Shaft Steelwork Modifications

for the Mining of the No 2A Sub-Shaft Pillar

J J VAN DER WESTHUIZEN

S e c t i o n E n g i n e e r

H a r t e b e e s f o n t e i n D i v i s i o n o f Av g o l d

S Y N O P S I S

La t e sha f t p i l l a r ex t r ac t ion i s a lways a s soc ia t ed wi th damage to

the sha f t . I f t he sha f t i s t o be kep t fu l ly ope ra t iona l du r ing and

long a f t e r t he ex t r ac t ion o f t he r ee f , means to p reven t damage to

the sha f t s t ee lwork , s e rv i ces and wind ing equ ipmen t mus t be in

p l ace be fo re the p i l l a r min ing ope ra t ion s t a r t s .

This paper descr ibes the shaf t s tee lwork modif ica t ions and the shaf t

layout to suit future hoist ing operat ions at Avgold 's Hartebeestfontein

Go ld mines ' No 2A sha f t a f t e r min ing o f t he p i l l a r.

I N T R O D U C T I O N

No 2A sha f t i s a c i r cu la r sub ve r t i ca l sha f t t o No 2 sha f t . Be fo re

the sha f t p i l l a r p repa ra t ion work s t a r t ed , t he sha f t was se rved by

two men & ma te r i a l w inde r s - "A" and "B" - and one rock winde r -

"C" - . These winde r s a r e s i t ua t ed on t r ans fe r l eve l . The sha f t i s

d iv ided in to s ix compar tmen t s .

The fo l lowing ob jec t ives were se t du r ing the p l ann ing phase :

• Main ta in i t s dewa te r ing pumping capab i l i t i e s . Th i s sha f t i s

u sed to pump be tween 10 Ml and 12 Ml o f wa te r da i ly to

t r ans fe r l eve l . Wa te r sou rces a re f rom min ing ac t iv i t i e s a t

No ' s 2A, 4 and 5 sha f t s , a s we l l a s f rom S t i l fon te in Go ld

mines ' Sco t t sha f t .

• To ma in ta in the men , ma te r i a l and rock ho i s t ing capab i l i t i e s

o f t he sha f t .

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• Modi f i ca t ions to t he s t ee lwork in the sha f t t o be such tha t i t

wi l l accommodate the expected ver t ica l and hor izonta l ground

movemen t w i th min ima l add i t i ona l ma in tenance .

• To mine the No 4 sha f t p i l l a r v i a t h i s sha f t .

MODELLING AND STRAINS

Modellings were done to predict the horizontal and vertical displacements

o f t he sha f t ba r r e l . The X and Y d i r ec t ions g ive the ho r i zon ta l

( la teral) displacement f rom the or iginal centre l ine of the shaf t barrel

(Tab le 1 and F igu res 1 , 2 ) wh i l e t he Z d i r ec t ion g ives the ve r t i ca l

up and down d i sp l acemen t (F igu res 3 , 4 ) f rom f ixed po in t s on the

sha f t ba r r e l cen t r e l i ne .

These d isp lacements wi l l induce e i ther tens i le or compress ive s t ra in

in to the s t ee lwork . The magni tude o f the s t ra in wi l l va ry accord ing

to the r e l a t ive pos i t i on o f t he s t ee lwork wi th r e spec t t o t he r ee f

i n t e r s ec t i on .

This strain is measured in millimetres per metre shortening or lengthening

o f t he sha f t ba r r e l o r s t ee l . A l so , ca l l ed mi l l i - s t r a in .

Fo r s t r a ins o f 0 ,4 mi l l i - s t r a in and lower, no spec ia l mod i f i ca t ion

to ex is t ing s tee lwork i s necessary. For s t ra ins h igher than 0 ,4 mi l l i -

s t r a in , damage to s t ee lwork and shaf t ba r re l l in ing can be expec ted .

As can be seen (F igu re 5 ) , s t ee lwork in s t a l l ed in t he Z d i r ec t ion a t

the reef intersect ion area wil l exper ience a compressive s t ra in , which

wil l tend to buckle the guides. Above and below the reef intersect ion,

s teelwork ins ta l led in the Z direct ion wil l exper ience a tensi le s t ra in ,

wh ich wi l l t end to shea r t he bo l t s a t t he gu ide to gu ide and gu ide

to bun ton connec t ions .

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Figu re 1

P re f e r r ed min ing s equence - s t ep s 0 … 7

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Figu re 2

P r ed i c t ed Sha f t Ba r r e l Movemen t (X + Y Di r ec t i ons )

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Fig

ure

3

Sh

aft

Ve

rti

ca

l D

isp

lac

em

en

t (w

ors

t c

as

e)

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Fig

ure

4

Sh

aft

Re

lati

ve

Str

ain

(w

ors

t c

as

e -

ve

rti

ca

l)

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Fig

ure

5

Ve

rti

ca

l S

tra

ins

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Figu re 6

La t e r a l S t r a in s

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Table 1

P r e d i c t e d m a x i m u m H o r i z o n t a l X + Y m o v e m e n t

From Figure 6 , the shaf t ba r re l above the ree f in te r sec t ion wi l l t end

to ride in one direction while the shaft barrel below the reef intersection

wi l l t end to r ide in a d i f f e ren t d i r ec t ion . F rom the mode l l i ngs , t he

cen t re l ines o f the "upper and lower" ba r re l s would be 300mm apar t

a t t he r ee f i n t e r sec t ion . The r e su l t an t o f t hese l a t e r a l movemen t s

wi l l cause a sha rp t r ans i t i on po in t a t t he r ee f i n t e r sec t ion . A t t h i s

po in t t he gu ides wi l l t end to bend , bun tons wi l l be de fo rmed and

misa l ignmen t be tween consecu t ive bun tons wi l l r e su l t .

SHAFT LAYOUT ALTERATIONS

The o r ig ina l l ayou t o f t h i s s ix -compar tmen t sha f t , s e rved by th ree

winde r s , i s shown in F igu re 7 .

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The sk ips were ope ra t ing in the ou te r wes t and eas t compar tmen t s .

In each o f t hese compar tmen t s t he ou te r gu ide i s f i xed d i r ec t ly t o

the shaft wall by means of wall brackets. Any inward ground movement

w i l l cause these gu ide - to -gu ide open ings to r educe .

F rom the p red ic t ed g round movemen t i t was c l ea r t ha t t hese ou te r

compar tmen t s wou ld need to be abandoned .

The dec i s ion was made to conve r t t he "A" winde r t o a rock winde r

(Figure 8. Therefore, i t was necessary to rearrange the whole loading,

sp i l l age hand l ing and t i pp ing a r r angemen t s .

SUPPORT OF THE SHAFT WALL

Al though the support of the shaf t wal l i s not an engineer ing funct ion,

t h i s suppor t work wou ld no t have succeeded wi thou t a f a i r amoun t

o f eng inee r ing inpu t .

" M o b i l e p l a t f o r m "

Th ree spec ia l b ig in spec t ion cages were a t t ached be low the th ree

conveyances o f t he "A" , "B" and "C" winde r s . The f loo r a r eas o f

t hese in spec t ion cages were des igned to cove r t he who le a rea o f

the compartments. Gates on each inspection cage allowed for travelling

f rom one in spec t ion cage to t he o the r.

When a l l i n spec t ion cages were pa rked ad jacen t t o each o the r, a

work ing "p la t fo rm" cove r ing ha l f t he sha f t was e s t ab l i shed . Th i s

enab led the d r i l l i ng o f ho le s and in s t a l l a t i on o f rock s tuds , cone

bo l t s , rope anchor s and wi re o r we lded mesh .

The Seco type S36 dr i l l ing machine , used to dr i l l the 6m long ho les ,

was at tached to a ver t ical ly mounted pipe inside one of the inspect ion

cages. There was no need to dismantle this machine when the inspection

cage was lowered o r r a i sed to a new pos i t i on .

Al l wa te r and compressed a i r man i fo lds were ins ta l l ed pe rmanen t ly

aga ins t the roof o f the "B" winder inspec t ion cage f rom where these

se rv i ces were p iped v i a PVC hoses to t he d r i l l i ng mach ines on a l l

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t he in spec t ion cages .

To ensu re tha t no acc iden ta l mov ing o f t he in spec t ion cages cou ld

t ake p l ace , each in spec t ion cage was f i t t ed wi th an IST 2000 vo ice

and tone r ad io communica t ion sys t em. Th i s enab led the winde r

brakes to be locked and unlocked the same way as a hardwired lockbell

sys t em. A l l s igna l s exchanged be tween the d r ive r and the pe r sons

on the inspec t ion cages were recorded on the Deebar event recorder.

Bat tery opera ted f luorescent l ights were ins ta l led on each inspect ion

cage , wh ich p rov ided adequa te i l l umina t ion o f t he work ing a rea .

Wa t e r a n d c o m p r e s s e d a i r s u p p l y

Between s ta t ions , water and compressed a i r were tapped off ex is t ing

co lumns f rom the neares t upper s ta t ion by means o f PVC hosep ipes .

For t he a rea above the f i r s t s t a t i on , wa te r fo r d r i l l i ng was t apped

off f rom the c lea r wa te r-dewate r ing co lumn a t th ree se lec ted po in t s

th rough p re s su re r educ ing va lves . A t t he same pos i t i ons in t he

sha f t , compressed a i r was t apped o ff t he compressed a i r co lumn .

M a t e r i a l a n d s h i f t h a n d l i n g

The inspection cages of the "B" and "C" winders were, for al l practical

pu rposes , pe rmanen t ly pos i t i oned a t t he work ing a rea .

The "A" winder was used to t ransport pump shif ts , contractor workers

and fo r emergency pu rposes .

Addi t iona l cage doors were ins ta l l ed on the shaf t s ide o f the bo t tom

decks of the "A" winder to enable contractor shift changes and material

to be hand led to and f rom the in spec t ion cage o f t he "B" winde r i n

the sha f t .

MINING OF THE REEF SLOT

Because the pos i t i on o f t he r ee f i n t e r sec t ion wi th the sha f t was

jus t above 28 l eve l s t a t i on , i t was dec ided to deck o ff t he sha f t

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Figu re 7

No 2A Sha f t - O ld Pe rmanen t Sha f t Sec t i on

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Figu re 8

No 2A Sha f t - New Pe rmanen t Sha f t Sec t i on

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Figu re 9

P ro j ec t : 2A Sha f t P i l l a r Min ing

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Figu re 10

No 2A Sha f t - Long i t ud ina l Sec t i on t h ru Tower S t ee lwork

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wi th a t empora ry p l a t fo rm (F igu re 9 ) on to wh ich r emova l o f t he

conc re t e l i n ing and b l a s t ing o f t he r ee f s lo t rock cou ld be done .

a hoppe r.

t i on .

The p l a t fo rm cons i s t ed o f two l aye r s o f 228mm x 76mm grade V5

t imber planks wi th chequer p la tes on top. The pla t form res ted f i rmly

on the ex i s t i ng s t a t ion f loo r bun ton se t .

Rock was sc raped o ff t h i s p l a t fo rm by means o f a s c rape r, up a

f ab r i ca t ed r amp and in to

Al l sha f t s t ee lwork , co lumns and cab le s were p ro t ec t ed f rom these

con t ro l l ed b l a s t ing ope ra t ions .

SHAFT STEEL MODIFICATIONS

To accommodate the predicted vert ical and lateral shaft barrel s trains,

some fo rm/s o f mod i f i ca t ion to the s t ee lwork a re necessa ry.

P ipe co lumns and cab le s mus t a l so be made to accommoda te the

expec ted ve r t i ca l and l a t e ra l d i sp l acemen t s o f t he sha f t ba r r e l .

To r ea l i s e t he se t ob jec t ives fo r t he sha f t , a ma in tenance in t ens ive

s t ee lwork mod i f i ca t ion me thod such a s s lo t t i ng c l ea t s and cha i r

p la tes for guides and buntons wi l l not be pract ica l . The const ruct ion

o f a s t ee l t ower to span the po r t ion o f t he sha f t where h igh s t r a ins

and d i sp l acemen t s w i l l occu r i s t he be t t e r so lu

The re was a cho ice be tween two types o f hange r t owers : a b raced

tower and a non-braced tower. The b raced type tower i s much more

r ig id in des ign and no wind ing speed l imi t a t ion th rough the tower

i s necessa ry, r ega rd le s s o f t he l eng th o f t he tower. The non-b raced

type towers on the other hand are very f lexible in design and winding

speed th rough the tower mus t be s low. The b raced type tower i s

more expens ive than the non-b raced type due to the s t ee l vo lume .

In ou r ca se , i f a ve r t i ca l s t r a in o f 0 .4 mi l l i - s t r a in and h ighe r was

to be accommoda ted , t hen a t ower l eng th o f 220 me t re s was to be

cons t ruc t ed . I f a ve r t i ca l s t r a in o f 1 .0 mi l l i - s t r a in and h ighe r was

to be accommoda ted , a t ower wi th a l eng th o f 115 me t re s needed

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Fig

ure

11

To

p o

f T

ow

er

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Fig

ure

12

Bo

tto

m o

f T

ow

er

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t o be cons t ruc t ed . In t he l a t t e r ca se , t o accommoda te a reas w i th

ve r t i ca l s t r a ins be tween 0 .4 and 1 .0 mi l l i - s t r a in , t he gu ide to gu ide

and gu ide to bun ton connec t ions mus t be s lo t t ed . The one end o f

each bunton should a l so be modi f ied to inc lude a s lo t t ed connec t ion

be tween the bun ton end and the suppor t cha i r p l a t e .

Because the lateral dislocation will be at its peak at the reef intersection,

the tower wi l l ac t a s a t r ans i t i on pa th ac ros s t h i s d i s loca t ion .

Due to t ime and cost constraints the shorter tower was chosen. (Figure

1 0 )

M a i n f e a t u r e s o f t h e t o w e r.

• The top o f t he tower (F igu re 11 ) cons i s t s o f two bun ton se t s ,

which are braced to each other with s ix diagonal girders , which

res t f i rmly in to moi l ed ou t pos i t i ons in t he sha f t wa l l rock .

The whole tower i s suspended f rom th is " top of tower" bearer,

wh ich i s s i t ua t ed ha l fway be tween 26 l eve l and 27 l eve l .

• The bo t tom o f t he tower (F igu re 12 ) i s s i t ua t ed on 29 l eve l

s t a t ion . To ca t e r fo r t he sho r t en ing o f t he sha f t , t he " l egs o f

the tower" will sag into fixed "pots" on 29 level station. Allowance

of 640mm has been made fo r s agg ing o f t he tower.

• A gu ide t ake up fac i l i ty (F igure 13) was ins t a l l ed on 29 l eve l

s ta t ion . The leng th of the t ake up spacer was 640mm to a l low

for t he sagg ing o f t he tower.

• To accommoda te the ve r t i ca l shor t en ing o f the sha f t , ve r t i ca l

mounted bel lows type compensators (Figure 14) were ins ta l led

for the clear water, mud and compressed air columns just above

29 l eve l s t a t i on . A l l t he compensa to r s were manufac tu red

to a l low for ver t ical shortening of 750mm. The pressure ra t ing

fo r t he compensa to r s o f t he c l ea r wa te r and mud co lumns a re

40 ba r and 10 ba r fo r t he compressed a i r co lumn .

• La te ra l r e s t r a in t s (F igu res 15 , 16 ) were in s t a l l ed be low 27

and 28 l eve l s t a t i ons in o rde r t o keep the compar tmen t s o f

the tower aligned with the station landing rails. These restraints

1161

were designed to accommodate ver t ica l movement of the tower

a s we l l a s concen t r i c sha f t ba r r e l movemen t .

• To keep the ex i s t ing cages in se rv ice , the compar tment where

the HT feede r s and o the r cab le s a r e p re sen t was l e f t open on

the s t a t ion s ide , i . e . w i thou t any b rac ing members . Th i s was

done because o f t he l ack o f c l ea rance be tween the f ron t o f

t he cage and the sha f t cab le s .

In

i t

16

a ted .

ed .

t .

o rde r t o keep th i s compar tmen t f rom open ing o r c los ing ,

was necessary to ins ta l l s tab i l i s ing apron s tee lwork (F igure

) a round the pe r ime te r o f each bun ton se t .

• The HT feede r s and o the r cab le s were l e f t a t t he i r r e spec t ive

pos i t i ons aga ins t t he sha f t wa l l .

C o n s t r u c t i o n o f t h e s t e e l t o w e r

Each o f t he 38 s t ee l s e t s t o be f i t t ed were a s sembled , marked and

bundled together. This was done on a j ig on surface, which s imulated

the i r pos i t i on in t he sha f t . By do ing th i s many sma l l p rob lems

were e l imin

Construction of the steel tower steelwork commenced with the blasting

o f t he s ix s lo t s i n t he sha f t wa l l fo r t he l egs o f t he s ix d i agona l

suppor t g i rde r s . Dur ing th i s pe r iod the sha f t was a l so comple t e ly

decked o ff one bun ton se t be low these s lo t pos i t ions . Al l s t ee lwork

a s soc ia t ed wi th the top o f t he tower a t bun ton se t s 295 and 296

were ins ta l led whi le the shaf t was s t i l l decked off wi th the p la t form.

F rom bun ton se t 296 downwards to bun ton se t 332 , t he s t ee lwork

between bunton sets was just a repeti t ion of the same layouts . (Figure

1 7 )

Be tween bun ton se t s 332 and 333 the tower s t ee l and gu ide t ake

up a r r angemen t s were in s t a l l

A t 27 , 28 and 29 l eve l s t a t i ons i t was a l so necessa ry to r emove

and r e ins t a l l t he k ing pos t s , s c reens and sha f t ga t e s approx ima te ly

1 me t re away f rom the sha f

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Figu re 13

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Fig

ure

14

Be

llo

ws

Ty

pe

Pip

e C

om

pe

ns

ato

r

1164

The bun ton end s tubs were cu t and r emoved f rom the bo t tom o f t he

tower upwards in a p rede te rmined pa t t e rn to p reven t any sudden

load ing on pa r t s o f t he uppe r t ower.

Both b ig inspec t ion cages o f the "A" and "B" winders were a t t ached

be low the new sk ip b r id l e s o f t he "A" winde r. Bo th in spec t ion

cages were c lu t ched to the work ing a rea and a s t he in s t a l l a t i on o f

the new s t ee l p rog res sed , t hey cou ld on ly go downwards . Th i s was

because these two compartments became smal ler wi th the ins ta l la t ion

of t he add i t i ona l s t ee lwork .

A sma l l e r i n spec t ion cage was a t t ached be low the cage o f t he "B"

winder. When parked next to the inspect ion cages of the "A" winder,

a working platform was established. This winder was used to transport

pump sh i f t , con t r ac t worke r s and ma te r i a l t o and f rom the work ing

a rea .

Af t e r comple t ion o f t he s t ee lwork in s t a l l a t i on p rocess , bo th b ig

inspec t ion cages be low the "A" winde r b r id l e s were r emoved on

31 l eve l .

Due to the predicted ground movement and nature of the tower steelwork

des ign , t he use o f t he "C" winde r be low 26 l eve l became obso le t e

and could not be utilised to assist with the installation of the steelwork.

(F igu re 2 )

ACTUAL GROUND MOVEMENT AND TOWER BEHAVIOUR

TO DATE

The f irs t dis t inct concrete l ining fai lure due to horizontal and vert ical

g round movement was no t i ced 3 months a f t e r min ing o f the window

and inne r p i l l a r had s t a r t ed .

The cracks in the concrete l ining above and below the reef intersection

a re gene ra l ly i n a ho r i zon ta l p l ane a round the sha f t . The wes t e rn

half of the shaft barrel is suffering most of the damage and deformation.

At va r ious pos i t i ons above and be low the r ee f i n t e r sec t ion , "bags"

o f l oose chunks o f conc re t e a r e accumula t ing beh ind the we lded

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Figu re 15

La t e r a l Res t r a in t De t a i l

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Figu re 16

Pos i t i on o f La t e r a l Res t r a in t s

1167

Fig

ure

17

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mesh l i n ing suppor t .

A t some p laces l a rge p i eces o f c r acked conc re t e l i n ing and loose

rocks a re push ing ou t t owards the tower.

The sha f t cab le s , wh ich were l e f t aga ins t t he sha f t wa l l , a r e be ing

pushed out towards the t ravel l ing path of the nor thwest compar tment

cage o f t he "B" winde r.

The a rea o f mos t conce rn i s j u s t be low 28 l eve l s t a t i on where the

wes te rn ha l f o f t he sha f t ba r r e l i s showing s igns o f fo ld ing in on

i t s e l f . The e ff ec t o f t h i s i s t ha t t he ba r r e l i s s t a r t i ng to s t r ang le

the tower. (F igu re 18 )

Some o f t he washe r s o f t he rope anchor s and rock s tuds , wh ich

fo rm pa r t o f t he ba r r e l suppor t , a r e a l so s t a r t i ng to push aga ins t

the tower.

Some guide to bunton bol t connect ions just above the tower a t bunton

se t 295 f a i l ed due to ve r t i ca l s t r a in .

The centre buntons at bunton sets 291 and 292 bent due to horizontally

induced s t r a in caus ing a l l t he compar tmen t s o f t he "A" and "B"

winde r s t o c lose by e i the r 50mm ac ross t he gu ides o r open up by

50mm ac ross t he gu ides .

The wes te rn s ide and cen t re bun tons ju s t be low the tower a t bun ton

sets 334, 335 and 336 were also bent due to horizontal ground movement.

A l l t hese bun tons have been cu t and sp l i ced .

To da t e - end Oc tobe r 97 - t he 640mm gu ide t ake up gap f ac i l i t y

on 29 l eve l has been r educed to 540mm ind ica t ing tha t t he tower

has c losed 100mm re l a t ive to t he tower top and bo t tom on 29 l eve l

s t a t i on .

A se i smic even t o f magn i tude 3 ,3 occur red on 11 Oc tober 97 wi th in

the shaf t p i l lar. The tower and shaf t suppor t s tood up wel l to conta in

the e f f ec t s o f t he damage to the conc re t e l i n ing .

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Figu re 18

No 2A Sha f t - New Pe rmanen t Sha f t Sec t i on Sha f t Ba r r e l

De fo rma t ion ( Immed ia t e Area be low 28L)

1170

LESSONS LEARNT

• The pos i t i ons o f bun tons and sha f t co lumns in the a rea o f

the shaft that must be spanned by a tower or similar construction

must be surveyed, to exact ly determine thei r re la t ive posi t ions

to each o the r ;

• Bigge r t o l e rances to be a l lowed when des ign ing new s t ee l

tha t mus t be f i t t ed to o ld sha f t s t ee lwork ;

• The exac t pos i t i on o f t he r ee f i n t e r sec t ion wi th in the sha f t

must be de termined before any s tee lwork des ign can be made;

• The pos i t i on o f t he d i agona l g i rde r s fo rming the top o f t he

tower must be carefully selected on the site. The ground condition

and shaft concrete l ining propert ies must be taken into account;

• The pos i t ion o f the bo t tom end o f the tower mus t be ca re fu l ly

se l ec t ed on s i t e t o avo id s t a t ion a reas and fou l ing o f ma in

p ipe suppor t g i rde r s ;

• The posi t ion of the shaft column compensators must be selected

on s i t e t o ensu re tha t t he downward movemen t o f t he tower

does not foul the stat ic part of the compensators. I t is important

tha t a l l p ipe c lamps are in pos i t ion to hold the co lumns s teady

in the i r pos i t i ons ;

• The pos i t ion o f add i t iona l co lumn beare r s , i f necessa ry, mus t

be se l ec t ed on s i t e ;

• I f t he r ee f i n t e r sec t ion i s no t s i t ua t ed nea r a l eve l , means to

remove blast ing debris eff ic ient ly f rom the temporary plat form

cover ing the sha f t mus t be tho rough ly p l anned ;

• Fu tu re s l i ng ing r equ i r emen t s t o work ing s t a t ions wi th in the

tower to be de t e rmined ;

• The pos i t ion of ho les in the foo t p la tes o f new bracke ts which

mus t be in s t a l l ed aga ins t t he sha f t wa l l mus t be such tha t

the ex i s t i ng s t ee lwork does no t i n t e r f e re w i th the d r i l l i ng o f

such ho le s i n t he sha f t wa l l ;

• The bolts, nuts and washers schedule must be drawn up properly;

• The sha f t wa l l suppor t pa t t e rn and the pos i t i on o f t he rope

anchors , rock s tuds and cone bo l t s mus t be such as to p reven t

them f rom foul ing the tower and the edges of the conveyances

when they are pushed out into the shaft due to ground movement;

• The l eng th o f t he tower mus t be ca re fu l ly p l anned ;

1171

•

•

•nts , which were instal led just below 28 level ,

t

•

cu t

f r equen t ly to a l low fo r a gap o f a t l ea s t 10 - 20mm a t a l l

t imes . The use o f a s t i f f bu t a c rushab le space r t o ca t e r fo r

sudden l a rge ve r t i ca l movemen t shou ld be inves t iga t ed .

The Eng inee r who i s i n cha rge o f a p ro j ec t l i ke th i s , shou ld be

re l i eved o f h i s no rma l du t i e s t o enab le h im to devo te a l l h i s ene rgy

and t ime to the p ro j ec t .

Al l addi t ional s tee lwork, bol ts and nuts necessary to const ruct

t he tower mus t be ga lvan i sed ;

HT feeders and o ther cab les should be removed f rom the shaf t

wa l l in the tower a rea and be a t t ached to the tower s tee lwork ;

The use o f l a t e r a l r e s t r a in t s mus t be ca re fu l ly cons ide red .

The la teral restrai

s tarted to strangle the tower causing the northwest compartmen

to become sma l l e r. I t a l so caused some b races and d iv ide r s

t o bend s l i gh t ly ;

The p roposed gu ide t ake up a r r angemen t was too f l imsy in

design and was changed to a more rigid spacer take up arrangement.

The d rawback wi th th i s t ake up space r i s t ha t i t mus t be

C O N C L U S I O N

Unde r s t and ing o f t he Rock Mechan ic s mode l l i ngs and the des ign

c r i t e r i a fo r t he sha f t s t ee lwork mod i f i ca t ions i s v i t a l .

1172