Shaft Works

ABSTRACT

Prestea central shaft, one of the main active surface shafts of New Century Mine was

surveyed to ascertain it vertical alignment, lateral and horizontal motion that has occurred

since its existence. The survey was from shaft collar to 30 level even though previous

survey conducted for similar purpose in 1984 focused on 9 to 16 levels which was the

area that had undergone considering earth movement. The method used for the survey

was the plumb bob method by taking perpendicular offset measurements from a freely

suspending weighted wire at the corners of each compartment of the shaft to the shaft

walls and its lining.

The whole project from surface to 30 level was undertaken in two phases due to plumb

wires touching either the cage or the setts between 9 and 16 level. The first phase

spanning a period of three weeks from January to February 2007 saw to completion of

that for the shaft collar to 9 level. The second phase, which continued from 9 to 30 level,

was subdivided into batches of three (9 to 17, 17 to 24, and 24 to 30 levels) due to short

piano wire lengths. In general, the shaft was straight with some of the steel setts displaced

towards southwest and the others corroded.

TABLE OF CONTENTS

TABLE OF FIGURES.........................................................................................................1

1 INTRODUCTION.......................................................................................................2

1.1 Background..........................................................................................................21.2 Objectives............................................................................................................31.3 Scope of Work.....................................................................................................3

2 METHODOLOGY......................................................................................................4

2.1 Resources Used....................................................................................................42.2 Possible Sources of Errors...................................................................................52.3 Precaution............................................................................................................52.4 Set-Up..................................................................................................................72.5 Measurements......................................................................................................8

3 OBSERVATIONS.......................................................................................................9

4 DISCUSSION AND CONCLUSION.......................................................................10

5 RECOMMENDATION.............................................................................................11

x = 6.80mm...............................................................................................................17....................................................................................................................................17

APPENDICES…......13-20

TABLE OF FIGURES

Figure 2-1 Set-up of the Pulley for the Piano Wires..............................................7

Figure 1 Central Shaft Compartments from Surface to 30 Level (Plan View).....12

Figure 2 Plumb Wires Installed from Surface Collar to 9 Level and Code for their

Corresponding North and South Offsets (Plan View)...................................13

Figure 3 Positions of Plumb Wires Installed From Surface Collar to 9 Level And

Code for their Corresponding East and West Offsets (Plan View)...............14

Figure 4 Positions of Plumb Wires Installed from 9 Level to 30 Level (Plan View)

.....................................................................................................................15

Table 1 Plumb Wires and their Corresponding Codes for Measurement............17

Equation 1...........................................................................................................18

DETAIL SURVEY

1 INTRODUCTION

The object of survey is to produce, in general a graphical or numerical form, a

representation of natural and fabricated features in order that engineering works

can be located in their correct position on the ground. To carry a survey into a

mine through a shaft by means of heavily weighted fine wires hung vertically in

the shaft, the line of sight passing through the wires at the surface is thus

transferred to the mine workings. An important piece of work: in mineshafts, and

in transferring courses or bearings from one level to another.

While executing maintenance works on a shaft of an underground mine, it is

essential to maintain the vertical alignment of the shaft for the smooth working of

cages. The position of the center of the shaft should be known throughout the

shaft and needs to be transferred at various levels in the mine. Shaft detailing

and survey was as thus undertaken to graphically represent the shaft in three-

dimension (3D) and determine the position of the shaft sets, the verticality of the

shaft, and earthwork volumes.

The whole project from surface to 30 level was undertaken in two phases due to

a number of reasons with the first phase spanning a period of three weeks from

January to February 2007. The first phase covered surface to 9 level and the

second phase, which continued from nine to 30 level, was subdivided in batches

of three.

1.1 Background

New Century Mine is a shaft mine situated at Prestea. The Central Shaft is one

of the two active shafts of the Underground Mine. It serves as the main entrance

to the 35 level underground mine at Prestea with an interval of 150 meters

between levels and as emergency exit to Bondaye Main Shaft because they are

inter-connected. It is a 4-compartment shaft with a portion of the fist and second

compartments serving as ladder way and opening to service pumps, cables, etc,

Survey Department 8/3/2007 2

DETAIL SURVEY

the other portion for the skip cage. The third and fourth compartments are used

for man-riding and carrying equipments and machines up to surface and down to

underground.

It became imperative for shaft maintenance to be carried out on the shaft since

most of the sets were worn-out and rusty making it unsafe for hoisting. A shaft

survey was therefore undertaken to plot the shaft and its members in three-

dimension.

1.2 Objectives

The main objectives for the shaft plumbing is

to measure with precision the positions of shaft steels

to provide reference points for future bunton installation

to determine the vertical alignment of the shaft and the shaft lining.

to determine volume of earthwork between shaft sets and the walls

1.3 Scope of Work

Setting out of plumb wires at the corners ends of the compartments

Checking alignment of hung plumb wires

Measuring perpendicular offsets from plumb wires to the steel sets, walls

and guides

Establishing controls at level stations to take coordinates of plumb wires


DETAIL SURVEY

2 METHODOLOGY

The conventional shaft survey techniques make use of plumb wires suspended

from the top of the shaft in order to transfer the position of a point and that of the

direction of a plumb plane from the surface to the pit bottom underground.

Plumbing a shaft mechanically means lowering a thin wire into the shaft using a

winch and a guide weight. This method is known as the Plumb Bob Method.

Empirical methods show a divergence of 0.00ft (0.00mm) to 0.10ft (30.00mm) for

every 4000 feet (1220.00m) of plumb line suspended. The longest plumb wire

suspended was about 900 feet (275.00m) which would have a divergence range

of zero feet (0.00mm) to 0.0223097 (6.80mm) if the wires are assumed to have a

steady divergence with depth increase.

For a measurement carried out with a tape measure which gives measurement

accuracy of decimals of a centimeter (1mm), the fractional error per meter depth

would be 40441.00mm; an error of 1.00mm divergence for every 40.00 meter

depth reached which is not significant as thus the plumb bob method used being

adequately accurate and acceptable.

Coordinates difference for plumb line suspended from 24 level was taken for 24

and 30 levels and the corresponding divergence for each plumb line and as such

the mean divergence for. The coordinate difference measured at 17 level, their

corresponding divergence and the mean divergence calculation is attached as

equation 1.

2.1 Resources Used Piano wires running round a pulley

Plumb bobs (25-10kg - which do not exceed the tensile strength of wire)

Pair of pliers

Nails (2-5’’) and Hammer


DETAIL SURVEY

Wooden Boards (4”x6”x8’), (1”x2”x2’)

Eye bolts of 4mm diameter.

Engine oil and Grease

Polythene bags

Total station

Steel tape

2.2 Possible Sources of Errors

The determination of the position of the freely hanging plumb bobs and as such,

the vertical position of the plumb wires is subject to a variety of influences, such

as:

rotational oscillation of plumb bob

longitudinal oscillations of plumb wire

mechanical load the weight imposes on the wire

thickness of wire

mechanical stretch and stiffness of wire

precision of position detection - the error obtained in coordinates of the

plumb wire which is consecutively transmitted to the calculated positions

of the other points since the offsets were taken from the plumb wire

The rotational oscillation of the plumb bob is overlapped by longitudinal

oscillations of the wire. If these are asymmetric to the pendulum oscillation, then

additional movements are induced, this can then cause a significant shift of the

apparent rest position if measures are not put in place to eliminate them.

2.3 Precaution

The following precautions were taken to reduce if not eliminate the above-

mentioned errors as much as possible. Other precautions were taken for safety

reasons and workload reduction involved.

A thorough inspection was done to make sure the plumb wires and as the

plumb bobs touched nothing. This was done to ensure the plumb wires Survey Department 8/3/2007

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DETAIL SURVEY

from which the plumb bobs were suspended pointed directly to the earth's

center of gravity; used to determine the true vertical from a given point.

The rotational oscillation of the plumb bob and longitudinal oscillations of

the wire were taken care of by damping the heavy weighted bobs in highly

viscous oil.

Heavy plumb bobs were hung on thin wires to make the wires taut. This

eliminates errors introduced by mechanical stretch and stiffness of wire

and that of the thickness of wire. This also ensures verticality of plumb

wires.

The plumb wires were guarded from any disturbances since any

displacement in the wire will cause an error in the readings taken.

The position of the plumb wires were measured with utmost accuracy

since a significant error in the coordinates would introduce errors in the

positions of points obtained since the offsets were taken from the plumb

wire.

The following precautionary measures were taken to make work easier and for

safety reasons.

Polythene bags were used to cover the piano wire to prevent wires from

rusting.

Smaller plumb bobs were used to lower the wires before replacing with

bigger and heavy plumb bobs.

Eye bolts were fixed to each plumb line at sets 2 and 10 of a vertical

distance of 14.095m to serve as guide in case any displacements.

A wooden platform built to form a base for drums containing the oil to be

used for damping and falling objects from finding the underlying bottom of

the shaft.

2.4 Set-Up


DETAIL SURVEY

A reconnaissance survey was undertaken to determine appropriate points where

all plumb lines could be seen to establish controls.

Piano wires coiled around a winch as shown in figure 2.1 and fixed to a wooden

board - to ensure stability and firm grip to the ground - were stationed close to

the corners of the compartment to be measured. The plumb wires were lowered

with the help of light weighted bobs from the starting base station (surface collar,

9, 17, and 24 level gangways) to their corresponding destination base stations (9,

17, 24 and 30 level gangways) respectively.

A wooden platform was built four (4) sets below the corresponding destination

level within the specified compartment to form a worktable for drums containing

the oil to be used for damping and also prevent falling objects from getting to the

shaft bottom.

The light plumb bobs were replaced with the heavy ones to make the wires

adequately taut. The plumb bobs were dampened by putting them in the drum of

oil.

Figures 5-1, 5-4 and 5-5 show a diagram of the shaft compartments and the

general set-up for the plumb lines.

Figure 2-1 Set-up of the Pulley for the Piano Wires

2.5 Measurements


DETAIL SURVEY

After the plumb wires had been set-up, an inspection was again conducted to

make sure the wires were hanging freely. Some few minutes was allowed to

elapse to make sure the wire and bob are in a state of equilibrium.

Perpendicular offsets were then taken from the plumb wires on the northern and

southern side of the shaft to their respective north and south wall plates, north

and south walls, end plates, dividers and guides.

The observational procedure was repeated for each set down the shaft. The

vertical interval between one shaft set to the next was measured as the cage

moved down. The label mapping code used for the measurement is attached as

table 5-1. Figures 5-2, 5-3, 5-4, and 5-5 show diagrams of the set-ups for the

various modes of measurement. The same measurement procedure and code

format were used for all the phases.

The coordinates of the plumb wires were then measured with a total station to be

used to compute the coordinates of the various components of the shaft lining.

The positional set-up of the plumb lines was altered and thus giving the different

sets of offset readings. The calculations involved are outlined as equations 2, 3,

4, 5, and 6.


DETAIL SURVEY

3 OBSERVATIONS

The shaft lining from surface to three (3) level were intact due to its

concrete walls.

From three (3) level to nine (9) level had good sets with a couple of

corroded ones with some portions replaced with buntons.

A vertical plane put through the middle of the shaft’s DTM from surface to

9 level was within limit.

The vertical alignment of the shaft sets from surface to 17 level was

skewed towards the west up to thirty centimeters (30cm) in an average

gradient of 0.0414% ( 1 in 0.0004141) as its depth increased down the

shaft.

Most of the sets between 12 and 16 level were worn-out.

The plumb wires hanged from 9 to 17 level at the transferred position of

the plumb wires from surface to 9 level touched most of the shaft sets

between 12 and 15 levels.

There was so much water in the shaft.


DETAIL SURVEY

4 DISCUSSION AND CONCLUSION

Survey Department 8/3/2007

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DETAIL SURVEY

5 RECOMMENDATION

Survey Department 8/3/2007

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Plumb line3 2 1

E C A

BDF

Not drawn to scale

Figure 2 Central Shaft Compartments from Surface to 30 Level (Plan View)

Not drawn to scale

12

N

South Wall Plate DividersShaft Walls Cage Guide North Wall Plate Plumb Wires

No 1 Compartment No 4 CompartmentNo 2 Compartment No 3 Compartment

Ladder way Pipes and Cables Vent

Plumb line3 2 1

E C A

BDF

Figure 3 Plumb Wires Installed from Surface Collar to nine Level and Code for their Corresponding North and South Offsets (Plan View)

Not drawn to scale

13

NA

B

C

D F

E

J

IG

H

EG2CG

EG1

AGGG IG

GN2 GN1 IN2IN1EN2EN1

HS1 JS2

CN2 CN1

HS2 JS1DS2

AN2 AN1

DS1BS2 BS1 FS2FS1

Plumb Wires

Plumb line3 2 1

E C A

BDF

Figure 4 Positions of Plumb Wires Installed From Surface Collar to nine Level And Code for their Corresponding East and West Offsets (Plan View)

Not drawn to scale

14

A

B

C

D

F

E

J

IG

H

BW2BW1

DE

FE HW JE1 JE2

AW1CE EE

GWIE1

1E2AW2

Plumb line3 2 1

E C A

BDF

Figure 5 Positions of Plumb Wires Installed from 9 Level to 30 Level (Plan View)

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NA

B

C

D F

E G

H

FROM PLUMB WIRE

TO POSITION CODE FROM PLUMB WIRE

TO POSITION CODE

A North Wall plate AN1 F South Wall FS2

A North Wall AN2 F East Divider Set FE

A West End plate AW1 G North Wall plate GN1

A West Wall AW2 G North Wall GN2

A Guide AG G West Divider Set GW

B South Wall Plate BS1 G Guide GG

B South Wall BS2 H South Wall Plate HS1

B Western end plate BW1 H South Wall HS2

B Western wall BW2 H West Divider Set HW

C North Wall plate CN1 I North Wall plate IN1

C North Wall CN2 I North Wall IN2

C East Divider Set CE I East End plate IE1

C Guide CG I East Wall IE2

D South Wall Plate DS1 I Guide IG

D South Wall DS2 J South Wall Plate JS1

D East Divider Set DE J South Wall JS2

E North Wall plate EN1 J East End Plate JE1

E North Wall EN2 J East Wall JE2

E East End plate EE

E Guide EG

F South Wall Plate FS1

Table 1 Plumb Wires and their Corresponding Codes for Measurement

Equation 1

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for every 4000 ft (1220m)

If , then

x = 6.80mm

KEY WORDS

Shaft or Cage guides

Conductor made of wood, iron or steel, or wire rope; used to guide the cages in the shaft and

to prevent them from swinging and colliding with each other while in motion.

Shaft inset

The point where a horizontal tunnel intersects a shaft.

Shaft lining

17

The timber, steel, brick, or concrete structure fixed around a shaft to support the walls. In

modern shafts, a concrete lining is generally favored as a permanent shaft support.

Shaft mine

A mine in which the vein is reached by a vertical shaft which may vary in depth from less than

100 ft (30 m) to several thousand feet.

Or a mine in which the main entry or access is by means of a shaft.

Shaft pillar

A solid block of ore left around the shaft where it crosses the lode, for protection against earth

movement.

Shaft plumbing

The operation of transferring one or more points at the surface of a vertical shaft to plumb line

positions at the bottom of the shaft; a method to ensure that a shaft is sunk in the true vertical

line.

Survey operation in which the orientation of two plumb bobs is measured both at the surface

and at depth in order to transfer the bearing underground.

Shaft section

A drawing or log giving details of the structure and the nature of strata intersected by a shaft.

Shaft set

A Supporting frame of timber, masonry, or steel that supports the sides

of a shaft and the gear; Composed of two wall plates, two end plates, and

dividers that form shaft compartments.

A system of mine timbering similar to square sets. The shaft sets are placed from the surface

downward, each new set supported from the set above until it is blocked in place. New wall

plates are suspended from those of the set above by hanging bolts. Blocking, wedging, and

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lagging complete the work of timbering. At stations, the shaft posts are made much longer

than usual to give ample headroom for unloading timber and other supplies.

Shaft signal

Code of electric ringing, or for shallow depths, knocking, among the onsetter or hitcher at the

shaft bottom, the banksman at the top, and the engineman who operates the winder. Signals

inform the latter as to type of load, etc. A telephone is also installed.

Tensile Strain

Deformation along a line segment that increases in length when a load is applied along that line.

Tensile stress

The stress state leading to expansion; that is, the may be increased until the reach of tensile strength, namely the limit state of stress.

The formula for computing the tensile stress in a wire is:

Where σ is the tensile stress, F is the tensile force over the rod and A is the cross-sectional area of the rod.Units for tensile stress are newtons per square meter (N/m², also called Pascals, Pa)

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Shaft Works

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