Methods of overburden<billing in geotechnicalconstruction- a genericclassificationBy DA Bruce, BScPhD, CEng. MICE,MASCE, MAEG, MHKIE, FGS

fii)ates)&QFKalt eFtat ) t. 8)il

~bites ~ ineitnieil ivll ~ ~ etag yq i~ i ta o

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~ i3iecpt ~ laimaxia ~ I'inii10i T

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BackgroundThe construction of specialist groundimprovement and support systems usuallyinvolves the drilling ofholes 60mm to250mm in diameter and to maximumdepths of 100m. It is very rare that theselimits are exceeded in drilling for groundanchorages, grout holes, minipiles(pinpiles) and in situ reinforcing.

The methods available for drilling in rock—or other materials which will provide anopen hole without the need forsimultaneous wall support —are wellknown and easily classified (egMcGregor 1967)'.Thus, depending on thegeologic conditions, the purpose of thedrilling, the economic implications andthe proclivities of the interested parties,rock drilling is most commonly conductedby purely rotary methods (from diamondcoring to blind tricones) or by rotary-percussive systems featuring either tophammers or down-the-hole hammers(Bruce, 1989)3.Within each broadcategory there is, of course, a wealth ofoptions with respect to equipment,flushing characteristics and operationaltechniques. However, the field remainsfundamentally simple and relatively finite.

In marked contrast, the various methodscurrently available for drilling overburdenpresent a substantially different picture.Overburden offers intrinsically far moreproblematical variability to the the driller:to rock masses'ardness andabrasiveness must be added many otherrelevant properties for consideration.Contractors and manufacturers have thusdeveloped different systems to optimisedrilling performance and economics,often specially designed to combatparticular local conditions. As a result,there is currently on the market apotentially bewildering range ofoverburden drilling systems, and it wouldseem that the promotion ofany givensystem often owes less to the groundconditions than to the experience andresources of the contractor in question.

The purpose of this paper is therefore toprovide a generic classification of themethods used to drill holes in soilsgenerally. In some cases the soilcharacteristics or hole geometry maypermit the open holing referred to above.In other cases it may be possible totemporarQy stabilise holes by using a mudfoam flush. This review, howeveraddresses conditions which necessitatehole stabilisation by the use of some formof casing, typically retrieved at a laterstage and reused. Seven basic categoriesof systems are identified.

It should be noted that only contemporaryproduction methods have beenconsidered, thereby excluding options

synonymous with high cost (eg diamonddrilling) or restricted geologicalcompatibility (eg vibrodriving). As a finalword of introduction, it will become clearthat numerous references have beenmade to speciTic companies, systems andproducts. No endorsement or favouritismshould be implied, although care has beentaken to name reputable andrepresentative sources.

Methods of overburdendrillingThe following classification is offeredbroadly in terms of increasing compexity,with the exception of Type 7 (hollow stemauger).

Type l:Single tube advancementIn appropriate ground conditions with theproper equipment this is the cheapest andfastest method. There are two variants:~ Drive drilling and~ External flush (wash boring)Drive drilling. This is, in principle, apercussive system in which the steelcasing is drilled with the leading endterminating in either a knock off driveshoe or bit Fig. I.No flush is used. A littlerotation is necessary to prevent the stringuncoupling during driving and to reducedeviation potential (recorded for the76.1mm size being as much as 1 in 7.5).

Rarely however, are sizes over 101.6mmpractical, except in particularly loose,gravelly or sandy conditions, and the76.1mm system appears to be theoptimum in terms of cost effectiveness.

kr(rt(&65I Ii tl eni ~~ ci ~//~ ti ti 80percussion head1'/0 to H 55

percussion heedcentral flushing1'/0 to H55

flushing heed tor drive drilling1'/I" lOH55 gt 38IO178

fhl&ltt llilted

g 4 ~ 'htttttttft

) tttI t n!IGI I

transition nipplefor flushing headiir 38 to 178

drive dnlling tubelength 0.5 lO 3 malarQt 38 lo 178

connection nipple3t 38 to 178

drive shoelit 38 lo 178

drive bilQl 38 lo 178

percussion bitgt 38 to178

rotary b<t

tp 38 lo 178grouling mpplefir 38 lo 178

Hg. 1.ComJhonents ofdrive drfZHngsystem plntte).GROUND ENGINEERING OCTOBER . 19B9

25

-81

Production figures ofup to 260m/day areclaimed for this size in favourableconditions, to maximum depths of 40m.This system was used recently in thesaturated fluvial deposits in Cairo, withgreat distinction.

-82

-84 to -89

I|mdExternal tiush. Again a single casing tubeis advanced to the final depth, but in thiscase the drilling mechanism is rotary (andnot percussive), and the casing terminatesin an open crown, or bit, and not a closedpoint. Water flush of proper volume andpressure is passed continuously downthrough the casing during drQling andwashes debris out and away from theleading end. The water born debris thentypically escapes to the surface aroundthe outside of the casing, but may equallybe 'lost'nto especially receptive upperhorizons. Depending on the purposes ofthe drilling, this system maybe especiallyuseful or potentially dangerous. Forexample, if ground anchorages are to beformed by subsequent pressure groutingthrough the casing during its withdrawal,the washing will have helped promote abulb of larger diameter, and so a fixedanchorage ofhigher load bearingpotential. Conversely, if the drilling is tobe conducted through highly sensitivesoils under particularly delicatestructures, the uncontrolled washing ofthe soil may prove inadvisable. However,even in this case, the system should not berejected if good practice andcommonsense can together verify itsapplicability.

AQ sizes of casing can be used with thisapproach, but the most commonapplications of anchoring, minipiling andin situ reinforcement usually involvediameters of 100mm to 200mm.

Type 2:Rotary duplexIn the most common situations, whenground conditions and job requirementscombine to eliminate the easy option ofsingle tube advancement, some methodfeaturing the simultaneousadvancementof internal rod (with bit) andexternal casing (with crown) must beadopted. Such methods may collectivelybe referred to as duplex.

The basic method, which most frequentlycarries the term duplex, is purely rotary. Itrelies for its penetration performance onvariations of rig thrust, head torque androtational speed, and Qushingcharacteristics, other factors being equal.The major components are illustrated inHg. 2 for a typical size, and are

GROUND ENGINEERING OCTOBER 1989

Order-no.

178-80178-81178-82178-83178-84178-85178-86178-87178-88178-89178-90

Name

transition flange with Wirth-thread 63,5ejection flushing head 63,5 x 177,8tube 177,8 x 900mm

casing crown button type 178 x It 180mm

tube 63,5 x 900mm

tube 63,5 x 1500mm

tube 63 ' x 2000mm

tube 63 ' x 2500mm

tube 63,5 x 3000mm

tube 63~5 x 3500mm

rotary bit tI 149,2mm with transition to tube 63,5

~ Outer casing (rotated)~ Casing crown~ Inner driQ rod (rotated)~ Drill bit (usuaQy tricone)~ Duplex head/transition Qange,

connecting to the rotary head of the rigI

Ifa large number of hard obstructions isforeseen, it is possible to exchange adown-the-hole hammer for the tricone bit,to hopefully fragment the obstruction andso permit the casing to be rotated downwith less resistance (eg) Bruce and Yeung,1983)s.Equally, in especially difficultground conditions, reverse circulationmay be used. Duplex is most commonlyused as a high production tool in soft andvariable ground conditions, and usuallywith powerful hydraulic rotary heads. As aconsequence, many contractors mayfavour rather more robust systems thanillustrated in Fig. 2 and, as example, Fig. 3shows the heavy duty range manufacturedby Euro-Drill. However, where conditionsare less onerous, or environmentalrestraints are signiQcant, standard Qushcoupled or jointed casing, or water wellcasing with appropriate rod types may beused, in accordance with local nationalstandards.

Type 3:Rotary percussiveconcentric duplexThis method, historically typified by theAtlas Copco OD72 system, is a duplexmethod wherein both rods and casingsare simultaneously percussed and rotatedHg.4. In its early years of use it was

driven by mainly air hammers withrelatively restricted torque capacity.Therefore, the applicability was regardedas limited, and other methods, notablyODEX, with far less emphasis on rotationalpower were developed. More recently,however, there is clear evidence of aresurgence of the method as a result of theincreasing availability ofhigher torquehydraulic top hammers. By way ofillustration, it maybe noted that rotarypercussion duplex was the preferredproduction drilling tool of aQ majorcontractors on Mass Transit RailwayCorporation related works in Hong Kong.Ground conditions were extremelyonerous, featuring gritty decomposedgranites with large fresh rock relicts. Thismarket for grout hole installation alone,was conservatively estimated at about200 000m ofdrilling per year, in the late1970sand early 1980s.

I

Although the Atlas Copco system isavailable in only one size, othermanufacturers can supply sizes asin Table 2.The casings are, of necessity, high qualitysteel, and have modified rope formthreads and wall thicknesses of around12mm (as opposed to 6mm for ODEX).One consequence is that the unit weight ishigh, and normally 2m casing lengths areused in the larger sizes. Drilling on withthe rods into rock or other stable strata isaccomplished without the necessity tochange the bit. Both insert and button

Hg.2. Components ofl7?Smm rotary dnplex system P&tte).

'A mm dia HEAVY DUTY CASINO

types are available for bits and casingshoes. As with other forms of concentricduplex, in especially sensitive ground, thebit can be retracted up into the casingbehind the casing shoe, to minimisecavitation of the ground and promotegood flush return. The opposite is done inparticularly competent ground. Flushingwater is best introduced via an externalflushing device and should have aminimum rate of about 100litres/minute-at up to 2N/mm .To improve flush returnfurther, sleeving can be inserted betweenadjacent couplers on the rod string topresent a constant annular volume andreduce local pressure drops and resultantblockages.

Assuming that sufficient torque (say to6000Nm) is available at the hammer, andadequate pull-out force can be applied(say around 40kN) then rotary percussiveduplex may be regarded realistically as aviable and robust production method forholes to 60m depth. Clearly, however, forthe deeper drQling associated with waterwells or mineral prospecting it may not bethe most cost effective option.

Type 4:Rotary percussiveeccekktric duplexRestricted in terms of torque availabilityand faced with the increasaing demandfor a system to penetrate the difficultScandinavian glacial deposits reliably,Atlas Copco and Sandvik jointlydeveloped the very successful ODEXsystem in 1972.This percussive duplexvariant features a pilot bit with eccentricreamer, which cuts a hole of diameterslightly larger than the casing. Themanufacturer states that its performanceis not impaired hy gross changes in theground from loose soil to fresh igneousrocks; the method cuts straight throughohstructions or shoulders them aside.Early experience in Britain (Patey, 1977)also confirmed its ability to deal withartificial ohstructions such as slag andother foundry spoil, typical of fill depositsin old industrialiised areas. Good results inloose scree type deposits, rip rap, andthrough old piled foundations have alsobeen confirmed.

The principle of the operation is illustratedin Fig.5. In (a), the single piece pilot bit(concentric) is shown drilling beneath thecasing; rotation has been applied to therod string, swinging out the reamingdevice (eccentric) which is enlarging thehole so facilitating the advancement of thecasing (percussed only). The reamer is

I/I

Ii

Manufactured with replaceable tool joints that

can be replaced with the minimum of equipment

end minimum of down time.

SIZE A B c

3 'I 38" 23 35

45" 4*.i

3 41"

41" 51"

6i" 6t"

J 6'm dia

337" 33" 3" 33"

HEAVY DUTY DRILL kIODS

Supplied with two threads which are inter-

changeable with existing dnll pipe

The strength is created by the area of torque

transfer being increased at the point of joint

contact All standards of manufacture relating

to B S 4019 rods are apphed to these rods

TYPE OF ROD A

NWY HD

B O.L

5'10'

5'"10'"

t7

8 mm diaREUSABLE TOOL JOINTS ARE SUPPLIED

AS STANDARD

A mm dra

Eyg.3.Heavy duty rotary dkgrlexsystem. Note that the recommended rock hit~ovum sizes for the four mail'or casing types are 2%",38",4'", and HVreslkectiveiy fHuro lhill).

litss

V/1

Upper pail of illagushing heed158 .lo Hss

q i@j]flushing ring hushing beh 738oiT 15

lube connechon e 78 lo 178

II/IIIIL I Q( I 8 II I I III

connecgon nipplee 78 to 176

dialing lubelength 0.5 to 3 melargt 78 to 178

casing crowngf 76 to 178

sw

couplingTsgor Tas

blear md T38 or 7S5hingih 1 —3 meteror special lengths

Inner bhT 38er T85

ginuhllg Captfl 76 lo 178

Hg.4. Componentsofrotary percussiveduplexsystem PFutte).

held in the correct position by stop lugs 30m. When drilling is complete SVg. 5fh)during drilling. Cuttings are transported the rods are counter-rotated, so closingupwards past the guide device, inside the the reamer and permitting the withdrawalcasing to exit via ports at the driving cap. of the rod and hit assembly. Drilling onFlush is usually water, although air can be into rock must then he done with a suitableused, and foam is common for depths over rock bit Fig. 5(c).ODEX is available with 27

GROUND ENGINEERING OCTOBER 1989

SystemDesignation

o.d. (mmj i,d. (mm/

42.4 1 551.0 18635 3576.1 50889 64

101.6 721 08.0114 3 881 33.0 108177.8 150

Recommendedtube lengths

(must be portableby 2 men/

3.0m3.0m3.0m3.0m2.5m2.0m2.0m2.0m2.0m1.5m

28

J.~ 'v o

yaDC,oo

o.s

.

OO>'sill

~ I It)

A When dnlling, the reamer ol the ODEX bit swingsout and drills a hole larger than the external diameterof ttie casing tube.

B When the required depth has been reached, thedrill is reversed and the reamer swings in to its mini-

mum diameter, allowing the bit to be lifted up through

the casing, which is lettin the hole.

C Drilang can continue with an ordinary DTH drill bit

Hg.S. Operating principle ofODEXPl tins Copco).both top hammer and down-the-holeoptions and selection reQects groundconditions, hole diameter, hole purpose,and the type of rig and head available. Inthe former case, Fig. 6(a), part pf thepercussive energy is transferred from thetop hammer, via a shank adaptor, to adriving cap above the casing. For down-the-hole drilling, Hg. 6 (b), the percussiveenergy is transferred to the casing fromthe hammer by a special bit tube with adriving (or impact) shoe. The casing istherefore pulled down, again withoutrotation, from its lower end. In both cases,however, the steel must be strong enough

GROUND ENGINEERING OCTOBER 1989

to resist the percussive energy of thehammer either in compression (tophammer), or in tension (down-the-hole).Also, where it is to be extracted, thethreaded casing must also have sufficienttensile strength, particularly in thethreaded zones, and this parameter oftendictates the practical depth to be drilledunder any given conditions. Indeed,where ODEX 76 has been employed as aproducton drilling tool under adverseconditions, the typically thin-walled rotarycasing of the standard system has had tobe altered by specialist contractors,within, of course, the limits imposed by thegeometry of the other elements of thesystem.

Regarding the anticipated longevities ofthe key components of the ODEX and ODsystems (for comparison), Atlas Copcohas published the indicative guidelinesreproduced in TaMe 3.It should be noted,however, that the relatively recentdevelopments of high torque rotary andpercussive drill heads have breathed newlife back into conventional and simplerconcentric duplex systems, as describedabove. Therefore the use of top driveeccentric duplex is becoming rarer. Onthe other hand, the demand remainsstrong especially in the water wellindustry for the drilling of large diameterholes in which the casing may be left inpermanently. In such cases the down-the-hole variants still have much to offerespecially when the dr)IIer has availableonly a standard medium sized drill rig with

rotary head, and has experience in down-the-hole drilling.

Most recently Halco has developed itsown eccentric duplex system called SimCas Hg. Z. As the reaming device is inonly two pieces, the operation is claimedto be simpler and more robust than thethree piece ODEX equivalent. A similarsystem is also offered by Hutte and byWeaver &Hurt (Bulroc overburdendrilling system).

TaMe 1.Standard drive drillingsfses(ffatte).

ODEX SystemPilot Bit 200- 600 drilled metresReamer 100- 300 drilled metresGuide 400-1 200 drilled metres

The various items are normallyconsumed in the following ratios:1 guide; 2 pilot bits; 4 reamers.

OD SystemExtension Tube

1000-1500 drilled metresTube Coupling 800-1000 drilled metresRing Bit 150- 400 drilled metresAdaptor Sleeve

1000-1200 drilled metresCross-Bit 300- 500 drilled metres

ODEX and OD SystemsShank adaptor, flushing head,driving cap 800-1000 drilled metresExtension Rods

1000-1500 drilled metresCoupling Sleeves

800-1000 drilled metres

TaMe 3.Indicative gaidelines onlife oflltlas Copco OD and ODEXcompanents(ll ties Copco).

Sizes NW Casing HW Casing

Pilot Hole orBit DiameterUnderreamedHole Dia (Max)Pin ConnectionPilot BitConnection BoxFeed Pressureto OperateOptional FeedPressure

73.0 mm 95.2 mm

92.0 mm 117.4mm"NW" Rod "HW" Rod

"NW" Rod 2/4 API

29.1kg/sq cm 65.8kg/sq cm

14.0kg/sq cm 32.4kg/sq cm

Assembly Size NW Size HW

DeSCriptiOn Pair lvo Weight Part No Weight

Underreamei

Iless Pilot Bit)

Optional

Underieamed

Hole Dia's

21145 12.2kg 2l 144 18.5kg

To 111.1mm To 152.4 mm

Table 4.Specfffcations for casingandeneamingsystem (licker Dry).

Q.d(mm)

mtn t.d.(mm)

CasingCrown o.d. Bit dia.

(mm) (mm)

88.9101.6108.0

'14.3

1330'77.8

'4728288

108150

92104112116135182

60677783

103146

Table 2.Standard percassive daplextdses (llatte) ('enotes common sisesfordoable head drilllntrsection).

Hole die.(mmJ

140155170190230

Stem o.d.(mmJ

76.188.9101.61 08.01 14.3

Stem i.d.(mm/

5064728288

TaMe 6.Hollow stem angers fHatte),

In summary, a major attraction of ODEXtype systems is that the effective efficientdepth ofpenetration is not primarilydependent on driving torque, since thepresenter of the greatest steeVgroundcontact area, ie the casing, is not rotated.However, the system remains relativelysophisticated, and its success is verysensitive not only to operator skill andexpertise, but to the quality of the casingand its joints, and the efficiency of theflush

Tyye S.Rotary or driven dnylexand eneamingSeveral such systems have beenconceived and employed with varyingdegrees of technical and commercialsuccess in recent years. One of the moresuccessful-the casing underreamer, of

Table S.SpecfHcatfoa far doaMe headdrill, with aftherrotary orrotarf/pereassfve option jor inner drill striate%num).

OPERATINGHETHOD

OPTION A OPTION 8OUTER CASING Rotated * Rotated *

INNER ROD Rotated * Percussed/Rotated *

Service weightincluding base plate kg 630 700

Oil flow rate(front/rear rotary mechanism max. 1/min 160/170 160

Oil flow rate (percussivemech. for inner string) max. 1/min -/85

Operating pressure (front/rear rotary/percussion mech.) max. bar 210/260/- 210/170/170

Torque(front/rear rotary mechanism) max. Nm 8000/4000

Number of revolutions+(front/rear rotary mechanism) max. rpm 110/145

Number of blows max. min

8000/4000

110/110

-/1800

Connection threadouter/inner drill strings to be specified to be specified

Hole diameter

Flushing medium

mm 100-300

air/water

100-300

air/water

* Clockwise or counterclockwise, but inner and outer drill strings alwayscounter rotating.

GROUND ENGINEERING OCTOBER 1989

29

!

Recormnsnded casing dimes'osrrxaflc I Americsnstandard (mm) [

standard (in)

Ore tube INam. Reamed diam.

For top hammersODEX 76 W/T eeg 57

COP 1238

OOEX 127 W/T eeg 57COP 1238

W: max. O.D. 89min. I.D. 78mm. wsa tickness 4.5 mm

T: 88.9 x 77.8 R.H. thread

W: max. O.D. 142min. I.D. 128min. waa tickness 5 mm

T: 140 x 128 R.H. Ihresd

3'ls3%s

3'lr x 3'I ~

5'sir ~

51II~

5 lr x 5 br

R 38 (I'b) 96 13 I»)

R 38 (I'b) 162 (6sls) [ (( I

For DTH hammersOOEX 00 W/T COP 32

A 30-15W: max. O.D. 115 4'lr

min. I.D. 102 4min. waN dxcknsss 5 mm

T: 114.3x 101.6LH. thread 4'b x ~

76 (3) 123 (4'siss)

ODEX 115 W/T

ODEX 140 W

COP 42DHD 24DHD 340 AA 34-15

OHD 15DHD 350A 43-15

W: max. O.D. 142min. I.D. 128mm waN thickness 5 mm

7: 140 x 128 L.H. thread

max. 0 D. 171min. I.D. 157mm. wsN thickness 5 mm

5'sl ~

5'hs

5'Ir x 5'Iis

6sls6'ls

76 (3) 152 (6)

89 (3'Ir)

89 (3'lr) 187 (7sls)

114 (4'lr)

ODEX 165 W COP 62OHO 16DHD 360A 53-15

max. 0 D. 196 Txsmin. I.D. 183 7'lsmin wsN Ihickness 5.5 mm 114 (4'lr) 212 (8"br)

ODEX 215 W OHD 3$0A 63-15

max OD 257rnm ID 241min. wsa thickness 6 rnm

109'b

114 (4'lr) 278 (torslrs)

140 (5'b)

T = threaded casmg tubes W = welded ca»ng tubes

Hg. (L Comparison of(a) top 7 er (let), and (h) down-the-hole ODEXsystem (right), and data on system shee (fftlas COJIco).

Acker Drill- is taken as atypical example.In principle, an oversized hole is cut by abit, and the following casing is eitherdriven or rotated. As shown in Hg. 8theunderreaming is not conducted by theeccentric bit system of ODEX, but byactivating outwards cutting blades abovethe pilot hit. Thus if the overburden is soft,resistance is low, the blades remainretracted and the casing advances in thesimple duplex manner. However, whenhard layers are encountered the bladesopen and cut the clearance necessary forthe advancement of the casing. At Qnaldepth, thrust is removed from the driQstring, the underreamer blades fall in, andthe string can be extracted. The systempermits either subsequent or concurrentadvancement of the casing, relative to therods.

Two sizes (TaMe 4)are available,designed for heavy duty applications andthe installation ofNW or HW flush jointeddrill casing. Diamond faced cutter bladesare available for replacing the twincarbide insert blades when drillingextremely hard materiaL Diamond pilotbits are also commonly used to replaceroller, rock or drag type pilot bitscommonly used for drilling averageoverburden materials.

The undeneamer is operated at speedsnormally used for tricone or drag bits. Thethrust required for the I17.4mmunderreamer is about 4000N and for the92.0mm model is about 2000N. The waterrequirements are similar to those fornormal rotary drilling. The system iscapable ofpenetrating boulders, rockdebris, timber and steel.

Type 6:Double head duplex dzQliug30 This rotary duplex method is claimed to

GROUND ENGINEERING . OCTOBER 1989

mer

dapter

Sleeve

Cap

on Rod

6 Casing

,Ill

7 )ting Coupeng

0 Guide

g Reamer

8 Pilot Bit

be especially quiet, and to ensure minimal [

ground disturbance, and consistent costeffective penetration to over 80m in eventhe most difflcult ground conditions. It isdistinguished from conventional rotaryduplex by the fact that the rods, andcasings, are simultaneously rotated but inopposite senses. The inner drill rods, withright hand rotation cany either a down-the-hole hammer (air or water activated)in hard conditions, or some form of rotarybit in soft ground. Typical rotary energyrequirements are 2500N torque at 40rpmto8hpm.

The casing, with left hand rotation,terminates in a substantial crown which

1. Rotation unit2. AdapterX Drill pipe4. Discharge head5. Guide sleeve8. Down-the-hole drill7. Casing tube8. air sleeve9. Guide device

10 Reamer11. Pilotbit12. Casing shoe

I I~sss 8~ ssaIII~~ sss4 —"5,

920

cuts a slightly oversized hole, thusreducing casing/ground resistance.Rotational speeds are lower than inconventional duplex drilling (15rpm to30rpm) the advantage of the torqueavailahiTity (to 8000Nm).

However, the beneflts of the counterrotation are that the combined action ofthe casing and rod cutting is enhanced,and the prospect of flush debrisblockages in the casing/rod annulus isminimised due to its dynamic boundaries.Water flush is typically40 litres/minute to 60 litres/minute at1 SN/mm .In addition, the counter rotationhelps to ofhet natural tendencies for holesto deviate and, in conjunction with the stiff,thick walled casing used Table 2, holes ofexceptional straightness (say within1 in 100)can be routinely formed.

1 stertor tUbe (2 y Apl Rsg)For MACH 40 90 nm r 1340 nm long

For MACH 48 90 nm 4 1285 nm long

This system is driven by special doubleheads with both Klemm and KruppTaMe 5being prime examples. Theseheads can be mounted happily onrelatively smaQ and mobile track rigs ofsufficient hydraulic output isle l.Aparticular feature is the faciTity to movecoaxially the upper rotator (turning therods) about 300mm relative to the casingrotator. This affords the driller extra scopein selecting the relative advancement ofrod bit and casing shoe in response toground conditions. The lower rotator canalso work in high gear (say 30rpm), lowtorque range) or low gear (say 18rpm,twice the torque previously available). Inaddition the upper rotator can bereplaced with a rotary percussive headand the down-the-hole hammer omitted,as noted in Table S.As with otherpercussive, duplex variants, a retrievableunderreamer can be used to precut thesoil to a diameter just larger than thecasing shoe.

Double head duplex is common onEuropean sites with particularly difficult

. ground but restricted access. It was alsoused under simQar conditions recently atthe Hines Auditorium in Boston (Bruce,1988, 1989)swhile its use is growing- with

the increasing popularity of dieselhydraulic track rigs- on both coasts of theUnited States. In Canada, a project hasrecently been completed underground inNorth Ontario where the 133mm casinghas been drilled, straight, to 80m depththrough loose mine bacldill containinglarge boulders ofup to

SOON/mm'ompressive

strength, in headroom of 4m,at outputs equivalent to over SOm/shift.

Type 7:Hollow stem augerAuger drilling is a long establishedmethod ofdrilling cohesive soils with theminimum ofhard inclusions, and featuresthe rotation ofwhat is basically a screwinto the ground. The continuous fhghtauger may be in one part (as used in boredpiling works) or in connecting sections.The basic method uses a solid stem (orcore) to excavate the hole, which, whenthe auger is withdrawn, will remain onlydue to the natural competence of theground and the absence ofgroundwaterpressures. As noted earlier, such openhole methods are not the subject of thisdiscussion.

Casing O.D.

Casing I.D.

Maximum drill-through dia.

3. Guide tta»tgl nef Oulef dem 4 935 ITm leflgsl

4. Down-thedude hemmerMACH 40 93 nm Nnsr dern. ~ 900 mn long

MAcH 48.93 nm Nrlsr dem 4 gfg nm eng

5. Casing shoe122 nm rrer dern ~ 139.Tnm oner dern. 4 135 nm long

8 Driver121 fNfl OUler delTI r 125 ITTS INlg

7. Eccentric bk120 INTI rsrrsclsd 180 nsn mlsfnlsdPlol 80 nm dern

OPTIQNAL —Her&nels sridl tntsglst shock sbsofbesMACH 405 93 nm dern 4 tdl4 nm long

soon sls nor ses 90 mn esm 4 syso nm snrg

MAOH 485 93 rrm den: 4 1242 rrsn long

soon moner Ives 90 nm Nsm 4 1000 rrm long

DTH

i,)mOPESDetLLESC PULUNC

Sim-Cas 3 Sim-Ces 4 Sim-Cas 5 Sim-Cas 5

114mm 140mm

101.6mm 125.5mm

1 67mm

149.2mm

1 94mm

178mm

98mm 120mm 146mm 172mm

2. CooingType PW1238 INTI Ivlsr dern 4 1397 fNU SUIsf dsrfn 4 3048 nvfl loni

Much recent development has focused onhollow stem augers, which permit waterand/or grout to be pumped to the bottomof the hole, allow placing ofanchor bars or

Halco down-the-hole hammer types

Hg.?.Detaas oMm Cas system PKalco).GROUND ENGINEERING OCTOBER 1989

Mach 308 Mach 48/408 Mach 5V/50V Mach 6V/60V

Water Inlet

DrHI Head

Swivel

'19>ueh SratemFof plaolrl9 oaalrlg.

Rod Chunk

Ro(M>on Rods

HoaagonCoualngHominal~Ite totemliats

'125mm (in)115(~i)140 (5i)1$0 (Si>

Auool Sores200'250'350mm (in) mm ( n> mm (in)

140 (Si)160 (Si)205 (6)255(10)305 (12)

205 (8)255 (10)3DS (12)355 (14)405(16)

305 (12)355 (14)405 (16)450 (1$)510 (20)560 (22)610 (24)

lr'r2"

continuous stn>ht D ametei (D)

400mm (in)

305 (12)355 (14)405(16)480 (18)510 (20)560 (22)510 (24)660 (26)710 (2$)760 (30)

Halt O ~(Sit tutIna d ~ I

IIIIII ( Iri >

130 (5)155 (6>180 (7)230 (9)2$0 (11)340 (13i)395 (15i)460 (1S)510 (20)570 (22i)820 (24i)690 (27)740 (29)$00 (311)850 (33i)

Wash CuH>ngs Hots Augm and hola dmmoters haw been mended to nearest t"

D

Standard lengths (i) 1.0, 1.5 and 3 m (3 3. 5 and 10(t).mherlongtht and sugardmmmers ttsd Iv ave>abls

Nesow Stem Adeem Mtn I/Ocanlm tube

mm (m)

old H 5 Augerflight

mm (m)

o/d AugerSn

Itlm (In)

wlh 9

60 (2i) 145 (5l)100 (4) 215 (Si)130 (5) 255 (10)150 (6) 305 (12)

160 (6i)240 (9i)2$0 (11)340 (13i)

Q$/XZXrz'C.: Ã / '

I I

I

I +IU

EJg.9.Standard sfses ofcantfnuousfltght, and hollow stem augers Pfands England).

Hg.8. Operatfng yrtucfirle ofcasingundaneanrer system plcjfor).

grout tubes, or enable drilling on intounderlying strata for soil sampling or rocksocketing. Generally, however, asemphasised by the range of standardsizes Hg. 9and the capacities of typicalrotary head models, the whole concept ofaugering is still related to the largerdiameter Gelds of cast in situ piles,prebored pile holes and sand drains.

To reduce power requirements and allowadequate clearance for the flights, augerbits (or cutting heads) cut a hole 10% to12% larger than the auger diameter. Thepitch of the fights is 609() to 80% of theoutside diameter of the auger so as toreduce the tendency of the cuttings to rollback down the hole.

Expanding auger bits are available for usewith continuous flight augers for boringinside casing. The auger bit has an outsidediameter equal to the continuous fightauger, but expanding wings increase thecutting diameter to the outside diameter ofthe casing. During drilling the auger ispositioned so that the wings are just belowthe lower edge of the casing which maythen be advanced as cutting proceeds.

32 Reversing the rotation causes the wings tc

GROUND ENGINEERING OCTOBER 1989

fold back, enabling the auger and bit to bewithdrawn without disturbing the casing.

For applications within our Geld ofinterest, Table 6 shows typical sizes forhollow stem auger systems.

Final remarhsThis classification has been proposed inan attempt to offer a dispassionateoverview ofoverburden drilling methods—as distinct from commercially proposedsystems. It is believed to encompasscurrent practice in Western Europe andNorth America, while the research for thepaper turned up no additional or alternatetechnologies pubiished in other parts ofthe world. The author therefore hopes thatthe ciassification will prove useful for thenon specialist, and a target of constructivecriticism and embellishment bycolleagues more knowledgeable andintimate with the business.

Xchnowledgements

This concept ofclassification wasdeveloped out ofpresentations at Drillex,1984,Toronto, and the annual groutingcourse at St.Louis, Mssouri. It wasnurtured by colleagues at NicholsonConstruction Company, and friends inBritain. It was conceived out ofnecessity.

Technical and commercial hrochuSes fromAcker Drill Co. USA

Atlas Copco SwedenBohler Austria

Casagrande ItalyEuro-Drill UK

Halco UK

Hands-Eng)and UK

HongdrilVFEDCO Hong KongHutte West GermanyKlemm West GermanyKr pp West GermanyMontabert FranceNicholson USARodio indyWeaver and Hurt UK

Whth West Germany

References

1.McGregor K(1987.The drilling of rock, 1st Ed. CRBooks Ltd., London. 308pp.

8.Bruce DA(1989).'Contemporary practice ingeotechnical drilling and grouting.'eynote lecture,First Intl. Canadian groudng conference, Toronto, 18April, 38pp.

3.Bruce DA and Yeung CK(1983).'Minipiling at HongKong Country Club.'Hong Kong Contractor,November, pp. 13-18.

4. Patey DW (19TI).'Grouting old mine workings atMerthyr Tydfill'round Engineering, November, 4pp.

S.Bruce DA (1988, 1989).'Aspects ofminip)Tingpractice in the United States.'round Engineering,81(8),pp. 30-33and 38(1)pp. 3S-39.