Measured short-term ground surface response to EPBM ......EPBM tunnelling in London Clay M. S. P. WAN , J. R. STANDING†,D.M.POTTS† andJ.B.BURLAND† Earth-pressure-balance machines

Measured short-term ground surface response toEPBM tunnelling in London Clay

M. S. P. WAN�, J. R. STANDING†, D. M. POTTS† and J. B. BURLAND†

Earth-pressure-balance machines (EPBMs) were used for the construction of Crossrail tunnelsin London, providing opportunities for field investigation of consequent ground response. Analysedresults from an instrumented research site in Hyde Park with extensive surface and subsurfacemonitoring arrays are presented and discussed. The Crossrail tunnels at the site are 34·5 m belowground, deeper than those in most case histories of tunnelling in stiff clay in the UK. This papercharacterises the tunnelling-induced ground response, both ‘greenfield’ and in the proximity of theexisting Central Line tunnels, dealing with measurements at the ground surface. A companion papercovers the subsurface ground response. Vertical and horizontal ground surface displacements wereobtained from manual precise levelling and micrometer stick measurements. Several key findings willbenefit future tunnelling projects involving EPBMs. Volume loss values measured at the instrumentedsite were low, being less than 0·8% and 1·4% for the first and second tunnel drives respectively, highervalues being associated with ground softening from the first tunnel construction. Smaller volume losseswere recorded in the vicinity of the existing Central Line tunnels, comparedwith the greenfield location,suggesting that their presence inhibited the development of ground movements. Asymmetric settlementtroughs developed due to either the nearby pre-existing tunnels or the construction of the first tunnel.Marginally smaller values of trough width parameter, Ky, were determined for these deeper tunnelscompared with previous greenfield ground case histories. Resultant vectors of ground surfacedisplacement were directed to well-defined point-sinks above the tunnel axis level.

KEYWORDS: field instrumentation; ground movements; monitoring; settlement; tunnels & tunnelling

BACKGROUNDIn major cities like London, constructing new tunnelsinevitably influences nearby existing structures above andwithin the ground. Much has been learnt about the complexinteractions between the ground and existing undergroundstructures from new tunnel construction reported through casestudies.With advances in tunnelling technologies and practicesand construction materials, engineers and researchers con-tinuously endeavour to update and improve their understand-ing of ground and structural responses to tunnel construction.Recently a comprehensive research project has been run byImperial College London to investigate the effect of tunnellingby modern earth-pressure-balance tunnel-boring machines(EPBMs) on existing tunnels (Standing et al., 2015). Fieldmeasurements at an instrumented site in Hyde Park formed anintegral part of the overall research project.

Short-term tunnelling-induced ground surface dis-placements are still frequently predicted using empiricalapproaches (Attewell, 1978). Vertical displacements are esti-mated using a Gaussian formulation where there are twounknowns: volume loss (VL) and the trough width parameter(K ). Of these, volume loss is the more difficult to predict,it depends on various factors such as method of tunnelling,ground and groundwater conditions, and the time periodbefore support to the excavated ground is provided. In thispaper volume loss is taken to be the volume of the surfacesettlement trough divided by the nominal volume of the

excavated tunnel. The K value is the ratio of the surfacedistance between the tunnel centre-line position and thepoint of inflection, iy (sometimes referred to as the troughwidth factor), to the depth to the tunnel axis, z0 (i.e.K= iy /z0). Horizontal displacements at the surface are oftenestimated by assuming that resultant vectors of displace-ments are directed towards a single ‘point-sink’, usuallytaken to be the tunnel axis. Thus, after predicting the verticaldisplacement, the horizontal displacement can be readilycalculated: it is zero directly above the tunnel and reaches amaximum at the offset distances iy. Horizontal strains (εhy)can be obtained by differentiating the horizontal displace-ments. There are two distinct zones with compressive strainsbetween the points of inflection either side of the tunnelcentre line (where εhy=0), beyondwhich strains are tensile. Inthis paper the measurement data are discussed in the contextof these empirical prediction approaches.After describing the instrumented field site, the monitor-

ing results are presented and discussed with the aim of char-acterising the ground surface response induced by tunnellingwith EPBMs, both in ‘greenfield’ conditions and in theproximity of existing tunnels. The greenfield ground responseis compared with those from other well-instrumented green-field sites, for example, Nyren (1998) and Withers (2001) forthe Jubilee Line Extension (JLE) and Selemetas (2005)for the Channel Tunnel Rail Link (CTRL). In a companionpaper, the nature and mechanism of subsurface ground dis-placements are studied and correlated with measured EPBMoperation variables.

CROSSRAILTUNNELLING ANDINSTRUMENTED SITEThe Crossrail project involves construction of 21 km of

twin-bore tunnels and nine underground stations beneath� Geotechnical Consulting Group LLP, London, UK.† Imperial College London, London, UK.

Manuscript received 12 April 2016; revised manuscript accepted23 September 2016. Published online ahead of print 16 November2016.Discussion on this paper closes on 1 October 2017, for further detailssee p. ii.

Wan, M. S. P. et al. (2017). Géotechnique 67, No. 5, 420–445 [http://dx.doi.org/10.1680/jgeot.16.P.099]

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Downloaded by [ Imperial College London Library] on [10/08/17]. Copyright © ICE Publishing, all rights reserved.

central London. The instrumented site in Hyde Park lieson the tunnel alignment which runs from the Royal Oakportal west of Paddington Station to Farringdon Station.The first tunnel-boring machine (TBM1) was used to con-struct the westbound tunnel and passed beneath the HydePark instrumented site in late November 2012, whereasthe second, TBM2, used for the eastbound tunnel passedbeneath the site in early February 2013. Average drivingspeeds were about 110 m per week.On the northern boundary of Hyde Park, just east of

Lancaster Gate, the TBMs passed beneath the existingLondon Underground (LUL) 3·8 m dia. Central Linerunning tunnels below Bayswater Road at a skew angle ofabout 40° (as shown in Fig. 1 along with a longitudinalsection of the eastbound Crossrail tunnel). At the cross-ing, the axes of the Central Line and Crossrail tunnelsare about 24 m and 34·5 m below ground level (mbgl),

respectively: the clearance between the respective tunnelinverts and crowns ranges from 4·3 m to 5·0 m. Both pairsof tunnels are within the London Clay Formation (LCF).Extensive field instrumentation was installed just east ofVictoria Gate, within Hyde Park and on Bayswater Road, toinvestigate the ground response close to the existing tunnelsand also in the greenfield condition.

SITE GEOLOGYThe stratigraphy at Hyde Park is typical of that within

the London Basin with deposits from the LCF, LambethGroup and Thanet Sand resting on Chalk bedrock. As partof the Hyde Park instrumentation installations, a 68-m deepborehole (denoted HP6 – Fig. 4(a)) was sunk by rotary coredrilling through the whole thickness of LCF and part of theLambeth Group. Continuous triple tube core barrel samples

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GROUND SURFACE RESPONSE TO EPBM TUNNELLING IN LONDON CLAY 421


were transported to Imperial College for detailed logging.The lithological units of the LCF, as characterised by King(1981), were identified by visual inspection and moisturecontent measurements (Standing & Burland, 2006).

Figure 2 shows the soil descriptions and stratificationof the ground determined from borehole HP6, together withthe relative depth of the Central Line and Crossrail tunnels.At the instrumented site, the Chalk bedrock is inferred to beabout 80 mbgl from deep boreholes at Paddington and HydePark, overlain by a thin layer of Thanet Sand (about 3·5 mthick) and about a 15 m thickness of Lambeth Groupdeposits. A 1·7-m deep sand-infilled channel was encoun-tered below the London Clay, which had eroded the upperunits of the Lambeth Group. The base of the LCF, which hasan overall thickness of about 57 m, is at 61·5 mbgl. There is a3-m thick layer of Terrace Gravel above the LCF, with a thinlayer of made ground at the surface. Most of the 7·1 m dia.Crossrail tunnel excavation is within the lower level of theLCF unit B (B1 and B2), while its invert is within the morepermeable A3ii unit.During borehole drilling at the site, three horizons with

large concentrations of claystones were encountered withinthe LCF, the greatest being from 29·5 to 30 mbgl. The im-plication of these on the ground permeability and the ground-water regime has been discussed byWan & Standing (2014b).It is possible that these extensive claystone horizons mightalso affect the response of other instruments such as inclino-meters and extensometers.

INSTRUMENTATION LAYOUTAND MONITORINGThe instrumentation layout, shown in Fig. 3, was designed

to monitor the ground responses induced by the passage of

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WAN, STANDING, POTTS AND BURLAND422


both TBMs. There are 38 boreholes in total, each accom-modating one or more instruments.Ground surface measurements were made predominantly

using surface monitoring points (SMPs) of a design similarto that described by Nyren (1998). Within the boundary ofHyde Park there are two lines of SMPs, the X-line and Y-line,both being transverse to the Crossrail alignments, on whichvertical and horizontal displacements were measured byprecise levelling, total stations and a micrometer stick. TheseSMPs incorporate BRE-type sockets (BRE, 1993) into whicha removable survey plug can be screwed with good positionalrepeatability for manual surveying (Standing et al., 2001).A greenfield response is expected across the entire X-line.Along the Y-line, the SMPs are positioned to measure, in thesouthwest part, the greenfield ground response and, in thenortheast part, the ground response under the potentialinfluence of the Central Line tunnels (for the case of thefirst, westbound, tunnel drive). Different responses would beexpected for these two parts. Another line of SMPs (Z-line)comprised typical survey nails installed in the kerbstones onthe northern pavement of Bayswater Road, which runs abovethe Central Line eastbound running tunnel. Detailed plansindicating the locations and nomenclature of the SMPsand borehole instruments are shown in Figs 4(a) and 4(b). Itis worth noting that both the X- and Y-lines cross the NorthCarriage Drive and so there are gaps in the lines at thesepoints.Details of the instruments and their installation are

described by Wan & Standing (2014a). The performanceand uncertainties and errors associated with the measure-ment techniques, including precise levelling and micrometer

stick measurement, were assessed and reviewed during thepre-construction period (Fearnhead et al., 2014; Wan, 2014).Although measurements were taken for the duration of eachTBM passage using robotic total stations, set up to sight tooptical prisms screwed into sockets installed into the headsof the SMPs, these are not presented in this paper. Totalstation measurements have the benefit of providing displace-ments in three orthogonal coordinate directions. However,better accuracy was achieved from the measurements madewith the precise levelling and micrometer stick, and so onlythese are presented. Displacements in the third direction,longitudinal to the TBM drives, were small and results fromthe total station monitoring could not be interpreted reliably.In addition to the micrometer stick measurements, opticalfibres were installed independently within a narrow trenchby a research team from ETH Zurich to measure horizontalstrains. The set-up and measurements are described byHauswirth et al. (2014) and the results are compared withthe micrometer stick measurements later in this paper.

TUNNEL-BORING MACHINESThe Herrenknecht EPBMs that passed beneath the site

had a total length of 150 m, with a rotating full-face cutter-head of 7·1 m dia. and a leading shield body 11 m long.The two EPBM cutter-heads have identical dimensions andarrangements of cutting tools on the cutting wheel. Eachcutter-head has eight radial arms which are equipped withoptional cutting configurations of clay spades (210 mmprojection from the hard face) or ripper tools (140 mmprojection). The cutter-head of TBM1 was configured using

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Fig. 4. Location plan of instruments: (a) Z-line and Y-line SMPs and borehole instruments; (b) X-line SMPs (continued on next page)



the traditional clay spade while that of TBM2 had a standardripper system. At the ends of four of the radial arms are432 mm dia. cutter discs which define the bore diameter of7100 mm (Fig. 5). Although the reason for the differentcutting configurations used for the two TBMs is unknown tothe authors, it is thought that the cutting option (ripper orclay spade) should not have a significant effect on theachieved volume loss per metre advance of the cutter-head.Soil passed into the plenum chamber behind the cutter-headthrough apertures, providing a nominal opening ratio of 55%at the face. The shield body was tapered in shape with theouter diameter varying from 7·08 m at the front to 7·05 m atthe rear. An Archimedes screw conveyor, connected to thesealed pressurised plenum chamber, was used to remove spoil.The face pressure was controlled by the rate of spoil removal,with the aim of minimising changes in earth pressure at thefront of the cutter-head. Precast concrete lining rings, formedof seven segments and a key-piece, were erected withinthe shield body and the shield was advanced by a seriesof hydraulic jacks pushing against the newly erected lining.The inner and outer diameters of the rings were 6·2 m and6·8 m, respectively, and had a nominal length of 1600 mm(there was a 60 mm taper so 1570 mm and 1630 mm on thenarrowandwide sides, respectively). The annular void betweenthe erected tunnel lining extrados and the excavated groundwas grouted by means of injection ports located within thetail skin of the shield. The tail grout was pumped continuouslyas the shield advanced. The grout used was a two-part mixcombining a retarded grout (with proportions of water:cement: PFA: bentonite of 1·00: 0·25: 0·10: 0·05 and a smallamount of retarder) with an accelerator prior to exiting theinjection ports.

Eight pressure sensors were distributed behind the cutter-head to measure the face pressures and other pressure sensorswere also present in the pressurised chamber and the screwconveyor. The tunnelling contractor used a real-time systemto monitor closely a number of operation variables, includingthe machine position, advance speed, face pressure, tail groutpressure, tail grout volume and weight of excavated materialon the conveyor belt. These provide useful information forconstruction control as well as for assessing their effects onthe ground response to the construction.

SURFACE MONITORING RESULTSThe monitoring data have been divided into five distinct

periods.

(a) Period 1 – pre-construction (12 October 2011 to19 November 2012).

(b) Period 2 – construction of the westbound tunnel byTMB1 (19 November 2012 to 30 November 2012).

(c) Period 3 – interim phase before TMB2 arrived(30 November 2012 to 3 February 2013).

(d ) Period 4 – construction of the eastbound tunnel byTMB2 (3 February 2013 to 12 February 2013).

(e ) Period 5 – long-term monitoring (12 February 2013onwards).

Data from the base-line monitoring during period 1 arediscussed by Fearnhead et al. (2014), whereas this paperconcentrates on the short-term responses observed duringperiods 2 and 4.

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The sign conventions for presentation of the monitoringresults are as follows.

(a) Positive (+)x means the longitudinal distance aheadof the TBM cutter-head.

(b) xf is the longitudinal horizontal distance between thecutter-head and the monitoring point/line in question.(�)xf means the cutter-head is in front of andapproaching the monitoring point/line while (+)xfmeans the cutter-head is progressing beyond themonitoring point/line.

(c) Positive (+)y means the transverse horizontal distancefrom the tunnel axis to the left-hand side when lookingin the direction of tunnel advancement.

(d ) Negative (�)z means the downwards vertical distancefrom the ground surface.

(e) u, v and w are the displacements in the directions andsenses of x, y and z, respectively.

( f ) The depth of the tunnel axis below ground surface isdenoted by z0 (a positive value).

The TBMs passed beneath the site at the Z-line SMPs first,followed by the Y-line SMPs, and subsequently the X-lineSMPs. Figs 6(a) and 6(b) show the cutter-head advance time-lines, chainage locations of the instruments, and the timesof precise levelling surveys during the passages of TBM1 andTBM2, respectively.It can be seen from Fig. 6(a) that the first tunnel con-

struction was suspended a number of times for up to 30 h at atime. These suspensions resulted from multiple delays inremoving excavated spoil from the tunnelling shield becauseof failures of the conveyor and hopper muck-away systemwhen the first TBM was passing beneath the Paddington andHyde Park area. The face pressure was thought to be fully

maintained during the suspensions. One such suspensionoccurred when the TBM1 cutter-head was about 5 m in frontof the Y-line SMPs (xf =�5 m). A total of five precise levell-ing survey sets were performed during the 30 h of suspension.Vertical displacements of less than 0·2 mm were measured,which is within the precise levelling measurement accuracy.This suggests that the construction break of 30 h did nothave a significant effect on the measured ground surfacedisplacements.

VERTICAL DISPLACEMENTSThe vertical displacements for periods 2 and 4 presented in

this paper refer to incremental displacements with referenceto when the TBM cutter-head distances were about 100 m infront of the instrument lines (i.e. xf��100 m).

Vertical displacements on Z-line (periods 2 and 4)The Z-line SMPs, being located above and along the

existing eastbound Central Line alignment, allowed thedevelopment of vertical displacements on a line at a skewangle to the TBM advance direction to be measured. Theprogressive settlement troughs developed along the Z-lineas TBM1 and TBM2 passed the line are shown in Figs 7(a)and 7(b), respectively (note that the perpendicular hori-zontal distance of the monitoring point from the TBM axis isplotted, rather than the distance along the Z-line). Across thesettlement trough obtained from any one survey, the longit-udinal distance between the cutter-head and each ZSMPis different because of the skew angle between the Z-lineand the TBM driving direction. For this reason, the short-term transverse settlement trough for a particular cutter-headlocation cannot be readily obtainedwithout some adjustment

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to the measurement results. Equally, the volume loss andtrough width parameter for the Z-line cannot be determineddirectly from the settlement troughs shown in Figs 7(a) and7(b). Nevertheless, a general pattern of the developing maxi-mum settlement location shifting as the cutter-head positionvaries is evident, with the final maximum settlement occurr-ing and remaining at or near the TBM centre-line location(y=0). The maximum settlements recorded were 5·1 mmand 9·5 mm for thewest- and eastbound tunnels, respectively.This general pattern is similar to that observed in the existingPiccadilly Line tunnel when the TBM used to construct theHeathrow Express tunnels passed beneath it, also at a skewangle (Cooper et al., 2002).

Vertical displacements on X- and Y-lines (period 2)Vertical displacements of YSMPs are plotted against the

relative position of the cutter-head (xf ) to the main Y-line

during the passage of TBM1 in Fig. 8(a). Vertical settlementsstarted to develop when the cutter-head was about 14 m infront of the instrument line (xf =�14 m or �0·4z0). Whenthe cutter-head was directly beneath the Y-line, a surfacesettlement of 1·7 mm was measured at YSMP11 (above thetunnel centre-line), or about 30% of the total maximumsettlement (5·6 mm) measured in the short term. Immediatesettlements essentially ceased when the TBM1 cutter-headhad passed 35 m beyond the main line (xf = 35 m or 1·0z0).Fig. 8(b) depicts the development of the transverse settlementtrough on the main Y-line SMPs as TBM1 passed, the maxi-mum settlement was always at the location of the TBM1centre-line, that is, either at YSMP11 (y=0 m) or YSMP12(y=2·5 m).The locations of SMPs Y12A, Y13A and Y14Awere offset

from the main line to avoid a tree root. As a consequencethere is a clear step within the developing settlement profiles(e.g. when xf = 1·5 m and 9·8 m), which closed once TBM1

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XSMP chainage: 2258 m

Chainage of TBM1 cutter-head

YSMP chainage: 2155 m

ZSMP5 chainage: 2087 m

ZSMP precise levellingsurvey during period 2

YSMP precise levellingsurvey during period 2

Note: extensometer reference heads and Y-lineSMPs were measured in the same survey loops

XSMP precise levellingsurvey during period 2

XSMP chainage: 2261 m

YSMP chainage: 2161 m

ZSMP9 chainage: 2109 m

Chainage of TBM2 cutter-head

ZSMP precise levellingsurvey during period 4

YSMP precise levellingsurvey during period 4

XSMP precise levellingsurvey during period 4

Note: extensometer reference heads and Y-lineSMPs were measured in the same survey loops

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Fig. 6. Time of precise levelling survey loops: (a) during passage of TBM1 (westbound tunnel – period 2); (b) during passage of TBM2 (eastboundtunnel – period 4)



had passed. For similar reasons SMPs Y21 to Y24 werealso offset from the main line with Y20 and Y21 being at thesame distance y (Fig. 4(a)), but as these points were furtherfrom the centre-line of TBM1 the effect is not so noticeable(Fig. 8(b)).Similar overall responses to those on the Y-line were

observed on the greenfield X-line as shown in Figs 8(c) and8(d). At this location the maximum settlement was 8·3 mmand 30% of it had developed when the cutter-head wasdirectly beneath the line.A clearer picture of the surface movements emerges when

the results are normalised by dividing by the relevantmaximum observed settlement. The normalised longitudinalsettlement troughs that developed above the TBM centre-lineposition during TBM1 passage are shown in Fig. 9(a). Thenormalised settlements (w/wmax) for extensometer HP20(Fig. 4(a)), YSMP11, XSMP15 and ZSMP5 (where the maxi-mum settlements occurred) lie within a well-defined narrowband with surface settlements confined to a cutter-headdistance range of �15 m, xf, 35 m. Such a well-definedrange is remarkable when it is considered that the four

measurement points are spread over a horizontal distance ofmore than 150 m, one being in Bayswater Road (ZSMP5)where the Central Line tunnels could have an influenceand the other in Hyde Park greenfield ground (XSMP15).This suggests a consistent contribution of surface settlementfrom the actions of the EPBM tunnelling. Longitudinaltrough length factors, ix, determined from these normaliseddisplacement plots range from 11·2 m to 12·6 m for the fourmonitoring points, with corresponding trough length par-ameters (Kx) ranging between 0·32 and 0·37. The normalisedvertical displacements (w/wmax) directly above the cutter-head (i.e. when xf = 0 m) ranged from 24% to 36%, whichis somewhat larger than the range of 5–20% reported byWithers (2001) for the EPBM tunnelling in the LambethGroup and Thanet Sands for JLE construction.The normalised transverse settlement troughs measured

along the X-line and Y-line SMPs and the main line of rodextensometer reference heads (close to the Y-line) at the endof the TBM1 passage are shown in Fig. 9(b). Note thatnegative y distances relate to the southern half of the troughin accordance with the sign convention given in the section

2

1

0

–1

–2

–3

–4

–5

–6

–7

–8

–9

–10

–11

–20 –10 0 10Transverse offset from TBM1 axis, y: m

Verti

cal d

ispl

acem

ent,

w: m

m

2

1

0

–1

–2

–3

–4

–5

–6

–7

–8

–9

–10

–11

Incr

emen

tal v

ertic

al d

ispl

acem

ent,

∆w: m

m

20 30 40 50

–20–30 –10 0 10Transverse offset from TBM2 axis, y: m

(a)

(b)

20 30

Z1 Z2 Z3 Z4 Z5 Z6 Z7 Z8 Z9 Z10

Z11

Z12

Z13

Z14

Z15

Z16

Z17

HP

25

Z1 Z2 Z3 Z4 Z5 Z6 Z7 Z8 Z9 Z10

Z11

Z12

Z13

Z14

Z15

Z16

Z17

HP

25

18/11/2012 17:50, xf = –22·3 m19/11/2012 05:00, xf = –10·8 m19/11/2012 21:20, xf = 10·8 m20/11/2012 11:10, xf = 22·7 m20/11/2012 21:00, xf = 36·7 m21/11/2012 05:00, xf = 48·3 m23/11/2012 02:00, xf = 68·1 m24/11/2012 06:00, xf = 77·6 m29/01/2013 15:30, xf = 671·5 m(end of Period 3, prior to TBM2 arrival)

Note: distance xf varies for different ZSMPsas Z-line is at a skew angle to TBM advance.Distance xf values shown refer to ZSMP5

Note: distance xf varies for different ZSMPsas Z-line is at a skew angle to TBM advance.Distance xf values shown refer to ZSMP9

04/02/2013 10:10, xf = –41·1 m05/02/2013 09:30, xf = –12·6 m05/02/2013 17:35, xf = –1·2 m05/02/2013 21:30, xf = 3·9 m06/02/2013 03:30, xf = 11·8 m06/02/2013 10:45, xf = 24·8 m06/02/2013 23:15, xf = 35·9 m07/02/2013 05:30, xf = 46·0 m07/02/2013 15:45, xf = 59·6 m07/02/2013 21:15, xf = 67·9 m

Fig. 7. Development of settlement troughs for Z-line SMPs during passage of (a) TBM1 (period 2) and (b) TBM2 (period 4; note: incrementalsettlement troughs shown)



entitled ‘Surface monitoring results’. It can be seen that thethree normalised settlement troughs are broadly similar inshape except for the northern part of the X-line at a distancegreater than 20 m from the TBM1 axis, where the settlementsare significantly greater than for the Y-line and extensometerreference heads.

The detailed characteristics of the transverse troughs can bereviewed by comparing the trough width factors (iy) andvolume losses (VL) derived from the measurements. Theformer are derived by plotting the logarithm of normaliseddisplacements (ln(w/wmax)) against the square of the normal-ised transverse offset distances ((y/z0)

2) as shown in Fig. 10 forthe X-line SMPs. If the trough is of aGaussian form, the data,when plotted in this way, should lie on a straight line passingthrough the origin. In the case of the X- and Y-line SMPsand the extensometer line, only data points closer to the TBMaxis (generally ln(w/wmax).�1·0, or w/wmax. 0·36) form astraight line, indicating that the measured displacements nearthe ends of the troughs do not exactly follow the idealisedGaussian curves. For the purpose of comparing the Gaussian

approximations, lines are only fitted through the measure-ment points closer to the TBM centre-line (w/wmax. 0·36).The Gaussian curves with the iy values so determined areplotted together with the measured displacement valuesfor the X-line and Y-line SMPs and the main extensometerline in Figs 11(a)–11(c). The iy values for the southern- andnorthern-half troughs have been determined separately.The symmetry of the settlement troughs is assessed by

comparing the trough width factors between the southern-and northern-half troughs. It can clearly be seen fromFig. 11(a) that, with almost the same iy values (15 m) orKy values (0·44) for both halves, the settlement trough forthe X-line was essentially symmetric. This agrees with theexpected tunnelling-induced greenfield ground response.The reason for the group of points on the far northern-halftrough (XSMP25 to XSMP30, see Fig. 4(b)) lying beneaththe fitted Gaussian curve is not understood. It is this samegroup of points that are at a considerable offset from thestraight line in Fig. 10. A possible cause might be the NorthCarriage Drive, although it did not have the same effect on

1

0

–1

–2

–3

–4

–5

–6

–7

–8

–9

1

0

–1

–2

–3

–4

–5

–6

–7

–8

–9

1

0

–1

–2

–3

–4

–5

–6

–7

–8

–9

Verti

cal d

ispl

acem

ent,

w: m

m

1

0

–1

–2

–3

–4

–5

–6

–7

–8

–9

Verti

cal d

ispl

acem

ent,

w: m

m

–60 –50 –40 –30 –20 –10 0 10 20 30 40 50 60 70 80Distance of TBM1 cutter-head from Y-line SMPs, xf: m

(a)

–50 –40 –30 –20 –10 0 10 20 30 40Transverse offset from TBM1 axis, y: m

(b)

North Carriage Drive Hyde Park Bayswater Road

YSMP2YSMP4YSMP6YSMP8YSMP10YSMP12YSMP14YSMP16YSMP18YSMP20YSMP22YSMP24

Y1

Y2 Y3

Y4

Y5

Y6

Y7

Y8

Y9

Y10

Y11

Y12

/Y12

A

Y14

A/Y

14

Y20

/Y21

Y15

Y16

Y17

Y18Y

12A

Y13

AY

14A

Y19

Y22 Y

23Y

24

Y13

A

20/11/2012 16:00, xf = –39·9 m21/11/2012 06:00, xf = –20·8 m21/11/2012 12:15, xf = –12·7 m22/11/2012 09:20, xf = –4·5 m23/11/2012 05:30, xf = 1·5 m23/11/2012 09:25, xf = 6·0 m23/11/2012 12:10, xf = 9·8 m23/11/2012 14:30, xf = 14·0 m23/11/2012 18:25, xf = 19·4 m24/11/2012 03:30, xf = 29·8 m25/11/2012 01:00, xf = 42·7 m

Fig. 8. Ground response during passage of TBM1 (period 2): (a) vertical displacements of Y-line SMPs plotted against cutter-head position;(b) development of settlement troughs for Y-line SMPs; (c) vertical displacements of X-line SMPs plotted against cutter-head position;(d) development of settlement troughs for X-line SMPs (continued on next page)



the Y-line, as will be seen shortly. In hindsight it would havebeen useful to have installed some levelling studs across theroad surface to understand its overall response (even ifreadings were only taken occasionally).In the case of both the Y-line SMPs and the main extenso-

meter line, the northern-half troughs had larger iy valuesthan the southern counterparts, as shown in Figs 11(b)and 11(c), possibly reflecting the influence of the CentralLine tunnels on the surface settlements. The influence of thepre-failure soil stiffness and stress history of the groundon tunnelling-induced surface settlements, investigated usingnumerical analysis, has been reported in the literature (e.g.Addenbrooke et al., 1997; Grammatikopoulou et al., 2008).Construction of the Central Line tunnels more than a centuryago and the consequent change of the stress regime in thesurrounding ground would have reduced the soil stiffnessand therefore led to the wider tunnelling-induced surfacesettlement troughs measured on the northern halves of thelines (closer to the existing tunnels), compared with thosemeasured in greenfield ground to the south.

The ratios of trough width parameter to trough lengthparameter (Ky/Kx) determined for the three surface moni-toring lines were found to be greater than unity (1·0 to 1·3),and agree with findings from other London Clay sites such asthe JLE project (Nyren, 1998) and CTRL project (Selemetas,2005; Wongsaroj et al., 2006).The overall volume loss values are obtained from averaging

the values for the two half-troughs and, although not deter-mined from the actual area under the transverse settlementprofile, give an indication of the effectiveness of the tunnelconstructionmethod in controlling the ground loss. The overallvolume loss values relating to the Y-line SMPs and the mainextensometer line reference heads are consistent (0·44% and0·48%), while that for the X-line SMPs is considerably greater(0·78%). As there are negligible differences in either the strati-graphy or the EPBM operation variables between the Y- andX-lines, the lowervolumes lossesat theY-linemight suggest thatthe presence of the Central Line tunnels may have inhibitedoverall ground movements from the Crossrail tunnel construc-tion (already evident in the asymmetry of the settlement

1

0

–1

–2

–3

–4

–5

–6

–7

–8

–9

1

0

–1

–2

–3

–4

–5

–6

–7

–8

–9

1

0

–1

–2

–3

–4

–5

–6

–7

–8

–9

Verti

cal d

ispl

acem

ent,

w: m

m

1

0

–1

–2

–3

–4

–5

–6

–7

–8

–9

Verti

cal d

ispl

acem

ent,

w: m

m

–60 –50 –40 –30 –20 –10 0 10 20 30 40 50 60Distance of TBM1 cutter-head from X-line, xf: m

(c)

–40 –30 –20 –10 0 10 20 40 5030 60Transverse offset from TBM1 axis, y: m

(d)

North Carriage DriveNorth Ride

XSMP1XSMP3XSMP5XSMP7XSMP9XSMP11XSMP12XSMP13

XSMP16XSMP17XSMP19XSMP21XSMP23XSMP25XSMP27XSMP29

XSMP14

26/11/2012 09:40, xf = –41·0 m28/11/2012 05:00, xf = –30·6 m28/11/2012 15:10, xf = –19·0 m28/11/2012 21:30, xf = –11·0 m29/11/2012 06:00, xf = –4·4 m29/11/2012 09:10, xf = –0·8 m29/11/2012 13:20, xf = 4·9 m29/11/2012 17:30, xf = 10·4 m30/11/2012 00:30, xf = 14·3 m30/11/2012 09:35, xf = 21·6 m30/11/2012 16:20, xf = 31·8 m30/11/2012 19:25, xf = 35·6 m01/12/2012 09:50, xf = 51·6 m

X1

X2

X3

X4

X5

X6

X7

X10X10A

X8

X9

X10

X11

X12

X13

X14

X15

X16

X17

X18

X19

X20

X21

X22 X

23

X25 X26 X

27 X28

X29

X30

Fig. 8. Continued



troughs). Additionally, in numerically modelling the groundresponse to tunnel construction at Hyde Park (but without thepresence of the Central Line tunnels), Avgerinos (2014) foundthat the ground heaved at 50 mbgl at the location of HP21 (thepoint initially used as the datum for the field measurementson the Y-line). This would result in apparently greater verticaldisplacements than in reality. The measurements were re-analysed in relation to another datum (HP24 at 40 mbgl)which, although shallower, is further from the zone of tunnelinfluence. The results presented are relative to this more stabledatum. Inmaking this further adjustment, values of settlementand volume loss become even smaller than those based onHP21 and therefore are even less than those determined for theX-line. This factor, concerning the stability of the datum used,might therefore also contribute to the differences involume lossbetween the two sections, as well as the presence of the CentralLine tunnels. Values of various characteristics relating to thelongitudinal and transverse vertical displacement profiles at thefour surface monitoring lines are summarised in Table 1.

–0·2

–0·1

0·1

0·2

0·3

0·4

0·5

0·6

0·7

0·8

0·9

1·0

1·1

1·2

–60 –50 –40 –30 –20 –10 0 10 20 30 40 50 60 70 80 90 100

0

Nor

mal

ised

ver

tical

dis

plac

emen

t, w

/wm

ax

–0·2

–0·1

0·1

0

0·2

0·3

0·4

0·5

0·6

0·7

0·8

0·9

1·0

1·1

1·2

Nor

mal

ised

ver

tical

dis

plac

emen

t, w

/wm

ax

Distance of TBM1 cutter-head from instrument, xf: m

–50 –40 –30 –20 –10 0 10 20 30 40 50 60Transverse offset distance from TBM1 axis, y: m

(a)

(b)

HP20 (y = 0·0 m)YSMP11 (y = 0·0 m)XSMP15 (y = 1·05 m)ZSMP5 (y = –0·2 m)

Extensometer reference headsY-line SMPsX-line SMPs

Fig. 9. (a) Longitudinal profiles of normalised surface vertical displacements during passage of TBM1 (period 2); (b) transverse profiles ofnormalised surface vertical displacements after passage of TBM1 (period 2)

0

–1

–2

–3

–4

Ln(w

/wm

ax)

0 1 2

North ofNorth Carriage Drive

(y/z0)2

3 4

Best fit for initial straight line portion

Slope = –2·718 =2(iy /z0)2

–1

= 0·43iyz0

X-line SMPs, TBM1

Fig. 10. Determination of trough width parameters by plottingln(w/wmax) against (y/z0)

2



–60 –50 –40 –30 –20 –10 0 10 20 30 40 50 60Transverse offset distance from TBM1 axis, y: m

(a)


(b)

0

–1

–2

–3

–4

–5

–6

–7

–8

–9

Verti

cal d

ispl

acem

ent,

w: m

m

0

–1

–2

–3

–4

–5

–6

–7

–8

–9

Verti

cal d

ispl

acem

ent,

w: m

m

South North Ride North Carriage Drive North

SouthNorth Carriage Drive

North

Gaussian approximation(south)iy = 15·1 mKy = 0·442VL = 0·78%


Gaussian approximation(north)iy = 15·0 mKy = 0·439VL = 0·78%


XSMP measurement

Measurement data in plot:Survey set no. X2730/11/2012 19:25, xf = 35·6 m

Measurement data in plot:Survey set no. Y3624/11/2012 07:00, xf = 34·3 m

Gaussian approximation(south)Gaussian approximation(north)

YSMP measurementGaussian approximation(south)Gaussian approximation(north)

0

0·1

0·2

0·3

0·4

0·5

0·6

0·7

0·8

0·9

1·0

w/w

max

00·10·20·30·40·50·60·70·80·91·0

w/w

max


(c)

0

–1

–2

–3

–4

–5

–6

–7

–8

–9

Verti

cal d

ispl

acem

ent,

w: m

m

SouthNorth Carriage Drive

NorthBayswater Road

Gaussian approximation(south)iy = 13·0 mKy = 0·374VL = 0·47% Gaussian approximation

(north)iy = 13·6 mKy = 0·392VL = 0·49%


Extensometer measurementGaussian approximation(south)Gaussian approximation(north)

00·10·20·30·40·50·60·70·80·91·0

w/w

max

Fig. 11. Gaussian approximation of surface vertical displacements measured at the end of passage of TBM1 (period 2) for: (a) X-line SMPs;(b) Y-line SMPs; (c) extensometer reference heads



Vertical displacements on X- and Y-lines (period 4)Similar trends of vertical displacements were observed as

TBM2 passed beneath the site. Normalised longitudinal andtransverse profiles, based on incremental vertical displace-ments of the X- and Y-line SMPs and the main extensometerline, are shown in Figs 12(a) and 12(b), respectively.The development of the longitudinal profiles of normalised

incremental settlements for HP23, YSMP17, XSMP19(located at or near the TBM2 centre-line) agree well witheach other (Fig. 12(a)), as observed during the passage ofTBM1. For ZSMP9, above the TBM2 centre-line, there is aslight deviation from the other lines after the cutter-headhad passed the instrument line. This deviation could reflectthe effect of the Central Line tunnels ‘shielding’ the Z-lineSMPs from the surface settlement, although the same effectwas not observed for the passage of TBM1.Incremental surface settlements occurredwithin the cutter-

head distances of �20 m, xf, 35 m for the X- and Y-lineand extensometer reference heads. The trough length factors(ix) derived from the measurements are broadly consistentand range from 12·7 m to 14·8 m, with corresponding troughlength parameters (Kx) being between 0·37 and 0·43. Theseare slightly larger than the values determined from theTBM1 case, indicating slightly longer longitudinal settle-ment troughs. The normalised incremental vertical displace-ments (Δw/Δwmax) directly above the TBM2 cutter-head were38–39%, which is larger than the case for the passage ofTBM1. This implies that a higher proportion of surfaceground settlement occurred in front of the TBM2 cutter-head, compared with the TBM1 case. This may be explainedby the ground ahead of TBM2 being softened by the firsttunnel construction.The normalised incremental transverse settlement troughs

measured after the passage of TBM2 are shown in Fig. 12(b).The southern-half troughs are wider than the northern-halftroughs for all the three monitoring lines. This is most likelyto result from the ground on the southern side being dis-turbed and softened by the passage of TBM1. The effect ofthe passage of TBM1 appears to be greater than the effectof the presence of the existing Central Line tunnels andtherefore dominates the shape of the incremental settlementtroughs. This is reasonable considering the closer proximity,larger diameter and much more recent construction activity.Best-fit Gaussian curves for the incremental vertical

displacements for the X- and Y-line SMPs and mainextensometer line are compared in Figs 13(a)–13(c). Thesouthern-half troughs of incremental settlement (i.e. theside where TBM1 was located) have larger trough widthparameter Ky values than the northern-half troughs. Corre-sponding Ky values are quite consistent (0·42,Ky, 0·47for southern-half and 0·29,Ky, 0·33 for northern-halftroughs), irrespective of whether the monitoring lines are ingreenfield ground (X-line) or near the Central Line tunnels(Y-line), confirming the dominant effect of the first tunnelconstruction (TBM1) on the subsequent ground response. Aswith the X-line SMP results from period 2, incrementalvertical displacements at larger transverse offsets (i.e. furtheraway from the TBM2 centre-line) have a larger downwardmagnitude than would be predicted by the Gaussian curvesfitted through the data points closer to the TBM centre-line.An alternative Gaussian curve that passes through thesedata points, but not those close to the centre-line, is also givenin Fig. 13(a).Similar to the case of the TBM1 passage, the ground

beneath the X-line SMPs had a greater overall volumeloss (1·18%) than that beneath the Y-line SMPs (0·82%)and main extensometer line (0·82%) due to TBM2 passage.Measurements at all three monitoring lines indicate thatlarger incremental volume losses were induced by TBM2T

able

1.Su

mmaryof

surfacevertical

displacements

andsettlementtroughsfortheTBM1passage(westbound

constructio

n,period

2)

Z-lineSM

Ps

Extensometer

reference

head

sY-lineSM

Ps

X-lineSM

Ps

Rem

arks

Longitudinaltrou

ghRelativedisplacementw/w

max

whenx f=0m

24%

36%

30%

30%

x 50%:m

7·9

5·3

7·8

6·4

x 50%

=x f

whenw/w

max=50%

Lon

gitudina

ltrou

ghleng

thfactor,i x:m

12·4

12·4

11·2

12·6

2ix=x 8

6%–x 1

4%x 8

6%=x f

whenw/w

max=86%;

x 14%

=x f

whenw/w

max=14%

Trou

ghleng

thpa

rameter,K

x0·36

0·36

0·32

0·37

Kx=i x/z0

Transversetrough

Maxim

umvertical

displacement,w:m

m�5

·1�5

·8�5

·6�8

·3Locationof

maxim

umdisplacement

ZSM

P5

(y=�0

·2m)

HP20

(y=0·0m)

YSM

P12

(y=2·5m)

XSM

P15

(y=1·05

m)

South

North

South

North

South

North

South

North

Tran

sverse

trou

ghwidth

factor,i

y:m

N/A

13·0

13·6

11·6

13·7

15·1

15·0

Trou

ghwidth

parameter,K

y0·37

0·39

0·34

0·40

0·44

0·44

Ky=i y/z0

Volum

eloss,VL

0·47%

0·49%

0·40%

0·48%

0·78%

0·78%

VLob

tained

from

best-fitGau

ssiancurves

Overallvo

lumeloss,VL:%

0·48%

0·44%

0·78%

Ky/Kx

N/A

1·03

1·08

1·06

1·25

1·19

1·19



compared with TBM1. As the EPBM operation variablessuch as the face pressure, tail grout pressure and tail groutvolume were similar for TBM1 and TBM2 (discussed later),this confirms once again that the higher volume loss inducedby TBM2 results from the ground being softened by the firsttunnel construction.Various characteristics relating to the longitudinal and

transverse incremental vertical displacement profiles meas-ured along the four lines are summarised in Table 2.

Comparison with previous surface settlement case studiesThe responses at Hyde Park are now compared with those

from instrumented sites for: (a) the JLE project at St James’sPark where 4·85 m dia. tunnels were constructed by open-face shield TBMs (Nyren, 1998); and (b) the CTRL projectat Dagenham where 8·16 m dia. tunnels were constructed

by EPBMs (Selemetas, 2005; Standing & Selemetas, 2013).The first site, being also located in central London, sharesa similar geology with the Hyde Park site. The first west-bound tunnel at St James’s Park was constructed at a depth(z0 = 31·0 m) comparable to the Hyde Park Crossrail tunnels(z0 = 34·6 m). At the second site at Dagenham, slightly largerdiameter tunnels than those for Crossrail were constructedusing comparable EPBMs, with applied face and tail groutpressures similar to those of the EPBMs beneath Hyde Park.However, the CTRL tunnels at Dagenham were constructedat a shallower depth (z0 = 18·9 m) with a significantly thinneroverburden and cover of London Clay.The development of the longitudinal profiles of normalised

surface settlements above the centre-line of the first TBMpassing beneath each of the three sites is shown in Fig. 14.When the cutter-head was directly below the monitoringline, about 30% of the total settlement had occurred for the

–0·2

–0·1

0·1

0·2

0·3

0·4

0·5

0·6

0·7

0·8

0·9

1·0

1·1

1·2

–60 –50 –40 –30 –20 –10 0 10 20 30 40 50 60 70

0

Nor

mal

ised

incr

emen

tal v

ertic

al d

ispl

acem

ent,

∆w/∆

wm

ax

–0·2

–0·1

0·1

0

0·2

0·3

0·4

0·5

0·6

0·7

0·8

0·9

1·0

1·1

1·2

–0·2

–0·1

0·1

0

0·2

0·3

0·4

0·5

0·6

0·7

0·8

0·9

1·0

1·1

1·2

Nor

mal

ised

incr

emen

tal v

ertic

al d

ispl

acem

ent,

∆w/∆

wm

ax

Distance of TBM2 cutter-head from instrument, xf: m

–60 –50 –40 –30 –20 –10 0 10 20 30 40Transverse offset distance from TBM2 axis, y: m

(a)

(b)

HP23 (y = 0·0 m)YSMP17 (y = –1·2 m)XSMP19 (y = 0·0 m)ZSMP9 (y = –1·1 m)

Extensometer reference headsY-line SMPsX-line SMPs

Fig. 12. (a) Longitudinal profiles of normalised incremental surface vertical displacements during passage of TBM2 (period 4). (b) Transverseprofiles of normalised incremental surface vertical displacements after passage of TBM2 (period 4)





XSMP measurementGaussian approximation(south)Gaussian approximation(north, X25–X30 excluded)

YSMP measurementGaussian approximation(south)Gaussian approximation(north)

Gaussian approximation(north, X25–X30 included)

Gaussian approximation(north, excluding X25–X30)iy = 11·4 mKy = 0·331VL = 0·98%


Gaussian approximation(north, including X25–X30)iy = 14·9 mKy = 0·435VL = 1·28%

Measurement data in plot:Survey set no. X5112/02/2013 15:40, xf = 35·3 m


SouthNorth Ride North Carriage Drive


North

South North

XS

MP

25X

SM

P26

XS

MP

27X

SM

P28

XS

MP

29X

SM

P30

TBM1axis position

TBM1axis position

0–1–2–3–4–5–6–7

–9–8

–12–13–14

–10–11

Incr

emen

tal v

ertic

al d

ispl

acem

ent,

∆w: m

m

0–1–2–3–4–5–6–7

–9–8

–12–13–14

–10–11

Incr

emen

tal v

ertic

al d

ispl

acem

ent,

∆w: m

m


(a)


(b)

0

0·1

0·2

0·3

0·4

0·5

0·6

0·7

0·8

0·9

1·0

∆w/∆

wm

ax

0

0·1

0·2

0·3

0·4

0·5

0·6

0·7

0·8

0·9

1·0

∆w/∆

wm

ax

Extensometer measurementGaussian approximation(south)Gaussian approximation(north, excluding HP25)





South North

TBM1axis position

Bayswater Road

0–1–2–3–4–5–6–7

–9–8

–12–13–14

–10–11

Incr

emen

tal v

ertic

al d

ispl

acem

ent,

∆w: m

m


(c)

0

0·1

0·2

0·3

0·4

0·5

0·6

0·7

0·8

0·9

1·0

∆w/w

max

Fig. 13. Gaussian approximation of incremental surface vertical displacements measured at the end of TBM2 passage (period 4) for: (a) X-lineSMPs; (b) Y-line SMPs; (c) extensometer reference heads



EPBM tunnelling (Hyde Park and Dagenham), whereasabout 50% of the total settlement had occurred for the open-face shield tunnelling (St James’s Park). This confirms thatwith open-face shield excavation a greater proportion ofsurface settlement originates from the ground movement infront of the shield, which is countered by the provision of facepressure with EPBMs. For EPBMs, greater proportions ofoverall ground movement originate from radial deformationsaround the shield body (especially when it is tapered) and tailvoid closure.The forms of the normalised longitudinal surface settle-

ment profiles for the Hyde Park and St James’s Park sites aresimilar, even though the tunnels were built using differentconstruction methods (i.e. open-face shield as opposedto EPBM). Values of trough length parameter (Kx= ix/z0)determined from fitting cumulative probability functioncurves through these profiles are very close (0·31 and 0·33).However, the shapes of the profiles for Hyde Park andDagenham are very different, despite the tunnels at both sitesbeing constructed by comparable EPBMs. The groundsurface at Dagenham experienced smaller settlement andeven upward displacements (from face pressure and tail-skingrouting) when the TBM shield body was passing, followedby a more rapid settlement as the TBM tail progressedbeyond the monitoring line. This reflects the fact that thetunnel at Dagenham was constructed at a shallower depthwith the axis-level overburden pressure (�340 kPa) roughlyhalf that at Hyde Park (�650 kPa), while at both sites themeasured tail grout pressures were similar (between 150 and200 kPa).The normalised transverse surface settlement profiles for

the three sites are presented in Fig. 15. The three profilesagree well for the range of measurements with w/wmax. 0·4,close to the TBM centre-line position, and can be approxi-mated by one single Gaussian distribution with Ky=0·43.This confirms that the trough width parameters of the im-mediate surface settlement trough are independent of thetunnelling method but dependent mainly on the type ofground (O’Reilly & New, 1982). The deviation at larger offsetdistances of the measured surface settlements from theapproximated Gaussian curve is larger at Hyde Park thanthe other two sites. Currently no definite reason has beenidentified for this but, as discussed earlier, a plausible reasoncould be the presence of the road (North Carriage Drive)where the relatively stiff sub-grade and sub-base layer mayhave influenced the surface ground response.The surface settlement trough width factors (iy) and trough

width parameters (Ky) determined from the three sites areplotted against the tunnel depths (z0) in Figs 16(a) and 16(b),respectively. Data from recent case histories along with thosereported by O’Reilly & New (1982) and Mair & Taylor(1997) are presented in the same figure. Tunnel depths are lessthan 30 m in most of the earlier cases: the Hyde Park andSt James’s Park results contribute deeper tunnel cases to thedatabase. The Ky values for all the deeper tunnels fall withinthe range 0·40,Ky, 0·45. The values of iy and Ky fromHyde Park are marginally smaller than those determinedfrom the O’Reilly &New (1982) relationship, confirming thatdeeper tunnels have slightly narrower surface settlementtroughs than shallower tunnels.In order to investigate potential relationships between

the volume loss and face pressure for the three instrumentedgreenfield sites, the measured volume losses are plottedagainst the ratio of the TBM face pressure to overburdenpressure, as shown in Fig. 17. The limited case history datapresented in the figure suggest a trend of decreasing volumeloss with increasing face pressure ratio for tunnelling inLondon Clay. Other factors such as the geology and tunnel-ling procedure are also likely to influence the volume loss.T

able

2.Su

mmaryof

increm

entalsurface

vertical

displacements

andsettlementtroughsforTBM2passage(eastbound

constructio

n,period

4)

Z-lineSM

Ps

Extensometer

referencehead

sY-lineSM

Ps

X-lineSM

Ps

Rem

arks

Longitudinaltrou

ghRelativeincrem

entaldisplacementΔw/Δwmax

whenx f=0m

35%

39%

38%

38%

x 50%:m

5·7

4·2

3·7

4·2

x 50%

=x f

whenw/w

max=50%

Lon

gitudina

ltrou

ghleng

thfactor,i x:m

16·9

14·8

12·7

13·0

2ix=x 8

6%–x 1

4%x 8

6%=x f

whenw/w

max=86%;

x 14%

=x f

whenw/w

max=14%

Trou

ghleng

thpa

rameter,K

x0·49

0·43

0·37

0·38

Kx=i x/z0

Transversetrough

Maxim

umincrem

entalv

erticaldisplacement,Δw:mm

�9·5

�10·2

�10·3

�13·8

Locationof

maxim

umincrem

entaldisplacement

ZSM

P8

(y=�4

·7m)

HP23

(y=0·0m)

YSM

P17

(y=�1

·2m)

XSM

P19

(y=0·0m)

South

North

South

North

South

North

South

North

Tran

sverse

trou

ghwidth

factor,i

y:m

N/A

15·0

10·1

14·5

10·9

16·0

11·4

Trou

ghwidth

parameter,K

y0·44

0·29

0·42

0·31

0·47

0·33

Ky=i y/z0

Volum

eloss,VL

0·98%

0·66%

0·93%

0·70%

1·38%

0·98%

VLob

tained

from

best-fit

Gau

ssiancurves

Overallvo

lumeloss,VL

0·82%

0·82%

1·18%



In the case of the JLE open-face tunnelling underSt James’s Park, the short-term greenfield volume lossmeasured from surface monitoring after the first tunnelconstruction was found to range from 3·3% to 3·5% south ofthe lake, and from 1·5% to 2·0% north of the lake (Standing& Burland, 2006). It should be noted that different tunnellingprocedures, involving different excavation sequences andlengths of unsupported tunnel heading in front of theshield, were adopted on either side of the lake. Another im-portant contributing factor to the difference in the measuredvolume losses was that the upper 4·5 m of the London Claywas found to have been eroded south of the lake. The two

ranges of volume loss south and north of the lake are shownin Fig. 17 (as an open-face shield was used the face pressureratio is zero).For the CTRL tunnelling under the Dagenham instru-

mented site, Standing & Selemetas (2013) reported a short-term volume loss of 0·2% measured from the surfacemonitoring after the first tunnel construction. The facepressure was about 200 kPa or about 44% of the overburdenpressure at the tunnel axis level. By comparison, for theCrossrail tunnelling under Hyde Park, the short-termgreenfield volume losses measured at the X-line and Y-lineSMPs are 0·78% and 0·44%, respectively. The face pressure

–0·2

–0·1

0·1

0

0·2

0·3

0·4

0·5

0·6

0·7

0·8

0·9

1·0

1·1

1·2

–0·2

–0·1

0·1

0

0·2

0·3

0·4

0·5

0·6

0·7

0·8

0·9

1·0

1·1

1·2

Nor

mal

ised

sur

face

ver

tical

dis

plac

emen

t abo

ve T

BM

axi

s, w

0/w

0,m

ax

Normalised distance of TBM cutter-head from instrument, xf /z0

–1·5 –1·0 –0·5 0 0·5 1·0 1·5 2·0

Hyde Park (YSMP),Crossrail, westbound (TBM1)St James’s Park, JLE, westbound(Nyren, 1998)

St James’s Parkix = 9·8 m = 0·31z0x50 = –0·4 m = –0·01z0

Hyde Park (YSMP11)ix = 11·4 m = 0·33z0x50 = 6·8 m = 0·20z0

Dagenham, CTRL, up-line(Selemetas, 2005)

Project Location TBM typez0 RCrossrailJLECTRL

Hyde ParkSt James’s ParkDagenham

34·6 m31·0 m18·9 m

3·55 m2·43 m4·08 m

EPBMOpen shieldEPBM

z0 = tunnel axis depthR = tunnel external radius

Fig. 14. Longitudinal profiles of normalised surface vertical displacements measured at three instrumented sites in London

0·1

0

0·2

0·3

0·4

0·5

0·6

0·7

0·8

0·9

1·0

1·1

1·2

Nor

mal

ised

sur

face

set

tlem

ent,

w/w

max

–2·0

–1·8

–1·6

–1·4

–1·2

–1·0

–0·8

–0·6

–0·4

–0·2 0

0·2

0·4

0·6

0·8

1·0

1·2

1·4

1·6

1·8

2·0

Normalised transverse offset distance, y/z0

Normalised Gaussian approximation:

w/wmax = exp–(y/z0)2

2(iy /z0)2

= 0·43iyz0

North Carriage Drivein Hyde Park

Crossrail TBM1 WB,Hyde Park (XSMPs)JLE WB,St James's Park (Nyren, 1998)CTRL up-line,Dagenham (Selemetas, 2005)Gaussian approximation

Fig. 15. Transverse profiles of normalised surface vertical displacements measured at three instrumented sites in London



was about 200 kPa or about 30% of the overburden pressureat the tunnel axis level.

HORIZONTAL STRAINS AND DISPLACEMENTSHorizontal movements on X- and Y-lines (periods 2 and 4)The results from measurements using a micrometer stick on

the X- and Y-lines are presented in this section. The micro-meter stick measured changes in distance between pairs ofSMPs, providing average horizontal strains over their 2·5 mspans (Standing et al., 2001). Transverse horizontal displace-ments (v) are calculated by summing the change in spansbetween SMPs along a continuous monitoring line from anassumed stationary point (where v=0). For both lines thishas been taken to be the point directly above the tunnelcentre-line position since the outer points of the lines areconsidered to be within ground influenced by the tunnellingworks. In the case of the X-line, its continuity was interruptedby the North Ride bridle path (between XSMP16 and

XSMP17). As the settlement trough and the transversestrain profile for the greenfield X-line are almost symmetrical,it is assumed that the transverse horizontal displacement atXSMP23 (y=26·3 m) is of the same magnitude as that atXSMP4 (y=�26·4 m) but with an opposite sign. In thisway the displacements for XSMP17 to XSMP22 have beensummed from the assumed displacement at XSMP23, asshown in Fig. 18(a). The maximum displacements either sideare very similar, with 2·3 mm on the southern side (XSMP8,y=�16·4 m) and 2·2 mm on the northern side (XSMP20,y=18·8 m). These maximum displacements are the sameas that along the southern side of the Y-line (2·2 mm atYSMP6: y=�12·5 m), indicating again that the southern halfof the Y-line SMPswas outside any influence from the CentralLine tunnels. Marginally larger maximum horizontal displa-cements of 3·0 mm developed on the northern side (YSMP18to YSMP22: 17·5 m, y, 25·0 m), as shown in Fig. 18(b).A succession of transverse horizontal strain (εy) profiles

measured on the X- and Y-line SMPs as TBM1 progressed is

O'Reilly & New (1982) case histories dataMair & Taylor (1997) additional dataRecent case histories data reported after 1997Crossrail, Hyde Park

O'Reilly & New (1982) case histories dataMair & Taylor (1997) additional dataRecent case histories data reported after 1997Crossrail, Hyde Park

West Ham (Macklin & Field, 1998)

West Ham (Macklin & Field, 1998)

Heathrow T5 array 4 (Jones et al., 2008)

Heathrow T5 array 4 (Jones et al., 2008)

CTRL up-line, Dagenham (Standing & Selemetas, 2013)CTRL down-line, Dagenham (Standing & Selemetas, 2013)

CTRL up-line, Dagenham (Standing & Selemetas, 2013)CTRL down-line, Dagenham (Standing & Selemetas, 2013)

JLE westbound, St James’s Park (Nyren, 1998)

JLE westbound, St James’s Park (Nyren, 1998)

JLE eastbound, St James’s Park(Nyren, 1998)

JLE eastbound, St James’s Park(Nyren, 1998)

O’Reilly & New (1982)iy = 1·1 + 0·43z0

O’Reilly & New (1982)Ky = iy /z0 = 0·43 + 1·1/z0

Crossrail eastbound (TBM2),X-line northern half

Crossrail eastbound (TBM2),X-line northern half

Crossrail eastbound (TBM2), X-line southern half

Crossrail eastbound (TBM2), X-line southern half

Crossrail westbound (TBM1), X-line

Crossrail westbound (TBM1), X-line

iy = 0·3z0 iy = 0·4z0 iy = 0·5z0

Transverse trough width parameter, Ky: m(b)

0

0 5 10Transverse trough width factor, iy: m

(a)

15 20 25 30

0·1 0·2 0·3 0·4 0·5 0·6 0·7 0·8 0·9 1·0

0

10

20

30

40

50

Dep

th fr

om g

roun

d le

vel t

o tu

nnel

axi

s, z

0: m

0

10

20

30

40

50

Dep

th fr

om g

roun

d le

vel t

o tu

nnel

axi

s, z

0: m

Fig. 16. Values of surface settlement (a) trough width factors and (b) trough width parameters plotted against depth from three instrumented sitesin London



shown in Fig. 19. After TBM1 had passed, maximum com-pressive horizontal strains of 250 to 300 με had developedabove the centre-line at both lines. Strains change fromcompressive to tensile at about y=±17·5 m and y=20 m forthe X- and Y-lines, respectively, with maximum tensile strainsof about 130 με and 100 με. The strains at offset of y. 25 mon the X-line (XSMP27 to XSMP30) should be tending tozero, but the measurements are erratic and deemed not to bereliable (Fig. 19(a)).

Profiles of incremental transverse displacements along theX- and Y-line SMPs at the end of periods 2 and 4 are com-pared in Fig. 20(a) where it can be observed that, in general,the incremental displacements recorded at the end of period 4are larger than those at the end of period 2. Despite thescattered nature of the incremental transverse strains shownin Fig. 20(b), the same trend is clearly evident, with greaterstrains developed during period 4 than period 2, for bothtensile and compressive regions.

Point-sink locations determined from measurementsHaving measurements of both vertical and horizontal

surface displacements, the resultant vectors can be plotted toinvestigate the point-sink commonly assumed for determininghorizontal surface displacements. The vectors for both X- andY-lines for periods 2 and 4 (the latter based on incrementaldisplacements) are presented in Fig. 21. Broken lines have beenextrapolated from the vectors to assess whether there is aclearly defined point-sink and its location. It is immediatelyevident that there are well-defined point-sinks for both X- andY-lines, but in quite different locations. Almost all the surfacedisplacement vectors relating to the greenfield X-line aredirected towards a clear point at the tunnel crown position forboth periods (Figs 21(a) and 21(c)). The point-sink for thepassage of TBM2 is located slightly southwards, towards thepreviously constructed westbound tunnel. The extrapolatedlines for the three southernmost points shown are directed atmuch steeper angles, indicating greater components of verticaldisplacement than the other points. This can be attributed tothe ground disturbance from the westbound tunnel construc-tion and is corroborated by the wider southern-half settlementtrough width shown in Fig. 13(a).

Clearly defined point-sinks are evident from most of theextrapolated vectors relating to the Y-line, but in this casethey are located 2·5D to 2·0D above the tunnel centre-lines(Figs 21(b) and 21(d)). In comparing the response from thetwo lines the location of the resulting point-sinks can bedirectly related to: (a) the vertical displacements, which weresignificantly larger on the X-line (compare Figs 11(a) and13(a) with Figs 11(b) and 13(b)) causing a downwardsshift of the point-sink; and (b) the horizontal displacements,which were greater on the Y-line (compare lines in Fig. 20(a))causing an upwards shift. In the case of the Y-line, for thepassage of TBM1, there are markedly greater horizontalcomponents of displacement at the northern end of the line,with them increasing towards the vicinity of the CentralLine tunnels. This trend reverses for the passage of TBM2with greater and increasing horizontal components to thesouthern end of the Y-line in the vicinity of where thewestbound tunnel was constructed (although the southern-most points are beyond the centre-line of the tunnel).For both X- and Y-lines the point-sink locations are above

the centre-line of the tunnels, the position commonly adoptedwhen predicting surface horizontal displacements. Using thisassumption would lead to an under-estimation of horizontaldisplacements. Reasons for the difference in point-sinklocations at the two lines cannot be given definitively, andare probably related to a combination of the two factors (a)and (b) given above. In this case study the magnitudes ofhorizontal displacement are very small (,5 mm) and rela-tively small differences in their values may have a significanteffect on the point-sink location. However, there is in factgood confidence in the measurements, as discussed in the nextsection where comparisons are made with optical fibremeasurements. The reason is more likely to be related to themeasured settlements (and volume losses) being smaller thanthose at the X-line (because of the presence of the Central Linetunnels). If the vertical components of the resultant displace-ment vectors relating to the Y-line (shown in Figs 21(b)and 21(d)) were increased, the position of the point-sink wouldbe deeper, but still above the axis of the tunnels. It is worthnoting that Nyren (1998) also observed well-defined point-sink locations about 2D above the axis of the tunnels inSt James’s Park for the JLE project, where the groundstratigraphy and conditions are similar to those in Hyde Park.

Comparison of measurements with micrometer stick andoptical fibre sensorsA set of optical fibre sensor cables was installed in

a shallow trench starting from and transverse to thewestbound centre-line and running parallel to the X-lineSMPs at an eastwards offset of 34 m: details are reportedby Hauswirth et al. (2014). It was thus possible to measure,with a much greater spatial resolution (1 cm) and precision(2 με), the surface horizontal ground strains and to generatea continuous transverse profile. As shown in Fig. 22(a),the results from the optical fibre sensors compare well withthe micrometer stick measurements on the X-line SMPsfor the passage of TBM1, with the point where strainschange from compression to tension being the same, despitethe lower accuracy of the micrometer stick measurements.Profiles of transverse horizontal displacements derived fromthe measured strains are shown in Fig. 22(b). For the opticalfibre sensors, the displacements are derived by integratingthe strain profile from the far end (y=�60 m) where zerodisplacement is assumed. Within the 25-m distance from thetunnel centre-line, the horizontal displacements derivedby both measurement methods agree very well, with verysimilar profile shapes and discrepancy in magnitude less than0·5 mm (thus also giving confidence in the assumptions

St James’s Park volume loss after Standing & Burland (2006)Dagenham volume loss after Standing & Selemetas (2013)

St James’s Park, south of lakeJLE, open-shield

St James’s Park, north of lakeJLE, open-shield

Hyde Park, X-lineCrossrail, EPBM

Hyde Park, Y-lineCrossrail, EPBM Dagenham

CTRL,EPBM

Ratio of face pressure/overburden pressure at tunnel axis

Vol

ume

loss

, VL:

%4·0

3·5

3·0

2·5

2·0

1·5

1·0

0·5

0

0 0·1 0·2 0·3 0·4 0·5

Fig. 17. Comparison of measured greenfield volume losses and facepressure ratios at three instrumented sites of tunnelling in LondonClay



discussed earlier for determining the horizontal displace-ments along the X-line).

CORRELATION BETWEEN SURFACE SETTLEMENTAND EPBM OPERATION VARIABLESIt is widely accepted that the EPBM tunnelling technique

is able to reduce tunnelling-induced ground movementsby controlling operation variables such as the face pressureand tail grout volume and pressure. Construction of thetwo tunnels beneath Hyde Park provides an opportunity toinvestigate correlations between measured surface settlementvolume losses and EPBM operation variables. In addition tothe X- and Y-line SMPs monitored by the Imperial Collegeteam, ten lines of SMPs (in the form of survey nails onpavements) were installed along the tunnel alignments withinHyde Park and monitored by the Crossrail tunnel contractorBFK (BAM Nuttall, Ferrovial Agroman and KierConstruction). The locations of the monitoring lines alongthe tunnel alignments are shown with the associated volumelosses determined in Fig. 23(a). The start and end chainages

relate to the boundaries of Hyde Park, namely fromBayswater Road (ch. 2100 m) to Park Lane (ch. 3000 m).Variations in selected EPBM operation variables as eachTBM passed beneath Hyde Park are shown in Figs 23(b)–23(e). The data points shown in the figure are the rollingaverage values over ten lining rings, or 16 m lengths of tunneldrive. The volume losses derived from the surface settlementmeasurements range from 0·4% to 0·9% for the passage ofTBM1 and 0·6% to 1·6% for TBM2. In all cases the volumelosses induced by TBM2 are greater than those from TBM1,attributed to ground softening after the construction of thefirst tunnel.Average face pressures for both TBM1 and TBM2 are

about 200 kPa, with a variation of ±50 kPa over their 1 kmpassages beneath Hyde Park, as shown in Fig. 23(b), whileaverage tail grout pressures are about 100 kPa for TBM1and 200 kPa for TBM2 (Fig. 23(c)). These pressures aresignificantly smaller than the in situ overburden pressure(�650 kPa) and variations from the mean values are rela-tively minor. As a consequence of this, combined with thesmall magnitudes of volume losses determined, no clear

3

2

1

0

–1

–2

–3

–4

Tran

sver

se h

oriz

onta

l dis

plac

emen

t, v:

mm

3

2

1

0

–1

–2

–3

–4

Tran

sver

se h

oriz

onta

l dis

plac

emen

t, v:

mm

27/11/2012 23:10, xf = –36·7 m28/11/2012 18:00, xf = –14·1 m29/11/2012 09:15, xf = –0·8 m29/11/2012 18:00, xf = 10·6 m30/11/2012 05:50, xf = 18·5 m30/11/2012 11:30, xf = 24·4 m30/11/2012 16:40, xf = 32·3 m01/12/2012 11:20, xf = 52·7 m

Displacement is assumed zero at y = 0 mfrom which displacements of XSMP1 to XSMP16 are summed

Displacement of XSMP23 is assumed to havesame magnitude as XSMP4 but opposite sign.Displacements for XSMP17 to XSMP22are summed from XSMP23

Transverse offset distance from TBM1, y : m–40 –30 –20 –10 0 10 20 30

Transverse offset distance from TBM1, y : m

(a)

(b)

–20 –15 –5–10 5 10 150 20 3025 35

20/11/2012 16:20, xf , = –39·6 m21/11/2102 15:45, xf , = –8·6 m23/11/2012 02:10, xf , = –1·7 m23/11/2012 15:45, xf , = 15·4 m24/11/2102 06:15, xf , = 33·7 m26/11/2012 11:35, xf , = 62·1 m

Note: assume v = 0 mm at y = 0 m

Y5

Y6

Y7

Y8

Y9

Y10

Y11

Y12

A

Y13

A

Y14

Y15

Y16

Y17

Y18

Y19

Y21

Y22

Y23

Y24

X5

X4

X3

X2

X1

X6

X7

X8

X9

X10

A

X11

X12

X13

X14

X15

X16

X17

X18

X19

X21

X20

X22

X23

3

2

1

0

–1

–2

–3

–4

3

2

1

–1

–2

–3

–4

0

Fig. 18. Transverse profiles of transverse horizontal displacements from micrometer stick measurements during passage of TBM1 (period 2) at:(a) X-line SMPs; (b) Y-line SMPs



relationships are evident between volume loss and facepressure or tail grout pressure.

Variations in the average weight of excavated material,measured on the belt conveyor, are shown in Fig. 23(d)with values given in tonnes per shield advance of one liningring width (i.e. 1·6 m). Although the excavated soil wasmixed with soil-conditioning fluid/foam, which would havechanged its bulk density, the weights give a useful indicationof the amount of soil excavated. The weight of excavatedmaterials was roughly constant for both tunnel drivesbeneath Hyde Park, with weights varying within a narrowrange of 125–135 t/ring. Both values are larger than thetheoretical weight (about 122·5 t/ring) of soil excavated by a7·10 m dia. cutter-head assuming a bulk unit weight of19 kN/m3 for the London Clay spoil (shown as a broken linein the figure). Apart from the conditioning fluid/foam added,the weight in excess of the theoretical value is likely to reflectsome degree of ‘over-excavation’ by the cutter-head as aconsequence of inward ground movements towards the faceand cutter-head periphery. Given that the dimensions of theTBM shields for both tunnels were identical (and hence so

was the weight of theoretical excavated materials), it isevident from the figure that the amount of ‘over-excavation’by the TBM2 cutter-head was always larger than that ofTBM1. This corroborates with the larger volume lossesmeasured at the ground surface when TBM2 passed beneathHyde Park (suggesting greater inward ground movementstowards the tunnel).Tail grout volumes injected per advance of one lining ring

are shown in Fig. 23(e). This grout was injected to minimisefurther ground movement into the annular void between cutdiameter of the tunnel excavation (7·1 m) and the outerdiameter of the newly erected tunnel lining ring (6·8 m).The theoretical volume of the annular void is 5·24 m3/ringadvance (1·6 m). It can be seen from the figure that theapplied tail grout volumes were mostly lower than this value,probably because of inward ground movement, but withgreater volumes injected from TBM2 because of the higherapplied grout pressures (Fig. 23(c)). An assessment of thedifferent components of volume loss (e.g. at the face, shieldbody, tail skin) is given in the companion paper where resultsfrom the subsurface instrumentation are discussed.

200

100

0

–100

–200

–300

–400

–40 –30 –20 –10 0 10 20Transverse offset distance from TBM1, y: m

30 40 50 60

Aver

age

horiz

onta

l stra

in, ε

y: µε

(+ve

= te

nsile

)

200

100

–100

–200

–300

–400

0

200

100

0

–100

–200

–300

–400

–40 –30 –20 –10 0 10 20Transverse offset distance from TBM1, y: m

(a)

(b)

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age

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in, ε

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(+ve

= te

nsile

)

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27/11/2012 23:10, xf = –36·7 m28/11/2012 18:00, xf = –14·1 m29/11/2012 09:15, xf = –0·8 m29/11/2012 18:00, xf = 10·6 m30/11/2012 05:50, xf = 18·5 m30/11/2012 11:30, xf = 24·4 m30/11/2012 16:40, xf = 32·3 m01/12/2012 11:20, xf = 52·7 m

20/11/2012 16:20, xf , = –39·6 m

21/11/2102 15:45, xf , = –8·6 m

23/11/2012 02:10, xf , = –1·7 m

23/11/2012 15:45, xf , = 15·4 m

24/11/2102 06:15, xf , = 33·7 m

26/11/2012 11:35, xf , = 62·1 m

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Fig. 19. Transverse profiles of average transverse horizontal strains from micrometer stick measurements during passage of TBM1 (period 2) at:(a) X-line SMPs; (b) Y-line SMPs



SUMMARYAND CONCLUSIONSVertical and horizontal surface ground displacements

measured (by precise levelling and micrometer stick) at aninstrumented site in Hyde Park during the passage of twoEPBMs at 34·5 mbgl have been analysed and discussed.Three locations were monitored, two in the close proximity ofthe existing Central Line tunnels and the other in a greenfieldcondition. Measurements of horizontal displacements wereconfirmed by independent monitoring using optical fibretechnology. Robotic total station measurements were alsotaken during the tunnel construction but had a reducedaccuracy and so are not reported.Theobserved settlement troughs canbe reasonablymodelled

using the commonly adopted empirical Gaussian formulation.The transverse surface settlement trough width parameter (Ky)determined for the greenfield ground is smaller than valuespreviously reported for case histories for similar ground con-ditions but involving tunnels shallower than 30 mbgl. TheHyde Park data, together with the St James’s Park (JLE) data,

indicate that, for tunnels with axis levels deeper than 30 mbgl,Ky falls within a range 0·40,Ky, 0·45.Asymmetry of surface settlement troughs is evident in cases

where the ground has been softened by previous tunnel con-struction, that is, close to the Central Line tunnels or after thefirst (westbound) Crossrail tunnel was constructed. Widerhalf-troughs develop on the side closer to pre-constructedtunnels. The effect was greater for the larger 7·1 m dia.Crossrail tunnel (compared with the 3·8 m dia. Central Linetunnels) which, being more recently constructed, also meantthat little subsequent consolidation of the ground (and hencepartial re-strengthening of it) would have taken place.In general, volume losses measured at the main lines of the

SMPs in the instrumented site were low, being less than 0·8%and 1·4% for the first and second tunnel drives respectively,higher values being associated again with ground softeningfrom the first tunnel construction. However, smaller volumelosses were recorded in the vicinity of the existing CentralLine tunnels, compared with the greenfield location,

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–15 –10 –5 0

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0–10–20 10 20 30 40 50 60–30–40–50–60

5 10 15 20 25 30

Incr

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X-line, xf = 32·3 m (end of period 2)Y-line, xf = 33·7 m (end of period 2)X-line, xf = 34·9 m (end of period 4)Y-line, xf = 34·8 m (end of period 4)

X-line, xf = 32·3 m (end of period 2)Y-line, xf = 33·7 m (end of period 2)X-line, xf = 34·9 m (end of period 4)Y-line, xf = 34·8 m (end of period 4)

Note: the first micrometer stick measurementin period 4 for X-line was taken when x = –5·1 mas the base reference for incremental strains

Fig. 20. Transverse profiles of (a) incremental transverse horizontal displacements and (b) average incremental transverse horizontal strains frommicrometer stick measurements at the end of periods 2 and 4



0

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–30 –20 –10 0Transverse distance from TBM2 centre-line, y: m

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Note:Precise levelling measurement at xf = 31·8 mMicrometer stick measurement at xf = 32·3 m

Note: Precise levelling measurement at xf = 34·3 mMicrometer stick measurement at xf = 33·7 m

Note: Precise levelling measurement at xf = 35·3 mMicrometer stick measurement at xf = 34·8 m

WB tunnel(TBM1)

WB tunnel(TBM1)

WB tunnel(TBM1)

WB tunnel(TBM1)

EB tunnel(TBM2)

EB tunnel(TBM2)

Scale10 mm

Scale10 mm

Scale10 mm

Scale10 mm

Note:The first micrometer stick measurementin period 4 was taken when xf = –5·1 mas the base reference for incremental horizontaldisplacements, which implies the actual horizontaldisplacement magnitudes could be slighter greater.Precise levelling measurement at xf = 30·8 mMicrometer stick measurement at xf = 31·0 m

Fig. 21. Surface displacement vectors after passage of TBM1 measured at: (a) X-line SMPs; (b) Y-line SMPs. Surface incremental displacement vectors after passage of TBM2 measured at: (c) X-line SMPs;(d) Y-line SMPs

WAN,ST

ANDIN

G,POTTSAND

BURLAND

442


suggesting that their presence inhibited the development ofground movements.Surface horizontal displacements, determined from

micrometer stick measurements, were of the same formas those determined using a ‘point-sink’ assumption inconjunction with the Gaussian formulation. Resultant dis-placement vectors derived from the field measurements weredirected to well-defined point-sinks located at distances of0·5D to 2·5D above the tunnel axis level. The lower location (atroughly the tunnel crown) was observed for the greenfieldcondition – reasons for the differences are not clear.EPBM operation variables were studied to investigate

possible correlations with the surface ground response at theresearch site and also for another ten sections monitored byprecise levelling within Hyde Park. Generally, variations in

face or tail grout pressure were relatively small and this,in conjunction with the small magnitudes of volume lossdetermined, means correlations between them could not bereadily identified.Greater masses of excavated spoil were measured within

the TBM2 shield compared with TBM1, suggesting a greaterdegree of ‘over-excavation’, again because of ground soft-ening from the first tunnel construction (corroborated withthe measured values of volume loss).

ACKNOWLEDGEMENTSThe authors wish to acknowledge the Engineering

and Physical Sciences Research Council (EPSRC)(EP/G063486/1) and Crossrail who were the major sponsors

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Optical fibre measurement data are from Hauswirth et al. (2014)

Optical fibre sensor (trench), xf = 31·8 mMicrometer stick (X-line SMPs), xf = 32·3 m

Optical fibre measurement data are from Hauswirth et al. (2014)

Optical fibre sensor (trench), xf = 31·8 mMicrometer stick (X-line SMPs), xf = 32·3 m

–60 –50 –40 –30

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–60 –50 –40 –30 –20 –10 0Transverse offset distance of TBM1 axis, y: m

Fig. 22. Comparison of transverse profiles of (a) transverse horizontal strains and (b) transverse horizontal displacements measured by opticalfibre sensors and micrometer stick after passage of TBM1 (end of period 2)



for this field component of the research project. Many thanksare due to the Imperial College research team, especiallythe Imperial College technician Mr Alan Bolsher, andthose others who helped take the field measurementsduring the 24-h surveying periods. A thoughtful review ofthe instrumentation plan by Mr John Dunnicliff is alsogreatly appreciated. The support provided by the Royal

Parks, London Underground Limited and WestminsterCouncil during the installation work is gratefully acknowl-edged. The authors are also grateful to the main joint ven-ture contractors BFK, in particular Mr Ivor Thomas, forproviding data and information relating to the TBMs, theiroperational variables and the settlement monitoring dataacross Hyde Park.

1·81·61·41·21·00·8

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Overburden pressure at tunnel axis level

Overburden pressure at tunnel axis level

Westbound construction (TBM1)Eastbound construction (TBM2)

Theoretical weight or volume of excavated material(assuming excavation diameter = 7·10 m, andspoil bulk unit weight = 19 kN/m3)

Theoretical volume ofshield tapering and tail void closure

Theoretical volume oftail void closure only

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Fig. 23. Variation of measured surface volume losses and recorded EPBM operation variables with TBM chainage: (a) measured volume loss atground surface; (b) measured face pressure behind cutter-head; (c) applied tail grout pressure; (d) weight of excavated materials on belt conveyor;(e) tail grout volume injected



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Documents

Measured short-term ground surface response to EPBM ......EPBM tunnelling in London Clay M. S. P. WAN , J. R. STANDING†,D.M.POTTS† andJ.B.BURLAND† Earth-pressure-balance machines