Shaft sinking ppt..underground mines
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shaft design for underground mines, for the ore passing, .ventilation, uses in get workers and equipments into or out on the surface etc....
Transcript of Shaft sinking ppt..underground mines
- DEPARTMENT OF MINING ENGINEERING MUET JAMSHORO (11-04-2014)
- Introduction Definition Shaft collar Shaft sinking methods Down-the-hole shaft sinking method Wood/steel piling Open caisson Cementing process Freezing process Types of shafts
- shaft sinking, excavation from the surface of an opening in the earth. Shafts, which are generally vertical, are usually distinguished from tunnels, which are horizontal. Little difficulty is experienced in shaft sinking through solid rock, which contains little water. Shafts sunk in loose water-bearing soils and lined with cast iron or with concrete masonry 1 to 2 ft (30-61 cm) thick, built in sections as the work advances. Shaft sinking through rock is generally accomplished by blasting. Diameter and depth depends upon the type of the shaft Shafts are usually circular or rectangular.
- Shaft: A vertical or inclined tunnel from surface for the conveyance of men, materials, hoisting ore, pumping water and providing ventilation. Sinking: The work in excavating a shaft. Shaft sinking: It may be described as an excavation of vertical or inclined tunnel from surface for conveyance of men, materials, ventilation, pumping water, in addition to hoisting ore and waste rock. It is also called Shaft Construction or Shaft Mining.
- On the surface of an underground mine, a collar is required for a shaft or raise entry, Collars are also required For ventilation shafts, service shafts, and for all raises that reach surface. collars are normally lined with concrete
- There are different methods of shaft sinking/construction. Actually three possible methods allowing a shaft to me sunk through highly weathered over burden on the basis of Excavation and Wall support. These are; 1. Down-the-hole Shaft sinking Methods 2. Remote Shaft sinking Methods 3. Raiseboring Method
- Down-the-hole-Shaft sinking method 1. Rock bolting & meshing 2. cast-in-place lining 3. pre-cast lining 1. Drilling & blasting 2. shaft-boring mucking 3. V-mole with pilot hole
- Drilling & blasting: A shaft is constructed by drilling holes and filling them with explosives. Using this method, drilling and blasting can sink around 5-10 metres in one blast. This is very labour-intensive, unsafe and has high running costs. The most viable alternative for shafts up to 100m in length. Mucking: The operation of loading broken rock by hand or machine, usually in shafts or tunnels. Note: Muck, any useless material produced in mining. mucking out cuttings from the bottom of the shaft. Usually this would require some skip-hoisting, bucket-hoisting or clam-shell-grab equipment.
- V-mole with pilot hole The V-mole is an improvement on the concept of the shaft boring machine. Before boring, a pilot-hole is drilled, to assist in both cuttings removal and guiding the machine along the correct path. The V-mole uses grippers to hold on to the side of the shaft . The V-mole is a costly machine not suited for drilling short shafts.
- Rock bolting and meshing A wire mesh is fastened to the walls with evenly spaced rock bolts. Rock bolting is a commonly used, cheap method. The rock-bolts increase normal stresses on joints so that shear failure along joints becomes more difficult. Often rock bolts and mesh are used as a basis for shotcreting. Water in-flow during shotcreting severely reduces the quality of shotcrete.
- It is possible to cast concrete rings as the shaft sink progresses. This method provides a smooth, watertight and permanent lining for the shaft. The casing can be reinforced to cope with horizontal stresses (i.e. ring- shaped reinforcement) making the casing elements more economical.
- In sands, mudstone and sandstone, steel, pre-stressed concrete or composite liners with a smaller diameter (i.e. up to the 4.5 dia: )than the shaft are lowered after drilling out the hole. Concrete can then be poured behind the walls to create the lining.
- a) Wood/Steel Piling The first set of piles, forming a circle around the shaft site is started at the surface. As the piles are driven down, the ground is excavated, and a circular crib is put in every few feet. In this way the shaft is sunk in a series of short wooden cylinders. b) Open Caisson In this method the shaft is started by digging a shallow excavation and placing a cutting shoe on the bottom of the pit. The ground inside and just under the shoe is excavated and the lining is built up as the shoe sinks.
- c) Cementation Process Cavities and fissures are filled with quick-setting cement under high pressure then allowed to set. Cement pumps are designed for pressure as high as 5000 lb/sqin. d) Freezing Process This method was first used in 1883. The wet round is artificially frozen and then blasted and excavated as though it were solid rock. From 20 to 50 holes are drilled on the circumference of a circle. Circulating pipes are placed in the holes and a calcium or magnesium chloride solution is pumped through the pipes to freeze the ground.
- Shaft type Diameters (m) Depths (m) Mining ventilation 1-6 50-1500 Mining ore passes 3-7 50-1500 Mining access shafts 5-10 50-1500 Water treatment shafts 1-3 20-100 Tunnel access shaft 5-20 10-50