Use of Forward Probe Coring Methods and Rexote Sensingfor Investigation of Geological Conditions ahead of

Drill and Blast and TBM Tunnel Drivages

T.G. CarterColder Associates, Toronto, Canada

ABSTRACT Design of tunnels and mine openings through areas of fractured and faultedground demands attention to detail in unravelling the geology of the area through whichthe tunnel is to be excavated. For pressure tunnels in particular, where high static anddynamic water pressure conditions can exist, detailed attention to local site geology isimperative to ensuring that design requirements of minimal leakage and resistance tohydrofracture are maintained.

Forward probe drilling and long angled underground diamond core drilling methods provideuseful tools that can aid prediction of major fracture intersections ahead of tunneldrivages. These methods, coupled with effective pre-design use of remote sensing andgeophysical techniques provide a rational means by which the tunnel engineer can gaininformation necessary for design of both temporary and permanent support elements.

INTRODU~TI0N

Compiling adequate investigation data on mainly by prediction or avoidance of mixed-ground conditions ahead of an advancing face conditions. Secondly, it would allowexcavation face poses a commonplace problem prediction of any offsets in the stratain tunnelling. Collection of accurate pre- which could indicate zones of faulting ordesign and pre-excavation information is disturbance where grouting or localizedespecially critical where significant extra rock support might be required tonatural (static) or induced (dynamic) water suit encountered ground conditions.pressure problems are anticipated.

For the TBM drivage of the twin submarineaccess tunnels for the new Donkin-MorienCoal Mine off Cape Breton Island, NovaScotia, Canada, (Figure 1), it wasrecognized that detailed prediction aheadof the drivages would help earlyrecognition of problem ground conditionsthat could give rise to inflows of seawaterat static heads in excess of 180 psi. Theacquisition of reliable stratigraphic dataahead of the tunnelling advance was alsoseen as a useful means for optimizingtunnel drivage lengths to within horizonsof better quality rock.

0 0 00 30 •0 5O~

As a full face TBM drivage was envisagedfor the tunnels, such optimization was seento serve two purposes. Firstly, it wouldlikely help in minimizing cutter changesand excavation problems during drivage,

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ATL ANTIC

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NOVASCOTIA

Figure 1 Location PlanDonkin-Morien Mine Access Tunnels

(1990). Proc. ISRM International Symposium on Static and Dynamic Considerations in Rock Engineering,

Mbabane, Swaziland, pp. 91-101.

For the waterways for the Drakensberg HydroPower Scheme, on the borders between Natal,South Africa and Lesotho, (Figure 2),acquisition of geological data on rockconditions ahead of the various drill andblast tunnels was deemed critical not onlyfor rock support design but also from thehydraulic design viewpoint. Accurate,detailed geological information was soughtspecifically for optimizing the locationsof the necessary transition zones betweenthe concrete-lined pressure tunnels and thesteel-lined penstocks in order to resisthydrofracture under the high dynamic waterpressure heads imposed on the tunnelsduring operation.

DRAKENSBERG SCHEME

The Drakensberg Pumped Storage Scheme,comprises an upper reservoir, twin headraceand pressure tunnels and a single tailracetunnel connecting the main cavern complexto a lower reservoir; (Pyzikowski, 1982).The works have been constructed withinessentially horizontally bedded sedimentaryrocks comprising mudstones, siltstones andsandstones which in places are transectedby dolerite infilled faults and dykes andby steep angle shear and normal faults.

At the design stage, the locations of thetunnels, and the elevations of the crownsand intersections for the main caverns wereoptimized on the basis of an evaluation ofthe available site investigation geologicaldata within the constraints imposed byhydraulic and construction requirements.

Hydraulic considerations were of extremeimportance for the layout of the pressuretunnels and penstocks. Due to the geometry

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of the overall scheme, the maximum internalhydraulic pressure head at the downstreamend of the pressure tunnels was envisagedto vary from 500m.(static) to more than600m. (static plus water-hammer). Thus, asrock cover in the vicinity of the maincaverns was only 180m. at the proposedelevation of the scroll casings of theturbines, part of the original layout ofthe scheme envisaged that a section of thepressure tunnels would be steel-lined toobviate hydrofracture problems (De \Jitt,1983; Sharp and Gonano, 1982).

In order to achieve the maximum possiblecover immediately upstream of the powerstation and hence minimise hydrofracturepotential within the concrete-lined part ofthe tunnel while also limiting the requiredlength of steel lining, a ruling minimumgrade of 1 in 20 was adopted from the maincavern complex, as far upstream as theinitially proposed end of the steel-linedpenstocks (Figure 3). Upstream of thistransition, a maximum grade of 1 in 10 was

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Figure 2 Site Location of theDrakensberg Pumped Storage Scheme

HEADRACE TUNNELS

-SURGE SHAFTS

2907m. TO HEADRACE INTAKE

P ENS TOC K S

LOCATION OF FAULTSA AND B

163L+m. TO TAILRACE OUTFALL

MACHINE HALL

HALL

SCALED ZOO 40Dm.

Figure 3 Arrangement of Waterways adjacent to the Main Cavern Complex at Drakensberg

selected to ensure efficient tunnelling andconcrete lining operations (Eastwood and deWitt, 1982).

Elimination of areal hydrofracture of thetunnel lining and rock mass by the elevatedpressures in the concrete lined pressuretunnels was central to the design concept.Accordingly, considerable effort wasexpended during the project design phase indetermining the onset of hydrofractureunder different stress regimes and fordifferent rock materials, (Bowcock etal.,1976; Gonano and Sharp, 1983). To thisend, a full scale test chamber wasconstructed in an area of weak rock andtested in order to refine pertinent designparameters, (Sharp and Gonano, 1982).

In parallel with this work, all availablegeological site investigation data wasevaluated to optimize the location for thetransition from the steel-lined penstocksto the concrete lined pressure tunnels.Considerable emphasis was placed in thisevaluation on ensuring that the transitionsection would be located in the mostmassively bedded, highest modulus, leasthydrofracture prone rock - a thickly beddedsandstone unit if possible. At the tenderstage, therefore, the transition zone waslaid out to fall within one of the thickest

MHTE

sandstone units recognized from detailedstratigraphic correlation of the deepsurface diamond drillhole core log data;(ie. in the Delta Sandstone horizon, referto Figure 3).

Similar geological optimization was carriedout to position the cavern crowns. In orderto assist crown excavation and avoid shearoverstress problems at the haunches, thecrowns were selected to follow thin, butdistinct sandstone units, (Sharp et al.,1979, Mellors and Sharp, 1982). The machineand valve pits were also carefully laid outto maximize excavation within sandstone.Detailed design layout of the total complexwas also optimized to avoid intersectingdykes or unfavourably oriented structuraldiscontinuities. As a further design aid,summary 3D geological compilation diagramswere prepared for critical intersectionareas and for the overall main caverncomplex (Figure 4). These diagrams, anddetailed longitudinal and cross-sectiongeological compilation drawings were usedthroughout construction to check excavationcompliance with design crown elevations.Stringent blasting control was alsomaintained to ensure minimal damage to thethin sandstone or interbedded sandstone-siltstone units selected to constitute thecavern crowns. (Hallier et al., 1982.)

UN 48

TRANSFORMER HALL

UN 43

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GROUP

NTERSEOOEO SAI~STDNE AND SILTSTDNE GROUP I

GROUP III

GROUP V

Figure 4 Isometric Diagram showing Summary Geology of Power Station Complex

Within the main caverns and access tunnels,detailed mapping disclosed no majordiscrepancies between as-predicted andas-encountered geology. This was not thecase upstream of the main cavern complex,however. Here, over several discretestretches of the twin Pressure Tunnels, thestrata was disrupted by two major faults,the attitude and disposition of which wereonly fully established as a result of acomprehensive programme of undergroundprobe drilling and exploratory excavations.

Unlike the tailrace and main cavern sectionof the scheme, where exploratory headingshad been driven as part of the pre-designphase investigations; prior to driving thePenstock tunnels, no pre-constructionexploratory works had been advancedupstream of the Power Station Complex. Thetunnel alignment geology for the PressureTunnels was therefore entirely based oncorrelation between surface drillholes,with structural geological interpretationbased on terrain evaluation and remotesensing data from:

o Low and high level aerial photographsand Landsat satellite mosaics;

o Surface geological maps and traverseinformation; and,

o Detailed geophysicalsurface seismic andtraversing, down-holecross-hole seismic work).

data, (frommagnetometer

logging and

Originally, the layout, in plan, of thetwin pressure tunnels and four penstocks,were symmetrical with the centre-line ofthe Power Station Complex (as shown onFigure 2 in Bowcock et al., 1976). However,because of faulting, this needed somemodification in plan (refer to Figure 5).Alterations were also required in verticalalignment to ensure that the criticalsteel- to concrete-lined transition zoneswould remain in high modulus sandstone asa precaution against areal hydrofractureunder high operating water pressure heads.

o CONSTRUCTION STAGE INVESTIGATIONS

The requirement for additional geologicalinvestigations of the Penstock/PressureTunnel transition area only really becameapparent when excavation of the Drainage

Figure 5 General arrangement of Pressure Tunnels and Penstocks showing locationsof Exploratory Pilot Headings and Diamond Cored Probe Hole Fans.

Access Tunnel (DAT.) was well advanced. Atthis stage, slight discrepancies werebecoming evident between actual mappedelevations of discrete stratigraphic markerhorizons compared with those predicted fromthe original site investigation data.

Stratigraphic dips were a few degreessteeper than the surface holes would havesuggested. This suggested that either asignificant roll or fault existed orsomething was wrong with the original corelogging or borehole survey data. With over3000m. of diamond drilling and in excess ofiSOOm. of seismic and magnetometertraversing having been carried out over thePressure Tunnel alignment, checking all ofthe base data proved time consuming.Nevertheless, checks were made of allobvious correlation inconsistencies in anattempt to sort out the geology.

Stratigraphic Correlation

As the basis for evaluating the likelihoodof some major geological anomaly (fault orfold structure) affecting the strata inthe area immediately upstream of the maincavern complex, the detailed stratigraphiccorrelation diagrams prepared for the wholescheme alignment were re-assessed. Although

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these drawings had been found remarkablyaccurate throughout the entire PowerStation Complex, when detailed correlationwas attempted with some of the deep surfaceholes to the north of the caverns severalstratigraphic correlation discrepancieswere identified.

In particular, in the area of the proposedPressure Tunnel/Penstock Transition Zone,the comparison suggested that either therewas an error in the data or some form ofstructural disturbance existed in thevicinity of one of the original surfaceboreholes ( hole GP22 - see Figures 3 and5 for location). All of the other data inthe immediate area, including that from theexcavation of the Main Cavern Complex andfrom some 2 km of tunnelling, supported thehypothesis of undisturbed horizontallybedded sedimentary rocks. In consequence,the collar location, elevation and attitude(from Sperry Sun multishot surveys) of holeGP22 were rechecked and the core relogged.Sedimentary analysis techniques and pain-staking refitting of core fragments wereemployed to check right-way-up structuresand verify the correctness of the corewithin the boxes. Despite detailed re-logging of the core and thorough survey re-levelling of the collar elevation of the

FAULT ZONE COnSINtIOg Of200mm -300mm thick brecc,adipping ~O49R towards32Oo~36Oo magnetic

Figure 6 Drainage Access Tunnel and Extension showing mapped geology and drillholes

hole, the data still suggested a verticaloffset of 26 metres in the stratigraphywhen compared with the Main Cavern area.

Investigation Rationale

As it was deemed critical that the steel-concrete transition zone be located withinhigh modulus ‘unfractured’ sandstone awayfrom faulting, a decision was reached toevaluate further the hypothesis thatunanticipated geological structuralcontrols were responsible for the lack ofstratigraphic correlation between the PowerStation Complex and the borehole CP22 area.

Accordingly, with much of the upstreamtunnelling close to the caverns alreadycompleted, it was decided that the DAT.should be continued as a pilot heading(Figure 5) as thiswould provide additionalgeological data while not significantlycompromising construction schedules.

Remote Sensing Evaluation

In parallel with the re-evaluation of theGP22 data, the available Landsat imageryand air-photos were re-assessed and thesurface geophysical traverse informationre-interpreted.

- Air-photo Interpretation : Although theaerial photographs had been criticallyexamined prior to the start of the originalsurface investigations, it was consideredworthwhile to completely re-examine them tospecifically check for structural featurescrossing the alignment in the area betweenborehole CP22 and the Main Cavern Complex.

In general, most of the geological featuresevident on the photographs crossed thescheme almost at right angles. Somedolerite dykes however obliquely traversedthe tunnel alignment (Figure 5). These hadall been identified during the initial siteinvestigations, Bowcock et al, 1976; GolderAssociates, 1977).

When the photographs were re-examined butwith specific focus on the area aroundhole GP22, no definitive correlation couldbe established that could explain theanomaly within the stratigraphy. It wasnoted, however, that topographically, thescheme alignment in the area of the holepassed adjacent to a re-entrant valleywhere the escarpment ridge formed somethingof a promontory. In consequence, attentionwas addressed to checking whether theoverall face of the escarpment as well asthe re-entrant valleys were structurallycontrolled.

- Satellite Imagery Assessment : Fieldmapping of the major sandstone horizons onthe escarpment hillslope yielded littleadditional information because of the lackof continuity of good outcrop. However,some of the jointing trends mapped in thesandstones did suggest parallelism of majorelements of the structural fabric with theescarpment face and with the axis of there-entrant valleys.

The black and white Landsat image scanswere therefore critically re-examined toassess whether any further light could beshed on possible regional scale featuresparalleling the scheme alignment.

Although one north-south Landsat lineationparalleling the scheme alignment had beenrecognized at Pre-Tender stage, it hadnever been found possible to confirm thison the ground from detailed trenching oroutcrop mapping, or from magnetometer orseismic traversing. Nevertheless, it wasbecause of this possible lineation thatborehole CP22 had originally been drilled.Thus, the conundrum remained that, based onthe recovered core, the lithologicalsequence at the hole was inconsistent inelevation with that now proven at the MainCavern Complex. The decision was thereforemade to temporarily stop Pressure Tunnelconstruction and embark on a comprehensiveprogramme of underground probe drilling andpilot heading development aimed at:

a) verifying the extent of the geologicalproblem at the Transitions,

b) resolving the stratigraphy along thePressure Tunnels sufficient that designdecisions could be made, and,

c) using this data, establishing viablegeological conditions for locating thesteel/concrete Pressure Tunnel Tran-sition Zones in non-hydrofracture pronestratigraphy.

Strata Control Drilling

Immediately that full face excavation ofthe DAT. and Penstocks were stopped,drilling cubbies were slashed into thesidewalls at critical locations along theDAT. so that excavation of 2m square pilotheadings could be continued while coredrilling was initiated. This drillingprogramme was laid out to rapidly establishthe stratigraphy above the twin PressureTunnels. The initial holes were thereforedrilled as fans of upward inclined cross-strata holes radiating outwards from

several locations following the advancingface of the DAT Pilot Heading, (Figures 5and 6).

Drilling was started on a 24-hour shiftoperation using one air-powered screw-feedunderground rig and one skid-mountedconverted surface rig. The results obtainedfrom the holes were analysed and plotted onsite during each day shift. Once data beganto be acquired and it was realized that thegeology was fairly complex and involvedmultiple fault intersections, additionalrigs were mobilized. It was found that thedemands of long uphole drilling could onlybe met using conventional skid mountedhigh-torque surface rigs. The small bar-and-arm mounted air-powered undergroundrigs were soon proved incapable of coringthe 100 - 150 m. long upwards inclinedholes required in order to explore outwardsfrom the pilot excavations. These longholes were drilled at 250 upwards in orderto optimize the cross-cutting of sufficientstrata to allow stratigraphic correlationfrom one hole to the next. Although thelarger, skid mounted, rigs were found wellcapable of drilling these raker holes, theywere found to be of limited capability whendrilling vertical up-holes in excess ofabout 60m. However, by careful planning ofhole layouts, this limitation did notunduly compromise the investigation data.

From start to completion of the two month,24 hour per day, fast track programme ofdrilling, which resulted in the discoveryand delineation of two major, previouslyunidentified faults, over 40 undergrounddrillholes varying in length to 160m., weredrilled and logged. Some 250m. of explor-atory adits were also developed and all ofthe tunnel sidewalls were mapped to assistin correlation of the drillholes.

Excavation of first the Pilot Tunnels andthen the full-face Penstock drivages,confirmed the core-drilling data that twomajor faults and several minor cross-shearsexisted all within a 60m wide band crossingthe scheme alignment (Figure 5). Thedetailed mapping also confirmed thestratigraphic offsets suggested by the holeGP22 data.

Because of the stratigraphic disruptioncreated by these two major fault zones,which are shown in detail on Figures 6 and7, several design changes were necessary tothe locations of the Pressure Tunnels andthe steel-concrete transition zones. Thesechanges were made to minimize risk ofhydrofracture induced cracking byoptimizing the tunnel alignments to ensure

that the transition zones:

a) avoided the low-modulus fractured rockconditions associated with the faults,and,

b) if possible, could be preferentiallylocated within high-modulus sandstone.

The detailed configuration of Fault A,which dips at 450 to the north and trendseast-west across the scheme alignment about430m. upstream of the Machine Hall, isshown on Figure 6. The fault, is actuallycomprised of two main shear planes separ-ated by 2 m. to 4 m. of downwarped strata.It is bounded on either side by a zone ofdisturbance up to 30 metres wide. Based onstratigraphic correlation a combined down-throw of some 9m to the north occurs acrossthe two planes.

Fault B, which trends sub-parallel topenstock 1/2 and intersects Pressure Tunnel1/2 at an oblique angle some 680 m upstreamof the Machine Hall, was found to be muchmore complex than Fault A. It was found tovary in character along the schemealignment, comprising two well developedparallel shear planes approximately 1 metreapart bounding a brecciated and mylonitizedzone in the Pilot Heading driven east ofPenstock 1/2, (refer Figure 5) but changingto series of discrete planes and thinbrecciated zones where it crosses the re-aligned Pressure Tunnel, (Figure 7). Based

Figure 7 Composite Isometric Drawingof Face Happing Records for Pressure

Tunnel 1/2 through Fault B

on sidewall mapping and the results of thediamond core drilling, it was found thatoverall, the fault dips to the east atbetween 55 and 7Q0 and down throws thestrata approximately 20m. also to the east.

SANDSTONE 25 % SOISTONEIV NVSBEODEO SANDSTONE 555 5575 XLV

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Furthermore, complete correlation was foundbetween this area and the core logging ofthe old surface hole CP22, thus confirmingthe anomalous stratigraphic interpretationthat originally led to the probe drillingprogramme.

Although the details of the geometry of thefaults was only fully appreciated once theywere exposed in the Pilot Headings, withoutthe data from the inclined core drilling itwould have been impossible to complete thestratigraphic and structural correlationsnecessary for revising the Pressure Tunnellayouts to those shown on Figure 5. Infact, to avoid intersection with Fault B inthe critical area of the steel to concretetransition section, the alignment of boththe Penstock and Pressure Tunnel 1/2 wereadjusted and the steel to concrete tran-sition section was moved further upstreamto an area away from the direct influenceof the faults (Figures 5 and 6).

DONKIN-MORIRNTEN DRIVAGES

The sub-seabed tunnels required for accessto the productive coal horizon to be minedat Donkin (Cillman, 1982), necessitated aninitial pair of parallel tunnels to bedriven for 3km offshore at a decline of upto 20% (Figure 8). The twin tunnels were tobe excavated through a sequence of gently

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dipping sedimentary rocks into groundwithin which, based on offshore geophysicalsurveying there was some possibility ofstructural disturbance. As only limitedoffshore drilling had been feasible, - forsubmarine coal reserves a 1km. exclusionbarrier is required around each explorationhole - the decision was reached to conductunderground core drilling ahead of thetunnel drivages to provide information forstratigraphic control and grade predictionpurposes as well as data on possible gas orwater problems.

Onshore portalling was completed for thetwo required drivages (#2 and #3 Slopes) bydrill and blast methods and tunnelling wasinitiated also using drill and blastmethods on Slope #3, with upward inclinedforward strata control holes, similar tothose laid out for the Drakensberg tunnels,being drilled from the tunnel face atweekends. This, #3 tunnel, was driven drilland blast to ch. 1027m. during which tine,TBM trials were carried Out on Slope #2using a 4m. diameter prototype hard rockTBM. The success of this trial led todesign and construction of a full face7.6m. diameter TBM (Hunter and Lovat, 1984,Marsh et al., 1986). As both probe holedrilling for gas and water prediction wasa requirement, and contingency schemes forgrout-hole drilling and rock-boltinstallation needed to be developed for thefull-face TBM design, it was decided to

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Figure 8 General Arrangement of Donkin-Horien Mine Access Slopes and Summary Geology

mount a full capability coring rig ontothe machine so that strata control holescould be executed directly from the TBM.

a TBM - mounted drill-rig

The rig position on the TBN, as shown onFigures 9 and 10, was optimized to allow:

- forward on-axis probe drilling,- radial holes, including vertical holes

up and down, for bolts or instruments,- 350 raked upward and forward holes for

cross-strata geological coring, and- fan pattern radial holes for grouting

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Figure 10 Access Port Arrangements for Use of the Coring Rig for Drilling StrataControl, Instrumentation and Probe Holes through the TEN Head and Shield Assembly

Prior to selection of the rig for use onthe TBM, several underground trials ofdifferent types of rigs were carried out.These were aimed at establishing both thesuitability and efficiency of various rigsfor achieving good core recovery in typicalcoal measures strata. The trials were alsodirected towards checking whether it waspossible to achieve the desired setup, rodhandling and coring rates necessary toguarantee drilling an upwards raked stratacontrol hole to at least 30 metres ahead ofand above the face within the limited fourhour daily TBM maintenance period.

Rod-tripping was seen generally as the mosttime consuming operation, however coringspeeds in different materials also affectedrig performance, especially for the lowertorque types tested. Conventional top-headchuck machines were compared to flat-bed

Figure 11 View of trailing edge of TENshield showing Modified Longyear ERS 38mounted for Strata Control Drilling

Figure 9 Modified Longyear EHS 38 RigRod Aligmment Arrangement for drilling

350 upwards Strata Control Holes

0.48 m

UPWARDS CROSS STRATA HOLE

MACHINE

~—F-I.42m

feed rigs in order to check maximum coringand rod-handling speeds in a forward andupward mode. Various thin kerf and non-coring bits were also tested to evaluatemaximum penetration rates. After someinitial evaluations, and followingcomparative field trials of a Diamec 251(flat-bed feed) and a Longyear EHS 38, thedecision was made to use a modified Long-year rig incorporated onto the tail sectionof the TBM. (Figure 9). The decision wasbased not only on the performance of therig, but also on the availability ofservice/backup to the tunnel location andon the compatibility of the drillrig’shydraulics with the power-pack componentsof the Lovat M-300 TBM.

The primary purpose for building the drill-rig right onto the TBM was for forwardgeological prediction. However, in additionto the requirements of drilling for coreretovery and strata prediction, the rig wasequipped for rapid probe drilling usingnon-coring synthetic diamond “Chrisset”bits, penetration rates for which arecomparable to normal air-rotary percussion.This allowed the rig to be also used foron-axis drilling of forward probe holes forgas or water intersection control purposes.Further, because of the rig’s placement atthe rear of the main shielded section ofthe TEN, (Figure 11) it was suitablyplaced, if the need arose, for drillingradial, forward-raked grout-holes, or fordrilling rockbolt holes for placing supportbehind the shield section, or for drillinginstrumentation holes as required.

After some initial trials of the LongyearEHS 38 rig mounted on the TBM, a scheduleof weekend core drilling was developed toallow forward geological prediction withoutinterference to normal TBM operating shiftrequirements. In general, one 45m. long 350

upwards inclined diamond BQ cored stratacontrol hole was drilled over the tunnelcrown every two weeks and one lOOm. longuncored probe hole was drilled every weekdirectly along the tunnel axis ahead of theface for gas and water control.

Other holes which were drilled with therig, including those for extensometers andvertical upwards strata investigation holeswere also drilled at weekends or withinscheduled maintenance breaks or otherprogrammed shutdowns so as not to interferewith tunnelling advance, which peaked atabout 30m/day (Marsh et al.,1985). Thedata obtained from the drilling was timelyand like the Drakensberg probe drilling,helpful in optimizing tunnel grades tomaximize excavation within good sandstone.

It also helped significantly by providingexcellent forewarning of coal and muds toneintersections that tended to affect thecutter performance of the Lovat TBM.

Conclusions

Probe hole drilling ahead of tunnellingneed not be considered only as a percussiondrilled hole advanced the regulatory 3m. orother required distance to check for waterand gas occurrences. With modern equipment,cored hole drilling is both practical andquick and can provide vital information onground conditions unattainable by open holetechniques even with recourse to use ofdown-hole geophysical tools.

25~35o upward inclined diamond cored probeholes ahead of sub-horizontal tunnels inbedded sedimentary rock can be of immensevalue for predicting geological conditionsahead of the face. For such probe holes tobe both drillable and analyzable within thetight time frames required to keep up withmodern TBM drivage rates, careful choice ofdrills and coring equipment is vital. Withthe increasing availability of small, buthigh torque flat feed rigs for undergrounduse and improved thin kerf coringequipment, such probe holes can be viablyexecuted and evaluated within limited tinewindows in a tunnelling schedule (such asweekends or maintenance shifts). This makestheir use feasible and attractive for bothTEN and drill and blast drivages wheregeological conditions are not entirelycertain or where potential geological orwater inflow problems may be disruptive.

Geophysical and remote sensing techniquesincluding satellite imagery can aidunderstanding of structural geologicalconditions, but must be correlated to harddrillhole data in order to be of value tothe tunnelling engineer. It is suggestedthat integration of surface remote sensingtechniques with well planned strata controland forward cored probe drilling layoutsconstitutes possibly the best approach forinvestigating long tunnel alignments.

Acknowledgements

The author wishes to thank the ElectricitySupply Commission of South Africa and theCape Breton Development Corporation ofCanada for their permission to publish thematerial presented in this paper. Thecontribution of the author’s colleaguesfrom within Golder Associates and otherorganizations who were involved with theprojects is also acknowledged. Specific

recognition is due to Dr.T.W.Mellors andMr.P.J.Terbrugge for their contributions tothe successful completion of the drillingstudies for the Drakensberg Pressure TunnelTransition Design and to Mr.R.C.F.King forhis contribution to the execution andimplementation of the strata controlprogramme in the Donkin-Morien Tunnels.

References

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De Witt N.J. (1983) Constructing theDrakensberg Pressure Tunnels. Water Powerand Dam Construction. 15 pp.

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Palmer J.H.L., Lovat R.P., and Marsh J.C.,(1985). Performance of a 7.6m Diameter FullFace Tunnel Boring Machine Designed for aCanadian Coal Mine. Proc. 4th InternationalTunnelling Symposium, Brighton, England.

Sharp J.C and Gonano, L.P.,(1982) RockEngineering Aspects of the Concrete LinedPressure Tunnels of the Drakensberg PumpedStorage Scheme. Proc. ISRM Symposium - RockMechanics Related to Caverns and PressureShafts. Aachen. Vol 2., pp.717-733.

Sharp J.C., Endersbee L.A. and Mellors T.W.(1984) Design and Observed Performance ofPermanent Cavern Excavations in weak,bedded strata. Proc. ISRM. Conf. Cambridgepp.493-507

Sharp .3.C., Pine R.J., Moy D., and ByrneR.J. (1979) The Use of a Trial Enlargementfor the Underground Cavern Design of theDrakensberg Pumped Storage Scheme. Proc.4th Congress Tnt. Soc. Rock. Mechanics,Montreaux.

Sharp J.C. and Mellors T.W. (1982) RockEngineering Investigation and DesignStudies for the Drakensberg Pumped StorageScheme. Civ. Engr. in South Africa. Vol 24,#8 pp.399-416

Whiteway P. (1985) TEN Drives to Coal Seamunder the Atlantic. The Northern Miner,March 21st. pp B3-B7.

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M-300 Tunnel Boring Machine

The M-300 is a fully shielded open face rockboring machine fabricated for driving a 14.5 KM(9 mile) access decline at the Donkin-MorienDevelopment Project on Cape Breton Island inNova Scotia, Canada. The design and develop-ment of this innovative tunnelling equipment wasfunded by Canada’s National Research Council,the Cape Breton Development Corporation andSupply and Services Canada for July 1983delivery.

Design Features

The cuttinghead is equipped with inter-changeable roller disc cutters and drag type car-bide teeth to facilitate the most efficient cutterselection for the varying rock conditions.

The cuttinghead can be rotated clockwise orcounter-clockwise at variable speeds not ex-ceeding 92 meters/minute (302 feet/minute) tominimize the possibility of a methane explosioninitiated by sparks created by the cutters.

The machine has been designed for a gassymine application and is equipped with intrinsical-ly safe electrics and flame resistant hydraulics tomeet the requirements of Canmet certificationand Labour Canada standards. The unit alsofeatures a ventilation system to control dust andmix methane with air to acceptable levels in anefficient manner.

The machine has a back-up system for main-taining all required services including electrics,hydraulics, ventilation, dust control, cooling,storage, repair, etc.

Technical Specifications

The machine is propelled by 24 pushing jackswith a 1.7 meter (5’ 8”) stroke and is equippedwith a mechanical rib erector and rib expander tofacilitate lining operations.

The machine has a 11.5 meter (38’) longprimary conveyor with a 1.2 meter (4’) wide beltand a 170.0 meter (560’) long trailing conveyorwith a 1.2 meter (4’) wide belt. The trailing con-veyor consists of detachable and interchangeablesections that are post supported on pipe skates.

Bore Diameter: 7.6 meters (25’) (Nominal)Overall Length: 6.3 meters (20’ 9”) (Nominal)Total Connected Horse Power: 2050 H PEstimated Overall Weight: 350 tonne (344 tons)

This project is another example of Lovat’s con-tinuing commitment to innovation and leadershipin the design and manufacture of tunnellingequipment.

LOVAT TUNNELEquipment Inc.441 Carlingview Drive,Rexdale, Ontario M9W 5G7Telephone (416)675-3293Telex 06-989167