Shaft Sinking R M Bhattacharjee
Jun 19, 2015
Shaft Sinking
R M Bhattacharjee
Shaft sinkingWhy shaft is required?Why shaft sinking so critical?What factors influence selection of shaft?What are the hazards of shaft sinking?What are the major operations of shaft
sinking?
Why shaft is required?
To provide an entry to mineral deposit at deeper horizon
To ensure safe travel of men to place of work underground
To provide passage for ventilating air of required quantity
For transport of material, mineral or machines
To provide passage for taking down sources of energy , electrical, pneumatic, or hydraulic and communication system
To act as sump at pit bottom
Why shaft sinking is a critical operation?
Shaft is the life line of a mineIt should remain serviceable throughout the
entire life span of a mineStability and integrity of shaft and its fittings
are safety criticalShaft sinking involves high capital
expenditure – has high impact on costShaft capacity determines the economics of
mine
Hazards of shaft sinking
Stability of ground or sidesNoxious or toxic gasesTemperature and humidityFall from heightSlip / trip and fallHit by objects / machines / buckets / grabs
etcRestricted work placeBlasting projectilesWater – drowning
What factors influence selection of shaft?
Installation from surface or undergroundVertical or inclinedTonnages to be hoistedSize of mining equipment to be loweredAmount of water to be handledVentilation requirementThe type of ground through which shaft is to
be sunk throughPosition of shaft in relation to ore body
Location of shaft
Position wrt deposit’s geometryProduction shaft – at geometrical work load
centre of depositOre handled in tonne-km should be equal, as
far as possible, from all sidesFor flat deposit, protection pillar around shaftFor steeply dipping deposits, on footwall side
of ore body
Location of shaft
Position wrt surface topographyShaft collar at least 5 m above recorded HFLAway from places of public utility and water
bodies Within an easy access to infrastructure
facilitiesEnough space around to establish necessary
facilities and construction
Location of shaft
Position wrt geological disturbances, water table and ground conditionType of strata through which shaft will pass
throughPassing through geologically disturbed strata
should be avoidedLoose ground, water bearing strata, mud and
running sand areas offer difficulties and require special treatment
SHAFT SITE SELECTION
SINKING CYCLE
DrillingBlastingMuckingHoistingSupport or shaft liningAuxiliary operations
DewateringVentilationLightingShaft centering
SINKING METHODSORDINARY
METHODSSPECIAL
METHODSPiling
Wooden Steel Concrete
Caisson Pneumatic Without pumping With pumping
• Freezing
• Grouting
Cement
Clay
Chemicals
• Shaft drilling & Boring
General arrangements for shaft sinking
SEQUENCE OF SINKING OPERATION - DRILLING
Sinkers – 32-38 mm dia holesShaft jumbos (with no. of drifters) – 40-55mm
dia holesHole length – 1.5 to 3 m for sinkers /upto 5m
for shaft jumbosDrilling pattern – Wedge cut / pyramid cut /
step cutWedge cut popular in rectangular shaft
whereas pyramid cut for circular shaftStep cut where make of water is high and x-
section is large
SEQUENCE OF SINKING OPERATION - DRILLING
No. of holes depend on hole dia, shaft dia, type of strata
N = 2.55A + 22A is cross sectional area in m2
For circular shaft, in holes are drilled 3 to 5 concentric circles
Ratio of holes 1:2:3 or 1:2:3:4:5
Drill jumbo
Advantage of drill jumbo:Enhanced Sinking rate and productivityReduction in cost of sinkingReduced human and machine populationSmall crews – better management
LimitationHigher capital cost of rigs and sparesSkilled maintenance and operationKibble winder and opening through working
stage – to be matched with jumbo dimension
Wedge cut
Pyramid cut
DrillingBy pneumatic drill – rotary percussiveAir pressure > 80 psiHollow drill steels fitted with detachable bits
tipped with tungsten carbideShape of drill bit depends on strength of rockNo. of drills used / jumbo
Arrangement of holesConcentric ringsCut holes at an angle towards the centreSumpers / Inner easers / Outer Easers / Side
holes or trimmers or flankersAngles of holes reduces towards the outer
rings and side holes are vertical
Pyramid cut with jumbo
Step cut
Drilling with shaft jumbo
Longer hole blasting
Earlier holes were about 4 feet longNow holes of 4 to 5 meter length are drilled
by jumbosCut holes of 3.5 inches to 7.9 inches are
drilled to provide initial free faceEmulsion explosives are less expensive,
faster in loading, providing full borehole coupling, reduces drilling time and results better fragmentation
BlastingHigh density water resistant explosive such
as Nitro-glycerin based explosive Aluminum based water gel explosiveWater gel slurriesUse of emulsion explosives with boosters and
NONEL detonators
Blasting
Weight of explosives per cubic meter of rock blasted depends on Nature of rockStrength of explosiveDegree of fragmentation requiredDepth of pull
No. of holes varies from 80 to 100Weight of explosives per hole
Total explosivesNo. of holes750 – 1 kg per hole of 6 ft
BlastingWater or sand clay mixture as stemmingStemming used – 3:1 sand clay mixture for
dry shaft or sand alone in wet shaftSeries – parallel connectionsBlasting cable from surfaceMain shot firing cable suspended from
surfaceMust be able to support its own weight2 core cable or 2 separate single core placed
on opposite sidesPVC insulated single wire armoured and
seathedCoiled on drum
Removal of debrisDifficulties
Presence of waterLimited spaceTime required for installing mucking
equipmentOccupies about 50-60% of sinking cycle
Mucking efficiency depends onSize of rock fragmentsHoisting depthShaft cross sectionWater inflow rate
Removal of debrisBroken debris loaded into kibbles or bowks,
manually or mechanicallyMore than one kibbles are used at shaft
bottomMechanical loaders use compressed air
operated grabThe grab consists of a ring of powerful steel
jaws or fingers which can be opened or closed by comp air operated by a man at shaft bottom
The grab hangs from a control tower or frame mounted on the permanent lining
The tower can be raised or lowered by a winch at the surface
Lashing and muckingLashing unit is a mechanical device
incorporating hoisting, slewing and radial traversing mechanism for handling of the cactus grab
Types of shaft muckerArm loaders like cactus grab / cinderman
mucker / backhoe muckerRocker shovel Scraper
Cinderman mucker
HoistingHoisting / Lowering of men, material and
muck by temporary hoist, headgear and other attachments
Main componentsHead gear with pulleys
Substantial construction Capable of withstanding load upto 120-150 te Compact to enable erection of permanent structure Bolted construction for easy dismantling Central pulley for sinking rope Two side pulleys for walling platform ropes All three ropes are locked coil, non-spinning type Platform ropes also act as guide ropes for rider to
keep the kibble steady in the shaft when being raised or lowered
HoistingHoisting / Lowering of men, material and
muck by temporary hoist, headgear and other attachments
Main componentsRider
Permanent guide ropes are not possible to be installed while sinking in progress
When a walling is used, the scaffold ropes with an appliance RIDER may act as guide ropes for the kibble above the point where scaffold is suspended in the shaft
Davis and Barker’s Cone sinking rider is well known The vertical limbs should be long enough to prevent
canting of the rider
HoistingHoisting / Lowering of men, material and
muck by temporary hoist, headgear and other attachments
Main componentsRider
At the centre of the cross bar of the rider, a circular block with hole large enough for the detaching hook to pass through to prevent over winding
Mounted loosely on the winding rope is a collapsible spider or guide sleeve which fits into the central hole (and remains there, so keeping the rope steady) when the rider is at rest on the walling scaffold and the kibble suspended from the spring hook, below that level
When the kibble is above the scaffold, rider is lifted by the carrier cone inserted in the bridle chain, which engages in the underside of the block
GENERAL ARRANGEMENTS FOR SHAFT SINKING
Walling platformUsed for construction of side wallsDia of the platform is slightly less than dia of
the shaftSuspended by two ropes, which also act as
guide ropes for the kibbleEach rope carries two bridle chains secured
by shackles to four bolts A no. of rubber rings, supported by clamps,
are secured to each rope to relieve the impact of ride
The platform has a central opening for passage of the kibble
To keep the platform steady when persons are at work, four stout iron keys or bolts are pushed out to rest on the top of finished section of walling or in holes left in walling
Walling platformDuring sinking, scaffold is suspended within
50 ft above shaft bottomThe scaffold should be as close to the shaft
bottom to guide the kibbleWhen blasting, scaffold should be raised
temporarilyBesides being used for walling, scaffold also
provides protection against falling materialsIt may also be used as emergency means of
exit in case of anything wrongNo of rope ladders are attached to the
scaffold reaching to the bottom
Walling Platform
SEQUENCE OF SINKING OPERATION
SEQUENCE OF SINKING OPERATION
GENERAL ARRANGEMENTS FOR SHAFT SINKING
GENERAL ARRANGEMENTS FOR SHAFT SINKING
GENERAL ARRANGEMENTS FOR SHAFT SINKING
GENERAL ARRANGEMENTS FOR SHAFT SINKING
Temporary support of sides
Temporary support of sidesWhen one round of shots fired and debris
removed, support of sides are necessaryDone by system of steel curbs or skeleton ring
with close lining of wooden backing deals or steel plates
Mild steel curbs of 4-5 inch deep, 1 inch thick and 6-8 ft long segments with overlap and joined by bolts or fish plates
Each curb is suspended from the one above by 6-8 s-shaped steel hooks or hangers
Every third or fourth ring must be additionally supported on plugs placed into holes horizontally drilled into the strata
Wooden backing deals about 5-6 ft long are placed close together behind the curbs and each deal is provided with its own wooden wedge to tighten the structure
Temporary support of sides
In all steel arrangements, curbs are channel sections and are butt jointed by fish plates and four steel pegs
Curbs are supported by hangers and are backed by steel plates provided with a hook enabling them to be suspended behind the curbs
Very quick to install and can be reused many times
Temporary supports are removed, section by section, as the permanent lining is built up.
Permanent lining of shaftsTypes of shaft lining
Brick walling – dry shaftsConcrete blocks -Monolithic concrete – Most commonly usedcast iron tubbing – heavily watered shaft
Function of shaft liningTo prevent deformationTo prevent decrepitating due to influence of
atmospheresThickness of lining
Stresses to be resistedNature and strength of material used for lining
Permanent lining of shafts
Stresses on shaft liningCompressive in nature – from outside to inside
of shaftDepends on
Dia of shaftDepth of shaftNature of strataPresence of water
Tensional stress may be developed locally due to presence of faults, cavities, or other weaknesses
Permanent lining of shafts – Brick walling
Suitable for compact and fairly dry strata, where stresses are not high
14 inch walling is adequateOften 9 inch walling is sufficientLime mortar or cement mortar is used
Walling curbEach length of brick work is built up from a
walling curb laid on a specially prepared bed of strong ground
The curb may be of cast iron or concreteCast iron curb is a L shaped ring, 10-18 inch
wide and ¾ to 1 ½ inch thick, divided into number of segments
Ends of segments have vertical flanges, for bolting adjacent segments
Curb bed must be specially prepared, smooth and level
Curb should be truly circular and horizontalIts centre should coincide with the shaft
centre
Cast iron walling curb
Erection of brick wallingWhen approaching the site of the curb, size
of shaft is gradually increased or laid back about 2 ft all round
Inside dia of the curb is the finished dia of the shaft
Walling is built up from the curb, beginning about 2 ½ to 3 ft thick and gradually decreasing to normal thickness
To maintain verticality, side plumb lines are suspended from the curb above
Temporary supports are removed in sections as walling ascends
All spaces behind walling are packed solid with ashes, broken rocks or bricks or with concrete
Walling a shaft
Erection of brick wallingWhen a length of walling is completed,
sinking is continued at a reduced diameter, in alignment with the inside of walling
Shaft is then widened out to its ordinary size, some 2-3 m below, to leave a strong ledge of stone, as at L, to support the walling
The thicker portion serve to divide the entire shaft wall into separate portions independent of each other, each carrying out its own weight
If ever one portion is collapsed or had to be removed, other parts would not be disturbed
Erection of brick wallingWhen next lower length of walling is built up,
it is continued of the required thickness until it reaches the point W
The front portion of the ledge beneath the last curb is then cut away, a narrow width at a time, but upto the full height, so as to make room for the remainder of the walling
This is called underpinning of the walling curb
Concrete walling curb
In this case, the ground is cut back about 2 ft in
wedge form so as to key the concrete curb into
the strata
To form the curb, to retain the wet or plastic
concrete in position, shuttering is placed
Shuttering (S) are steel sheets, curved to suit the
circumference of the shaft and having angle irons
A riveted to them to enable adjacent segments to
be securely bolted together
Concrete walling curb
At the shaft bottom, each segment of the first
shuttering ring rests on a sleeper
The complete ring, when bolted up, must be
carefully leveled and centered
Small debris of 6 inch height is placed behind the
ring, followed by a layer of sand covered with
brattice cloth
One or more rings of bricks may be laid so that
they may be removed later to enable the length of
the walling to be keyed into the above
Concrete walling curb
Concrete is now placed behind the shuttering
ring
Is well rammed to fill all cavities next to the
strata and prevent formation of air pockets in
finished concrete
The second ring of shuttering is then placed,
centred, leveled and filled up same way
Temporary lining is removed as concreting
procedes
Concrete walling curb
Advantages of concrete curbThey are self supporting and underpinning is
not requiredThey can be applied in any groundLess liable to damage from blasting when
sinking is in progressVery strongLong length of walling can be carried on a
single curb
Monolithic concrete lining
Monolith is a pillar or column consisting of
single stone
Monolithic concrete lining is one built up
with a single mass of concrete instead of
with concrete blocks
Monolithic concrete liningAdvantages
Can be constructed rapidly and at low costHigher Compressive strength (3000-5000 psi)
compared to brick lining (800-1500 psi)The concrete extends right back to solid strata,
filling up all cavities and irregularities and this adds to the rigidity and strength of the lining
It presents a smooth surface to ventilating current
Suitable for water bearing strata owing to its capacity to settle under water , its freedom from joints and its ability to withstand pressure when injecting liquid cement behind to seal off feeders
It can be rendered immensely stronger by steel reinforcement, where necessary
Erection of concrete walling
A round of shots, below the length to be lined, is fired and the broken rock roughly leveled and left in position in readiness for resumption of sinking
First shuttering ring is then truly centered, leveled on sleepers or wooden blocks
A base is prepared for the concrete behind the ring
When the length of shaft to be lined has been sunk and temporarily supported, a concrete curb is built up and shuttering rings are added progressively to retain the plastic cement
Erection of concrete walling
A second ring is addedConcrete is fed from surface via pipe and
armoured hose until the space behind the two rings is nearly full
During filling, concrete is well rammedAll temporary supports are removed in
succession as work proceeds and further rings of shuttering added as required
Shuttering must be left in position until such time concrete is set
To facilitate the removal. Back of the shuttering are cleaned and well greased each time
Erection of concrete walling
When the rising wall reaches the next section of wall above, care is needed to make a good joint
A spl L shaped grouter ring is mounted on the last shuttering ring
When concrete has reached within an inch or two of the top wall, fine grout of sand and cement is poured in to close the gap
Grouter ring is filled to the topWhen grouter ring is removed, the excess
material is dressed off
Erection of concrete walling in water bearing ground
Back corrugated sheets are placed all round the shaft and are held in position by skeleton curbs and wedges
These sheets serve the purpose of temporary lining and also of keeping water away from concrete during walling
At suitable point, where walling is to begin, a temporary water garland is formed to catch water flowing behind back sheeting and is led into pipes from which it is discharged down into the shaft
Erection of concrete walling in water bearing ground
A base is prepared to receive concrete and first ring of shuttering and first length of steel reinforcement are erected
Concreting is now begun, skeleton curbs being removed stage by stage
Further rings of shuttering and steel reinforcement are added
Space behind the back sheeting is filled with clean gravel by removing portions of the back sheeting at intervals
Horizontal relief pipes are laid in the concrete at regular interval, extending through holes in the shuttering
Later on, after removing the shuttering, fine grout of cement and sand is injected to seal behind the back sheeting
Erection of concrete walling in water bearing ground
Cast Iron Tubbing
An alternative method of permanent lining of shaft sunk through heavily watered strata
Mostly associated with freezing process, where there is difficulty in setting of concrete
Tubbing is inserted while the ground is still frozen, so that the sinkers work under dry condition
Later, the ground is allowed to thaw slowly so that water pressure may build up gradually behind the tubbing
Water Ring Garland
Water Ring GarlandCast iron garland is having a channel around its
inner circumference to catch the water draining down the shaft sides
Garland consists of a no. of segments, which when bolted together, form a circle having same dia as finished dia of the shaft
Each segment is an open-topped casting of 18 inch wide, 4 ½ inch deep
One or more of the segments provided with an outlet hole into which is screwed a nipple from which 2 inch dia pipes convey water away to pumps at shaft bottom
To avoid front edge of the space water-ring projecting into shaft space, the walling above the ring is laid back about 4 inch and is brought back gradually to normal dia above 5 ft above
Special Methods of Shaft Sinking
When the strata through which shaft s to be sunk include deposits of loose or unstable ground, such as mud, sand, gravel, or alluvium, or when they contain excessive quantities of water which can not be dealt with by sinking pumps, or when both difficulties occur together, it is necessary to adopt special methods of shaft sinking
Special Methods of Shaft Sinking
Pile sinking or PilingCaisson sinkingFreezingCementation
Piling SystemSuitable for sinking through loose ground
near surfacePiles may be of either wood or steelThe system consists of driving down into
loose ground a circular lining of wooden backing deals, which are called piles
Piles vary in length from 6 ft to 15 ft, are 3 inch thick and 6-8 inch wide
Each pile is shod at bottom with an iron point or shoe
Piles are driven down by heavy mallets , and are placed skin to skin to form a complete circular ring
They are held in place by wooden curbs or rings, placed at intervals of 2 to 3 ft
Piling SystemSuitable for sinking through loose ground
near surfacePiles may be of either wood or steelThe system consists of driving down into
loose ground a circular lining of wooden backing deals, which are called piles
Piles vary in length from 6 ft to 15 ft, are 3 inch thick and 6-8 inch wide
Each pile is shod at bottom with an iron point or shoe
Piles are driven down by heavy mallets , and are placed skin to skin to form a complete circular ring
They are held in place by wooden curbs or rings, placed at intervals of 2 to 3 ft
Piling System
When the piles are driven a short way down, a curb is fitted within them
The ground inside is cut awayThe piles are kept about 2 ft in advance of
the excavationPiles are driven down one by one until hard
ground is reachedA walling curb is then laid and a strong wall
is built up in front of the piles, the space behind suitably packed
Piling SystemEach successive ring of timbering is of
smaller dia than the previous oneIt is necessary to start with larger dia, which
depends on depth of the running ground and dimension of the timber
For a shaft dia of 15 ft, with 8 ft long, 3 inch thick and 6 inch square curbs, starting dia is ?
There is a limit of depth beyond which it would be impracticable to use wooden piling system, as enormous excavation is required
Steel Piling System
Much stronger than wooden pilesCan be driven with much greater force with
piling hammer
Caisson Methods
Suitable for running ground at somewhat greater depths
Three typesSinking drum processForced drop shaft methodPneumatic caission method
Sinking drum process
Sinking drum process
Similar to pilingLining of the shaft is formed in advance of
excavationPiles are replaced by cylindrical drum of
brick work and steel or of RCC, fitted with a steel cutting shoe at its lower end
The brick work is 12-18 inch thick, resting on wooden curb fitted with steel cutting shoe
Other wooden curbs are built into the cylinder at intervals of 3-4 ft, and are tied together by wrought iron rods to increase strength of the structure
Sinking drum process
The drum sinks gradually by its own weight as the shaft is excavated
Further brickwork is added at the topCare must be taken to ensure drum descends
verticallySometimes wooden boards are placed
outside the drum to reduce friction
Sinking drum process
AdvantagesLining is built on surface, where construction
is safest and cheapestDrum acts as permanent lining for finished
shaftCost of temporary timbering is eliminatedWeight and strength of drum sufficient to push
aside boulders etc that would stop timber or steel pile
Sinking drum process
DisadvantagesSometimes difficult to keep the drum verticalSkin friction increases rapidly with depthDanger of drum being sticking altogetherIn running ground, large amount of excess
material is often excavated, resulting in subsidence of surrounding surface and damaging adjacent structuresIt is not advisable to install permanent headgear and winding engines till sinking through loose ground completed
Forced drop shaft method
Forced drop shaft method
Applicable to cases where beds are known to consist of alternate tough and loose ground in which ordinary sinking drum will either refuse to descend or would not sink far enough to prevent excessive quantities of loose material entering the shaft from below cutting shoe
Forced drop shaft method
It consists of jacking or forcing down by hydraulic rams one ( or more) cast iron drums of internally flanged tubbing within a preliminary caisson of brick work or concrete
The brick work caisson may form the walling in the upper part of the shaft
The hydraulic rams re-act against a massive cast iron pressure ring erected on top of brick work caisson, connected by number of stout vertical anchor bolts and guide bolts to a strong anchor ring
Forced drop shaft method
Anchor bolts are embedded in the brick workGuide bolts are close to the inner periphery
to form guide for tubbingPressure and anchor rings are strong to
resist enormous pressure of ramsWhen the tubbing has been forced down,
another ring is added to the top
Forced drop shaft method
AdvantagesMuch greater depth of loose ground can be
piercedDiameter of excavation is not excessiveMore certain method
Pneumatic caisson method
Designed for waterlogged quick sand or mudLower portion of the drum is converted
virtually into a diving bell by means of partition or diaphragm, 6 or 7 feet above the shoe
Compressed air at a pressure exceeding that of the surrounding water is led into the chamber so formed
An airlock is mounted on top of the chamber to permit passage of men and materials
The caisson sinks by gravity
Pneumatic caisson method
Pneumatic caisson method
DisadvantagesWorking in compressed air is injurious to
health – cause caisson sicknessLimiting depth is about 100 ftSlow progress and costlyCompressed air is liable to be vitiatedRelatively higher temp of comp air
Freezing process
Suitable for any kind of heavily watered strata, including quick sands
The process is formation of large cylinder of frozen ground in the centre of which it is possible to sink by ordinary method
No requirement of pumping
Freezing process
Freezing is accomplished by boring a ring of holes through the
permeable strata, slightly outside the size of the shaft and
by circulating through steel tubes in these holes a solution of cold brine which slowly absorbs heat from the ground and progressively lowers its temperature to freezing point
Eventually a temperature well below freezing point is reached in order to obtain an ice wall of sufficient thickness and strength to resist pressure of water in the strata
Freezing process
Four stages of shaft sinking by freezing process:BoringFreezingSinking Thawing
Boring
Number of vertical holes (20-50) drilled at a short distance from the outside circumference of shaft
Verticality is essential to ensure that ice wall is continuous
All the holes are lined with steel tubes, to prevent caving
Lining tubes are withdrawn after inserting freezing tubes
Freezing
Two concentric freezing tubes are inserted in each borehole
An outer tube of 5 inches dia, sealed properly at its base
An inner tube of 2 inches dia open at the lower end and reaching nearly to the sealed end of larger tube
Outer tubes are connected at the surface to a circular main or distribution pipe
Inner tubes are similarly connected to another main
Both mains are fitted with valves and cocks to control circulation of brine
Freezing
Brine is usually a solution of Cacl2
The brine takes up heat during its passage through the tubes
The brine must be sufficiently cooled by refrigerator
Freezing process
Brine circuit
Brine, at a temp of about -20 o C to -50 o C is pumped down the inner tube A and goes to the bottom of hole
It then ascends between inner and outer tubes A & B, extracting heat from the surface
It then passes into a brine tank where it comes in contact with spiral coils of refrigerator or ammonia evaporator
By this the brine is cooled in readiness for passing once again through freezing tubes
Ammonia circuit
Through the coils of the evaporator , refigerating agent or anhydrous ammonia is circulated
It reaches to the bottom of the lowest coil of the evaporator coils as a liquid, but is converted in to gas at the temperature of the brine as it rises through the coil
The heat required for evaporation is taken from the brine, which is thereby cooled
The gaseous ammonia, on leaving the evaporator, passes through an ammonia compressor where it is compressed to about 150 psi, the temperature being about 70 o C
Ammonia circuit
From there, the ammonia passes through an oil separator into the coils of condenser or liquefier
Under the influence of cooling water at atmospheric temperature, it liquefies
It again expands into a gas at the evaporator
Freezing
Circulation of the brine may be carried out in all the boreholes simultaneously
Ice wall will grow slowly around each freezing tube until the cylinders of ice join together
The time required for ice wall to form varies from two to six months, depending on the size, depth of shaft and nature of strata
Sinking
Sinking of shaft through frozen ground is carried by ordinary method
No pumping necessaryIf ice wall is effectively formed, shot firing
may be carried out without restrictionOnly Low freezing explosives must be usedWhere depth is moderate, shaft is timbered
temporarily with steel curbs with backing deals
Permanent lining is built up in sections
Sinking
The upper part of the shaft, above the water level may be lined with brickwork or concrete
From water level down to impermeable strata beneath water bearing strata, a water tight lining is provided by cast iron tubbing backed up by concrete
Cement mortar behind may be prevented from freezing by mixing with water containing 6-7% caustic soda or CaCl2
Sinking
In deep shafts, where pressure to be resisted is very high, permanent lining should be inserted ring by ring backed by concrete as soon as sufficient ground is excavated
Frozen ground is plastic and liable to deformation under great pressure
ThawingWhen shaft has been sunk through wet
ground, freezing may be stopped and ground may be allowed to thaw
Originally thawing was effected by blowing steam through freezing tubes
This caused breakage of freezing pipes, leakage of water and cement through tubbing and unequal distribution of pressure on shaft lining due to irregular thawing
Later, freezing plant was stopped, and brine was heated and circulated through freezing tubes
Shaft was also filled with hot water to ensure thawing of thin cylinder of ice, immediately next to tubbing and so prevent development of local pressure
Thawing
In modern practice, brine is merely warmed and circulated at such temperature and in such a way that thawing begins at the bottom of the tube and progresses gradually top wards
Shaft not being filled with hot waterShaft remains free for thorough inspection
and any defect remedied at once
Cementation
Cementation implies injection of liquid cement through boreholes into strata to fill up any cavities, fissures, cracks, and thereby strengthen and consolidate the strata, rendering it impervious to water
Applicable for firm but fissured water bearing strata where inflow of water would otherwise be excessive and unmanageable
It can be successfully used to seal porous rocks or fissures containing sand and other fine loose material
Not suitable for running sand
Cementation – Pre-silicatization
Certain kinds of porous rocks possess very high frictional resistance to penetration
Their natural porosity allows a considerable inflow of water
This difficulty may be overcome by pre-treating the ground with certain chemicals like silicate of soda and sulphates of alumina
This process is called silicatizationThe ground reacts with the chemicals to form
a gelatinous precipitate of aluminium silicate which has a lubricating action to render the strata more receptive to cement
Stages of Cementation
BoringCementationSinking and walling
Boring
This is usually carried out with heavy percussive compressed air hammer drill
Bore rods are hollowHoles are drilled from within the perimeter of
the shaft on a circle more or less concentric with it
First series of holes are drilled from dry ground, if possible
Some of the holes should be drilled inclined radialy and tangentially so as to ensure interception of all fissures throughout the length
Boring
Each hole is lined with a stand pipe, grouted with cement
Above the top of the hole, fitted with stop valve to control water given off during boring
Boring is continued through valves and stand pipes
As soon as the hole reaches decided depth or encounters fissure containing water , bore rods are withdrawn and stop valves closed
Hole is then coupled with flexible hose to cement pipe range and injected with cement
Cementation
High pressure double acting ram pumps driven by compressed air or electricity used to inject cement
Cement mixing tank, silicate storage tank, sulphate dissolving and storage tank and pipe ranges are required for the cementation operation
Injection
For small fissures one injection of cementation may be sufficient
For large fissures, certain amount of cement is injected and cementation is suspended for few hours to allow setting of cement
Hole is then cleaned by boring and injection repeated until cavity is completely closed
Percentage of cement in mixture varies from 2-50%
Sinking and walling
Ordinary brickwork, cast iron tubbing, reinforced monolithic concrete lining are used with cementation
Staple Shaft / Blind shaft
Vertical shaft connecting two seams or horizons without reaching to the surface
Used for transport of mineral, men and material, and for ventilation
Widely used in horizon mining, for connecting two horizons
In in-seam mining, used in place of long inclined cross measure drifts
Staple Shaft vs Drifts
Advantages of staple shaftsLess time and less cost due to shorter lengthStaple may be located at suitable place free
from geological disturbances etc. where as drift may have to pass through difficult ground
Less costly repairingProtective pillar size is lessLess resistance to ventilation
Staple Shaft vs Drifts
Dis-advantages of staple shaftsDifficult access for repairingInterrupts transportation systemTransport of heavy equipment is difficultLess convenient for transport of men
Driving staple shaft
May be sunk downwards from upper level or raised from lower level
Raising is preferred, if possible, due to ease of mucking , blasted material falls down due to gravity
But raising requires god ventilation, good overhead support
Sinking staple shaft downwards
Similar to that of shaft sinking, may be with smaller dimensions
To accommodate winding pulley and frame work and providing sufficient height for raising and emptying kibbles, vertical excavation is needed
Winding engine installed at upper levelFolding doors and other arrangements
installedShaft sinking and lining proceeds normal
Raising staple shaft upwards
Dividing shafts into number of compartments to provide for debris, ladder way, ventilation
Centre stack method / four compartment staple
Requires great care and experienced person
Raising staple shaft - centre stack method
Three compartmentsLarger middle compartment A for stowage of
debris and also serves as platform for work men
B and C for ventilationIn B, ladder way provided for ascending and
descendingIn C , at the bottom, chute provided for
disposal of excess debrisCentre stack formed by placing pairs of steel
girders and sleepers
Raising staple shaft - centre stack method
For drilling and blasting, top of B & C provided with timber planks from sack girders to top of brick work
Drilling done upwards in concentric ringsBlasted materials fall on planksSupervisor ascends to examine roof and gas,
before allowing work menExcess debris disposed through C
Deepening by blind pit
Shaft Drilling and Boring
Sinking without explosiveEntry of crew is not required during sinkingSafe and economical
Shaft Drilling
Through aquifers or very weak formations, where conventional sinking is difficult, even with special methods, or economically impractical
Based on rotary drilling technology for gas and oil wells
Large dia holes (1.5 – 8m) upto 2000m depth
Shaft Drilling Heavy oil rig with rotary drill and drill string &
bit is usedBit equipped with roller cutters with teeth that
cut rock chips as the bit rotates at the bottomNo. And arrangement of bits vary with size of
holeStabilisers are used to control hole deviationRelatively low speeds for large dia holesVertical thrust varies from soft to harder
formations Drilling mud used to support shaft walls, cools
the drill bit and remove cuttingsDouble walled pipes with reverse circulation is
used for removal of cuttingsWire mesh screens separate cuttings from
drilling fluid, which is recycled
Shaft Drilling
MeritsAll operations carried out from surfaceEffectively deal with ground water, caving and
soft formationsSmooth wall surface at fast penetration rate
achievedLimitations
High capital costDifficulties in drilling through hard strata
Shaft Boring Machinehttp://www.herrenknecht.com/uploads/tx_torrvideoteaser/SBM_D-600_zusammenstelltung_26_02_2011_02_1_02.mp4
Some basic differences in comparison to horizontal tunnelling had to be considered in the development of this new shaft boring machine, which is similar to a conventional tunnel boring machine.
One major challenge was to raise the excavated rock from the shaft bottom and to transport it vertically through the machine up to the transfer point for shaft conveyance.
The solution: The cutting wheel was turned by 90 degrees and the rock is excavated in two consecutive steps.
Shaft Boring Machine
In the first step, the cutting wheel penetrates the rock like a circular saw, thus creating a slit with a depth of 1.5 meters.
In the second step, it rotates around the vertical axis of the machine to cut out the entire shaft profile. In doing so, the cutting wheel not only loosens the rock but also serves as a paddle wheel which transports the muck via integrated channels to the center.
There the material is transferred to a vertical belt conveyor, which transports it to the transfer point for shaft conveyance.
Up to 3 gripper systems brace against the shaft wall and thus stabilize the entire system during the tunnelling procedure.
Shaft Boring Machine
Vertical shaft sinking
Vertical shaft sinking machine
Shaft Sinking Machine consists of two main components – the shaft boring machine, and the lowering units.
The shaft boring machine is lowered into the launch shaft structure and attached firmly to the shaft with its three machine arms.
A rotating cutting drum equipped with chisel tools is attached to a telescopic boom.
This road header excavates and breaks the soil at the base of the shaft. The road header is telescopic, and can swivel up and down or rotate. Hence, the entire cross-section of the shaft plus an overcut can be excavated gradually.
The excavated material is removed hydraulically through a submersible pump and transported to the separation plant on the surface.
Vertical shaft sinking machine
The lower concrete ring of the shaft structure, also referred to as the shaft’s cutting edge, is bevelled and therefore cuts into the surrounding soil underneath.
In addition, the overcut of the road header-like telescopic boom and cutting drum below the shaft’s cutting edge in combination with the bentonite lubrication in the annular gap reduce the frictional forces between the shaft wall and the surrounding soil.
Vertical shaft sinking machine
The lower concrete ring of the shaft structure, also referred to as the shaft’s cutting edge, is bevelled and therefore cuts into the surrounding soil underneath.
In addition, the overcut of the road header-like telescopic boom and cutting drum below the shaft’s cutting edge in combination with the bentonite lubrication in the annular gap reduce the frictional forces between the shaft wall and the surrounding soil.
Vertical shaft sinking machine
On the surface, 3 to 4 lowering units with hydraulic cylinders are attached firmly to the ring-shaped concrete foundation around the shaft.
They are attached to the lower concrete base ring of the shaft structure by steel cables. In this way, the entire shaft structure can be held and lowered in a controlled manner during excavation.
Ring building takes place simultaneously on the surface using prefabricated concrete segments.
The simultaneous working processes (excavation, removal of excavated material, shaft construction, and lowering of the shaft structure) make it possible for VSM technology to achieve high advance rates of up to 5 meters per shift.
Raises
Raising with Jora lift method
Deepening by staple shaft