Tunnelling and Pipe Jacking Techniques

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The Hong Kong Institution of Engineers transaatons, Vol 16, No 2, pp 16-27

T unnellin g and P ipejack ing T echn iques forT rench less In sta lla tion o f D ra inage P ipe lin esHong Kong, a city on hilly natural terrain, with a total area of 1,000 square kilometres, hasa population of 7million Its developments mainly concentrate in 20% of the flat land in thecoastal area, mostly formed by reclamation from the sea. The rapid economic growth in the last20 years demands new infrastructure and upgrading of existing facntues. The crowded spaghetti-like complex of existing uti li ties and services underground in the l imited road space, and thebusy traffic, make such upgrading and construction of new features, by the conventional open-trench method, difficult The use of tunnell ing and pipejacking techniques could however resolvemost of the problems associated therewith, such as disturbance to traffic, major diversions ofexisting util ities, earth moving, and effect of inclement weati ier. This would also minimise publiccomplaints due to inconvenience and loss of business in the nearby shops as temporary trafficmanagement schemes are only required at the jacking and receiving shaft iocations. This paperdiscussesthe various types of tunnelling and pipejacking techniques adopted in Hong Kongfor drainage pipeline construction under different site constraints and ground condit ions, theirperformance, the problems encountered and the recommendations made.Keywords: Shaft Construction, Hand-dug Tunnels, Heading Construction, Earth Pressure

Balance Method, Slurry Pressure Balance Method, Tunnel Boring Machine,Ground Settlement, Control of Tunnel Alignment, Rescue Operation

IntroductionThe roads in the urban areas of Hong Kong are generally congested withunderground ut ili ties and services of di fferent types and sizes, at differentdepths. To meet the development demand, new features are constantlyadded and existing installations are upgraded over the years. This formsa spaghetti -l ike complex network, causing problem to accommodate morenew installations due to lack of sufficient space. Diversion of existingutil it ies and services to give room for such installations is diff icult as otherlocations in the vicinity may also be crowded with utilities and services. Inthe past, the installat ions were commonly carried out by the conventionalopen-trench method, requiring the implementation of temporary trafficmanagement schemes (TTMSs). These TTMSs are usually limited to nomore than 20 - 30 m in length in each stage, depending on whetherexisting buildings are located adjacent to the works site, due to therequirement of allowing space for access of fi re engines under emergencysituations, and other factors, such as access to shops or premises. Thislimited length of TTMSs could only allow limited utility diversion, andtherefore may not effectively resolve the problem. At some locations,the underground is congested with existing utilities and services inlayers, render ing such new Installations by the conventional open-trenchmethod impossible. Tunnelling and pipejacking can however minimisesuch effects as road openings are only restricted to the shaft locations,ie jacking shaft and receiving shaft between a pipeline, which can beselected to avoid conflicting with traffic and major utilities or minimisetheir diversions. Sometimes, tunnelling and pipejacking techniques areadopted solely to minimise traffic disruption, in extremely busy areas,or in response to public requests or complaints on the same concern,or even to avoid the felling of valuable trees.Pipejacking is a technique of pipeline installation, by hydraulically pushinga pipe string, effected either mechanically by a tunnel boring machine(TBM) or manually for excavation, from a jacking shaft to a receivingshaft. Jacking pipes are then added one after another to the end of thepipe string as the preceding pipe/ TBM advances. The excavated mater ia lsare then transported to the jacking shaft through a trolley system, forhand-dug tunnels and earth pressure balance (EPB) TBMs, and then

m

Wilson W SMOKMeinhardt (C8S) Ltd

KWMAKDrainage Services Department,Government of the HKSAR

lifted up to ground surface, or by a slurry discharge pipeline for slurryoperated TBMs. This procedure is repeated until the pipe string reachesthe receiving shaft [1[.The history of using pipejacking techniques for constructing drainagepipelines in Hong Kong is short, with the track record in 1989 that370 m of sewers, in diameter of 1,350 mm, located 6 - 14 m belowground, were constructed by TBMs under 5 drives, with a length rangingfrom 40 to 80 m, passing beneath major roads [2[. Since then, the scaleof pipejacking works has increased significantly, with the deployment ofdifferent types of TBMs operating in different modes, to account for theground conditions likely to be encountered, and also the introductionof hand-dug tunnels for constructing pipel ines crossing old seawal ls andcongested ut il ity zones, or ground suscept ible to art ificial obstruct ions.In some projects, some of the works by open-trench may need to bechanged to tunnelling and pipejacking techniques during the constructionstage, to suit constraints of traff ic and exist ing util it ies, and such is usuallycarried out by means of heading construction due to its simple setupand fast operation. Up to 2002, more than 14 km long pipelines, witha diameter range of about 450 - 3,000 mm, using such techniques,have been completed by the Drainage Services Department (DSD) ofthe Government of the HKSAR [3[.Between 1996 and 2006, some of the notable projects employingtunnelling and pipejacking techniques were the West Kowloon ReclamationHinterland Drainage Package 2 (Northern Portion) (with a length of morethan 1 km), the Central, Western and Wan Chai West Trunk Sewers (witha length of 6 km), the Aberdeen, Ap Lei Chau and Pok Fu Lam Sewerage- Stage 1B (with a length of 2 km), and the Wan Chai East and NorthPoint Sewerage - Trunk Sewers (with a length of 4 km), under differentgeological condit ions and depths.The Wan Chai East and North Point Sewerage - Trunk Sewers was the firstDSD project using slurry operated TBMs to construct curved sewers witha minimum radius of 320 m, and a S-shape sewer (404 m long), with acombination of straight and two curved sections (of radius 500 m) andpassing through an intermediate shaft and launching into the receivingshaft, both with the completion of the permanent shaft in advance [4[.

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Some other projects also use pipejacking or heading techniques but ina much smaller scale.

Geological ConditionsThe geological conditions in Hong Kong soils are highly variable in ashort length. The narrow strip of land along the seafront, adjacent to verysteep slopes, has been formed by cut and fill techniques in the terrainover the years, and generally consists of a thin layer of fill underlainby colluvium and completely to highly weathered granite near the hillsto a thick layer of fill, with different contents of boulders at differentdepths, overlying marine deposits, alluvium and completely to highlyweathered granite towards the sea. Depth to bedrock ranges from 1 to2 m to 10 to 30 m below ground in a downslope direction. There is awide range in particle size between materials in different areas. Verylarge boulders or corestones could exist at high levels of the ground.Metallic objects, anchors and cannons may also be expected in the oldfilling areas and in marine deposits.Groundwater levels tend to be high, generally 2.5 to 3.5 m below groundlevel, and tidal response affects much of the urban area.

Shaft ConstructionIn urban areas, due to constraints of traffic and existing utilities, some ofthe jacking and receiving shafts have to be constructed at side streets.They are generally constructed by sheet-piles in homogeneous clayeyto sandy ground (Fig 1) and pipe-piles in mixed ground conditions(Fig 2). Vibration and settlement monitoring are carried out during thepiling operation to avoid causing damage to adjacent utilities, services,roads and structures. More expensive pipe-piles are sometimes used inhard ground to minimise noise and vibrat ion. For sheet-pi les, to minimisevibration, boulder obstructions at intermediate depths are pre-boredbefore commencement of pile driving. At some locations, due to thepresence of hard materials at different depths, it would be difficult tomaintain the verticality of the sheet-piles during driving, and the toeof the sheet-piles would easily be damaged, causing the problem ofinterlocking with adjacent piles, often with insuff icient embedment length,and necessitating toe grouting as a remedial measure.Rectangular shaft is usually constructed because it is more easily tobe modified to accommodate existing utilities and services. However,at locations where these features are absent, circular shaft is used dueto the smaller member size of temporary works required. For a 1,800mm diameter TBM, the typical size of a shaft is generally 8 m x 8 mor 8 m in diameter. This generally would necessitate the occupation ofmore than two traffic lanes. As such, the construction has to be carriedout in stages, with one portion completed and decked-over before thecommencement of another, such that disruption to traffic could be

Figure 1- Temporary Shaft Formed by Sheet-piles

Figure 2 - Temporary Shaft Formed by Pipe-piles

minimised. At traffic sensitive locations, the receiving shaft could betemporar ily decked over after construction and re-opened to allow traf ficflow until the pipejacking drive is completed and the TBM can be liftedup to ground surface during traffic non-peak hours.In areas of congested utilities and services, it is usually difficult, if notimpossible, to have a clear shaft, by virtue of the long time requiredfor utilities diversion and the limited space. Therefore, unless theyobstruct the pipejacking operation such as lowering of TBM/ jackingpipes or removal of excavated material, these utilities and services aretemporarily supported inside the shaft, by steel frames. This, however,would create windows in the temporary works, entailing the erection ofsteel lagging plates as support and to prevent ingress of groundwater(Fig 3). Sometimes, the shape and size of a shaft need to be tailor-madeto suit ut ili ty constraint , resul ting in the use of a combination of sheetpi lesand pipe-piles to overcome the problem. In some cases, raking piles

Figure 3 - Steel Lagging Plates Provided in the Window of TemporaryWorks

have to be constructed to avoid interference with existing utilities andservices. The use of a concrete wall cast against the pipe-piles is alwaysrequired to ensure the stability of the shaft if watermains or drainagepipelines are in their close proximity as their bursting/ breakage couldsignificantly disturb the ground.For deep shaft, grouting is always required in the perimeter to ensurewatertightness, before excavation is to commence. After the shaft has beenformed, a thrust wal l and a launching! receiving eye are then constructedto allow the pipejacking operation. For multi-direction driving, a circularthrust wall can provide better orientation and transfer of loading.

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Depending on the size and depth of the shaft, and the ground conditionsencountered, each shallow shaft (less than 8 m in depth) generallyrequires 6 to 8 weeks for completion from piling to excavation. Theconstruction for deep shaft (up to a depth of 22 m) would however takea longer time, from 12 to 18 weeks, due to the high variation in groundcondit ions, particularly the rock content.These shafts are later used for construction of permanent shafts for futuremaintenance. As most of the shaft locations have different degree ofutility constraints, the location, size and shape of access and desiltingopenings of each permanent shaft may need to be tailor-made to suitthe site condition.

Modes of Tunnelling OperationsThree modes of operations are commonly adopted for pipejackingworks in Hong Kong. They are hand-dug tunnel, earth pressure balanceTBM and slurry pressure balance TBM. The contractor will, based onthe results of site investigation conducted in the design stage by theclient, assess the risk and carry out further investigation if doubt existsand select the most appropriate mode for the ground conditions likelyto be encountered.

Hand-dug TunnelHand-dug tunnel, formed by precast reinforced concrete segments astemporary lining and connected each other with a bolting system and arubber gasket at the joint to prevent ingress of water, can be constructedunder ei ther a free-air or a compressed-air environment.Free-air tunnel (Figs 4 and 5) is sui table for shal low pipel ines crossing oldseawal ls, artif icial obstruct ions and road junctions, usually less than 50 min length for a drive. Prior to tunnelling, the alignment of the pipeline isful ly stabil ised by grouting to ensure stabili ty. The excavat ion is effectedmanually by pneumatic tools or mechanically by a mini backhoe insidethe handshield (ie a protective tube in front of the pipeline to allowmanual excavation by workers), if the diameter of the tunnel permits(usually 1,800 mm or above). The excavated materials are transportedto the jacking shaft by a trolley system and then lifted up to groundsurface. The handshield is advanced by extending the hydraulic jacksinstalled with it, against the concrete segments erected at the rear asreaction. New segments are then added after the retraction of hydraulicjacks. The overcut between the ground and the segments is immediatelyf il led up with grout to prevent settlement. This procedure is repeated untilthe tunnel reaches the receiving shaft. Upon completion of the tunnelconstruction, a permanent pipeline is pushed inside from the jackingshaft and its annulus is filled up with grouting materials equivalent tothe strength of the overlying ground.Compressed-air tunnel (Figs 6 to 8) is applicable to grounds wheregroundwater table is high. Depending on depth, an air pressure of 1 to

Figure 4 - Launching of Hand Shield for Free Air Hand-dug Tunnelm

2 bars is required to balance the water head in the excavation face andbe maintained inside the tunnel round the clock to avoid flooding whichmay in turn affect tunnel stability. To ensure constant supply of air, astandby compressor is provided for emergency situations. Pressurisationand depressurisation is required in the air-lock installed on top of an airdeck erected in the jacking shaft, for personnel entering and leaving thetunnel respectively. A medical lock needs to be provided at the shaftlocation when the applied compressed-air pressure exceeds 1 bar. Therehave been some cases that air was found leaking through the porousground during tunnel excavation, resul ting in inf low of groundwater. Thisentailed horizontal grouting from inside the handshield to stabilise theground before further excavation could be proceeded with.The rate of excavation is generally 1 - 2 m per day for free-air tunneland 0.5 - 1 m per day for compressed-air tunnel, depending on theground conditions.

Heading ConstructionHeading construction is a simple form of hand-dug tunnel, and is widelyused to construct short pipelines, usually in the range of 10 - 30 min length, crossing road junctions or locations of congested existingutilities and services, in shallow depth, due to its easy setup and thusthe relatively low cost. The tunnel size could generally vary from 1.5to 2.5 m in diameter, depending on the size of pipeline to be installed.To tackle different site constraints and ground conditions, the methodof construction in each tunnel could vary, and the following cases aretypical examples.To suit the limited space in the jacking shaft which is a commonphenomenon in urban areas as constrained by exist ing uti li ties, the shieldhead can be tai lor-made by several short sect ions and connected together

Figure 5- Excavation in FreeAir Hand-dug Tunnel

Figure 6- General View of Compressed Air Setup in Jacking Shaft



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one by one by welding inside the jacking shaft before launching. Thisis then followed by steel sleeve pipes or precast concrete pipes whichare pushed forward into ground by a hydraulic system in the jackingshaft (Fig 9), with lubricant constantly injected under a pressure slightlyhigher than the overburden pressure, from the grout holes installed inthe pipes to minimise soil friction, and to avoid close-up of the overcut,causing ground sett lement, during the jacking operation.To determine the ground condition, probing is carried out in every2 - 3 m ahead of excavation. The ingress of water, if any, is controlledby the injection of grout, by means of horizontal and inclined holesfrom the shield head, prior to excavation. If instability is found in theworking face, steel shutter, in the form of plankings, needs to be erectedat the front of the shield (Fig 10), and the working personnel evacuateduntil the ground treatment is completed, by specialised working gangs,After pushing the sleeve pipeline into the receiving shaft, the annulus,formed by overcut, is filled up with grout, with a strength equivalent tothe overburden pressure, to avoid ground settlement.At narrow shaft locations where lowering the sleeve pipes is a problem,the tunnel lining could be formed by steel segments connected to eachother by welding (Fig 11).The advancement of the shield head iseffected by extending the hydraulicjacks installed with it against the steel segments erected at its rear(Fig 12). The overcut outside the segments is immediately filled up bygrout, through the holes provided at the crown and the axis at the twosides, after the completion of each ring in the tunnel. This method isgenerally applicable to the construction of small size of pipelines.

Figure 7 - Excavation in Compressed Air Hand-dug Tunnel

Figure 8- General View of a Completed Tunnel

Figure 9 - Jacking of Steel Sleeve Pipefor Heading Construction

Figure 10 - Steel Planking Erected in Excavation Face to Prevent Ingressof Groundwater

Figure 11 - Appearance of a Tunnel Formed by Steel Segments

For crossing major roads where underground boulder obstructions areexpected, the temporary works in the tunnel, formed by dri ll ing hor izontalpipe-pi les from one shaft to another, could effect ively penetrate throughsuch obstructions to act as temporary lining (Fig 13), thus ensuring thestability during excavation. Depending on ground and groundwatermHE HKIE TRANSACTIONS Volume 16 Number 2


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Figure 12 - Extension of Hydraulic lacks in Lead Pipefor Advancement

Figure 13 - Tunnel Formed by Horizontal Pipe-pilescondit ions, grouting may be required to stabilise the ground by inject ion,through the slot holes provided in the pipe-piles, before excavationtakes places. The permanent pipeline is then pushed into the tunnelafter excavation (Fig 14), and its annulus is filled up with lean concreteor grouting materials, as appropriate. This method is usually suitable forconstructing relatively large size of pipeline in deeper ground.For tunnelling in filling ground with low rock content in shallow depth,the temporary works could be in the form of a portal frame, constructedby driving several short sections of steel plankings or channels, in thedirection of excavation, ahead of excavation, and then supporting themby steel members after excavation (Fig 15). This method is howeverunsuitable for water bear ing ground due to the presence of gaps betweenthe plankings/ channels that the ingress of water could pose stabilityproblem in the tunnel, particularly during dewatering.The average production rate for heading construction is generally1 - 2 m per day. If large boulders or full-face rock are encountered in theexcavation face, their removal has to be carried out by pneumatic toolsas the size of the tunnel does not allow the use of heavy mechanicalplant. Hence, the rate of progress is generally slow, with 100 - 200 mmin length achieved per day. In addition, maintaining stabi li ty of over lyingground during boulder removal is always a problem.The heading construction method also enables the alignment of a tunnelto be adjusted, by lowering or shifting the shield head/ segments toeither side, to avoid conflicting with unexpected utilities or servicesencountered during excavation, thus giving more flexibility to resolvingthe problem, when compared with the TBM tunnelling.m

Figure 14 - Permanent Pipeline Installed in the Tunnel

Figure 15 - Hand-dug Tunnel Constructed by Steel Plankings with PortalFramesHeading construction, by means of steel plankings and portal frames,has become popular in Hong Kong recently, particularly for installingbranch sewers or drains where groundwater is usually not a problem.This is due to its easy setup, not requiring heavy machinery, and itsflexibility in handling obstructions. The downside of this method is thatconstruction may be dangerous if the soil cover is too shallow. Its left-in temporary works also takes up an underground space, filled withsteel sections, much larger than the pipes to be laid, typically 1.5 m x1.5 rn, to enable manual operat ion, thereby making the already congestedunderground space even more so and also imposing dif ficulties for futuremaintenance of the laid pipes.Earth Pressure Balance MethodEarth pressure balance TBM (Figs 16 to 18) is adopted for tunnellingthrough homogeneous ground made of clay, silt or sand, usually in thelayers of fill, marine deposits and alluvium. The cutting wheel generallyappears in spoke type, with tungsten carbide cutting bits mounted onthe surface and a screw crusher in the center. It is capable of excavatingsoft rocks of sizes up to 25% of the area of the cutting wheel.The system works on the principle of maintaining pressure in theexcavation chamber equal to the hydrostatic pressure in surroundingground. This pressure is constant ly monitored and control led by varyingthe speed of the screw conveyor. The excavated materials are transportedto the jacking shaft, by a trolley system, and then lifted up to groundsurface. When soft ground is encountered or excavation is carried out



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Figure 16 - Typical Pipejacking Works Using Earth Pressure Balance TBM(Courtesy of Herrenknecht AG)

Figure 17 - Mechanism of Earth Pressure Balance Method (Courtesy ofHerrenknecht AG)

Figure 18 - Transportation of Excavated Material in lacked Pipelinebelow groundwater, high water absorbent polymer or other condit ioningagents are added to the excavation chamber firmly grabbing the soil tostabilise the excavation face and to ease the mucking process.For jacking shaft, the works area required is less than that of the slurrypressure balance method, due to less plant required for the operation,

and could vary from 3.5 to 5 m in width (ie the width of the shaft) andbe generally in the range of 20 - 30 m in length. At locations wherespace is a problem, the size of the works area could be reduced bystacking some of the plant. For receiving shaft, the works area is muchsmaller and is only required when the TBM is lifted up from the shaftafter completion of the pipejacking works.Common sizes of TBMs range from 1,050 mm to 1,800 mm, but theuse of 2,600 mm diameter TBMs has been experienced. Due to theirsimple configuration, in particular only cutting bits are equipped in thecutting wheel and no telescopic section is provided at the rear of theTBM, these TBMs cannot cut through big boulder obstructions and aretherefore generally sui table for soft ground excavat ion. Manual removalof artificial obstructions ahead of excavation or change of damagedcutting tools cannot be done from behind the cutting wheel in mostof TBMs due to no man access in the front bulkhead. To account forunexpected ground conditions, the length of each drive is usually lessthan 100 m.A production rate of 6 - 8 m per day could be achieved in filling groundwith occasional boulders.There is another type of TBM using this operating mode but has differentconfiguration in the cutterhead and thus the cutting tools (Fig 19).Consisted of two main parts in the TBM and built of heavy gauge steel,the front bulkhead of the first part acts as support for the boring unitand seals the front chamber for pressurisation. This part of the TBM,called the shield, houses the machine operator's porthole, a spoil screwconveyor and an access chamber to the face of the TBM for manualexcavation under a compressed-air working environment. The secondpart is the telescopic tailskin which can extend to provide sufficientthrust to the shield and is also used for connecting the precast concretepipes/ segments behind. An articulated joint is provided between theshield and the tailskin, to enable steering of the shield so that the lineand level of the pipeline can be adjusted.In normal operation, this type of TBM is operated in closed mode, andexcavation is effected by a boom cutter or a mini-backhoe connectedto an articulated telescopic arm mounted on a fully rotating turret inclockwise or ant i-c lockwise direct ion, and the mucking chamber is undercompressed-air to balance groundwater. In this mode, transportationof the excavated materials is similar to that of the TBM with a cuttingwheel. In order to prevent loss of compressed-air, the excavated materia lsin the screw conveyor are always kept full. When the TBM is operatedin open mode for removing obstructions manually, the triangular steelpanels hinged to the leading edge of the shield, which act as shutters,are extended by hydraulic jacks operated from the driver's cabin, tosupport the overlying ground during the operation.There has been a case that the TBM was stuck in ground in the middleof a drive, due to the accidental opening of a valve in the front bulkheadwhich resulted in the ingress of soil and water in the TBM, causinginundation and damage. This TBM was finally recovered by a rescuetunnel constructed from the receiving shaft, and the stalled pipeline wasthen pushed to the receiving shaft through the rescue tunnel.

Slurry Pressure Balance MethodSlurry pressure balance TBM (Figs20 to 22), often cal led slurry shield, withcutting bits and disc cutters installed at suitable locations in the cuttingwheel, of semi-dome type or dome type, is widely used to constructpipelines in mixed to hard ground conditions under groundwater, to adepth up to 30 m. Common sizes of TBMs are 1,200 mm, 1,500 mmand 1,800 mm.The allowable jacking load in these TBMs ranges from 500 to 1,000tonnes(T}, whereas the allowable torque pressure is in the range of100 - 300 bar. The length of driving could vary from less than 50 -100 m to more than 500 m passing through a number of intermediateshafts in a single drive.The works area required for jacking shaft is generally 7 - 8 m wide and40 - 50 m long, for placing mobile crane, TBM control container, power

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EXCAVAllNG ARM

I l UCKWAGON

MIXER AND INJECllON PUMP

Figure 19 - Operation of an EPB TBM Using Mini-backhoe for Excavat ion (Courtesy of CSM BESSAC)

Figure 20 - Typical Pipejacking Works Using Slurry Pressure Balance TBM(Courtesy of Herrenknecht AG)

Figure 21 - Mechanism of Slurry Pressure Balance Method (Courtesy ofHerrenknecht AG)m

Figure 22 - General View inside a lacked Pipeline Installed by SlurryPressure Balance Methodpack, generator, desander, muck tank, bentonite mixer, grab lorry, andjacking pipes, etc. At certain locations, some equipment have to be puton decks to suit the limited size of the works area as constrained by siteconditions, or a satellite works area has to be provided in the vicinity.TBMs of 900 mm in diameter or smaller may be incapable of tunnellingthrough big rocks due to the size of the cutting wheel limiting thenumber and size of the disc cutters. Therefore, advanced drilling todetermine the ground conditions along the pipeline alignment needs tobe carried out prior to commencement of the work to minimise the riskof TBM stoppage and thus the rescue operation. There has been a casethat a 600 mm diameter TBM encountered full-face rock after leavingthe jacking shaft for about 1 m (Fig 23) and was stuck. The TBM wasfinally pulled back to the shaft and the rock obstruction was removedby percussive drilling prior to resumption of tunnelling.During the course of driving, bentonite based slurry, with a viscosityof 40 - 50 Marsh sec for sandy ground, is constantly pumped into theexcavation chamber, through a slurry charge pipe. This forms a cakeover the excavation surface, to stabilise the face and prevent the ingressof groundwater. The mix of slurry needs to be adjusted to suit thematerial in the excavation face. Sometimes, polymer has to be added to



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Figure 23 - View of Full -face Rock outside the Launching Eye of lackingShaft

slurry to increase the performance in adverse ground conditions, by, forinstance, decreasing the ground porosity or improving the properties ofthe excavated materials in soft ground to maintain the ground stabilityduring excavation. The excavated materials are then pumped to groundsurface and then separated by a desander, with the slurry being recycledfor use and the spoil disposed of off site. For clayey ground, no slurryis used and water under pressure is injected for the intended purpose.Lubricant is also injected to the overcut along the pipeline, throughthe lifting holes at the crown of the jacking pipes and the holes intheir axis, by an automatic system with pre-set timer and volume offlow (Fig 24). Intermediate jacking stations, each with 8 - 12 nos 50 -80 T hydraulic cylinders, are installed at pre-determined locations of thepipeline, usually every 80 - 100 m, to avoid excessive loading in themain jacking station. However, no intermediate jacking station can beinstalled in pipelines of 600 mm in diameter or smaller due to limitedspace. In addition, jacking pipes of such sizes do not have the holesfor injection of lubricant. Therefore, the jacking is generally limited toshort length, say 30 - 40 m.For rock excavation, disc cutters, each with single or double discs, witha diameter range of 200 - 300 mm, are equipped in the cutting wheeland each disc cutter exerts a thrust of 20 - 30 T onto the rock face,

forming vertical and radial cracks in circular kerbs at distances of 60- 100 mm. By repeated rotations of the cutting wheel and disc cutters,these cracks are enlarged and eventually cause the rock mass in betweento be broken into small fragments. The fragments are further reduced insize by the conical crusher at the rear of the cutting wheel, to a size ofnot more than 40 mm in diameter. In view of travelling a longer pathfor excavation due to their positions, gauge disc cutters (ie near the edgeof the TBM) usually require more frequent replacement than center disccutters (ie near the center of the TBM).For TBMs with a diameter of 1,500 mm or larger, a horizontal air-lock isgenerally provided at the rear for enabling inspection of the condition ofdisc cutters and making necessary replacement, through the man accessin the front bulkhead, under compressed-air. For tunnel ling through hardground, a telescopic section is equipped in the TBM or an intermediatejacking station is provided behind the TBM, to provide sufficient thrustfor excavation.The advancement rate of TBM is 100 - 200 mm/min in soft groundto 20 - 30 mm/min in hard ground. The TBM daily production ratedepends on the configuration of the TBM and could vary significantlyunder di fferent ground conditions.Based on DSD Contract No DC/2000/11 [5], 2 m per day in hardground to 30 m per day in soft ground, with an average of 4.5 m perday, could be achieved. A set of disc cutters is capable of completing2 shallow drives and 1.5 deep drives respectively, under typical HongKong soil conditions.In some cases,the pipeline has to pass through existing reinforced concreteseawalls, requiring the affected portion to be completed by hand-dugtunnel before the use of TBM to complete the remaining drive.

Ground SettlementTunnelling and pipejacking would induce settlement in surroundingground. The magnitude of settlement is greatly affected by groundconditions, type of tunnelling method, depth of tunnel and jackingspeed. The presence of underground utilities and services above thejacked pipeline would lead to under-measurement of surface groundsettlement due to their rigidity. It is necessary to estimate the settlementinfluence zone and to assess its effect on nearby roads, structuresand utility installations such that they can be safeguarded during theoperat ion and remedial measures taken, if necessary. Maximum groundsettlement occurs at the center line of the pipeline and diminishes tozero at a distance from its two sides.

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Figure 24 - Conditioning and Lubrication for lacked Pipeline mHE HKIE TRANSACTIONS Volume 16 Number 2


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The majori ty of ground settlement (70 - 80%) occur during and immediatelyafter completion of tunnel ling and pipejacking works. Further settlementwould continue, and its stoppage depends on the ground conditionsabove the jacked pipeline, for a few weeks to a few months.Dated back to 15 - 20 years ago, the settlement was monitored using nailsinstalled on pavement. However, th is type of instal lat ion is unable to detectsett lement accurately below rig id concrete pavement. In a project, a roadcollapsed due to the presence of cavities in ground without indication bythe monitoring data. After this incident, sub-surface settlement markers, inthe form of a steel rod, by coring through rigid pavement, are generallyadopted, with their installation at suitable intervals along the alignmentof the pipeline and at offset at both sides, prior to commencement ofa pipejacking drive. In flexible pavement, nail markers are used. This issupplemented by visual inspect ion that i f sett lement occurs, cracks woulddevelop in pavement. For structures sitting on shallow foundation, theircondition has to be assessed before commencement of tunnelling andpipejacking such that suitable monitoring devices such as tilt markersand settlement markers can be installed to monitor the ground behaviorduring the course of works.Under normal situations, the monitoring is carried out once a day. Thisfrequency however may have to increase if there are abnormal readingsor the magnitude of readings changes abruptly. In the event that if themeasured ground settlement exceeds the predicted value, the tunnellingand pipejacking works have to stop and an invest igation on the cause, andthe damage, if any, carried out, with remedial measures such as groundtreatment implemented, as necessary, prior to resumption of work.Through the proper operation of works, the ground settlement for mostof the pipejacking drives using TBMs could generally be controlledwithin 15 mm for most of the Hong Kong soils, although excessiveground settlement has been noticed in some drives due to unfavorableground conditions.

Control of Tunnel AlignmentThe pipejacking works in Hong Kong using TBMs generally follow theTunnel ling Specificat ion [6[ as guideline for control ling tunnel alignment,in that a tolerance of 50 mm and 35 mm is specified for line and levelrespectively. For the 4 km long pipejacking drives completed in OSOContract No OC/2000/11, under different ground conditions, 21% forline and 19% for level exceeded the tolerance, generally by 2 - 50 mm,despite the fact that the excavation face had been conditioned by slurryand sometimes by the addition of polymer, as necessary. Moreover,deviations in more than 100 mm were recorded at some locations in afew drives where the ground conditions were alternating. In addition,about 2% of the pipelines exceeded the tolerated 0.5 degree angulardeflection at pipe joint, resulting in the need to carry out a detailedinspection to ensure that there is no dislocation thereat. For excessiveopening in pipe joint, remedial measures have to be carried out. Thiscould be achieved by locally trimming the concrete at the pipe end forbetter bonding before applying nor-shrinkage epoxy, with a strengthequivalent to the pipe, to fill up the problematic location for preventionof ingress of water.The tunnel alignment is corrected by suitable extension or retraction ofthe steering cylinders installed in the TBM. A TBM with 4 nos steeringcylinders has better control in alignment than that with 3 nos Out-of-tolerance in alignment requires a long length to correct in order to avoidcausing damage to the jacking pipes.For pipejacking works using handshield for excavat ion and sleeve pipes/segments to construct the temporary tunnel, no tolerance is specifiedfor line and level as the tunnel will be large enough for installation ofthe permanent pipeline. However, allowance has to be made to accountfor the irregular profile of the tunnel, due to encountering differentground conditions during excavation, which could affect installation ofthe permanent pipeline therein to the required alignment.For the tunnel formed by horizontal pipe-piles or steel plankings/channels, its alignment may need to be adjusted to cater for unexpectedm

obstructions due to existing utilities and structures. In the worst case,the design of the permanent pipeline has to be modified to suit theactual site condition.

Rescue OperationsA TBM would be stuck in ground if obstructions are encountered duringexcavation. It is necessary to carry out a detailed investigation on itscause, and then replacement of the damaged part from inside the TBM.These obstructions could be natural or artificial. If the problem cannotbe overcome, the stalled TBM has to be recovered by means of a rescueshaft or a rescue tunnel, as appropriate, with the obstruction removed.The works would be delayed and new TBMs may need to be deployedfor ensuring the completion of other pipejacking drives on time, whichcould disturb the programme of works.Based on OSO's Report No RO 1005/2 [3[, about 2% of the pipejackingworks encountered obstructions, result ing in rescue operat ion.The selection of a rescue option depends on many factors such asthe damage in the TBM, the location of TBM stoppage with regard toits distance from the jacking shaft and the receiving shaft, the trafficconditions, and the ground and groundwater conditions, above theTBM, the constraints of utilities and services, and the effects on nearbystructures and facilities. The options may include but are not limited tochange of the damaged cutting wheel so that the TBM can continuethe remaining drive to the receiving shaft, removal of the TBM throughthe rescue shaft and completion of the remaining drive by anotherTBM from the receiving shaft to the rescue shaft, and constructionof a rescue tunnel from the receiving shaft, to overlap the TBM andthen the pipeline is pushed into the receiving shaft from the jackingshaft. As each option involves different degree of risk, its suitabilityneeds to be assessed carefully, with site investigation works carriedout at and in the vicinity of the stalled TBM, before a decision ismade.There have been two cases that a rescue shaft, formed by a combinationof sheet-piles and pipe-piles, in the size of 1.8 m x 5.2 m on top and2.5 m x 5.2 m at bottom and 16.5 m deep, and a rescue tunnel, with alength of 35 m and an internal diameter of 2,440 mm, using compressed-air pressure to balance groundwater, took about 8 months and 10months respectively for rescuing the stalled TBM, from investigation onthe cause of the problem, planning of rescue, construction, execution,to recovery of the TBM [7[.There has however been a case that a 1,350 mm diameter slurryoperated TBM encountered a steel box section when tunnelling in riverbed and could not advance further. The cutterhead of the TBM wasmoved backward by retraction of the steering cylinders, to enable thedriving, vertically, of a 900 mm diameter steel pipe for encasing the steelsection. An attempt to completely lift up this steel section through thissteel pipe was carried out but breakage occurred at the location partlycut by the disc cutters of the TBM, during the lifting operation. To enableman-entry for manual removal of the steel section, a steel plate, with aprefabricated hole to accommodate the steel section, was instal led in thecasing, with sandbags added on top of the plate to prevent uplift forcedue to water pressure, and the ingress of water in the steel casing wascontrolled by the use of a pump. The broken steel section was finallycut manually and removed, and the pipejacking works resumed.

Some Problems EncounteredThe following problems are commonly encountered during pipejackingworks and could affect the progress:For deep drive, high groundwater pressure requires additional jacking forceto advance the TBM against the pressure. Therefore, more intermediatejacking stations have to be installed at suitable intervals of the pipelineto ensure that there is sufficient thrust to push the pipeline forward. Inaddition, such high groundwater pressure also makes the TBM and thefirst few pipes moved back to the jacking shaft whilst new pipes arebeing added. This always requires the temporary fixing of a steel bracket



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in the TBM/ pipe to rigidly connect to the surrounding temporary worksas support dur ing pipe connect ion.A treated soil block, formed by grouting, is usually provided in the groundoutside the launching eye of the jacking shaft and the receiving eye of thereceiving shaft, to prevent ingress of water during the jacking/ receivingoperation and to support the TBM during launching and reception. Ingrounds with high content of boulders, the grout may not be able toprovide effective bonding between soil and rock. This would easilycause dispersion in the grout block when the TBM is breaking through.As a result, soil particles would migrate into the shaft, through the eyelocation, and settlement would occur in overlying ground, damagingutili ties and services.During the course of pipejacking, zig-zag line and level would occurin the pipeline due to encountering different ground conditions. Thiswould require rendering in the depressed sections to provide a uniformprof ile for the pipel ine, affecting hydraulic performance. Excessive 'out-of-to lerance' would also cause opening-up of pipe joints, causing ingressof groundwater and instability of the pipeline.Cracking of concrete in pipe could happen at locations where there isexcessive deviation in line and level caused by uneven distribution ofjacking force, as a result of unfavourable ground condit ions encountered.This would require a temporary steel lining for protection to completethe remaining drive before repair is carried out. In the worst case, thedamaged pipe has to be repaired immediately, with the spalled ordefective concrete removed and replaced by high strength non-shrinkageepoxy, before the pipejacking works can continue.When tunnelling through clayey ground, slow transportation rates inthe slurry discharge pipe always occurs, due to the plastic materialaccumulated in the inlet of the spoil disposal chamber. This necessi tateshigh pressure water to disperse such material through the nozzles providednearby. Pipe blockage is also found when obstructions such as timber,steel bars, etc are encountered, resulting in the long time to dismantlethe respective sect ions of pipes for clearance.Wear or damage in disc cutters is a normal phenomenon in TBM duringtunnelling, and replacement has to be made at the right time to ensuretheir proper function. There are however cases that they could notbe replaced from inside the TBM due to damage/ distortion of theirconnections, affecting the cutting capacity and losing the function offurther advancement.Excessive ground settlement or subsidence would occur in unstableground or due to improper control of the TBM, causing bursting ofwatermains or gas mains. Although settlement monitoring is carried outat regular intervals, this situation would still occur when there is a suddenchange in ground conditions not immediately noticeable to theTBM operator for necessary adjustment in the TBM. Excavation inbouldery ground or soft ground with boulders would also have such aphenomenon.Repeated extension and retraction of hydraulic jacks would causeintermediate jacking stations to leak, due to the rubber seal being tornout by such operation. This situation would be more critical in curvedal ignments under eccentric loading throughout the drive. No repair couldbe made until completion of the drive. If the leaked location is near theTBM, the tunnelling operation might be jeopardised.In porous ground, slurry injected from the TBM to balance groundwaterpressure would easily leak into ground, cause blockage to ductings ofutil it ies, and encroach into drainage features, affecting their function.The tunnel alignment is affected by ground conditions during driving. Itwould be difficult to control the alignment in soft ground with boulderembedment or in alternating ground with soft and hard materials as theTBM would tend to move faster towards soft materials. The hydraulicperformance of a pipeline would be affected should there be excessivedeviation in alignment.A TBM would be stuck in ground if it cannot cut through obstructionduring the course of driving. This would result in the rescue operation,and high frictional force would develop along the pipeline due to close-

up of the annulus, causing difficulty to further proceed with pipejackingworks.

DiscussionAppropriate Selection of Method to Avoid DelaysAccording to DSD Report No RD1005/2 [3], about 75% of the pipejackingworks were completed by TBMs using the slurry pressure balance method,1% by the earth pressure balance method and 24% by hand-dug tunnels.However, there is a rapid increase in the use of hand-dug tunnels, inthe form of heading construction, in recent years.Each of the pipejacking techniques is beneficial when used in a propermanner. Its performance is generally reflected by daily production rate,capacity in dealing with hard rock, control of line and level of pipeline,and ground settlement or heaving. It is therefore essential to choose theappropriate method to avoid timely and costly remedial measures if thework is stopped by obstructions or mechanical failure, which will causenuisance to the public and in turn lose the spirit of using them.Cost of Installation and Choice of TechniquesThe cost of pipeline installation using such techniques does not varywith depth except for the increased cost of providing deeper shafts andmanholes. In comparison with the convent ional open-trench method, thecost of the slurry pressure balance method, the earth pressure balancemethod, the free air hand-dug tunnelling method with grouting and thecompressed air hand-dug tunnelling method is higher in the order of 2 - 10times, whereas the construction time is usually faster in most cases.The choice of a technique lies with the designer or the contractor and isdependent on the degree of r isk that the project can accept. This is usuallygoverned by access, ground and groundwater conditions and accurateidentification and consideration of all other constraints. Increase in siteinvestigation works would reduce the risk but could not eliminate it.The earth pressure balance method, although relatively inexpensive oftunnell ing in soft ground, is unable to deal with large boulders and artif icialobstructions. Although access to the face through the airlock chamberin large TBMs is feasible, their removal will be inefficient due to limitedspace and the use of only hand tools. Breaking through the unknownthickness of boulders will pose a risk that there may be a sudden changein groundwater pressure endangering the worker. Therefore, the recenttrend is that slurry operated TBMs have been used as a substitute tominimise the risk of TBM stoppage due to the above problems.The slurry pressure balance method has demonstrated its good rate ofprogress in variable ground, but i ts use needs monitor ing of excavation asthe machine advances to eliminate settlement (too much excavation, notenough advance) or heave (too much advance, not enough excavat ion).Hence, the operator's experience, training and response when problemarises are crucial. Change of operator during the course of work shouldbe avoided as much as possible as the new operator would take a longtime before he becomes familiar with the TBM and the ground conditions.The density, viscosity, filtrate water and shear strength of the slurry haveto be tested on a regular basis and changed when any of these exceedsthe specified upper or lower bound limits to ensure its functionality. Theconfiguration in the cutting wheel should be capable of cutting throughextremely hard and abrasive rock and, on the other hand, excavatingsoil efficiently. The disc cutters provided have to be extremely wearresistant and capable of taking the maximum thrust of the TBMs. Toavoid excessive heat generation, disc cutters should be equipped withwater cooling system. Locally made discs are to be used with care dueto difficulty of controlling their quality during the heat treated process.In the event that a boulder zone is identified ahead of the drive, it maybe necessary to stabilise the soil above the affected area to minimiseground settlement caused by vibration or over-excavation during thecutting-through operation. This would also help to control the line andlevel of a pipeline. It may be worthwhile to note that up to now, noTBM is capable of cutting through large art if icial obstruct ions, especiallymetallic objects, resulting in its stoppage in ground.

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Problems with TBMsThe type of cutting wheel and TBM to be used and the expected advancerate depends on ground conditions and their variability likely encountered.A radical and unexpected change of ground conditions can prevent adrive from being completed and require rescue operation to permit thework to be completed. Likel ihood of obstruct ions, natural or artif icial, canalso prevent a drive from being completed, and the rescue of a stalledTBM could be time-consuming and expensive, affecting progress.Additional Features in New TBMsResearch in TBM technology has developed rapidly in recent years,based on the problems encountered in different projects under differentground conditions. New TBMs are now equipped with additional featuresthat allow increased and reliable performance under a range of groundconditions. To account for the high variability in ground conditions in ashort length, which is a main characteristic in Hong Kong soils, mixedground slurry operated TBMs have been widely adopted by contractorsto minimise the risk.Advantages of LubricantLubricant, applied along the jacked pipelines, has demonstrated to beeffective in lowering jacking forces and reducing the risk of pipe damagein most of the pipejacking drives. In long drives, automatic bentonitesystems with programmable valves should be used to ensure that lubricant,with the specified volume, is injected to the annulus of the pipeline inpre-fixed intervals, to serve the intended purpose.Laser Guidance SystemIn straight drives, the position of TBM is determined by the guidancesystem which relies on the laser beam transmitted from the laser deviceinstalled at the rear of the jacking shaft, to the target plate installed inthe TBM. However, in curved drives, the laser technology with the useof reference prisms and total survey stations is generally used in TBMswith diameters of 1,800 mm and larger. In small TBMs, the use of Gyrocompasses with hydrostatic grade correction is a common approach andhas demonstrated its accuracy.Problems with Disc CuttersThe performance of disc cutters for pipejacking works has a short historyin Hong Kong. In 1990's, most of the works were carried out in singledrives, with a length generally not exceeding 100 m, and in shallowdepth. It was until 1996 onwards that the scale of pipejacking workshas increased to a few kilometres in a contract, with also deep drivestunnelling through hard strata in ground. However, no complete recordon the respective performance could be traced except in OSO ContractNo OC/2000/11. This Contract showed that a total of 254 nos steel alloydisc cutters, with a diameter range of 250 - 300 mm, had been usedfor the 21 drives, averaging about 0.5 set of cutters for each shallowdrive and 1.5 sets for each deep drive. For TBMs with a diameter of600 mm to 1,800 mm, a set of disc cutters in the cutting wheel has6 - 12 nos. Depending on the ground conditions encountered, part icular lythe location, thickness and hardness of materials, some of the disccutters had to be replaced after the TBM had travelled a short length.This situation occurred in some long, curved drives with highly variableground conditions and the replacement of disc cutters in a 4 m drivelength had been experienced in the worst case. Replacement of morethan 30 nos disc cutters during the course of works in three drives hadbeen recorded. It is noted that a tunnel through moderately to slightlydecomposed granitic (M/SOG) bedrock, with strengths of 320 - 350MPa, achieved 4 m/day on average.Tunnel Alignment and Level AccuracyAlmost all the tunnel alignments, using TBMs, can be controlled within75 mm for line and 50 mm for level, as evidenced by OSO's threecontracts (Nos OC/95/05, OC/98/06 and OC/2000/11) which specifiedthe use of tunnelling and pipejacking techniques. In consideration of

m

the steering capacity of the TBMs available in the market, the angulardeflect ion of the jacking pipes, and the procedure of correct ing the 'out-of-tolerance', a tolerance of 50 mm for line and 35 mm for level, as statedin the Tunnel Specification, may not be applicable to all Hong Kong soilsfor pipejacking works, and hence should only be used with care.Hand-dug Tunnels and Heading MethodThe adoption of compressed air hand-dug tunnelling method wouldface a problem associated with air loss in porous ground, giving rise tothe necessity of carrying out ground treatment to safeguard the tunneland the personnel working inside. The switch on of compressors andgenerators around the clock to maintain the pressure in tunnel alsocauses noise problem. Although high cost and relative low productionrate make this method only applicable to short drives, the removal ofartificial obstructions can be warranted. However, after a few drives hadbeen completed under OSO Contract No OC/95/05, and following therapid development of TBM technology which allows pipejacking drives incurved al ignment and detects 'obstruct ion' ahead of TBM advancementthis method has not been used in recent years due to the risk involvedand the reasons stated above.Free air hand-dug tunnelling method in unstable ground would requirethe entire length of the drive being grouted to maintain stability of theroad above, prior to commencement of work. Vertical grouting appearsto be infeasible due to presence of congested utilities and services inshal low depths. Hor izontal grouting wil l cause drawdown of groundwaterduring the drilling operation and will blowout the ground or encroachinto ductings of utilities if the pressure is not properly controlled. If thegrouting is ineffective, compressed air still has to be used to balancegroundwater pressure.Heading construction is a method commonly adopted to constructshort pipelines crossing road junctions, utility crossings and entranceto carpark, in shallow depth. The completed works have demonstratedits effectiveness due to fast mobilisation of plant, simple setup on site,and flexibility in construction method to suit the space available. Due tol imited space, the tunnel excavation isgenerally carr ied out by hand tools.There have been cases that unexpected ful l- face rock was encountered,taking a long time for removal and affecting progress. Although problemsassociated with safety, environment and ground stability could be aconcern, there is a growing demand in recent years that this method isused to overcome site constraints, particularly those unexpected duringconstruction, thus minimising delay to the works.All the above methods have merits and demerits. Their choice should bebased on technical compatibi li ty with regard to ground and groundwaterconditions revealed by site investigation works, and other constraintsrather than only on cost. Detailed analysis of the risk, together withthe contingency plan, has to be given prior to finalising the decision.Inspection and maintenance of tunnelling shields, TBMs and their backupplant and equipment by competent personnel at regular intervals wouldminimise the downtime and maximise the production. Since each projectis different in nature, it is advisable to consult with specialists in the fieldand TBM manufacturers in the planning stage to ensure success.

ConclusionThe application of tunnelling and pipejacking techniques for drainagepipeline construction in Hong Kong has proved to be promising, generallywith less construction t ime and disturbance to the public , when comparedwith the conventional open-trench method. Some of the problems couldhave been avoided or minimised had suitable technique been selectedbased on detailed site investigation results and site constraints, and properplanning provided in advance. It is essential to include comprehensiverather than general requirements in the contract to fully cover eachactivity of works, which should be practical and specific with regardto the situation encountered, with the contractor's responsibility andactions being clearly defined, so that arguments between the client'sconsulting engineer and the contractor on problems, when occurring,could be minimised. The exper ience, training and attitude of the working



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and supervising personnel also have a significant effect on the successof works.Through the rapid development of TBM technology, long, curvedpipelines have been carried out in irregular, alternating soil and rockcomposition at different depths, in recent years. Tunnelling through thealready completed permanent shafts has also been carried out, withproper control of alignment, at a number of locations, to suit the projectprogramme. This also gives flexibility in selecting shaft locations to getrid of utility and traffic constraints, as well as the disturbance problemsto shops, in most cases.By the installation of a sonic soft-ground probing system in the TBM fordetecting hard materials in front of excavation and an electronic toolmonitoring system for detecting the wear limit of disc cutters, which isthe recent technology advancement in TBM, the risk associated withTBM stoppage, as a result of 'obstruction', which is a common problemin pipejacking works, could be minimised.Disc cutters have also been developed to have longer life and highercapacity in dealing with the ground conditions likely to be encountered.Artificial obstructions still have to be removed manually should therebe access in the front bulkhead of the TBM. Otherwise, the TBM wouldstop in ground necessitating rescue operation. This can be carried outby means of either a rescue shaft or a rescue tunnel, which is a time-consuming and costly operation, affecting the progress of works anddisturbing the public. Therefore, site investigation should be carried outas much as possible at suitable locations before the tunnelling methodand TBM is f inal ised.Tunnel ling and pipejacking techniques will cont inue to become popular forinstallation of drainage pipelines in the urban areas of Hong Kong as theycould eliminate most of the problems encountered by the conventionalopen-trench method and hence enable the works to be completed withleast inconvenience to the public and minimum diversion of existingutil it ies and services, and traff ic. These techniques are cont inual ly beingrefined and developed. Improvements cover both larger and smallerdiameters, longer drives, better control of alignment, faster and curveddriving, different ground conditions, and the ability to work deeper underwater. However, there are also certain constraints, such as no room forconstruction of jacking and receiving shafts at suitable locations dueto congestion of existing utilities and hence the lack of space for theirdiversion or close proximity to shops, insufficient clearance betweenoverlying utilities and the jacked pipeline using TBM for advancement,and unexpected underground artificial obstructions, which limit theapplication of such techniques.

AcknowledgementsThe authors wish to express their gratitude to the Drainage ServicesDepartment of the Government of the HKSAR, for permission of extractingthe materials from the respective projects, to publish this paper. Specialacknowledgement is given to Herrenknecht AG, and CSM BESSAC, fortheir permission of extract ing the photographs from technical brochuresin making Figs 16, 17, 20 and 21, and Fig 19 respectively.

References1. Thomson, J., Pipejacking and Microtunnelling. pp3-6. BlackAfrP. UK (1993).2. McFeat-Smith, I. , Tunnelling in Hong Kong in the 1990s. Tunnelling in Hong

Kong Seminar. Hong Kong (1993).3. Researchand DevelopmentSection.TrenchlessPipeInstallation and Renovation

Techniques.Review of Pipe Jacking/ Microtunnelling Techniques for Construct ionof Drainage Pipelines. Researchfr DevelopmentReportNo RD 1005/2. DrainageServicesDepartment, Government of the HKSAR.Hong Kong (2002).

4. Mok, WWS., Mak, M.K.W fr Poon, F.H.T.,Sewer Installation by Pipejacking inthe Urban Areas of Hong Kong. PartI - Planning, Design, Construction andChallenges.The HKIE Transactions. Volume 14, No 1,pp27-28. The HongKongInstitution of Engineers.Hong Kong (2007).

5. Mok, WWS., Mak, M.K.W fr Poon, F.H.T.,Sewer Installation by Pipejackingin the Urban Areas of Hong Kong. Part II - Performance of Works, LessonsLearnedand Improvements Proposed.The HKIE Transactions. Volume 14, No1,pp34-35. The Hong Kong Institution of Engineers.Hong Kong (2007).

6. TheBritishTunnelling SocietyandTheInstitutionof Civil Engineers.Specificationfor Tunnelling. pp36, 86-88 fr 106. ThomasTelford. UK (2000).

7 Mok, WWS., Pipejacked Tunnels - What to do If a Tunnel Boring Machine isStuck in Ground? TrenchlessConference in Macau. Macau (2007).

About the AuthorsWilson W SMOK BASe BA CEng R.P.E. (Civil aGeotechnical) CSci MICE MIMMM MHKIEEmail: [email protected] Mok graduated from the University of Windsorin Canada and has over 30 years practical workingexperience in a wide variety of geotechnical and civilengineering projects in both design office and site. Heis particularly experienced in dealing with design andconstructionassociatedwith geotechnicalinvestigationsand instrumentation, deepexcavations,tunnels, groundimprovements, settlement analysis, reclamation, siteformation, slope preventive measures, foundations

and sewerage works. Ir Mok has been involved in the design, supervision andadministration of more than 16 km long trunk drainage pipeline construction inthe urban areasof Hong Kong, using different types of trenchless techniques fromrelining, TBMsto hand-dug tunnelling, and has carried out extensive researchonsuch.He is the author/ co-author of severaltechnical papersin this aspect,and hispaper titled 'Sewer Installation by Pipejacking in the Urban Areas of Hong Kong',in two parts, has been awarded the HKIETransactions Prize 2007. He has beenSenior ResidentEngineer on a DSD contract, which involved the construction of4 km long trunk sewers, using pipejacking techniques.

K W MAK BSc Dip HE Delft PCLL MA Arb CEngMIEAust MICE MHKIE MIHTEmail: [email protected] Mak is currently Chief Engineer with DrainageServices Department. In the past few years, he hasparticipated in numerous large-scale and prestigiousdrainage and sewerage projects, including the WanChai Eastand North Point sewerage project, the firsttertiary sewage treatment plant at Ngong Ping, thelargest ultra-violet disinfection facility installation atSin Ho Wan sewage treatment plant, as wel l as the5 km long rainwater-intercepting tunnel in TsuenWan.

Previously, he spent six years in the then Works Bureaudealing with slope andwater policies. During his earlier years with the Drainage ServicesDepartment, IrMak received post-graduate training in river engineering in the Netherlands, andhad then worked in the ShenzhenRiverRegulation Project.He obtained a Masterof Arts in the areaof dispute resolution and arbitration. On top of his engineeringengagements, Ir Mak acquires legal qualification and is a non-practising Barrister-at-law of the High Court of the HKSAR.Ir Mak isthe co-author of the paper tit led'Sewer Installation by Pipejacking in the Urban Areas of Hong Kong', which hasbeen awarded the HKIETransactions Prize2007

raHE HKIE TRANSACTIONS Volume 16 Number 2
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Tunnelling and Pipe Jacking Techniques

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