Minova MAI SDA self drilling anchors€¦ · percussive drilling. During or following drilling, the...

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Minova MAI SDA self drilling anchorsDesign guide

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ContentsIntroduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Part 1

1 .1 Advantages of Minova MAI systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

1 .2 System components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

1 .3 Quality assurance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

1 .4 Installation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

1 .5 Technical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

1 .6 Corrosion protection systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

1 .7 Load transfer, safety concept . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Part 2

2 .8 Minova MAI soil nails R25 to R51N . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

2 .9 Minova MAI rock nails R25 to R51N . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

2 .10 Minova MAI piles R32N to T111N . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

2 .11 Summary and outlook . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

2 .12 Technical standards and literature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

Part 3

3 .13 Examples for calcutlation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

3 .13 .1 Corrosion loss . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

3 .3 .2 Load transfer length (external stability) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

3 .13 .3 Allowable pile load (internal stability) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

3 .13 .4 Dynamic stability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

3 .13 .5 Buckling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

Part 4

Figures and tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

4

Introduction

For more than 40 years, hollow core ancor rods with cold-rolled rope or trapezoidal threads, extendable to any length using couplers and fitted with drill bits, have been used as drill rods in various soils.

Grouted with cement grout, they can remain in the ground as stabilization means as soil or rock nails or micro-piles.

Minova MAI has further developed this technology. The drill bit is chosen dependent on the length and geology to be expected and the system is installed with couplers using rotary percussive drilling.

During or following drilling, the annular ring is filled with cement

grout through the hollow core anchor rod. The grout body thereby formed serves to transfer the load into the ground.

Minova MAI SDA self-drilling anchors have already received national and European approvals, e.g. [1 and 2]. Based on these approvals, the design bases for soil or rock nails and micropiles are summarized below.

The bases are European standards, specific national regulations are of course taken into consideration as well. Sections 2 to 8 (Part I) apply to

all Minova MAI SDA self-drilling anchors. As of section 9 (Part II), specific design verifications for soil or rock nails and micropiles are discussed. Part III presents examples and Part IV Figures and Tables. Table 7 lists the allowable loads for nails and piles.

For more detailed technical information please contact your local Minova representative or visit www .minovainternational .com .

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The most important advantages of the Minova MAI SDA self-drilling anchors are:

• Quick rates of installation by combining drilling, insertion and grouting in one single operation.

• Low-noise percussion drilling.

• No separate system installation, no casing and rod removal required. The drill bit remains in the ground serving as a spacer.

Fig 1.2. System components

• Choice of drill bits for the most diverse ground conditions.

• Identical installation principle for all ground conditions and systems.

• The hollow core anchor rod serves not only to flush the borehole with air or water during drilling, but also to grout voids and to carry out high-pressure injections of the annular space.

• Choice of high-quality grouts and mixers.

1 .2 Components

1 .1 Advantages of Minova MAI SDA self-drilling anchors

1 .2 .1 General

The system components are (Fig. 1.2):

• Drill bits of various diameters and types (as suitable for the respective ground).

• Hollow core anchor rods of various diameters with a continuous rolled left-hand thread and available in standard lengths of 1 m, 2 m, 3 m, 4 m and 6 m.

• Couplers to connect and extend the hollow core anchor rods, with centre stop for enhanced energy transfer and sealing.

• Solid plates or domed plates for connection to the structure.

• Hexagonal nuts for anchoring and locking.

The anchor rod made of high-quality tubes with continuous cold-rolled drill thread (standard left-hand rope or trapezoidal thread)

Various drill bits enable quick drilling of boreholes in diverse soil and rock conditions

Coupler with centre stop enabling direct end-to-end bearing between rods thereby minimizing energy loss during drilling

Domed plate made of cold-formed flat steel

Protection tube, if required

Grout

Nut Flat plate

• Flexibility in length by using couplers.

• Ability to work with small drill rigs without casing in narrow spaces.

• Enhanced corrosion protection.

• The high standard of QA systems consistently ensures high quality from production to installation of the injection anchors/piles.

• National and European approvals with CE marking.

• Neck protection tube for corrosion protection.

• Anchor grout or cement.

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1 .2 .2 Drill bits

1 .2 .3 Grout encapsulation

The grout filling, pressure-grouted up to 60 bar, forms the bond between ground and hollow core anchor rod. Tests have shown that the differing transverse strain behaviour of grout

The fully automatic continuous MAI grout pump (Figure 1.2.4) mixes all machine-compatible anchor grouts and cements. It is particularly suitable for injection operations and the

1 .2 .4 MAI grout pump

Fig 1 .2 .4 Grout pump

Bit Shape

Bit Type Clay Bit XX EX EC ES-F ES-D EY EYY ECC EXX ESS-F

Typ

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f so

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nd

Soft

cla

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oil

Loo

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ense

so

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, in

clu

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g b

and

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f so

ft r

ock

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so

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, in

clu

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and

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ock

Wea

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ted

so

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actu

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actu

red

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Med

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fr

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red

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form

atio

ns

Med

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form

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Stro

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orm

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SPT-N Value UCT (N/mm2)

< 40 -

< 40 -

< 50 < 50 -

> 50 < 10 Mpa

> 50 < 10 Mpa

> 50 < 10 Mpa

- < 50 Mpa

- < 50 Mpa

- < 70 Mpa

- < 100 Mpa

R32 (L&N&S 76 51 51 51 76 76 51 51 51

90 76

110 90

with R38 adaptor 130 90

R38 (N) 90 110 76 76 76 76 90 76

110 130 90

130 150

with R51 adaptor 150

175

R51 (L&N) 76 100 100 100 115 76

90 130 130 100

150 150

175 170

200

T76 (N&S) 130 130 130 120

150 145 150

175 175

200 200

T111 (L&N) 220 220 170

Fig 1.2.2 Drill bits

and steel tube does not induce longi-tudinal cracking in the service ability limit state. For aggressive soils suit-able cements must be chosen in accordance with EN 206-1.

grouting of boreholes. The pump achieves delivery pressures of up to 60 bar and delivery rates from 400 up to 2400 l/h.

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1 .3 Quality assuranceISO 9001 (quality management), OHSAS 18001 (safety management system) and as well as ISO 14001 (environ men-tal management) certi fied, Minova MAI and its suppliers are, according to the approvals, subject to internal and

The factory mixed dry cement-based grout with aggregates of up to 0.3 mm achieves high early strengths: After 1 day ~15 N/mm², after 7 days ~ 40 N/mm² and after 28 days ~50 N/mm². It is not prone to segregation, does not shrink, is frost resistant and conforms to the grout qualities specified in EN 445/447 and EN 14199/14490.

1 .2 .5 MAI anchor mortar

1 .4 InstallationFor rotary percussive drilling of coupled hollow core anchor rods, the nomograms for torque M and impact energy E shown in Figure 4 must not be exceeded, in order to prevent predamaging the steel. At the same time, the ancor rods are thereby tightly locked in the coupling area to ensure a virtually slip-free connection both under tension and compression. The minimum torque is 300/500 Nm.

Figure 4 . Torque Mt and impact energy Es during drilling

Range Parameter Type R Type T

R25 R32L R32N R32S R38N R51L R51N T76N T76S T111L T111N

Es, max/2 Es Joule 90 80 130 160 230 220 380 500 680 320 730

Mt Nm 350 500 700 750 1300 1850 2500 8950 10000 14800 21500

Et, max/2 Es Joule 130 120 200 250 330 320 550 690 950 400 970

Mt Nm 250 400 500 550 950 1350 1800 7000 7700 12300 17600

During drilling, impact energy Es and torque Mt must be limited to the pairs of values specified above. For applications using values outside the range specified above the torque-impact energy diagrams below must be observed.

external control (EN 10204). Minova offers a CE marked range of MAI SDA self-drilling anchors and Minova MAI holds several national and European technical approvals as well.

For further details please contact your local Minova representative.

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1 .5 Technical data of the hollow core anchor rods including accessories for rock and soil nails and micropiles .

The technical data of the hollow core ancor rods are summarized in Table 1, page 9.

The load-bearing element is a cold drawn steel tube with a defined chemical composition and fulfils the requirements of EN 14490 for metallic reinforcements. It is rugged and not susceptible to stress corrosion cracking, corresponding to reinforcement steel according to EN 10080.

The hollow core ancor rods compres-sive and tensile strengths as well as the tensile and compressive yield strengths are the same, which means that there is no Bauschinger

1 .5 .1 Hollow core ancor rods

effect. Table 2 below, specifies the shear stress for two limit cases, for pure shearing, e.g. in rock, and for shearing with bending deformation as occurs in slaty/fissured rock.

Finally, a note on the hollow core anchor rods' behaviour under seismic loads (low cycle fatigue): In general, geotechnical literature does not deal with seismic loading. Based on FE models and pseudo-statical analysis, the stresses in the soil/rock induced by seismic loading can be determined.

The seismic standards issued primarily for structural engineering, such as EN 1998 and DIN 4149, provide a

Table 2. Hollow core anchor rod - Minova MAI SDA self-drilling anchors allowable shear force

satisfactory basis. Bonded self-drilling anchors serve to absorb tensile forces. The full values of the Minova MAI self-drilling anchors' system' mechanical properties, not reduced by safety factors, can be assumed in computation.

The soil/rock will fail e.g. due to exceeding the shear/bond strength. Thereby, a large amount of energy is dissipated and thus also the seismic forces. If the Minova MAi self-drilling anchors are correctly positioned, the structure suffers deformation but will not collapse.

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1 Nominal diameter Da, nom mm 25 32 32 32 38 51 51 76 76 111 111

2 Outer diameter Da mm 24,7 31,3 31,3 31,3 38,0 50,0 50,0 75,4 75,4 111,0 111,0

3 Inner diameter Di 1) mm 14 20,6 18,5 15,0 19,0 33,3 30,2 51,0 44,0 85,0 75,5

4 Nominal cross sectional area S0 2) mm

2300 350 430 520 750 900 1070 1870 2400 3185 4395

5 Nominal mass m 3)

kg/m 2,35 2,75 3,4 4,1 5,9 7,05 8,4 14,7 18,85 25,0 34,5

6 Relative rib area fR ¾

7 Nominal yield load Fp0.2, nom 4) kN 150 160 230 280 400 450 630 1200 1500 2000 2750

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Nominal tensile load-bearing capacity

Fm, nom 4) kN 200 210 280 360 500 550 800 1600 1900 2640 3650

9 Yield strength Rp0,2 5) N/mm

2500 460 530 530 530 500 590 640 630 630 630

10 Tensile strength Rm 5) N/mm

2670 600 650 690 660 610 750 860 790 830 830

11 Rm / Rp0,2 6) -

12 Total elongation at maximum load Agt % ≥ 2,5

13 Fatique strength 2·σa 7) N/mm2

14 Notch effect according to EN 1993-1-9 N/mm2

15 Bond strength ak 8) N/mm2

16 Moment of inertia I 9) 10)

mm4

- - 29.800 33.300 75.700 197.000 211.000 863.000 977.000 3.580.000 4.110.000

Modulus of elasticity E ≈ 205.000 N/mm²

10) 16 not relevant for Soil and Rock Nails

Line Parameter

Type R Type T

0,12

6) Characteristic value as 10% fractile

7) Determined at an upper load of Fup = 0,7 * Fp0,2, nom

8) Characteristic value, determined in pull-out tests. The values

are based on a mean value with a slip of 0.01, 0.1 and 1.0mm

and a cement grout cylinder compressive strengt of ≥40 N/mm²

0,24

≥ 1,15


5) Computed based on nominal force and nominal cross sectional area,

rounded value

9) Determined in bending test. Relative to a modulus of elasticity

of 205 000 N/mm² and reduction by 5% to take the deviations in

the mass tolerances into account.

≥ 120

90

≥ 100

70

≥ 5,0

2,8 5,3

1) Mean value

2) computed based on nominal mass m , S0 = 10³ . m / 7,85

3) Allowable deviation - 3% to + 9%

Table 1. Hollow core ancor rods and rope thread Geometry and characteristics of the load bearing element

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The coupler and anchorage are desig-ned for the nominal load bearing capacity of the bars. In fatigue tests, an amplitude of 80 N/mm² was veri-fied at an upper load of 0.7 x Fp0.2 and 2 million load cycles.

See Example 3.13.4 page 30.

1 .5 .2 Accessories and load transfer to the structure (anchor body – concrete)

The dimensions of the couplers are shown in Figure 5 and those of the nuts in Figure 6 below. The solid plate anchorages and domed plates, including their main dimensions, are represented in Figure 7, page 11. Spacers and protection tubes, if required (sections 1.6, 1.8.2 and 2.10.2), are shown in Figure 8 page 11.

Figure 5 and 6. Dimensions of coupler, nut and minimum torque

Component Parameter Type R Type T

R32N R32S R38N R51L R51N T76N, S T111L, N

Coupler Outer diameter A mm 42.4 51.0 63.5 95 140

Length B mm 145 190 220 170 220 220 250

Minimum torque Nm 500

Anchor nut 1) Height C 1) mm 45 60 70 80 120

Width across flats SW mm 46 2) 50 2) 75 2) 100 2) 150 3)


1) The lock nut may be half as high 2) Hexagonal nut 3) Ring nut 160 mm Ø with 4 width flats

Dimensions of coupler, anchor nut and lock nut and minimum torque

Figure 5 . Coupler Figure 6 . Nut

SWThe faces may be either flat or domed

C

Seal

ing

Table 3 . Centre and edge distance (minimum values)

Mechanical anchorage without additional reinforcement (bursting reinforcement)

Concrete compressive strength > 25 N/mm2

Minimum concrete grade > C 20/25

C ..... concrete cover of structural reinforcement. The exposition classes according to EN 206-1 shall be taken into account.

Centre distance A Edge distance R

mm mm

R32N 170 75+C

R32S 220 100+C

R38N 260 120+C

R51L 280 130+C

R51N 340 160+C

T76N 470 225+C

T76S 520 250+C

T111L 620 300+C

T111N 730 355+C

*) for R32N and R32S only domed plates are used

Nail type*)

Nail type* Centre distance A (mm)

Centre distance R (mm)

R32N 170 75+C

R32S 220 100+C

R38N 260 120+C

R51L 280 130+C

R51N 340 160+C

T76N 470 225+C

T76S 520 250+C

T111L 620 300+C

T111N 730 355+C


*) European Technical approval guideline 013

In the serviceability limit state, the slip at the coupling is ~0.8 mm and at the anchorage ~0.3 mm. The load transfer to the structure was tested according to ETAG 013* (anchor body – concrete). The required centre and edge distances are listed in Table 3.

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Figure 7 . Domed plate and solid plate

R25 R32 R38 R51 T76 T111A mm 65 72 78 91 130 170B mm 30 30 30 30 40 50

Type TType RDimensions

R32 R38 R51 T76 T111A mm 76,1 76,1 88,9 114,3 159,0

d 1) mm 2,9 2,9 3,2 4,5 4,5L 1) mm 420 480 610 630 650A mm ≥ 63 ≥ 75 ≥ 80 ≥ 100 ≥ 160d mm ≥ 1 ≥ 1 ≥ 1,5 ≥ 1,5 ≥ 2L mm 300 300 300 300 300

1) For temporary use of the micropile wall thickness es may be reduced by 1.0 mm and length 100 mm

Type T

Plastic tube (smooth or corrugated)

Dimensions Type RComponent

Steel tube

R25 R32L R32N R32S R38N R51L R51N T76N T76S T111L T111NA mm 150 150 200 200 200 - - - - - -B mm 8 8 8 10 12 - - - - - -

Ø-C mm 30 35 35 35 41 - - - - - -D mm 25 25 28 28 28 - - - - - -A mm - - 95 120 140 150 180 250 250 300 350B mm - - 25 30 35 40 45 60 60 80 90

Ø-C mm - - 35 35 41 56 56 90 90 130 130

Type T

Solid plate


Domed plate

Figure 8a . Spacer

Figure 8b. Pile neck protection tube

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1 .6 Corrision protection systems

The service life of Minova MAI SDA self-drilling anchors is defined for the following applications:

• Temporary: system with a service life of up to 2 years

• Permanent: system with a service life of up to 50 years dependent on the ground conditions and a sacrificial corrosion that takes the time-dependent corrosion behaviour into consideration.

To reduce the corrosion rate (sacri fi-cial corrosion, see also EN1993-5), a hot-dip galvanized system according to EN ISO is also available. The acces-sories are hot-dip galvanized or equi-valently protected as well.

To ensure threadability, the thread surface of the accessories may remain ungalvanized. Should small voids become visible on the anchor nut end facing towards the bar, these must be filled with zinc dust paint.

– At pH values < 5 for bare and galvanized steel

– At pH values < 8 for galvanized steel

the corrision load is assigned to the next higher corrosion load, i.e.

low – medium medium – high high – limited service life

Soil parameters

Corrosion loads in soils

Ventilation low medium high

Soil parameters

moderate to very good poor to moderately good very poor to bpoor

Soil structure Mostly sand, gravel, friable rock (coarse to

medium grained)

High amounts of silt, fine sand (medium to

fine grained)

Possibly content of organic substances; high amount

of clay (fine grained), industrial waste, de-icing salt

Water content Low (draining) Generally medium (moist) Generally high, Water change zones

Neutral salinity

Low Possibly indreased Possibly high

pH-value 5 to 8 5 to 8 5 to 8

Soil resistivity in Ω

> 70 10 to 70 < 10

Table 4 . Criteria for evaloating the corrosion load in soil

Table 3 . Centre and edge distance (minimum values)

Mechanical anchorage without additional reinforcement (bursting reinforcement)

Concrete compressive strength > 25 N/mm2 Minimum concrete grade > C 20/25

C ..... concrete cover of structural reinforcement The exposition classes according to EN 206-1 shall be taken into account.


mm mm

R32N 170 75+C

R32S 220 100+C

R38N 260 120+C

R51L 280 130+C

R51N 340 160+C

T76N 470 225+C

T76S 520 250+C

T111L 620 300+C

T111N 730 355+C


Nail type*)

Nail type* Centre distance A (mm)

Centre distance R (mm)

R32N 170 75+C

R32S 220 100+C

R38N 260 120+C

R51L 280 130+C

R51N 340 160+C

T76N 470 225+C

T76S 520 250+C

T111L 620 300+C

T111N 730 355+C

The corrosion rate is dependent on the ground conditions.The corrosion load acting on metallic materials in soils must be evaluated in accordance with EN 12501-1 and EN 12501-2. The corrosion load is classified as:

• l, low

• m, medium

• h, high

The most important physical and chemical soil parameters are defined in EN 12501. The various corrosion loads are evaluated based on an informational listing of the most important soil parameters. These provide the basis for defining the respective corrosion rates of the systems and are listed in Table 4, see also [3]. If required, an expert must be consulted and EN 206.1 be observed.

13

Figure 9 shows the allowable corro-sion rates according to EN 14490 (nails) and EN 14199 (piles), depen dent on the service life and corrosion load. The thickness of the zinc layer is 85μm or higher.

The individual values are taken from an expert opinion and amount to:

µm/year:

EN 14490 allows even higher cross section losses, i.e. longer service lives. The decrease in load bearing capacity due to corrosion is defined in Table 5. Therein, the corrosion of the coupler is taken into consideration as well.

Years Steel Corrosion depth in mm

n m h

2A 0 0 0.2

B 0 0 0.1

7A 0.2 0.2 0.5

B 0 0.1 0.4

30A 0.3 0.6 -

B 0.1 0.4 -

50A 0.5 1.0 -

B 0.3 0.7 -

Legend

Soil aggresivness n low m medium h high

Steel A uncoated steel B galvanized, 85 µm 0 tabular values

Figure 9 . Criteria for evaluating the corrosion load in soil

Soil class Years for steel Years for zinc

l≤ 4 28 ≤ 2 8

≤ 4 7 ≤ 2 2

m≤ 4 35 ≤ 2 30

> 4 16 > 2 3

h≤ 4 68 ≤ 2 55

> 4 68 > 2 48

Table 5 . Loss in cross sectional area due to corrosion

Nail type Parameter Sacrifical corrosion depth in mm

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 1.0

R25 % 0 3 5 8 10 13 15 18 25

R32L % 0 3 6 8 11 14 17 19 27

R32N % 0 2 5 7 9 11 14 16 22

R32S % 0 2 4 6 8 9 11 13 18

R38N % 0 2 3 5 6 8 9 11 16

R51L % 0 2 3 5 7 8 10 12 17

R51N % 0 1 3 4 6 7 8 10 14

T76N % 0 1 3 4 5 6 8 10 13

T76S % 0 1 2 3 4 5 6 7 10

T111L % 0 1 2 3 4 5 7 8 11

T111N % 0 1 2 2 3 4 5 6 8

Example 1

See Example 3.13.1 page 29. The pile and nail necks are fitted with protection tubes. These are discussed in sections 2.8 and 2.10. They serve to transfer the load as well as to avoid local and macro-element formation at the critical joint structure/hollow core ancor rod system in moist soils.

Corrosion in mm x Da x 3,14

So

14

1 .7 Load transfer to the soil for rock and soil nails, piles and anchor as well as safety concept

The load transfer from the hollow core ancor rod to the grout is not a critical issue due to the high relative rib areas of the threads (fR = 0.12 for rope threads and 0.24 for trapezoidal threads). With a grout strength of ≥ 40 N/mm², allowable bond stresses τall x of 1.7 or 3.5 N/mm² may be transferred (characteristic bond strength τu = 2.8 or 5.3 N/mm²). With lower strengths, these values decrease proportionally.

1 .7 .1 Load transfer

The soil bearing capacity (external stability) is evalua-ted based on the ultimate skin frictions τM (kN/m²)specified in Figures 10a, b and 11. Additional τM values for rock are defined in section 2.9.3. The ultimate load-transfer length L can then be assessed based on the following dependency:

L= Ultimate load (kN) / (π x(Ø+0.05) x τM

L = Ultimate load transfer length τM = Ultimate skin friction

(Ø+0.05) = steel diameter + 2 x min. grout cover in mm

Figure 10a . Bond strengths for cohesive soils with post grouting [4]

These values must be verified by load tests. DIN 1054/4128 specifies very low τM - values between 100 and 200 kN/m² for tension and compression piles; load tests, therefore, always yield more favourable results. The load is usually increased to 0.8 ultimate load of the steel element or 0.95 yield-point load observing the 2 mm creep criterion according to EN 1997. With respect to the service load a safety factor of 2 is then required. See Example 3.13.2 page 29.

15

Figure 10b . Bond strengths for cohesive soils without post grouting [4]

Figure 11 . Bond strengths for non-cohesive soils [4]

16

The design concept of EN 1990 with partial safety factors for loads and resistance has also been included in EN 1997. Thereby, the resistance must equal or exceed the loads, multiplied by the safety factors γ . The loads are described in the load standard and express for the most part the 95 % fractile. The material is characterized by the 5 % fractile. Since the soil is not a clearly defined material, it is sometimes difficult to specify definite material parameters. In such cases, assessment with upper and lower limit values is helpful.

The safety factors listed to the right as examples, are defined in EN 1990, EN 1992, EN 1997, DIN 1054 and literature, e.g.[4]. Thereby, a distinction must be made between serviceability and ultimate limit states, the types of load combinations and safety classes. Minova MAI self-drilling anchors may not be used individually (do not use a single MAI SDA self-drilling anchor, always use a system to ensure redundancy).

1 .7 .2 Safety concept

γ load Permanent load 1.35 Favourable 1.0

Traffic 1.5

Internal stress 1.0

γ resistance Steel (yield strength) 1.15 Internal stability 1.0

Concrete (cylinder compressive strength under permanent load

1.5 Internal stability

Fatique, steel 1.15

Concrete 1.5

γ additional verifications

Cracks 1.0

Deformation 1.0 to 1.5

Stability, sliding, toppling 0.9 to 1.5

Uplift 1.05 to 1.4

Soil/general failure 1.0 to 1.5

Grout body 1.33 to 1.5 External stability

Result of load test 1.3 to 1.5 External stability

17

2 .8 Minova MAI SDA soil nails R25 to R51N

Soil nailing is a construction method used to maintain or increase the stabi-lity of soils by installing rein forcing elements (nails) according to the principles for the execution of geo-technical works. The soil rein for ced with nails forms a supporting struc ture.

The nails are primarily subjected to tensile loads. In addition, bending and shear loads may occur as well. The structure must be so designed that the nailing forms a redundant system. One single nail may not serve as the only load-bearing element.

2 .8 .1 Application

The principles for the application and execution of soil nail systems are specified in the application standard EN 14490: Soil nailing, and include information on the installation of soil nails, soil investigations, construction materials and products, design criteria and installation aspects as well as testing and surveillance of soil nail production. In addition, requirements regarding surface preparation, drain-age and facing are discussed as well. Annex A of the standard defines guidelines for the construction and testing of soil nail systems.

The pictures below show application examples.

Figure 12. Examples for applications of soil nails.

Variation of water

level

Variation of water

level

Avalanche barrierSlope stabilisation

Variation of water

level

Pit excavation

Variation of water

level

Strengthening of existing retaining structures

Fastening technology

18

2 .8 .2 Structual design

The material parameters of R25 to 51N have already been defined in section 1.5, Table 1 page 9. Dependent on the service life and soil aggressiveness, the corrosion protection systems specified in section 1.5 are applied (Figs. 13 and 14).

Plastic tubes in the neck area prevent local and macro-element formation in moist soils. They are not required for temporary nails. Solid and domed plates allow angle deviations between

Figure 13 . ATM Nail from R25 to R51N

Nail with domed plate Nail with flat plate

Flat plate

Coupler

Cement grout

Spacer

Permanent nail up to 50 years

Temporary nail system

Domed plate

Plastic tube

Shotcrete or structual concrete > C20/25

Load bearing element – hollow core steel bar

Nut (Annex 3)

the bar and plate up to 3°. For larger deviations, chamfered pipe connec-tions or cone-shaped precast concrete components can be used.

19

Figure 14 . Corrosion protection of the nail head

Flat plate

Grout

Grout

Plastic sheating Plastic sheating

Plastic sheating

Plas

tic

shea

tin

g in

sula

tio

n

rein

forc

emen

t/an

cho

r b

ar

Plastic sheating > 200 mm

> 200 mmPlastic sheatingDomed plate

Concrete

Shotcrete

Concrete

Reinforcement

Reinforcement

Concrete cover > 50 mm

Concrete cover > 50 mm

Sheet metal cap, galvanizedBar

Mut

Components galvanized

Temporary, up to 2 years Temporary, up to 50 years

> 200 mmPlastic sheating

Nail type Internal Ø Wall thickness

R25, R32 > 32 0.6

R38 > 38 1.0

R51 > 51 1.0

Dimensions of plastic sheating (smooth or corrygated)

Seperation (insulation) hollow-core bar / reinforcement in order to avoid macroelement formation in moist soils

20

2 .8 .3 Design

In general, the rock and soil nails are subjected to axial tensile loads and, as the case may be, to shear loads. Load transfer lengths are defined in section 1.7 page 14 (external stability).

For the nailed soil body (Fig.15,[4]), reinforced soil, the conventional sliding, toppling and soil failure verifications must be carried out for the acting loads (see EN 1997-1 or DIN 1054 and national standards). Special attention must be paid to water-bearing sliding zones.

Various safety factors for the design are defined in section 1.7.2 page 16. The soil nail standard EN 14490 specifies a global safety factor of 1.5 to 2 in the serviceability limit state with respect to the test load, for the 2 mm creep criterion. The allowable service loads dependent on the nail type are listed in Table 7 (internal stability).

External stability verifications (with safety factors) according to Wichter

a) Verification of sliding stability (e.g. DIN 1054, π > 1.5)

b) Verification of tipping stability (e.g. DIN 1054, Resultant force at core of base joint)

c) Verification of shear stability (e.g. DIN 4017, π > 2.0)

d) Verification of slope stability (e.g. DIN 4084, π > 1.4/1.3)

Figure 15 . Stability verifications

Table 7 . Allowable load-bearing capacity in the serviceability limit state for Minova MAI SDA soil and rock nails and micropiles (internal stability)

Based on assumptions of example 3:

Safety factors

Safety factors Permanent load, Traffic 1 .35, 1 .5

Ratio permanent load/traffic 2

Mean safety factor γload = 2/3 x 1.35 + 1/3 x 1.5 = 4

Safety factor steel γs = 1.15

Safety factor grout γc = 1.5

Grout cover c = 30 mm

fem cube strength fem = 40 N/mm2

Allowable load-bearing capacity of the hollow-core bar of the grout (if nationally permitted) no pint bearing pressure

Yield point load / 1.4 x 1.15 [(Ø+2x30)2-Ø2] x π/4x0.8x40/1.4x1.5

Type Yield-point load Fp0 .2 in kN

Allowable service load for nail, bolt, tension/

compression pile in kN 1)

Grout area in mm2 Allowable load-bearing capacity of grout in kN

Allowable service load for compression pile including grout in kN

1 2 3 4 5 6 = 3 + 5

R25 150 93.2 - - -

R32L 160 99.4 - - -

R32N 230 142.9 5840 89.0 231.9

R32S 280 173.9 5840 89.0 262.9

R38N 400 248.4 6406 97.6 346.0

R51L 450 279.5 7630 116.3 395.8

R51N 630 391.3 7630 116.3 507.6

T76N 1200 745.3 9985 152.2 897.5

T76S 1500 931.7 9985 152.2 1083.9

T111L 2000 1242.2 13282 202.4 1444.6

T111N 2750 1708.1 13282 202.4 1910.5

1) excluding grout

21

2 .9 Minova MAI SDA rock nails R25 to R51N

Similar in design to soil nails, rock nails serve to stabilize fractured and fissured rock. They fulfil the requirements specified in DIN 21521

2 .9 .1 Application and examples

Figure 16 . Examples for applications of rock nails .

The structural design of R25 to R51N corresponds to that of soil nails shown in Fig. 13, page 18. and Fig. 14 page 19. Additional technical data are defined in Table 1 page 9 and table 7 page 20.

2 .9 .2 Structural designVariation of water

level

Fore poling

Variation of water

level

Radial bolting

Variation of water

level

Root piling

Variation of water

level

Face stabilisation

Variation of water

level

Spilling

for rock anchors. Fig. 16 shows schematic representations of their application.

22

In general, rock excavations are verified using FE programmes. The nails absorb the tensile forces. In addition to the ultimate bond stresses for anchorages according to section 1.7 page 14, the following values are defined, see also [4].

2 .9 .3 Design

Weathered marl, chalk, weak schist 150 to 800 kN/m2

Weak limestone, hard slate, sandstone 800 to 1700 kN/m2

Dolomite, limestone 1400 to 2100 kN/m2

Granite, basalt, concrete 1700 to 3100 kN/m2

23

2 .10 Minova MAI SDA micropiles R32N to T111N

The piles are suitable to bridge soil layers with low load-bearing capa ci ties and to lay foundations in deep load-bearing soils.

2 .10 .1 Application and examples

Tension micropiles are also used to protect against uplift, to acti vate effective soil as ballast. In narrow spaces, they are used to strengthen existing structures. Fig.17 schema ti cally represents additional appli ca tions.

Figure 17 . Examples for applications of micropiles .

Variation of water

level

Variation of water

level

Mast foundation Foundation reinforcement

Foundation

Minova MAI SDA micropiles comply with EN 14199. The piles may thus be used under compressive, tensile and alternating loads.

Anti bucancy support

24

The technical data of R32N to T111N are listed in section 1.5, Table 1 page 9. The structural design is shown in Fig. 18 and Fig.19 page 25. Load transfer to the structure is specified in section 1.5.2 page 10.

The pile neck protection tube repre-sents an important detail in the pile head design (Table 6). To protect the joint between the construction ground and structure against corro sion under tensile loading (local and macro-element formation, in moist soils) a plastic tube extending into the pile and structure must be installed (dimensions see Fig. 8). The tube is not required for temporary piles. If in limit cases, under compression, the load is only transferred from the structure via the steel, the load is then distributed to the composite cross

2 .10 .2 Structural design

Load type of micropile 1)

Type of joint

Not force-fitted Force-fitted 2)

Load type of micropile

1)

Temporary micropile

Permanent micropile

Temporary micropile

Permanent micropile

Tension Plastic tube 3)

Plastic tube 3)

- Plastic tube3)

Compression Steel tube 3)Steel tube 3)

- Plastic tube3)

Alternating load Steel tube 3)Steel tube 3)

- Plastic tube3)

1) If piles are subjected to a compressive test load and subsequently used as structual piles, they must be fitted with a pile neck protection steel tube. 2) Form and force-fit construction joint beetween grout and structural concrete. For this, impuriti-es, cement laitance and loose cement grout must be removed and the cement grout of the pile head pre-moistened prior pouring. 3) 100 mm extension of the pile neck protection tube into the base.

Table 6 . Application of the pile neck protection tube

R25 R32 R38 R51 T76 T111A mm 65 72 78 91 130 170B mm 30 30 30 30 40 50


R32 R38 R51 T76 T111A mm 76,1 76,1 88,9 114,3 159,0d 1) mm 2,9 2,9 3,2 4,5 4,5L 1) mm 420 480 610 630 650A mm ≥ 63 ≥ 75 ≥ 80 ≥ 100 ≥ 160d mm ≥ 1 ≥ 1 ≥ 1,5 ≥ 1,5 ≥ 2L mm 300 300 300 300 300

1) For temporary use of the micropile, the wall thicknesses may be reduced by 1.0 mm and the length by 100 mm

Type T



Steel tube


Ø-C mm 30 35 35 35 41 - - - - - -D mm 25 25 28 28 28 - - - - - -A mm - - 95 120 140 150 180 250 250 300 350B mm - - 25 30 35 40 45 60 60 80 90

Ø-C mm - - 35 35 41 56 56 90 90 130 130

Type T

Solid plate


Domed plate

Figure 8 . Spacer, pile neck protection tube

Spacer

Pile neck protection tube

Base Concrete > C20/25

Structural design of the micropile

2 hexagonal nuts

Anchor plate

Coupler

Cement grout

Spacer

Soil

Drill bit

Temporary micropile

Permanent micropile

Pile neck protection tube

Load bearing element-hollow core steel bar

Figure 18 . Minova MAI SDA micropile R32N to T111N

R25 R32 R38 R51 T76 T111A mm 65 72 78 91 130 170B mm 30 30 30 30 40 50




Type T



Steel tube


Ø-C mm 30 35 35 35 41 - - - - - -D mm 25 25 28 28 28 - - - - - -A mm - - 95 120 140 150 180 250 250 300 350B mm - - 25 30 35 40 45 60 60 80 90

Ø-C mm - - 35 35 41 56 56 90 90 130 130

Type T

Solid plate


Domed plate

R25 R32 R38 R51 T76 T111A mm 65 72 78 91 130 170B mm 30 30 30 30 40 50




Type T



Steel tube


Ø-C mm 30 35 35 35 41 - - - - - -D mm 25 25 28 28 28 - - - - - -A mm - - 95 120 140 150 180 250 250 300 350B mm - - 25 30 35 40 45 60 60 80 90

Ø-C mm - - 35 35 41 56 56 90 90 130 130

Type T

Solid plate


Domed plate

R25 R32 R38 R51 T76 T111A mm 65 72 78 91 130 170B mm 30 30 30 30 40 50




Type T



Steel tube


Ø-C mm 30 35 35 35 41 - - - - - -D mm 25 25 28 28 28 - - - - - -A mm - - 95 120 140 150 180 250 250 300 350B mm - - 25 30 35 40 45 60 60 80 90

Ø-C mm - - 35 35 41 56 56 90 90 130 130

Type T

Solid plate


Domed plate

section hollow core anchor rod grout. The bursting forces thereby generated in the transfer zone must be absorbed by a steel tube or similar (dimensions see Fig. 8).

In general, this annulus is not required, if the con-struction joint structure/grout is formed in the same way as for direct load transfer.

25

Tension pile Compression pile

Lock nut with half the height of nut

Pile neck protection steel tube

Pile neck protection steel tube

Pile neck protec-tion tube

Plastic sheating

Anchor nut

Anchor plate

Anchor nut

Pile under alternating load

Figure 19 . Design of micropile head and micropile neck

Base Concrete > C25/30

Base

Insulation of hollow-core bar against the reinforcement of the connecting structure in order to prevent macro-element formation- example

Reinforcement

Plastic tube

26

The required transfer length to the ground (external stability) can be determined according to section 1.7. In general, the tensile and compressive load is only transferred through the hollow core anchor rod. In addition to the factors of safety defined in section 1.7.2 page 16, DIN 4128 requires a global safety factor of 2.0 with respect to the test load and of 1.75 with

2 .10 .3 Design

Figure 20 . Effect of uplift [4]

Soil

sub

ject

ed

to u

plif

t

Soil pressure σ below the base

respect to the yield strength of the steel. See Example 3.13.3 page 29.

Allowable service loads dependent on the pile type are listed in Table 7, page 20 (internal stability).

To activate the ballast from the soil body, the uplift pile must be designed according to Fig. 20.

Figure 21 . Buckling

System non-displacable displacable

Yie

ld s

tren

gth

For compressive loading, buckling verification may be of interest, if weak soil layers are penetrated. Fig. 21 shows the procedure. If the buckling stiffness is insufficient, a centralizer can be used in the upper areas to enhance stiffness. Couplers should be installed, if possible, outside of zones susceptible to buckling.

See Example 3.13.5 page 30.

27

2 .11 Summary and outlook

This paper is intended to assist design engineers in the design of geotech-nical stabilization measures using Minova MAI SDA soil and rock nails and Minova MAI SDA micropiles. The bases are European approvals and standards, supplemented by national building regulations.

The technical data have been taken from approvals [1 and 2]. The soil parameters and computation models are recommen dations. The person responsible for computation must be sure of the local conditions and, if required, seek advice from soil experts

and take local regulations into consideration.

The first part presents the data of Minova MAI SDA self-drilling anchors that apply for all applications. The second part discusses the structural design of Minova MAI SDA nails and micropiles.

The allowable internal stabilities are defined in Table 7 page 20.

Additional interesting results regar-ding installed hollow core anchor rod systems are listed in [6].

Information on Minova MAI SDA self-drilling anchors according to EN 1537 is available upon request.

An additional element for under-ground construction in rock is the Minova Swellex rock bolt (rock nail), which is not discussed in this paper.

28

ISO 10208: 1991 Rock drilling equipment – left-hand rope threads

EN 1537: 2001 Ground anchors

DIN 4128: 1983 Grouted piles

DIN 1054: 2005 Soil, Verification of the safety of earthworks and foundations

DIN 21521: 1990 Rock bolts

DIN 1054: 2005 Soil, Verification of the safety of earthworks and foundations

DIN 4128: 1983 Grouted piles

DIN 4125: 1990 Temporary and permanent anchors

DIN 4149: 2005 Seismic actions

ISO 9001 Quality management

ISO 14001 Environmental management

[1] European Technical Approval (ETA) 08/0277 Self-drilling rock and soil nail system Minova MAI, Types R25 to R51 based on CUAP 01.02/03:2008

[2] European Technical Approval (ETA) Self-drilling micropile system Minova MAI, Types R32 to T111 based on CUAP 01.03/10:2009

[3] Jungwirth, Jeltsch: Pragmatische Betrachtung zum Korrosionsschutz von geotechnischen Sicherungsmitteln gemäß europäischer Regelwerke; OIAZ N 2-3/ 2005, Vienna

[4] L. Wichter, W. Meininger: Verankerung und Vernagelung im Grundbau. Bauingenieur- Praxis; Ernst+ Sohn 2000

[5] Terzaghi, Jelinek: Bodenmechanik, Springer Berlin 1954

[6] Proceedings International Symposium: Ground anchors, Limelette test field results 2005-2007, Volume: 1, 2a+2b 14 May 2008

2 .12 Technical standards and litterature

ETAG 013: 2002 Guideline for European Technical Approval for post-tensioning kits for the prestressing of structures.

EN 206-1:2005 Concrete – Part 1: Specification, performance, production and conformity

EN 445:2008 Grout for prestressing tendons – Test methods

EN 446: 2008 Grout for prestressing tendons – Grouting procedures

EN 447: 2008 Grout for prestressing tendons – Basic requirements

EN 1990: 2003 Eurocode 1: Basis of design

EN 1991: 2002/9 Eurocode 2: Load assumptions

EN 1992-1-1: 2005 Eurocode 2: Design of concrete structures Part 1: General rules and rules for buildings

EN 1993-5: 2008 Eurocode 3: Design of steel structures Part 5: Piling

EN 1997-1: 2009 Eurocode 7: Geotechnical design Part 1: General rules

EN 1998: 2006-9 Seismic actions

EN 10080: 2005 Steel for the reinforcement of concrete – Weldable reinforcing steel – General

EN 10204: 2005 Metallic products – Types of inspection documents

EN 12501-1: 2003 Protection of metallic materials against corrosion – Corrosion likelihood in soil Part 1: General

EN 12501-2: 2003 Protection of metallic materials against corrosion – Corrosion likelihood in soil Part 2: Low alloyed and non alloyed ferrous materials

EN 14199: 2005 Execution of special geotechnical works – Micropiles

EN 14490: 2010 Soil nailing

EN ISO 1461: 1999 Hot-dipped galvanized coatings on fabricated iron and steel products – Specification and test methods

EN ISO 15630-1:2002 Steel for the reinforcement and prestressing of concrete Test methods Part 1: Reinforcing bars, wire rod and wire

ISO 1720: 1974 Rock drilling – Extension drill-steel equipment for percussive long-hole drilling – Rope threaded equipments 1½ to 2 inches (38 bis 51mm)

29

3 .13 Calculation examples

According to Fig. 9, page 13 the corrosion depth is 0.4mm (graph mB). The load-bearing capacity of the hollow core anchor rod thus decreases by 5 to 6 % according to Table 5, see page 13.

The load transfer hollow core anchor rod/grout is not decisive, since τu = 3000 kN/m².

According to section. 1.7.1 . . . . . . . L= Ultimate load kN/ (π x (Ø+0.05) τM) applies

Based on Fig.10b τM for 360 kN/m², with an estimated length of 7m Test: . . . . . . . . . . . . . . . . . . . . . . . . . L = 800/ (3.14 x (0.051+0.05) x 360) = 7.01m

Thus, an allowable load can be transferred, composed of 2/3 dead load γ=1.35 und 1/3 traffic load γ = 1.5 (γ mean = 1.4) (factors of safety according to section 1.7.2, γ grout =1.5): . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Allowable load = Ultimate load 800 kN/(1.35 x 2/3+1.5 x 1/3) x 1.5 = 380 kN

In the suitability test, see e.g. [4], with a transfer length of only 6 m, the failure load was 750 kN, with a creep criterion of 2 mm, so that an allowable load of (γ = 2 according to section.1.7.1) 750/2 = 375 kN is to be assumed.

According to the internal stability as defined in section 8.2 : 630/(1,15 x 1,4) = 391 kN would be permissible.

The lowest value is decisive: . . . . . . allowable N = 375 kN.

3 .13 .1 How large is the corrosion depth for a 80 µm galvanized hollow core anchor rod R51N after 30 years and medium soil aggressiveness according to Table 4, see page 13:

3 .13 .2 How long is the required load transfer length for Minova MAI SDA self-drilling anchors (external stability under tension or compression), type R51N, without postgrouting, in sandy marl, grout cover 25mm; Type R51N: Ultimate load 800, yield-point load 630 kN):

The yield-point load of T76S is 1500 kN. Using the same load factors as in the example above, the allowable load share of the steel is (γ=1.15): . . 1500/(1.35 x 2/3+1.5 x 1/3) x 1.15 = 1500/(1.4 x 1.15) = 932 kN

The share of the grout in composite piles is dependent on the local building regulations (not permitted in all countries): . . . . . . . . . . . . . . . . . . . . . Grout area (76+2 x 30)² - 76²) x π/4 = 9985 mm² (γ = 1.5)

According to EN 1992-1-1 9985 x 40 x 0.8/1.5 = 213 kN, divided by γ load = 1.4 results in . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 213/1.4 = 152 kN, together with the steel share 1084 kN total service load.

A cone resistance may not be assumed. The allowable internal stabilities for other types are summarized in Table 7, see page 20.

3 .13 .3 How large is the allowable pile load under compression (internal stability) for T76S, with a 30mm grout cover fcm, cube = 40 N/mm²:

30

For the above pile T76S the dynamic share of the service load shall be 225 kN. The amplitude in the steel is then (Steel cross-section = 2400 mm²) . . . . . . . . . . . . . . . . . . 225000/2400 = 93.8 N/mm²

The fatigue strength of the hollow-core bar is much higher, couplers and anchorages, however, only have a fatigue strength of 80 N/mm².

The allowable value in the serviceability limit state may only be assumed to be 80/1.15 = 69.6 N/mm².

Through an additional bond length lv in the structure and in the free length the high value of 93.8 can be reduced to = 69.6 N/mm²:

Load to be decreased . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . (93.8-69.6) x 2400 = 58080 N

Additional bond length in the structural concrete, τ = 3.5 N/mm² . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . lv = 58080/76 x 3 .14 x 3 .5 = 70 mm

Additional bond length in the free length, τ zul = 360/2 = 180 kN/m² = 0.18 N/mm² according to example 2 . . . . . . . lv = 58080/(76+2 x 30) x 3 .14 x 0 .18 = 756 mm

The required additional bond lengths may be taken into consideration in the application, so that the amplitudes to the anchorage and next coupler in the free length are = 69.6 N/mm².

3 .13 .4 Dymanic stability

The MAI SDA micropile T111N penetrates a weak soil layer. How thick may this layer be?

Simplified, the buckling length Lk can be estimated according to Euler case 1. Lateral soil support is not carried out. The grout stiffness outside and inside the hollow core anchor rod is disregarded, no unintentional eccentricity is assumed (cross section values according to Table 1 page 9):

3 .13 .5 Buckling risk in weak soil layers

Lk = Buckling length E = Modulus of elasticity I = Moment of inertia Pstreck = Yield-point load

If a buckling length of 1738/1.75 = 993 mm ~ 1m is conservatively chosen, the T111N pile can penetrate a moor layer of 1 m.

5. Buckling risk in weak soil layers

The hollow-core pile T111N penetrates a weak soil layer. How thick may this layer be ?

Simplified, the buckling length Lk can be estimated according to Euler case 1. Lateral soil support is not carried out. The grout stiffness outside and inside the hollow-core bar is disregarded, no unintentional eccentricity is assumed (cross section values according to Table 1):

Lk = ²/PstreckE·I·π = 000 500·3,14²/27000·411000 205 =1738mm


If a buckling length of 1738/1.75 = 993mm ~ 1m is conservatively chosen, the T111N pile can penetrate a moor layer of 1 m.

= 1738 mmLk =

31

4 . Attachments

Fig. 1 System Fig. 2 Drill bits Fig. 3 Grout pump Fig. 4 Allowable torque/impact energy Fig. 5 Coupler Fig. 6 Nut Fig. 7 Domed plate, solid plate Fig. 8a Spacer Fig. 8b Pile neck protection tube Fig. 9 Corrosion rates Fig. 10a Bond strengths for cohesive soils with post-grouting [4] Fig. 10b Bond strengths for cohesive soils without post-grouting [4] Fig. 11 Bond strengths for non-cohesive soils [4] Fig. 13 Minova MAI nails R25 to R51N Fig. 14 Corrosion protection of nail head Fig. 15 Stability verifications Fig. 18 Minova MAI piles R32N to T111N Fig. 19 Pile head design Fig. 20 Effect of uplift [4] Fig. 21 Buckling Fig. 22 Load distribution for a pile foundation [5] Fig. 23 Load polygon anchored wall [5]

4 .1 Figures

4 .2 Tables

Table 1 Hollow-core bar parameters R25 to T111N Table 2 Allowable shear force Table 3 Centre and edge distances Table 4 Criteria to evaluate the corrosion load Table 5 Cross section loss due to corrosion Table 6 Pile neck protection tube Table 7


If a buckling length of 1738/1.75 = 993 mm ~ 1m is conservatively chosen, the T111N pile can penetrate a moor layer of 1 m.

34

R25N R32L R32N R32S R38N R51L R51N T76N+S T111L+N

Outer ø A mm 33,7 42,2 42,4 42,2 51,0 63,5 63,5 95 140

Length B mm 150 145 145 190 220 170 220 220 250


Height C 1) mm 35 45 45 45 60 70 70 80 120

Width across flats AF mm 412) 462) 462) 462) 502) 752) 752) 1002) 1503)

Minimum torque Nm 3001) The lock nut may be half as high2) Hexagonal nut3) Ringnut ø160 mm with 4 width flats

Component Parameter

Typ R Typ T

Coupler

500

Nut

500

35

R25 R32 R38 R51 T76 T111A mm 65 72 78 91 130 170B mm 30 30 30 30 40 50




Type T



Steel tube


Ø-C mm 30 35 35 35 41 - - - - - -D mm 25 25 28 28 28 - - - - - -A mm - - 95 120 140 150 180 250 250 300 350B mm - - 25 30 35 40 45 60 60 80 90

Ø-C mm - - 35 35 41 56 56 90 90 130 130

Type T

Solid plate


Domed plate

36

Example 1

47


1 Nominal diameter Da, nom mm 25 32 32 32 38 51 51 76 76 111 111

2 Outer diameter Da mm 24,7 31,3 31,3 31,3 38,0 50,0 50,0 75,4 75,4 111,0 111,0

3 Inner diameter Di 1) mm 14 20,6 18,5 15,0 19,0 33,3 30,2 51,0 44,0 85,0 75,5

4 Nominal cross sectional area S0 2) mm

2300 350 430 520 750 900 1070 1870 2400 3185 4395

5 Nominal mass m 3)

kg/m 2,35 2,75 3,4 4,1 5,9 7,05 8,4 14,7 18,85 25,0 34,5

6 Relative rib area fR ¾

7 Nominal yield load Fp0.2, nom 4) kN 150 160 230 280 400 450 630 1200 1500 2000 2750

8

Nominal tensile load-bearing capacity

Fm, nom 4) kN 200 210 280 360 500 550 800 1600 1900 2640 3650

9 Yield strength Rp0,2 5) N/mm

2500 460 530 530 530 500 590 640 630 630 630

10 Tensile strength Rm 5) N/mm

2670 600 650 690 660 610 750 860 790 830 830

11 Rm / Rp0,2 6) -

12 Total elongation at maximum load Agt % ≥ 2,5

13 Fatique strength 2·σa 7) N/mm2

14 Notch effect according to EN 1993-1-9 N/mm2

15 Bond strength ak 8) N/mm2

16 Moment of inertia I 9) 10)

mm4

- - 29.800 33.300 75.700 197.000 211.000 863.000 977.000 3.580.000 4.110.000

Modulus of elasticity E ≈ 205.000 N/mm²

10) 16 not relevant for Soil and Rock Nails

Line Parameter

Type R Type T

0,12


7) Determined at an upper load of Fup = 0,7 * Fp0,2, nom

8) Characteristic value, determined in pull-out tests. The values

are based on a mean value with a slip of 0.01, 0.1 and 1.0mm

and a cement grout cylinder compressive strengt of ≥40 N/mm²

0,24

≥ 1,15


5) Computed based on nominal force and nominal cross sectional area,

rounded value

9) Determined in bending test. Relative to a modulus of elasticity

of 205 000 N/mm² and reduction by 5% to take the deviations in

the mass tolerances into account.

≥ 120

90

≥ 100

70

≥ 5,0

2,8 5,3

1) Mean value

2) computed based on nominal mass m , S0 = 10³ . m / 7,85

3) Allowable deviation - 3% to + 9%

49


mm mm

R32N 170 75+C

R32S 220 100+C

R38N 260 120+C

R51L 280 130+C

R51N 340 160+C

T76N 470 225+C

T76S 520 250+C

T111L 620 300+C

T111N 730 355+C

*) for R25 and R32S only domed plates are used

(no plate anchorages)

Nail type*)

50

Low Medium High

Ventilation Moderate to very good poor to moderately good Very poor to poor

Possibly content

of organic substances;

Mostly sand, gravel, High amounts of silt, high amounts of clay (fine-

friable rock (coarse to fine sand (medium to fine- grained), industrial waste,

medium grained) grained) de-icing salt

Generally high,

Low (draining) Generally medium (moist) Water change zones

Neutral salinity Low Possibly increased Possibly high

pH-value 5 to 8 5 to 8 5 to 8

Soil resistivity

in > 70 10 to 70 < 10

m

the corrosion load is assigned to the next higher corrosion load, i.e.

low → medium

medium → high

high → limited service life

- with pH values <5 for bare and galvanised steel

- with pH values <8 for galvanised steel

Soil parameters

Corrosion load in soils

Soil structure

Water content

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 1.0

R25 % 0 3 5 8 10 13 15 18 25

R32L % 0 3 6 8 11 14 17 19 27

R32N % 0 2 5 7 9 11 14 16 22

R32S % 0 2 4 6 8 9 11 13 18

R38N % 0 2 3 5 6 8 9 11 16

R51L % 0 2 3 5 7 8 10 12 17

R51N % 0 1 3 4 6 7 8 10 14

T76N % 0 1 3 4 5 6 8 10 13

T76S % 0 1 2 3 4 5 6 7 10

T111L % 0 1 2 3 4 5 7 8 11

T111N % 0 1 2 2 3 4 5 6 8

ParameterNail type

Sacrifical corrosion depth in mm

Corrosion in mm x Da x 3,14So

51

Temporary

micropile

Permanent

micropile

Temporary

micropile

Permanent

micropile

Tension Plastic tube 3) Plastic tube 3) - Plastic tube 3)

Compression Steel tube 3) Steel tube 3) - Plastic tube 3)

Alternating load Steel tube 3) Steel tube 3) - Plastic tube 3)

Load type of micropile 1)

Type of joint

Non force-fitted Force-fitted 2)

1) If piles are subjected to a compressive test load and subsequently used as structural

piles, they must be fitted with a pile neck protection steel tube.2) Form and force-fit construction joint between grout and structural concrete. For this,

impurities, cement laitance and loose cement grout must be removed and the cement grout

of the pile head pre-moistened prior to pouring.3) 100 mm extension of the pile neck protection tube into the base.

52

Based on the assumptions of example 3:

Safety factors Permanent load 1.35

Traffic 1.5

Ratio permanent load/traffic 2

Mean safety factor γload=2/3·1.35+1/3·1.5=1.4

Safety factor steel γs=1.15

Safety factor grout γc=1.5

Grout cover c=30mm

fem cube strength fem=40N/mm2

Allowable load-bearing capacity of Yield point load / 1.4·1.15

the hollow-core bar

of the grout

(if nationally permitted) [(Ø+2·30)²-Ø²]·π/4·0.8·40/1.4·1.5

no point bearing pressure

Yield-point load

Allowable service load for

nail, bolt, tension / Grout area Allowable load-bearing Allowable service load forFp0,2 in kN compression pile in kN ¹) in mm² capacity of grout in kN compression pile

including grout in kN

1 2 3 4 5 6=3+5

R25 150 93,2 - - -

R32L 160 99,4 - - -

R32N 230 142,9 5840 89,0 231,9

R32S 280 173,9 5840 89,0 262,9

R38N 400 248,4 6406 97,6 346,0

R51L 450 279,5 7630 116,3 395,8

R51N 630 391,3 7630 116,3 507,6

T76N 1200 745,3 9985 152,2 897,5

T76S 1500 931,7 9985 152,2 1083,9

T111L 2000 1242,2 13282 202,4 1444,6

T111N 2750 1708,1 13282 202,4 1910,5

¹) excluding grout

Type

The Ground Support Company

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Internet: www.minovainternational.com

February 2012

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