INTRODUCTION TO SHAFT AND SHAFT USE IN MINING
BY GIANT MINER
Shaft as related to underground mine is a vertical or an inclined opening extend from the surface into the ground to provide access to underground working area.
it not a news that we can mine the ore by surface and underground mining method. Now underground methods requires that the mining Engineers move into the subsurface with their equipments to extract the ore. We can't just disappear at the surface and appear in the underground like a magician! We provide an access into the ore without stripping the overburden materials.
These access are reference to two, the primary development and secondary development.
Shaft is a primary development opening as it has a life span greater than that of the mine. It provide access for personnel entrance into the underground mine, provide duct for ventilation, and many more.
Shaft can be classified into categories base on the following:
1 Base in uses
2. Method if excavation
3. Support system
4. Geometry
My joy is to give full explanation on all this today and give a detail explanation of them all... Also, to help give further explanation always send comment over so I can appreciate your reading.
Shaft type base on uses
This can categories into
1. Production shaft:
2. Exploration shaft
3. Service Shaft
4. Escape Shaft
5. Ventilation shaft
6. Combine shaft
Production shaft: is that having a skip conveyance that help in transporting mine materials and waste from Underground to the surface.
Service Shaft is mainly for the handling of personnel, workers and sometimes equipment from in and out the mine.
Ventilation shaft is also refer to as auxiliary Shaft by some textbooks especially the introduction to Mining textbooks. The main function o such is to support inflow and out flow of air into the Working area. Both for dilution and respiration. Underground is not surface, artificial air is required to keep miners alive. Exploration shaft are also refer to as the pilot shaft use for gathering geotechnical, geological, hydrogeological and other information about the ore deposit. Such shaft is sink to retrieve information for planning and Design seek. Escape Shaft are shaft sink to provide alternative evacuation for the mine workers Incase there is any emergency or incall for accident. I wish to have a talk on mine accident and environmental management soon. Components of shaft include, cage, skip, hoisting rope, hoisting drum, shaft liner, Shaft collar, shaft superstructure, and many more.
These all classified into Surface and underground components.
Cage is a conveyance or container use to move personnel in and outside the Shaft. Skip is a container design to be used for moving mine Run-off-mine and waste out of the Shaft during production and into the shaft during backfilling..(speaking like a professional now)
Rope is an energy supply components that assist in the hoisting of the conveyance.
The rope consist of three components, the wire, strand and the core. The wire is the smallest component or entity of a rope, the strand is two or more wire twisted together, the core is the center component of a rope. Selection of the rope is done base on the safety, compatibility, life span and cost. The rope can be use for three functions in a shaft system, for hoisting, for support and for guidance.
The hoist is a general name give to the outside components that controls the lifting and lowering of the conveyance in the Shaft. The hoist can be of two types, it can be friction hoist or drum hoist. The friction hoist involved a wheel been located above the shaft containing a rope passing through it into the Shaft. In such sinerio, the role is not whirr round the wheel but just pass through it, and the wheel is usually located above the shaft.
For drum hoist, it can be position at a distance from the shaft, and such drum allows the whirring of the rope round it. It consists of sheeves that centered the rope in the Shaft.
Okay, let me mention other classification of shaft
2. Base on geometry, this includes size and shape. Basically shaft with size (2m to 15m) is called small Shaft, 15-200m is medium size Shaft and >200m is large Shaft.
Also, that shaft can be of three main shape, 1. Circular 2. Rectangular 3. Elliptical shaft.
Actually, you may want to ask what is the advantage of this shape over the safety of the Shaft?
Speaking as a rock mechanics now, the insitu stress is naturally at equilibrium before excavation, any attempt to create excavation into the ground cause a great redistribution of the stresses, this cause the concentration of stress at some Region and relaxation of stress at other region. According to Dr Idris, a rock mechanics professional, a lecturer in the department of Mining Engineering, Federal University of Technology Akure, Stresses insitu will never leave after excavation, rather they become induce stress on the excavation wall. Such Stresses then become threat to the safety of the excavation wall. Examine 2D© a Boundary element method software shows that the circular shaft tends to have low wall damage zone as the induce stress distribute equally round the wall, unlike the rectangular shaft. Such opening with rectangular shape have high stress concentration at the 90° corner sides which make the wall liable to heaving, and oiling depending on the property and strength of the rock formation. This make the use of horse shoe shape in tunneling an advantage to redistribute the insitu stress in such a way that less Concentration is achieved all round the wall.
But as good as the circular shaft is, it only sink able using shaft boring machine SBM, which can inturn be very expensive, limited in high Strength formation
Prompt to this, the rock is DIANE (Discontinuous, inhomogeneous, e and non elastic)
in nature, this make the prediction of shaft wall stability inaccurate. Then, Mining Engineer need a means to garantee the safety of this wall and the life of mine workers. This lead me to the place of shaft classification base on support system.
Classification of Shaft base on support system can be divided into two broadly
1. Base on traditional approach
a. Permanent support: shaft with support system that are meant to stabilize the shaft throughout it life span
b. Temporary support: shaft with support system that are installed for short periods of time
2. Base on modern Approach
a. Primary support system: shaft with support system done before the excavation e.g the caisson and piling Techniques. Generally, the support system can be active or active, such kind of active supports are those which apply predetermined load or pressure on the shaft wall such as the grouted rock bolt and the hydraulic prop support
Finally, Shaft can be classified base on the excavation method, this implies the Technique use in sinking the Shaft. I talk like a Mining Engineer now, in overview, there are two techniques adopted for shaft sinking, mechanical method and conversation method. This methods are selected base on the following factors; Rock strength, shaft use, capital available among others.
The conventional method involve drilling and Blasting. Also known as the traditional approach. It involves the following operation cycle; drilling, charging, connecting, blasting, ventilation, loading and transportation if material, scaling of wall, bolting and drilling again for a new Blasting. This operation continues till we are done with the shaft sinking (excavation). The advantage of this Techniques are; ability to sink any shape shaft, ability to sink shaft in any rock strength nature, low cost of operation to mention few. Disadvantage of this Techniques are; poor/rough Shaft wall and back due to shock wave inconsistency, requirements for heavy support due to overbreak, environmental challenge, slow process among others.
The mechanical method involve the deployment of machine which bore the earth and create the shaft mechanically.
Also perform the supporting simultaneously.
Such equipment include shaft boring machine SBM. advantage include, fast sinking rate, smooth and stable wall, Perfect job, quick advance rate, it can be automated, little environmental effect and Many more. Disadvantages include, limited to circular shaft, limited to soft formation as hard rock damage dill bit, downtime during equipment breakdown among others. I talk like a professional now, shaft excavation method can be divided into two professionally,
1. Ordinary method
2. Special techniques.
The process of shaft sinking is divided into sinking from surface to the bedrock, sinking through the bedrock and sinking through unstable conditions. This lead to the above professional classification.
The ordinary method involve Drilling and Blasting when sinking through stable and Continuous rock formation. Such rock are stable and competent! The special techniques are use when the ground is unstable and incompetent such as sinking through sand, watery ground e.t.c. such techniques adopt in such case are: piling method, caisson method, grouting method, freezing method, shaft drilling and boring techniques.
Remember we go into the subsurface to extract, holes are created in the ground after excavation, it is the duty of Mining Engineer to back fill or support the excavated hole after mining has been done. By this the surface structure will be safe from holing and subsidence...
Remember mine it only when is safe, and when the environment is safe, this is what differenciate mining from other field. If you mine it unsafe, you are unsafe! Your Safety is your profit... Let make Mining a Better profession again.
Thanks
