface equipment, skilled workers, special methods in difficult ground and a long time before any production begins.
How is a shaft sunk through water-bearing ground?
With special methods such as ground freezing, cementation (grouting), dewatering and tubbing.
What is a headframe?
The tall structure above the shaft that supports the sheave wheel for the hoisting rope.
What is the difference between a shaft and an incline?
A shaft is vertical or nearly vertical, while an incline is a sloping opening driven at a lesser angle from the surface.
For more notes, visit the Indian Minerology homepage. If you have experience with shaft sinking or any question, leave a comment below. Thanks for reading!
0 Comments