by Q„H. S. Tupholme

Excavating forLondon'sNlew Victoria Line

FINSBURY

VICTORIA LINEPROPOSED TRACK LAYOUT

CIIS J l512c

The recently completed Victoria Lineis the first deep-level tube railway to bebuilt across the centre of London for 60years, and runs from Victoria Station for10$ miles (16.9km) through London'sWest End to Walthamstow in the north-eastern suburbs. The average tunnel

pth from ground surface to rail levelis about 70 ft (21.3m); the averagegradient is between 1:70 and 1:100,andno gradient is steeper than 1:40. Withinthree years from work starting on thefirst of the 21 shafts from which therunning tunnels were driven, about500,000 yd3 (382,280 m3) of earth wasexcavated from the 21 miles (33.8km)of 12 ft (3.66 m) diameter running tun-nels alone. In addition, some 300,000yd3 (229,360 m3) of earth has beenremoved during building of the 12stations for the new line.

Before work was started on themain section of the line full-scale testswere carried out on the digging equip-ment and tunnel linings in a 1 mile

(1.6km) length of double tunnel. It

was decided that about 1,910 yd(1,747 m) of single tunnel should bebuilt with flexible cast iron lining

designed by Mott, Hay & Anderson; andthe other 1,612 yd (1,474m) with pre-cast concrete lining to the design ofSir William Halcrow & Partners. Kin-

near Moodie constructed the tunnelin concrete from a site at FinsburyPark; and Edmund Nuttall, Sons 8 Co.,Ltd. the cast-iron lined tunnels drivenfrom the site at Netherton Road. Kin-

near Moodie also drove a short cast-iron lined section to link this experi-mental work with the existing stationtunnels at Finsbury Park. It was inten-ded that the experimental tunnels wouldeventually form part of the new line.

The tunnels were driven with drum

digger rotary shields and, 'using one ofthese shields, Edmund Nuttall drove a934-ft (284.7-m) length of tunnel, in-

cluding excavation and lining, in two

weeks. This is equivalent to a speedof 3$ ft (1.07m) of new tunnel perworking hour, a world record for driv-

ing and lining a tunnel of this sizethrough clay. It is almost twice thespeed considered to be good goingwith older tunnelling techniques. Thedrum digger shield was developed byKinnear Moodie and Arthur Foster Con-struction Engineers Ltd. It had alreadybeen used with success on the Metro-politan Water Board's Thames to LeaValley water tunnel. Though the shieldwas smaller in this case than that em-ployed on the Victoria Line, the prin-ciple is the same.

The drum digger used on the con-crete-lined tunnels has an external dia-meter of 14 ft (4.27 m), and that for thecast-iron lined tunnels 13 ft 1 in

(3.99m). The toothed inner drum canbe turned at up to 4 r.p.m. by sixhydraulic motors driving through gear-boxes. The forward movement of theshield is imparted by 14 hydraulic rams

24

spaced equally round the periphery ofthe shield and pushing against the lastcompleted tunnel ring. These rams areindividually controlled by an operatorstanding within the shield casing butbehind the rotating inner drum. Theseshields proved easier to guide thanearlier types and a very high standardof alignment was achieved, i.e., within+ / — 1-in (25.4-m) tolerance. TheKinnear Moodie drum digger, whichhas been described in InternationalConstruction (December, 1966), wasone of the machine types ordered fordigging the running tunnels: the otherwas the mechanical digging shielddeveloped by Sir Robert McAlpine &Sons Ltd. This has an external dia-meter of 13 ft 6 in or of 13 ft 1 in (4.11or 3.99m) when used with segmentserecfed in contact with the groundbehind the shield. The machine, whichhas a cylindrical body, can have a tailadded to enable segments to beerected inside the tail section if re-quired. One of the Victoria Line con-tractors, using the McAlpine machine,has reported a drive rate averaging350 ft (106.7m) of completed tunnelper week.

U0O

<C

0;

tIW~I!

L+"

4' J

/'18 3

12

I''

jo

[

36 ft!

Nine digging shields were ordered byLondon Transport, four from KinnearMoodie and four from McAlpine, theninth order being placed with JosephWestwood & Co. Ltd. For excavatingthe station tunnels, seven Greathead

type shields were built by W. Lawrence& Son (London) Ltd. These shieldsare over 21 ft (6.4 m) diameter, and arenot provided with mechanical cutters,the soil being excavated with power-

Cutaway drawing of the K. M. tunnelling machine. four of which were ordered by London Trans-port for use on the Victoria Line.

driven hand tools. The shields, how-ever, are also advanced by pressurefrom hydraulic rams against the ringsof the completed tunnel lining.

The experimental tunnels also pro-vided a valuable opportunity for testingthe tunnel linings. On one section, thelining is of unbolted flexibly jointed castiron segments. There are six segments,each 1 in (25.4 mm) thick, to every2-ft (210-mm) tunnel ring. One end ofeach segment is concave and the otherconvex, so that the segment ends formknuckle joints, each fitting into the nextin sequence. The segments wereplaced behind the shield when therams were withdrawn, the two seg-ments forming the invert being laid first,followed by the side segments and thenthose holding the roof were placed andheld by needles at the rear of theshield. The two segments forming thefloor of the tunnel were cast with smallrecesses at their upper ends and, whenthe segments had all been erected,hydraulic jacks fitted into the recessesexpanded the ring segments againstthe clay outside.

The pre-cast concrete lining is alsoof a new type. These segments weretested, the thicknesses ranging from4$ in to 9 in (114.3 to 228.6 mm). Thelarger size was found to be undulythick, while the thinner segment mightbe liable to break during handling. Asa result, a thickness of 6 in (152.4 mm)was chosen. The knuckle joints in theconcrete lining were subject to inac-curacies in manufacture and erection tothe extent that the point of contactcould be well off-centre. Mott, Hay &Anderson elected to retain this typ'e ofjoint, but to reinforce it to eliminate thedanger of spalling: Sir William Halcrow& Partners modified the joint to havetwo concave surfaces to ensure nearcentral contact. Other alterations weremade to the concrete lining to produce

28

21 19 16

e

C

P)

12ft Wheel centres20ft 0/A Length 6in

20s conveyor

e

tI

a shaped invert, which was consideredpreferable to two segments 6 in(152.4 mm) thick, and which at thesame time enabled a great saving in theamount of in situ concrete to be placedunder the track.

The flexible cast iron lining was re-commended by Mott, Hay & Andersonfor use on the length of running tunnelbetween Victoria and Oxford Circus,where the marginal advantage of usingthis type of lining was considered towarrant the somewhat higher cost com-pared with a concrete lining. With theabove and other improvements, reducedestimates were possible for all runningtunnels in good ground, resulting in atotal saving overall of some F3 m.London Transport placed a contractworth E5m for cast iron segments withStanton Staveley, Ltd., one-third of theorder being sublet to Head WrightsonIron Foundries Ltd. A further contract,worth some f104,000, for special typecast iron segments, was placed withHarland & Wolff.

It was obvious that problems wouldarise in constructing the new VictoriaLine in view of the complexities ofLondon's existing underground railwaysystem. Under the Victoria main linestation, for example, the 30-ft (9.14-m)diameter cross-over tunnel of the newline had only from 7ft to 6ft (2.1 to2.4m) of clay above it, and chemicalstabilisation of the gravel under themain line station was necessary. A con-tract for 8130,000 was placed with SoilMechanics, Ltd. for this work. Con-tracts were also placed with Cementa-tion, Ltd. for similar work, using TDM,one of Cementation's own single-shotchemical grouts. A layer of water-bearing sands and gravels 5 ft (1.5m)thick and 350 ft (106.7 m) long wasalso treated with TDM.

For tunnelling the south end of the

new line (i.e., at Victoria), which alsoincluded the enlargement of the run-ning tunnels for four 21-ft (6.4-m) dia-meter station tunnels, the tunnels beinglined with cast iron segments. Twoshafts were sunk to provide access forconstruction, one at Gillingham Streetand the other in the north-east cornerof Green Park. Both shafts were sunkwith a special hydraulic excavator con-structed by John Mowlem, the civilengineering contractors for this end ofthe line. This excavator was built byadapting the digging equipment of aMassey - Ferguson 220 digger. Ahydraulic power pack was incorporatedto replace the hydraulic power nor-mally provided by one of the tractors inthe MF range. The digger stood onits hydraulically operated stabilisingfeet and was held in position by aspigot which engaged in a bracketattached to either the cast iron shaftlining or the wallings of a timber-lined

Section through the McAlptne tunnelling mneChin, showing detegs oi tunnel lining. shaft. From this position the machineexcavated more than half of the shaftareas, loading the spoil into skips re-moved from the shaft by crane. Thedigger was then transferred to theopposite side of the shaft to completethe excavation cycle.

The new station at Oxford Circusproved to be something of a jigsawpuzzle in view of the complex alreadyexisting. Not only were there two exist-ing underground lines at this point, butalso a maze of electric cables, Metro-politan Water Board tunnels and G.P.O.mail delivery tunnels. In addition, theserious lack of surface area at OxfordCircus brought its own problems. Thiswas coped with by building a steelumbrella over the crossing of Oxfordand Regent Streets, so that surfacetraffic could still proceed; and by usingnearby Cavendish Square as a basearea, which was connected to OxfordCircus by temporary tunnels, builtsolely for the purpose of access. Thenew station at this point was part ofthe E6 m contract given to KinnearMoodie, and included driving 9,000 ft(2.743 m) of tunnel of 20 different dia-meters in blue clay, varying from 5ft(1.52 m) diameter for the smallersewer diversions to 27 ft (8.23 m) forone of the new station tunnels. Thetunnels are lined with some 40,000 castiron segments, bolted to form 5,400rings. The consulting engineers for thisrather daunting job were Sir WilliamHalcrow & Partners.

The construction of the new tickethall at Oxford Circus, being very closeto road level, was a complicated job.The concrete finish had to be of a veryhigh order and no bolts could bepassed through the soffit concretebecause of the risk of leaks. Becauseof the variation in the excavated groundlevel, it was impossible to use propsfor the shuttering, so a shutter schemewhich was self-supporting within thebay areas was specially designed byPhoenix Formwork. Standard Wall-forms were used in these bay areas,supported by Acrow adjustable joists.All the shutters were supported withRawlplug U-ties which hung over themain girders.

Ground Engineering 29

One corner of Oxford Circus is occu-pied by a large. department store, andthe southbound Victoria Line tunnelpasses immediately under the massivecolumn foundations of this 5-storeyblock. To prevent foundation settle-ment, underpinning had to be donebefore the tunnel could be driven, and

,8

the problem was to distribute the load Ifrom the present foundations evenlyover the arch of the proposed tunnel.A feature of this task was the smallclearance between the roof of the tun-nel and the underside of the founda-tions. So as to develop the necessarystrength in the restricted height, theconsultants decided to use prestressingtechniques; and the underpinning tookthe form of post-tensioned concreteblocks which act as beams to distributethe column loads over the tunnel arch.

The pilot tunnel was driven parallelto, and slightly below, the columnfoundations of the 5-storey building.From this tunnel, small rectangularheadings were driven to enclose thearea to be filled with concrete. Under-pinning was then carried out by driving

aefowr Some of the complexity involved in Above: Diagrammatic section showing theadding to an existing underground system is consolidation of water-bearing sands andshown by this model of the new ticket office gravels beneath Green Park, carried out byand access tunnels at Oxford Circus. the Cementation T.O.M. process.

IV

I,«>>

va *

v I

a sequence of narrow headings underthe foundations and immediately fillingthem with concrete so that only a nar-row strip of foundation was left with-out support at any one time. Ducts forthe prestressing cables were laid dur-ing concreting. This operation calledfor great precision by the setting-outengineers because each duct had toline up perfectly with its neighbour inthe adjoining heading. After all the con-crete had been poured, the cableswere threaded through ducts, ten-sioned and grouted.

The caulking of the cast iron seg-ments of the northbound station com-plex at Oxford Circus was done withPC4 cold caulking compound, anasbestos cement material made by Phil-plug, Ltd. This firm also supplied thegrummets for waterproofing tunnel seg-ments on the line. These grummetswere of two types: one, of hemp pre-dipped in a mineral gel; and the other,known as the "Oyster", uses low-density polythene. These grummetsaccommodate themselves to the shapeof the bolt holes and will withstand apressure of 3,000 Ib/in2 (211 kg/cm2).Damp patches on concrete linings areunsightly and correction is apt to becostly if carried out while the tunnelsare in operation. To cope with thisproblem, Laminor, Ltd., a member ofthe Drake & Gorham, Scull Group,developed a specification based ongrit-blasting adhesion surfaces, fillinggrooves and cracks with sealing com-pounds with low-shrinkage charac-teristics, followed by over-sealing withcompatible epoxide-type resins andglass reinforcement. The standard boltswere fully tightened and then sealedwith plastic foam, and the clusters ofbolts over openings in the tunnel wereshrouded with glass fibre mouldingsfabricated on site and afterwards filledinternally with plastic foam.

One of the more interesting jobs inconstructing the new Victoria Line wasthe building of step-plate junctions to

Ground Engineering 31

PICCAOILL YTUNNEL ABANDONED

C.T.5

EXISTiNG PICCADILLY PLATFORMSUSED FOR NORT+ISOUND VICTORIAUNE G NORTHBOUND PICCADILLY

''::'.V~'.~<i,'&ir~PiZ6'4"'+~

.~%ÃzPV.::4'i"PXPXZPFP:.'XISTING

OSS- OVERTUNNELS

CROSS PLATFORMINTERCHANGE

VICTORIA LINE

ONED

New tunnels shown bV heevV lines

<",.~iPiii'kzÃ/xiii/4Ã~Z

EXISTING NORTHERN CI--USED FOR SOUTHBOUND

S SOUTHBOUND PICCADIL

this shaft a space wasformed round the Piccadilly Line tunneland work started in the 21-ft 2EI-in

(6.54-m) diameter section of the step-plate, first working southwards to the29-ft 6-in (8.99-m) diameter headwall,and then northwards to the headwall atthe extremity of the 18-ft 6-in (5.64-m)diameter section. Another heading wasdriven, at the same time as the first,from the southbound tunnel at a pointabout 100 ft (30.5 m) north of thestation to enable the 12-ft 2-in (3.71-m)diameter cast iron lined diversion tun-

nel to be driven between the stationand the step-plate.

At the extremity of the access tunnela 16-ft 6-in (5.03-m) diameter turningchamber was built, and the 12-ft 2-in

(3.71-m) diameter diversion tunnel wasdriven south to the position of thenorth headwall of the step-plate junc-tion. From there a 7-ft (2.13-m) dia-meter pilot tunnel was driven as far asthe 21-ft 2E-in (6.46-m) diameter sec-tion of the step-plate. Whilst the levelsof the existing and future westboundPiccadilly Line within step-plate 18,north of the station, were nearly equal.at step-plate 17 south of the station, theexisting westbound line was on a fall-

ing gradient of 1:89 and the diversiontrack was required to rise at 1:90 tomeet it, thus producing a difference in

rail level of some 5ft (1.52 m) at thenorth headwall.

During the construction of step-plate

Peter Robinsoncolumn footings

3 rd.Basement

L

/

/

/I

/i )5I

/,,y'..'.

/y'ain

columnsStressing crossheading

Post tensionedcables

Ptu

Southboundstation tunnel

SECTION A-APlan and section of completed underpinning ol

join new tunnels to old. These step-plate junctions are formed by graduallyenlarging the size of the tunnel ringsfrom those carrying a single track atone end of the junction to large-

diameter rings capable of enclosingtwo tunnel mouths at the other. Thiswas done by encirclement of the exist-

ing tunnels, and diversions through

junctions of this type were carried outat Euston, Highbury and Finsbury Parkto give easy same-level interchangebetween the Victoria Line and theNorthern Line (City Branch), and theNorthern Line and the Piccadilly Linerespectively. The work was carried outwhile the trains continued to run.

A. Waddington & Son carried out theworks at Finsbury Park, including thediversion of the Piccadilly Line. Thefirst stage was the construction of twostep-plate junctions, which were built

by encircling the existing westboundPiccadilly Line tunnel north and southof the station at the ends of the pro-posed diversion. This was carried outwithout interrupting the train service.

PLANlarge department store at Oxford Circus.

The site of the north step-plate, whichwas to taper from 29 ft 6 in to 18 ft 6 in

(8.99 to 5.64m) i.d., was approachedfrom the southbound Victoria Line tun-

nel by a short adit and a drop shaft. At

Complicated arrangement of tracks at Finsbury Park Station, showing the positions of step-plate junctions Nos. 17 a 18.

Stressing long

p lot tun I

heading the base of

32

First train emerging from div I at the lower level at Step-plate 17

18 the new invert concrete was placedso as to give support to the existingrunning tunnel as close to the workingface as possible and, using temporaryprops, the maximum span of the tunnellining was limited to 5ft (1.52 m). Thisprocedure could not be used in step-plate 17, where the underside of theexisting Piccadilly Line running tunnelwas, for most of the length of the step-plate, at a higher elevation than theinvert concrete for the future track.During the construction of the en-circling tunnels, supports had thereforeto be provided which would initiallycarry the existing tunnel lining and thetrack after the lining had been dis-mantled. The supports were designedas steel trestles at 5-ft (1.52-m) spac-ing, with their legs bearing on theinvert of the new lining. A bolted jointwas provided at the surface of the in-

vert concrete so that the upper partcould be removed, leaving the centreleg and side supports in place.

60'20 t A

After the segments from the top andone side of the existing tunnel had beendismantled, the track bed concrete wasremoved from each pair of sleepers.When the invert segments at step-plate18 had been removed, the track wassupported on the new concrete. Atstep-plate 17 the track was supportedon 12 x 12-in (30.5 x 30.5wm) timberwaybeams resting on a timber shaped togive the appropriate superelevation:this in turn was supported on thetrestles. Each pair of waybeams withcross ties and struts formed a unit10 ft (3.05 m) long carried on threetrestles.

X~:ASECTION B-B

Detail of concrete lining, showing jacking pockets.

I—2ft+L-B

SECTION A-A

The 12-ft 2-in (3.71-m) diameterdiversion tunnel south of the stationwas connected in to the 16-ft (4.88-m)diameter existing Northern City Linetunnel. Where the new tunnel wouldbreak into the existing one, it wasnecessary to support the 16-ft (4.88-m)diameter lining by plugging the exist-ing tunnel with weak concrete. To mini-mise the use and breaking out of con-crete, the plug was rough-shuttered tothe profile of the extrados of the12-ft 2-in (3.71-m) diameter lining. Asimilar procedure was used at thenorth end of the station where the diver-sion tunnel intersected the over-runtunnel at an oblique angle.

i

While the stripping and loading ofthe waybeams and steelwork at thenorthern end of step-plate 17 was being~~rried out, London Transport Per-manent Way Department were workingat the Arsenal end of the step-platewhere 130 ft (39.6 m) of track wasslewed to the new alignment and sup-ported on reconditioning jacks. Thisleft a length of 92 ft (28 m) to be recon-structed, supported on reconditioningjacks and joined to the 80-ft (24.4-m)length previously laid, after dismantlingthe third section of track supports. Con-duc'tor rails and signalling equipmentwas then installed, and the new track

as topped and lined. The whole oftheahase elaborate works were completed" time and the track handed back forhe resumption of traffic.

. the

f/4 in Xf/4 in C hamfers

t/e in

1 s/4 in[

f/s

1stfiin

Clay

DETAIL OF JOINT BETWRINGS AT SEGMENTS A,B

holes ain '<3'fQ

Drainage recess

ELEVATION OF A RING OF LINING LQQXINGIN THE DIRECTION QF DRIVE

Derail of cast iron lining, showing jacking holes and pecking pieces.

Ground Engineering 33