MAI instructions 3 compressed.pdf

8/10/2019 MAI instructions 3 compressed.pdf

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MAI Hollow Bar SystemInstallation Instructions, Technical Notes

Section Content Page

1.0 Introduction....................................................................................................................11.1 On site with MAI Hollow Bar ............................................................................................2

2.0 MAI Hollow Bar - Technical Data ..................................................................................3

2.1 Cutting of Bars. Perforated Sections ...............................................................................3

3.0 Drill Bits: Selection and Performance .........................................................................43.1 Drill Bit Range .................................................................................................................53.2 Drill Bit Adaptor Sleeves ..................................................................................................5

4.0 Couplers: Cast and Machined ......................................................................................64.1 Seating and Sealing of Couplers .....................................................................................64.2 Hammer Couplers. Reducing Couplers..........................................................................6

5.0 Accessories ...................................................................................................................75.1 Load Bearing Nuts. Lock Nuts ........................................................................................75.2 Tapered Washers. Hemispherical Washers....................................................................7

5.3 Bearing Plates: Formed and Flat .....................................................................................75.4 Stub Tubes. End Caps ....................................................................................................85.5 Free Lengths ...................................................................................................................85.6 Borehole Spacers. Borehole Caps .................................................................................8

6.0 Installation Equipment ..................................................................................................96.1 Drill Rigs. Top Drives .......................................................................................................96.2 Hand Held Rock Drills .....................................................................................................9

7.0 Rotary Injection Adaptors...........................................................................................107.1 Component Parts and Assembly ...................................................................................107.2 Selection of Injection Adaptors for Drill Rigs .................................................................107.3 Locator Frame ............................................................................................................... 11

7.4 Rotary Injection Adaptor for Hand Held Equipment .......................................................127.5 Hex Shank Adaptor for Hand Held Equipment .............................................................. 12

8.0 Installation ...................................................................................................................138.1 Simultaneous Drilling and Grouting ...............................................................................138.2 Water Flush Drilling, followed by Grouting ....................................................................138.3 Air Flush Drilling, followed by Grouting .........................................................................138.4 Installation Rates ...........................................................................................................148.5 Limits of System: Clay, Rock, Concrete ........................................................................14

9.0 Grouting .......................................................................................................................159.1 Typical Grout Mixes .......................................................................................................159.2 Grout Pumps .................................................................................................................159.3 Grout Consumption .......................................................................................................159.4 Grouting Pressures .......................................................................................................169.5 Post Grouting ................................................................................................................16

10.0 Corrosion Protection...................................................................................................1710.1 Permanent Applications Classification .......................................................................1710.2 Limits of Borehole Grout as a Corrosion Protection Barrier ..........................................1810.3 Galvanizing of MAI Hollow Bar ......................................................................................1810.4 Sacrificial Corrosion Assessment ..................................................................................18

11.0 Stressing & Testing .....................................................................................................1911.1 Preparation of Testing Surfaces ....................................................................................1911.2 Alignment Loads............................................................................................................2011.3 Stressing and Testing Equipment ..................................................................................20

11.4 Testing ...........................................................................................................................2111.5 Guidelines for Design ....................................................................................................21

12.0 Applications ........................................................................................................... 23-24


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1.0 INTRODUCTION

This guide is written with the assumption that the installer is experienced in both drilling and grouting opera-tions.

MAI Hollow Bar System

The MAI Hollow Bar System is a fully threaded steel bar which can be drilled and grouted into loose orcollapsing soils without a casing. The bar features a hollow bore for simultaneous drilling and grouting anda left hand rope thread for connection to standard drill tooling.

Manufactured from heavy wall steel tubing, MAI Bar is cold rolled to form a standard rope thread profile(R25-R51). The rolling process refines the grain structure of the steel, increasing the yield strength andproducing a durable drill rod suitable for a range of applications. The standard rope thread of MAI Barproduces an excellent bond between the bar and grout as well as enabling connection to all conventionaldrill rigs and the use with a wide range of drill steel accessories and bits.

MAI Hollow Bar can be installed into a variety of different soils and ground conditions ranging from sand andgravel to inconsistent fill, boulders, rubble and weathered rock, as well as through footings and base slabs.Applications include: soil nails for road widening and railway embankments, ground anchors for temporaryworks and sheet pile tie back, mini piles for stabilisation of footings and underpinning, and roof bolts orspiles for tunnelling.


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1.1 MAI Hollow Bar - Installation Examples

6. Testing of soil nails. Displacement is measured bya dial gauge (mounted independently), with loadmeasured through a pressure gauge on the pump.

5. Underpinning of augered columns. The castin situ columns were used to ensure lateralstability at the top of the minipile.

3. Galvanized soil nails securing an erosion controlgeomat, to resist soil slip. The grass on the slopewas re-established by seeding the geomat.

4. Soil nails installed into sand. Simultaneous drillingand grouting offers increased productivity and isbeneficial to placement of the grout.

2. Temporary anchors for sheet pile tie back. Walingbeams and anchors were installed at two levels,to provide increased support to the wall.

1. Drilling with a tungsten carbide button drill bit.The drill bit shown, features ballistic buttons(optional) for increased productivity in soft rock.


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2.0 MAI HOLLOW BAR TECHNICAL DATA

(a) Figures quoted represent the average internal diameter of the bar

(b

) Based on characteristic steel strengths(c) Drilling depths are indicative only and are subject to ground conditions and drilling methods.

Available bar lengths are as follows: 2,3,4 and 6 metres. Additional lengths available on request.

Recommended maximum bar lengths.

R25N 2.0 metres.R32N 3.0 metres. 4.0 metre lengths can be used with care, preferably with a 51mm drill bit.R32S 4.0 metres.R38N 5.0 metres.R51L, R51N, T76N, T76S 6.0 metres.

Longer lengths require a travelling centralizer to prevent whipping during rotation. The centralizer can beengaged and disengaged from the chain feed as the drive head travels along the drill boom.

2.1.0 Cutting of Bars

MAI Hollow Bar can be supplied as cut or cut to length on site with a disc cutter. All bars should beprecision cut at right angles to ensure direct end bearing within the couplers.

2.1.1. Perforated Sections

Perforated sections are available for specialist applications. Typically this section is installed at the distal

end of the drill string to assist in placement of grout. Careful monitoring is required to ensure that the groutdoes not vent from the top hole (proximal end) only, missing the active bond zone.

Bar Size R25N R32N R32S R38N R51L R51N T76N T76S

Diameter over threads (mm) 25 32 32 38 51 51 76 76

Effective external diameter

of bar (mm)

22.5 29.1 29.1 35.7 47.8 47.8 71 71

Internal diameter of bar (a)(mm)

14 18.5 15 19 36 33 52 45

Effective cross sectional (a)area of bar (mm2)

244 396 488 717 776 939 1835 2400

Ultimate strength (kN) 200 280 360 500 550 800 1600 1900

Yield strength (kN) 150 230 280 400 450 630 1200 1500

Steel Grade Yld/Ult (N/mm2)(b) 660/805 560/720 570/740 540/700 580/690 670/840 660/880 630/790

E Modulus (N/mm2) 214,200 207,800 212,800 206,600 204,700 214,000 - -

Weight (kg/m) 2.3 3.4 4.1 6.0 7.0 8.4 15.2 19.7

Thread (left-hand) ISO 10208 ISO 1720 MAI

Maximum Drilling Depths (c)(m)

12 16 20 24 26 30 36 36


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3. DRILL BITS

XBudget cross cut drillbit suitable for soft soils.

Soil types: sandSPT N values: 0-25

XXTwo stage cross cutdrill bit, suitable forloose ground and fills.

Soil types: sand, clay,and some gravelsSPT N values: 0-35

EX / EXRHardened cross cut drillbit, suitable for themajority of applicationsincluding narrow bandsof soft rock.(EXR denotes retroflushversion)

Soil types: sand, fills,

gravelSPT N values: 0-60

EC / ECCHardened tri crescentdrill bit for increasedproductivity and betterflushing. (ECC denotestungsten carbide cuttingfaces, R32 only)

Soil types: chalk,

limestone marlsSPT N values: 0-60

EY / EYYHardened tri blade drillbit with a drop centrebutton face. Bladeface offers increasedcutting performance infills and chalk.(EYY denotes tungstencarbide blades)

Soil types: chalk, gravelSPT N values: 0-60

ESFHardened hemisphericalbutton profile drill bitsuitable for soft rock.

Soil types: gravel, soft rockSPT N values: 0-60

Small diameter ES drill bit

ESDAs above, but with dropcentre configuration.

ESSFTungsten carbide buttondrill bit for soft to mediumweathered rock, bouldersand rubble.Rock types: weatheredrock, stone walls, rubble.Compressive Strength (UCT):Up to 12.5 N/mm2 (RQD 100%)

Up to 50 N/mm2

(RQD 50%)

ESSDAs above but with dropcentre configuration forgreater directional stabilityin broken ground.

EXXTungsten carbide chisel drillbit. EXX is the hardest drill bitavailable, for: soft tomedium rock, hard seamsand concrete footings.

Rock types: Softersedimentary rocks i.e.marls, mudstones and siltstones.

Compressive Strength (UCT):up to 12.5 N/mm2(RQD 100%)up to 50 N/mm2 (RQD 75%)


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3.1 Drill Bit Range

Notes:

1. ECC = tungsten carbide blades, ESS = tungsten carbide buttons.2. EXX = tungsten carbide chisels.3. ESD, ESSD= drop centre drill face.4. ESF, ESSF= flat face drill bit5. Available with elongated side walls for strength.6. EYY drill bit comprises of a drop centre with hardened buttons; circumscribed by raised blades, faced

with square section carbide profiles (laid at 45, along the blade),7. Drill bit is known as T76 EYS 130, cutting face incorporates hardened buttons.8. Drill bit is known as T76 EYSS 130, cutting face incorporates tungsten carbide buttons.

Enlarged Borehole Diameters:

Borehole enlargement of 5 -10% greater than the cutting diameter of the drill bit is generally achievable.

This overcut is achieved through the action of rotary percussive drilling, together with a degree of drill biteccentricity caused by the slight spiral effect of the drill string.

Grout flush will also assist in borehole enlargement. In sandy or non-cohesive soils, borehole enlargement

can be as much as 50% (due to slump and washout), but is inconsistent over the borehole length.

The action of pressure reaming will significantly enlarge borehole diameters, but can only be employed

effectively in cohesive soils which are consistent over the full length of the borehole. Pressure reaming is a

specialist operation requiring deliverable grout pressures in excess of 250 p.s.i. and special valves in the

drill bits to facilitate grout jetting.

3.2 Drill Bit Adaptor Sleeves

Adaptor sleeves enable the use of a larger diameter drill bit with the bar, to increase the borehole diameterand achieve higher loads in poor ground. The use of larger diameter drill bits with small diameter MAI Barsshould be restricted to loose ground, in order to reduce the risk of torsional buckling in the bar.

The following adaptor sleeves are available:

R25/R32 R32/R38 R38/R51

Bar size Drill Bits (sizes in millimetres)

X XX EX EXR EY EC ECC ESF ESSF ESD ESSD EXX EYY

R25

42, 42,

4251 51

R32 5151, 51,

76 51 51 51 515

515

7676 76

R38 11076, 76, 76,

76 115766

90 90 90 906

R51 110 130 100 100 115 115

T76 1307 1308


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4.0 COUPLERS

The MAI Hollow Bar coupler features a patented design that enables direct end-to-end bearing betweeneach rod, reducing energy loss and ensuring maximum percussive energy at the drill bit. The coupler designfeatures a thread arrangement where the top half of the thread is rotated 180 0against that of the lower half,thus providing a centre stop for each bar. All couplers exceed the ultimate strength of the bar by 20%.

MACHINED COUPLERS

Available for: R25N R32N R32S R38N R51L R51N T76N

4.1 Seating and Sealing of Bars within Couplers

To enable correct seating of each bar within the coupler all bars must be precision cut at right angles toenable end to end bearing. A quarter turn back of the coupler on the lower bar will ensure optimum seatingof the upper bar within the coupler.

For multiple coupler applications utilising air flush installation (e.g. restricted access or limited head room), areduction of flushing pressure is unavoidable due to air leakage at the couplers. The application of a threadsealant, such as TF15, will help to reduce air loss.

4.2 Hammer Couplers. Reducing Couplers

Manufactured from thick-wall steel which is machined and case hardened. Both couplers can be used athigh wear locations, typically just below the hammer drive. A locking torque is normally applied to thehammer couplers at the permanent joint, to avoid release when additional MAI Bars are added (see section6.1.2b.).

Hammer Couplers

R25/R25 R32/R32 R38/R38

Reducing Couplers

R25/R32 R25/R38 R32/R38 R38/R51 T45/R51 H55/R51 H64/T76

Notes:

1. The R25/R32 coupler is supplied with a bridge to act as a centre stop.

2. When a step down (reducer) drive arrangement is used i.e. R38 shank drive to install R32 MAI bar,a locking torque should be applied at the R38 end to prevent the R32 MAI Bar climbing into theR38 chamber.

3. Step up drive arrangements are not recommended (except R25/R32, for hand held installation) asthe additional torque overloads the smaller drive.


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5.0 ACCESSORIES

The MAI Hollow Bar System offers a range of accessories to suit different applications. The followingheadings detail common components:

5.1 Load Bearing Nuts.

R25 to R51 T76

Forged hex nut with chamfered edges at both ends. Machined hex nut.

5.2 Tapered Washers. Hemispherical Washers

Tapered washers are available in pairs or individually for angles up to 25. N.B. An oversize hole within thebearing plate is required for articulating tolerance.

Hemispherical washers are available for R25 and R32 MAI bar to enable articulation of the bearing plate upto 20and 19respectively.

5.3 Bearing Plates

R25 to R38: Formed steel plate with centre hole.R51 to T76: Flat steel plate with centre hole.

Notes:

1. Plate sizes indicated are for information only. The Engineer must ensure that the plate size issufficient for the application.

2. Alternative plate sizes are available upon request.

3. Gusset details. For perpendicular termination on declined installations against vertical faces e.g.sheet piles, DSI offer a range of gusset assemblies to accommodate angular terminations.

Bar Size Plate Size mm Thickness mm Centre Hole mm Weight kg Articulation

R25N 150 x 150 8 32 1.4 7o

R25N 150 x 150 8 38 1.4 20o with hemisphere

R25N 200 x 200 10 32 3.1 7o

R25N 200 x 200 10 38 3.1 17owith hemisphere

R32N 150 x 150 8 36 1.3 7o


R32N 200 x 200 10 38 3.1 7o


R32S 200 x 200 12 38 3.7 6.5o

R38N 200 x 200 12 43 3.6 5o

R51L 200 x 200 30 56 9.4 3o

R51N 250 x 250 30 56 14.7 3o

T76N 300 x 300 40 80 28.2 3o


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5.4.0 Stub Tubes

Stub tubes provide a simple corrosion protection barrier in the critical area below the bearing plate.Experience has shown that moisture accumulates at the underside of the plate, combining with oxygen toattack the bar.

The stub tube comprises of a steel tube welded to the underside of the bearing plate, at the production

stage. The whole assembly is then galvanized.

The bearing plate/stub tube assembly is placed over a sheathed top section of MAI Bar. The sheathedsection provides supplementary protection between the grouted depth of the borehole and the bearing plate.

5.4.1. End Caps

End caps provide a corrosion protection cover at the face of the bearing plate by providing protection to theload bearing nut.

Fabricated from steel and galvanized, the end cap is bolted, over a rubber gasket, onto the face of the

bearing plate and filled with Denso Void Filler.

5.5 Free Lengths

Free lengths enable a prestress to be transmitted between the bearing face and the bond zone, through theuse of a debond tube. Free lengths are often required for sheet pile tie back applications.

The free length detail incorporates a MAI Bar within a high strength polypropylene tube which is sealed ontothe bar. Short lengths of bar remain exposed at each end to enable connection to the couplers and forconnection (and release with clamp grips) from the top end drive. For installation of the top section to thecorrect depth, in relation to the face of the structure, a short dummy bar is added as an extension betweenthe drive head and the sheathed MAI Bar. Alternatively the top section can be left proud, with the freelength tube and remaining section of bar cut back as required.

5.6.0 Borehole Spacers

Available for specialist applications. For general use the spacer is not required as it snags during rotationand interferes with grout circulation in the borehole.

N.B. The use of spacers does not guarantee comprehensive grout cover along the length of the bar as it is

impossible to control the grout within the borehole. A comprehensive grout barrier can only be ensured witha sheathed encapsulation, see 10.2.1.

5.6.1 Borehole Caps

Used for tunnelling, where inclined boreholes require sealing to prevent grout return. A setting sleeve isrequired to drive the borehole cap, 200-400mm along the MAI Bar, into the borehole. Simultaneous drillingand grouting is not possible with borehole caps.

R25 cap diameter 65mmR32 cap diameter 70mm

R38 cap diameter 95mm


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6.0 INSTALLATION EQUIPMENT

The following equipment is required for installation:

Drill RigTop DriveGrout Pump (section 9.2)Injection Adaptor; for simultaneous drilling and grouting, (see section 7.0)(or) Heavy duty coupler; for water flush or air flush drilling, (see section 4.2).

6.1.1 Drill Rigs

A range of drill rigs are suitable for installing MAI Bars. Selection of the appropriate rig depends on:

Scale of WorksAccess to Work FaceGround ConditionsDepth of Drilling

The following rig configurations illustrate the choices available:

Crawler Mounted - Hydraulic or Air Power- (Klemm, Htte, Ingersol Rand, Atlas Copco, Casagrande, Soilmec, etc.)

Excavator Mounted - The drill boom is mounted on the dipper arm, for over-reach applications.

Telehandler or Crane Basket - The drill boom is mounted on a special carrier for difficult access.

6.1.2 Top Drive

Both rotary and rotary percussive drives can be used. Rotary percussion is the preferred method of

installation as this reduces the strain on the drill string, offers greater directional stability and enables higherrates of production. Either hydraulic or air hammer drives are suitable, e.g. Krupp, Htte, Klemm.

To avoid release of components at the top end (i.e. at the rotary injection adaptor or reducing coupler, whenadditional lengths of MAI Bar are added, the following steps are recommended:

1. The number of top components be kept to a minimum.2. A locking torque is applied to all permanent joints. The torque should be sufficient to prevent

premature release but not excessive that final release is impossible.3. Grease the top end of each MAI Bar.4. For release of the MAI Bar, percussion combined with a feed pressure and clockwise rotation will

normally free the most recent joint (i.e. at the bar). If the MAI Bar does not release, rotation shouldbe limited to two turns only, as further rotation will unscrew the drill bit or couplers within the

borehole.

6.2 Hand Held Rock Drills

For use with R25N and R32N MAI Bar. This method of installation is utilised for small works in restrictedaccess or limited headroom applications. A variety of hand held equipment is suitable for installation of R25and R32 bars.

Hand held equipment works best when used in conjunction with an air leg or within a slide framearrangement, as high operator fatigue limits production rates. Sliding frames are easily fabricated or can besupplied. The air leg is placed within the frame and normally reacts off the rear cross brace.

For simultaneous drilling and grouting a rotary injection adaptor is required (see section 7.4). For air flushinstallation, a hollow hex shank is required (see section 7.5).


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7.0 ROTARY INJECTION ADAPTORS

Used for simultaneous drilling and grouting. The rotary injection adaptor enables drilling and grouting to becombined as a single operation, reducing construction cycles and ensuring optimum ground /grout bondwithin the borehole.

Figure 1Rotary Injection Adaptor

7.1 Component Parts and Assembly

The adaptor comprises of three components:1. Case hardened steel shaft featuring grout inlets leading to a hollow bore at the base (Figure 2).2. Steel grout bottle c/w a side inlet for attachment of the grout pipe.3. 4 No. seals, (two at each end).

To assemble the adaptor, the steel bottle is placed over the shaft and up against the top end flange.N.B. It is essential that the bottle is removed from the shank following grouting, for thorough cleaning ofboth components.

Figure 2Grout Bottleand Injection Shaft

7.2.1 Selection of Injection Adaptors for Drill Rigs

Selection of the correct adaptor depends on: the configuration of the drive shank from the hammer, size ofMAI Bar being installed and grouting pressure.

The majority of rotary injection adaptors are female/female configuration for strength, with internal R, T or Hthread profiles. The following table outlines the choice of injection adaptors available for different shank drives:

Notes:1. If the top drive is female, a balance rod is required to connect the two females together.2. Alternative shank configurations (e.g. T38 or Male/Female) are available on special order.3. Adaptor couplers or male/female changers are also offered. The use of additional components,

within the top assembly, will reduce the length of bar that can be installed.

Reference Shaft Shank Drive MAI Bar Grout Inlet Operating Pressure

R38F/R32 R32R38F/R38

R38 MaleR38

H55F/R51Female/Female

H55 Male R511" (BSP female) 0-100 psi

H64F/T76 H64 Male T76


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7.2.2 High Pressure Injection Adaptors 0-250 psi

High pressure injection adaptors are used for specialist applications, e.g. mines, tunnels or cohesive soils.Pressure reaming can only be used where there is no risk of heave and should be considered alongsidepost grouting, which may be more economical.

A range of high pressure two stage adaptors, similar to the standard versions, are available.

7.3 Locator Frame

The locator frame is used to position the grout bottle of the injection adaptor, on the central rotating shaftand prevent it from rotating. Its design enables the hammer to operate unrestricted whilst ensuring that thegrout bottle does not rotate with the shaft. As grout is pumped into the chamber of the bottle significanttorque is often built up between the rotating shaft and stationary bottle. Locator frames are usually bolted tothe drill sledge, see Figure 3.

Notes:

a. To position the adaptor within the frame and locate it on to the top drive; the adaptor should be

held in place below the hammer whilst the drive is slowly rotated into the flanged top end of theshank. Caution is required for this operation; with a locking torque (see section 6.1.2b) appliedonly when the operatives are clear.

b. The aperture within the window must be sufficient to accommodate the stroke of the hammer aswell as allowing a degree of float for the bottle, to prevent wear rings forming on the shaft. It mustalso prevent the bottle from rotating as the torque increases.

c. The locator frame should be positioned such that the side inlet of the bottle is within 5mm of thelower end of the aperture on the frame, with the hammer at full extension. This will allow thehammer to operate unrestricted as well as allowing for movement as described in (b).

d. Locator frames can either be supplied, or fabricated by the contractor.e. The standard locator frame offered by DSI requires drilling of bolt holes to fit the carrier assembly.

Figure 3Position ofLocator Frame


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7.4 Rotary Injection Adaptor for Hand Held Equipment

Suitable for use with R25N and R32N MAI Bar on restricted access applications (see section 6.2).

The hand held rotary injection adaptor consists of a 22 x 108mm (7/8 x 4 1/4) hex shank with an R25 ropethread (male) at the base. The grout bottle is positioned on the shaft, against the collar.

Figure 4Rotary Injection Adaptor forHand Held Equipment

Notes:

1. Only a low pressure version is available.2. The hex part of the shank is solid (there is no bore for an air needle). If an air needle is present at

the base of the chuck (within the drill), it should be removed and the port blanked off. On somehammer drills this restricts the piston, therefore the needle should be shortened to prevent contactwith the shank. In this way air can still exhaust at the sides of the shank.

3. The adaptor is assembled by sliding the grout bottle, over the threaded end of the shank, on to the

main shaft and up to the middle collar.4. For restricted access applications the shank increases the overall length of the hammer drill andbar, thus limiting the section length of MAI Bar that can be installed.Overall length of shank = 378mm.

5. For R32N MAI Bar a step up coupler (R25/R32) is used to connect between the bar and theshank.

6. Seals within the bottle should be greased daily.7. The bottle must be removed from the shank, following grouting, for thorough cleaning.

7.5 Hex Shank Adaptor for Hand Held Equipment

The hollow hex shank 22x108 (7

/8 x 41

/4) is used for air flush installation with hand held hammer drills. Acollar is provided below the hex profile, for the latch on hammer drills to locate onto. Length = 373 mm.

Figure 5Hex Shank Adaptor (hollow)for Hand Held Equipment


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8.0 INSTALLATION

The choice of drilling technique together with grouting method is dependent upon a number of variablesnamely: scale of works, site access, ground conditions and depth of boreholes.

The following drilling methods are used for MAI Bar installation:

Rotary Percussive Drilling- For all ground conditions, typically firm to hard ground. This method

enables high rates of installation, provides good directional stabilityand helps to consolidate the grout as the percussive action of the drillacts as a poker.

Rotary Drilling - For soft to firm ground and some chalks. Rotary drilling ensures thatthe drill bit cuts the material in the borehole. Not suitable for rubble orboulders.

Percussive Drilling - For Micro Piles in soft to medium firm ground. This method usesdisplacement combined with simultaneous grouting to form theborehole. Suitable for soils where flushing or cutting with a drill bit isdifficult, e.g. soft chalk or clay. Not suitable for ground conditionswhere the borehole closes down behind the piling head.

8.1 Simultaneous Drilling and Grouting

Suitable for all ground conditions from gravel to clay. This technique combines drilling and grouting as asingle operation ensuring that grout is placed to the full depth of the borehole. For ground conditions whereborehole collapse is anticipated or where subsequent grout pumping from the base of the borehole isproblematical, simultaneous drilling and grouting is the preferred option.

The percussive force of the hammer should be balanced with rotation of the drill bit, as advancing the drillstring with excessive percussion and feed pressure, but limited rotation, will restrict the formation of a trueborehole resulting in inconsistent grout cover. The flushing and grouting efficiency of the drill bit will also bereduced. Rotation Speed: soil nailing 120 - 150 RPM, mini piling 100 - 130 RPM.

Grouting pressure should be sufficient to maintain circulation at all times, with a small amount of grout returnvisible at the mouth of the borehole. A constant rotation should be maintained, therefore drill motors able todeliver sufficient torque are necessary.

Equipment required: Rotary Injection Adaptor (see section 7).

8.2 Water Flush Drilling Followed By Grouting

Water flush is used for soft rock conditions or areas where high drill bit wear is anticipated, as it offersgreater efficiency than grout in removing drill cuttings from the face of the drill bit, as well as helping to keepthe temperature and ultimately the wear of the bit to an acceptable level. On completion of drilling, groutcan be injected through the bore of the MAI Bar into the borehole.

In environmentally sensitive locations, requiring the control of grout flush at the surface, water flush is oftenused for the first 2 3 metres. Once a sufficient depth is reached, the water flush can be switched to agrout flush and simultaneous drilling and grouting employed as in section 8.1.

Equipment required: Hammer Coupler (see section 4.2) and grout line connector.

Note: For rigs without a central water flush facility, a water bottle is required.

8.3 Air Flush Drilling Followed By Grouting

Air flush drilling is used for soft ground where flushing with water or grout is problematical e.g. soft chalk orclay, or for mining and tunnelling applications. On completion of drilling the MAI Bar acts as a conduit for

grouting.

Equipment required: Hammer Coupler (see section 4.2) and grout line connector.


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8.4 Installation Rates

Rates of installation vary considerably and are subject to: ground conditions, drilling technique, boreholediameter and type of rig used. The following table is an indication of installation rates achievable with MAIHollow Bar.

Installation Rates - Metres per rig per day.

8.5 Limits Of System

Ground conditions featuring large fissures and voids or the presence of underground water are generally notsuitable for a drilled and grouted hollow bar. Post grouting does work sometimes in fissured ground or agrout sock can be provided if the bar can be withdrawn without borehole collapse. For saturated ground,

the use of a stronger grout mix followed by post grouting may offer a solution, but the presence of too muchwater will make grouting impossible.

8.5.1 Clay

Stiff boulder clays can generally be drilled with the MAI Hollow Bar. Simultaneous drilling and grouting is thepreferred method of installation to ensure best placement of grout. Grouting pressures up to 250 psi areoften required to ensure that the flushing ports within the drill bit are kept open and a grout returnmaintained. Use of higher grout pressures should be tailored to the ground conditions to prevent the risk ofheave. Wet clays are generally unsuitable for a Hollow Bar system.

Where the clay can be augered and a solid Gewi-Steel Threadbar placed, the auger will provide much betterremoval of the spoil and may be more cost effective.

8.5.2 Rock

For hard rock or where the rock is competent enough to enable open hole drilling the MAI Bar is not asefficient as conventional rock drilling equipment e.g. DTH (Down the Hole Hammers).

In tunnelling or rock bolting applications the MAI Bar used in conjunction with the ESS (tungsten carbidebutton) drill bit, provides the best combination for hard areas.

8.5.3 Concrete

MAI Bar will drill through concrete, but where the slab is over 50mm thick a conventional rock drill is moreefficient. Once a through hole is formed, a MAI Bar and drill bit can then be used to drill through theunderlying fill and into to firmer ground.

Installation Method Soil SPT N Value Bar/Drill Bit Diameter mm

R25/51 R32/76 R38/110 R51/130

Rotary Drill RigSand 20 - 40 100 - 180 120 - 200 110 - 190 110 - 190

Simultaneous drill/groutGravel 40 - 60 70 - 130 80 - 150 70 - 140 70 - 140

Fill 15 - 35 160 - 220 160 - 260 160 - 260 160 - 200

Rotary Percussive Drill RigSand 20 - 40 160 - 220 200 - 300 180 - 280 160 - 200

Simultaneous drill/groutGravel 40 - 60 100 - 150 100 - 200 80 - 180 80 - 160

Fill 15 - 35 180 - 240 220 - 320 200 - 300 180 - 220

Hand Held Rock DrillSand 20 - 40 70 40 - -

Simultaneous drill/groutGravel 40 - 60 40 - - -

Fill 15 - 35 80 50 - -


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9.0 GROUTING

Grout is an essential part of the MAI Hollow Bar system as it provides the bond between the bar and thewall of the borehole. Placement of the grout can either be combined with the drilling (see section 8.1Simultaneous Drilling and Grouting) or subsequent to the drilling (see sections 8.2 Water Flush Drilling, 8.3Air Flush Drilling).

As with all grouting operations thorough mixing of the grout is essential together with rigorous wash down ofall equipment following installation.

9.1 Typical Grout Mixes

Borehole grout type is determined by the Engineer, but OPC is in most cases perfectly adequate unless aspecific requirement is necessary, e.g., high early strengths. Curing times vary with the environment. Acompressive strength of 40 N/mm2is generally achieved within 3 to 7 days depending upon the ambienttemperature. To determine curing times relative to the site; grout cubes should be taken, for compressiontesting.

Grout strengths are invariably reduced as the drilled spoil is mixed with the grout (typically 40 N/mm2to20N/mm2). A grout strength of 20 N/mm2has been proven to be perfectly adequate for transferring loadbetween the bar and the wall of the borehole.

The most common grout mix comprises a water cement (w/c) ratio of 0.4. This is as close as practical to a0.38 w/c ratio (the optimum ratio for full hydration). A 0.4 w/c ratio is ideal for most drilling and groutingoperations where a continuous circulation of grout is possible.

Grout Mix Conversion Table

Weak Mixes w/c 0.50, 0.60: For boreholes where leaching of water from the grout is anticipated (e.g. chalk) aweaker mix may be necessary in order to maintain circulation.

Strong Mixes w/c 0.35, 0.38: Used in loose fills and sandy material where limited ground water is present.

9.2 Grout Pumps

A variety of grout pumps are suitable for injecting grout into the bore of the MAI Bar. Mono Pumpsincorporating a high shear colloidal mixer offer the best performance. Selection of the appropriate pump isdependent upon the application and its ability to perform the following functions:

1. Thorough mixing of the grout - to avoid blockages at the drill bit.2. Deliver a continuous volume - to ensure consistent grouting within the borehole.3. Maintain the required pressure.

9.3 Grout Consumption

Grout consumption is subject to a number of variables including: drill bit diameter, ground conditions, drillingtechnique, operator experience. The following table provides an approximate guide to grout consumptionfor each MAI Bar size:

MAI Hollow Bar Grout kg/m MAI Hollow Bar Grout kg/m

R25N 15-20 R38N 20-25R32N/R32S 20-25 R51L/R51N 20-30

T76N/T76S 25-35

Water Cement Ratio Water Volume (litres) Cement (kg)

0.38 38 100

0.40 40 100

0.45 45 100

0.50 50 100

0.60 60 100


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9.4 Grouting Pressures

For the majority of geotechnical applications except clay , a maximum pressure of 100 psi is normallysufficient to ensure full placement of grout when using simultaneous drilling and grouting. Where pressuresdo not exceed 100 psi standard air line components can be utilised. For clay, grouting pressures up to 250psi are sometimes required.

Where grouting is performed as a subsequent operation following drilling, e.g. mining and tunnelling , higherpressures are required. Typically pressures ranging between 200 and 400 psi are sufficient, althoughpressures up to 860 psi have been used in some underground applications. For pressures over 100 psi allgrouting components and hoses must be of hydraulic specification.

9.5.0 Post Grouting

Post grouting is defined as regrouting a borehole after the primary grout has set. The primary grout isnormally placed as the borehole is drilled, (see simultaneous drilling and grouting, section 8.1). The betterthe permeability of the surrounding ground, the greater the soil/grout bond. In cohesive soils with nopermeability, the primary grout will only fill the borehole and any local cavities, resulting in a low skin frictionand limited pull out capacity. If the primary grout column is post grouted under high pressure, the bondbetween the soil and the grout increases considerably. Post grouting will subject the ground to radialstresses, resulting in higher skin friction as well as creating an irregular borehole surface which interlocks

with the ground. Additional post grouting further enhances the bond.

Post grouting is a specialist operation which should only be carried out by experienced operatives. Its userequires careful monitoring and should only be employed in ground conditions where there is no risk ofheave.

9.5.1 Specialist Components/Plant

The following are required for post grouting operations:

a) Grout lines and components to hydraulic specification.b) Narrow gauge polypropylene tubing, 6,8 or 10mm (available from DSI) for removal of

primary grout from the bore of the MAI Bar.

c) Post Grouting Couplers featuring integral rupture valves (typically 3 No per borehole).d) A pump able to develop 400 or 600 psi.

9.5.2 Post Grouting Procedure

Two stage post grouting is normally the most economical for cohesive soils.

Stage 1 - Primary Grouting

Use simultaneous drilling and grouting to install the MAI Bar, maintaining grout circulation at all times with aslight return of grout at the mouth of the borehole. On completion of drilling, flush out the grout within thebore of the Mai Bar with water, by inserting a polypropylene tube to the full depth.

Stage 2 - Secondary Grouting

a) Let the primary grout cure for:- 2 to 12 hours; grout pumps up to 400 psi- up to 24 hours; grout pumps up to 600 psi

b) Connect up the high pressure pump to the MAI Bar.c) Fracture the primary grout column with high pressure water injection. Do not use

excessive water, only enough to achieve fracture.d) Inject grout into the bore of the MAI Bar up to a pressure of 200 psi. 75 to 100kg of grout is

normally required to complete this operation.

If a pressure of 200 psi cannot be achieved the following causes should be examined:

1. The presence of fissures within the ground.2. Grout passages between boreholes.3. Grout is venting in the top section of the primary grout or at other locations.


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10.0 CORROSION PROTECTION

Requirements for corrosion protection are defined by: lifespan, aggressivity of the environment(see ENV 206) and level of risk.

Lifespans are classified as:

a) Temporary Installations (up to two years)

Except for highly aggressive environments, self-drilling hollow bar systems are considered suitable for arange of temporary applications, including temporary anchors.

b) Permanent Installations (lifespans greater than two years)

For permanent installations, corrosion protection requirements are based on :

i) aggressivity of the environment (see ENV 206)ii) level of riskiii) application (see sections 10.1.1 to 10.1.3)

Corrosion protection systems, applicable to self-drilling hollow bars, are limited by the nature of installation.Sheathed sections (albeit for the free length only) are ineffective as the integrity of the smooth sheathcannot be assured following abrasion damage during rotary installation, borehole grout is not recognised asa permanent protective barrier (see 10.2) and protective coatings are subject to abrasion damage duringinstallation (see 10.3). For suitable permanent applications see 10.1.2 and 10.1.3.

10.1.1 Permanent Ground Anchors, Permanent Tension Piles

Self-drilling hollow bars are not suitable for use as permanent anchors or tension piles, as they cannotcomply with the corrosion protection requirements of either BS8081:1989 British Standard Code of Practice

for Ground Anchorages or EN1537:1999 Execution of Special Geotechnical Work - Ground Anchors. Forpermanent protection in accordance with both standards, see Dywidag Pregrouted Threadbar.

10.1.2 Permanent Soil Nails or Rock Bolts

Self-drilling hollow bar systems are generally considered acceptable for low risk applications (i.e. soil nails orrock bolts) in non-aggressive environments.

Supplementary protection can be added in the form of:

a) galvanized coatings (see 10.3)

b) a sacrificial corrosion allowance (see 10.4)

For permanent use in aggressive environments (e.g. coastal protection works) or high risk applications (e.g.supporting a structure), hollow bar systems are not acceptable as neither of the above supplementarycorrosion protection measures are sufficient to ensure adequate protection. For such applicationsPregrouted Gewi-Steel should be employed.

Note: Rock bolts are typically classified as having lengths up to 6 metres and lightly loaded. Applicationsincorporating longer lengths or higher capacities should be classified as Rock Anchors (see 10.1.1).

10.1.3 Permanent Mini Piles

Compression: suitable for certain applications (see European Standard: Micropiles, TC288/WG8)Tension: self-drilling hollow bar systems are not suitable (see 10.1.1)


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10.2 Limitations of Borehole Grout as a Corrosion Protection Barrier

BS 8081:1989 British Standard Code of Practice for Ground Anchorages and EN1537: 1999 Execution ofSpecial Geotechnical Work Ground Anchors, do not recognize borehole grout as a corrosion protectionbarrier for permanent anchors.

BS8081 - Principles of Protection (Section 8.2.3. paragraph 3)Grout injected in-situ to bond the tendon to the ground does not constitute a part of aprotection system because the grout quality and integrity cannot be assured.

EN1537 Permanent Ground Anchor (Section 6.9.3)Borehole grout is not recognized within the principles of protection for permanent anchors.

In reality, borehole grout can become contaminated by: drill cuttings, localised borehole collapse or groundwater. It is also difficult to control the bleed from the grout.

10.2.1 Grout Encapsulation, Grout Cover

Grout injected into the borehole during installation, does not constitute an encapsulated grout i.e. within asheath (as specified in BS8081), and is unable to offer the same level of protection.

Grout cover as provided by the borehole grout, whilst covering a significant proportion of the bar, cannot beguaranteed to provide a comprehensive barrier to all parts of the bar (see 10.2.2). Whilst simultaneous

drilling and grouting is the most effective way for placement of grout within the borehole and the action ofoverflushing will increase the amount of grout within the borehole, neither method is sufficient to ensurecomprehensive grout cover to the bar. In essence there is a lack of control over placement of the groutwithin the borehole.

The areas of highest risk are: 1) At the mouth of the borehole (the most aggressive area in respect of corrosion). Grout cover is

problematical in this zone for horizontally installed bars, as the grout will slump to the underside of the bar.

2) At the coupler location. The larger external diameter of the coupler results in reduced groutcover.

The only system that ensures full encapsulation of the bar, within an uncontaminated grout, is a sheathed

encapsulation (see Dywidag Pregrouted Threadbar).

10.2.2 Crack Width Control of Grout

Whilst crack widths in the grout of less than 0.1mm may be achievable on certain sections of the bar, crackwidths in the unconfined area at the mouth of the borehole or at coupler locations cannot be controlled. AsBS 8081 and EN 1537 do not recognize borehole grout as a permanent corrosion protection barrier, crackwidths of the borehole grout are irrelevant.

10.3 Galvanizing of MAI Hollow Bar

MAI Hollow Bar can be supplied galvanized to BS EN ISO 1461 with the nuts and couplers sherardized toBS 4921class 1 and passivated. For specific applications, only the top bar is galvanized, as this remains inthe critical area (in respect of corrosion) and is least damaged during installation.

The effectiveness of any coating applied to hollow bars is questionable, as the rotary nature of installationsubjects it to abrasion damage in coarse soils. In addition to abrasion, the use of stilsons or hydraulicclamps for the release of the bar from the drive head, can cut through any coating. Appropriate care shouldtherefore be taken to ensure that the coating is not damaged.

Duplex coatings are also available for specialist applications but should only be used where the integrity ofthe coating can be assured following installation.

10.4 Sacrificial Corrosion Assessment

Sacrificial corrosion assessment provides a basis for evaluating the lifespan of hollow bars in low riskapplications. The method involves classification of soils into different categories of aggressivity based on aranking procedure that incorporates tests for moisture content, pH value, redox potential and resistivity.Once the aggressivity of the soil is known, a corrosion allowance can be made for the design life of the bar(see TRL Report 380, section 4.3).


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11.0 STRESSING AND TESTING

Simultaneous drilling and grouting of hollow bars produces a bar that is fully grouted and therefore fullybonded over its entire length. It is not possible to isolate the borehole grout of the bond zone (stable zone)from the borehole grout of the wedge zone. (Sleeved free lengths debond the bar from the grout but do notisolate the grout of the bond zone from the grout of the wedge zone; packers or foam plugs are impracticalon rotary installed bars)

Therefore any test to establish the pull out performance in the bond zone will be influenced by load gener-ated in the wedge zone.

The influence of load generated in the wedge zone can be assessed by:a) Installing and testing a short bar in the wedge / retained zone only.b) Taking the load generated by a fully installed bar and dividing it by the overall length to give a load

in kN/m. This load in kN/m can then be multiplied by the length of bar in the retained zone tocalculate its influence. (Load in kN/m is a conservative approach, as the load per metre run in theretained zone would generally be lower than that of the stable / bond zone).

The overall objective of testing is to establish the bond stress between the grout and the ground in the bond /stable zone. Load generated in the wedge / retained zone (whilst providing a localised bonding effect) doesnot contribute to overall stability.

11.1.0 Preparation of Testing Surfaces

Testing of MAI Hollow Bar falls into two categories:

a) Soil Nailsb) Temporary Ground Anchors, Mini Piles and Rock Bolts.

Soil Nails are usually tested against a soft face on slopes. Due consideration should therefore be given toboth the angle and the area of the bearing surface to stress against.

Ground Anchors, Mini Piles and Rock Bolts are usually installed in applications where a hard face is readily

available for the jack to react against, e.g. sheet piles (for tie back anchors).

11.1.1 Perpendicular Bearing Surface - Soil Nail Testing on Slopes

It is essential that the jack and bearing apparatus are seated perpendicular to the installed nail. Failure todo so will result: in the bearing apparatus sliding up the slope, or the jack misaligning itself, creating a pinchpoint and producing inaccurate load readings.

The area of bearing surface should be calculated in relation to the bearing capacity of the soil. Insufficientbearing area will result in premature settlement of the bearing platform before the test load is reached,requiring the two hour operation having to be repeated with a larger bearing surface.


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11.1.2 Pocket Dimensions

To ensure that the bearing surface is perpendicular to the angle of installation, a pocket is normally cut intothe slope. Pocket dimensions vary, but as a rough guide are: 2.40m long, 1.75m deep and 1.5m high. It isimportant that there is as much bearing surface above the nail as there is below, e.g. 750mm. The cutting ofa pocket reduces the installed depth of the nail, therefore an additional allowance for depth of installationshould be made, to ensure that a sufficient length of nail remains embedded for the test (i.e. over install thenail).

11.2 Alignment Loads

An alignment load of 5-15 kN is necessary to ensure:

a) That the jack and bearing platform are sufficiently seated to compress any spaces betweenthe bearing surfaces.

b) The line of extension for the nail is kept constant: to ensure contact between the dial gaugeand the top of the bar. A circular plate (100mm diameter) on the end of the bar, will greatlyassist this operation.

11.3 Stressing and Testing Equipment

Sleepers: 6 No @ 1.5 metres long (3 No each side, vertical)

Spreader Beam: Comprising of 2 No 2.2 metre channels welded back to back with60mm clearance in the middle.

Hollow Ram Jack with Stool: Minimum of 150mm stroke to accommodate bearingplatform settlement.

Dial Gauge & Tripod: To provide an independent datum for recording nail extension.N.B. The dial gauge must be mounted on a fixed independent datum (nota cherry picker).

11.3.1 Exposed Bar Requirement for Jack Connection

The placement of the hollow ram jack over the bar can be achieved in two ways:

a) 1 metre of exposed bar (above the bearing platform) the jack is slid over the bar (if apocket is cut into the slope, sufficient bar is normally exposed).

b) Short lengths of exposed bar a draw bar and coupler are used to connect to the exposedbar (minimum 120mm) and run through to the back nut at the top of the jack.


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11.4 Testing

The following sections outline the range of tests that can be applied to MAI Bars, together with common loadfactors and general procedures.

11.4.1.1 Proving Test

The proving test is used to establish the pull out performance of MAI Bars. Test loads are significantlyhigher than would be applied to the main works as the objective is to demonstrate the bond performance inthe ground. In general terms the test load should not exceed 75% of the ultimate strength of the bar, exceptin special circumstances where a maximum load of 80% (of the ultimate strength) may be used with theengineers consent.

11.4.1.2 On-Site Suitability Test

This is an extended version of the acceptance test (see below), incorporating longer monitoring periods.

11.4.1.3 On-Site Acceptance Test

Applied to all bars within the main works. The following test loads apply:

a) Temporary Applications: 1.25 x working load.b) Permanent Applications: 1.5 x working load.

For locking-off of soil nails, a torque wrench is normally employed as the quantities are often large and atrelatively low loads. For ground anchors, a hollow ram jack is used as the loads are higher and greateraccuracy is required.

11.4.2 Load Increments

Load increments and hold periods should be determined to ensure a controlled displacement. Wherepossible, load increments should be concentrated around the predicted failure point to provide sufficientdata for detailed analysis of the peak load.

For soil nails with low loads progressive loading is preferrable to cyclic loading, as releasing the load tendsto cause misalignment of the jack and inaccurate extension readings.

11.4.3 Load and Extension Readings

Load is measured through a digital pressure gauge incorporated within the hydraulic circuit of the jack. Thedigital display ensures the maintenance of a constant pressure during hold periods.

Extension is measured by a dial gauge in contact with a plate at the end of the bar. The dial gauge ismounted on a tripod, independent of the jack bearing apparatus. Settlement of the bearing plate will noteffect extension readings on the dial gauge as it is mounted separately. Readings are only affected whenmisalignment occurs.

Data recorded is plotted on a graph to produce a load v displacement curve.


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11.5 Guidelines for Design

11.5.1 Pull out Performance

The critical factor affecting achievable loads for: soil nails, ground anchors and mini piles, is the ground/grout interface; not the tendon/grout interface. Selection of the correct installation method for the groundconditions is critical, as the placement of the grout directly effects the performance.

For outline design the following table provides an indication of working loads achievable with different bar/drill bit diameters:

Notes:

1. The above loads are quoted as examples only and do not constitute the basis of a working

design. It is recommended that site tests are carried out to ensure correct designassessments.2. Compression applications require sufficient lateral restraint from the surrounding ground.3. For tension applications sufficient overburden depth is required to prevent the risk of surface

heave.4. Loads quoted incorporate a factor of safety of 2.

11.5.2 Lifespan

Temporary Applications

By definition temporary applications cover a lifespan of up to two years. Self-drilling hollow bar systems areconsidered suitable for a range of temporary applications, provided that the environment is not tooaggressive.

Permanent Applications

For lifespans greater than two years or where the environment is classified as aggressive, the use of hollowbars needs to be carefully assessed on the following basis:

Soil Nails - suitable for low risk applications in mildly aggressive environments.Ground Anchors - not suitable.

Mini-Piles - suitable for certain applications in compression, but not tension.

Note: See Section 10 Corrosion Protection.

Application Soil Bar/Drill Bit Diameter mm

R25/51 R32/76 R38/90 R51/100 T76/130

Tension Cohesive Soil 5 7 9 10 13

kN/m Sand 8 12 14 16 20Gravel 12 18 21 24 31

Compression Cohesive Soil 10 15 17 20 26

kN/m Sand 15 22 26 29 38

Gravel 24 36 42 49 6


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12.0 APPLICATIONS

12.1 Soil Nails

MAI Hollow Bar is ideal for soil nailing as it offers high installation rates. Drilling and grouting can be com-bined as a single operation, reducing construction cycles and offering cost savings. Used for stabilisation ofrailway embankments as well as road widening (utilising top down construction), MAI Bar provides effectivereinforcement either as a soil nail or as a soil dowel.

12.2 Temporary Ground Anchors

Used for temporary works (e.g. sheet pile tie back), MAI Hollow Bar provides an effective anchor which canbe rapidly installed into gravels or collapsing soils without the need for a casing. Free lengths are availableif a prestress is required between the bond zone and the bearing face.

For permanent works or aggressive environments, hollow bar systems are not suitable as double corrosionprotection (in accordance with BS 8081 or EN1537) cannot be provided. The only choice for such applica-tions is a permanent bar or strand anchor (available from DSI).


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12.3 Mini Piles

MAI Hollow Bar is used as a micro injection pile for a range of applications, including: the stabilisation offootings, support to machine bases, underpinning of foundations, noise protection walls and avalanchebarriers. The continuously threaded profile lends itself to restricted headroom applications (e.g. basementsor under arches), where the bar can be cut and coupled to any length as well as enabling the addition offurther sections if deeper drilling is required on location. Buckling resistance compares favourably with thatof a solid bar. Not suitable for permanent tension pile applications (see Dywidag Pregrouted Threadbar).

12.4 Spiles and Rock Bolts

Installed into loose rock or collapsing soils, MAI Bar is used for forepoling at fault zones to provide a protec-tive umbrella at the tunnel face or as rock bolts for portal stability and NATM. Other applications includeface stabilisation, use as an injection conduit for grout or resin and as a self-drilling anchor for tunnel refur-bishment.

Tungsten carbide drill bits, wedge washers and articulating bearing plates complete the system for rockbolting applications.

Dywidag-Systems International Ltd.

Edition No 3. All information correct at time of printing.

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