PRESENTATION TOPICSHAFT SINKING

PRESENTED BYNIAZ M SHAHANI-11MN69 (GL)

AFTAB ALI KHOSO-11MN73NASIR ALI MIRJAT-11MN80NOMAN KHATRI-11MN76

DEPARTMENT OF MINING ENGINEERING MUET JAMSHORO

(11-04-2014)

SHAFT SINKING

Objectives

IntroductionDefinitionShaft collarShaft sinking methods Down-the-hole shaft sinking methodWood/steel pilingOpen caissonCementing processFreezing processTypes of shafts

Introduction 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.

Definition

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.

Shaft collarOn 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 withconcrete

Methods of shaft sinking

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

Wall support

1. Rock bolting & meshing

2. cast-in-place lining

3. pre-cast lining

Wall support

1. Drilling & blasting

2. shaft-boring mucking

3. V-mole with pilot hole

W a ll s u p p o r t

Excavation methodDrilling & 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 holeThe 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.

Wall supporting methodsRock 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.

Cast-in-place lining

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.

Pre-cast lining segments

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.

Shaft sinking methods

a) Wood/Steel PilingThe first set of piles, forming a circle aroundthe shaft site is started at the surface. Asthe piles are driven down, the ground isexcavated, and a circular crib is put in everyfew feet. In this way the shaft is sunk in aseries of short wooden cylinders.

b) Open CaissonIn this method the shaft is started bydigging a shallow excavation and placing acutting shoe on the bottom of the pit. Theground inside and just under the shoe isexcavated and the lining is built up as theshoe sinks.

c) Cementation ProcessCavities 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 ProcessThis 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.

Different types of shafts 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