Bill BAMFORD

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INTRODUCTION

PREDICTING TOOL WEAR AND REPLACEMENT RATES FOR MACHINE TUNNELLING1. Tests can be performed on solid rock

substance samples, for rock TBMs2. Tests can be performed on naturally

granular materials, for soft-ground TBMs (e.g. EPB machines, Slurry Shields)

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EXAMPLE : “TOTAL HARDNESS” METHOD

“Total Hardness”

is calculated from

Schmidt Rebound

Hammer Hardness

+

Taber Abraser Test

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EXAMPLE : SINTEF METHOD

CUTTER LIFE INDEX (CLI)

is calculated from

Sievers J-value

Drillability test

+

Abrasion Value Steel

(AVS) test.

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The Norwegian Abrasion Test :Norwegian Abrasion Value (NAV) : Tungsten Carbide Workpiece :

Percussive DrillingAbrasion Value Steel (AVS) :

Steel Workpiece : Hard-Rock TBMs

Soil Abrasion Test (SAT) : Steel Workpiece :

Soft-Ground TBMs

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SAT RESULTS (1)

• Prediction of soft-ground

tunnelling tool life from

lab SAT results;

• NB : lab testing is

conducted on dry

sand and sandy silt

materials.

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SAT RESULTS (2)

• Separate correlations,

for Slurry Shields

&

EPBMs

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•While the SAT (Soil Abrasion Test) is popular, and is being widely used, its fundamental weakness is that it is conducted on dry sandy materials, not widely representative of what most Slurry Shield and EPBM tunnelling operations are conducted in.

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SGAT

• The Soft Ground Abrasion Tester (SGAT) was recently designed and built at the NTNU in Trondheim, Norway.

• With the permission and assistance of its original designer, a second version has been built in Melbourne.

• It enables the abrasiveness of sandy materials to be measured, not in the dry, freely-flowing state, as per the SAT, but rather in the compacted and wet conditions in which they will be penetrated by TBMs.

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HOWEVER ….

• The required sample size to perform SAT is only a few kilograms;

• The required sample size to perform SGAT is a few tens of kilograms.

So, during exploration for a tunnelling project it may be difficult to obtain sufficient masses of material from the exploratory boreholes for significant SGAT testing to be performed.

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UNIVERSITY OF MELBOURNE RESEARCH

1. Investigate correlations between SAT & SGAT values, in comparable materials.

2. Investigate whether blending of different commercially-available sands can allow large quantities of a “synthetic” soil to be assembled in the lab, which will reliably mimic the properties of any natural sand or soil which has been supplied to the lab in small quantities.

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MATERIALS: Commercial Sands

Soil ID Specific Gravity Coefficient of Uniformity Coefficient of Curvature

BTS 2.62 2.23 0.83

MTS 2.60 1.50 0.86

WGS 2.69 5.71 1.19

Brown Turf Sand

(BTS)White Granitic Sand

(WGS)

Muckadilla Turf Sand

(MTS)

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MATERIALS: Naturally Occurring Soils

Soil ID Description Specific Gravity

F Sandy soil (Perth, AU) 2.58

M Mixture of clay, silt & sand (Melbourne, AU) 2.62

W Mixture of clay, silt and sand (Auckland, NZ) 2.64

Soil F Soil WSoil M

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BRTS NTNU MACHINE

SAT Test Piece

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BRTS SGAT MACHINE

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SAMPLE PREPARATION

Proctor

Hammer

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RESULTS & ANALYSIS- Results Comparison

SAT on “M” is not achievable, while SGAT on “M” is the greatest!SAT does not properly simulate field conditions (Density, Moisture content, etc.)

13.3 6.0 13.0 5.6 0 1.2

33.5 40.456.1

19.5

374.1

149.0

0

50

100

150

200

250

300

350

400

BTS MTS WGS F M W

We

igh

t L

oss (

mg

)

SAT

SGAT

NA

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RESULTS & ANALYSIS- Commercial Sands

0

20

40

60

80

100

0 2 4 6 8 10 12 14

SG

AT

Va

lue

(m

g)

Moisture Content (%)

WGS

MTS

BTS

1600

1700

1800

1900

2000

0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0

Dry

De

ns

ity

(k

g/m

3)

Moisture Content (%)

WGS

MTS

BTS

Compaction SGAT

Maximum abrasivity is not necessarily at the driest or densest condition

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RESULTS & ANALYSIS- Naturally Occurring Soils

Compaction SGAT

Changes in density and moisture condition didn’t affect SGAT value of “F"

1500

1600

1700

1800

1900

2000

0 5 10 15 20

Dry

De

ns

ity

(k

g/m

3)

Moisture Content (%)

F

W

M

0

200

400

600

800

0 5 10 15 20

SG

AT

Va

lue

(m

g)

Moisture Content (%)

W

M

F

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RESULTS & ANALYSIS- Basis for Classification

VL: Very Low Abrasivity

L: Low Abrasivity

M: Medium Abrasivity

H: High Abrasivity

V: Very High Abrasivity

More test data

is required… 0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0 20 40 60 80 100 120 140 160 180 200

SGAT (mg)

V

L

M

H

VH

22 43 76 147

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RESULTS & ANALYSIS- SGAT vs SAT Test Results

Soil ID Moisture content (%) Abrasivity (SGAT) Abrasivity (SAT)

WGS

2.3 Low

Medium

5.4 Medium

7.5 High

8.5 Medium

12.2 Very Low

M

4.8 Very High

NA

8.2 Very High

11.6 Very High

14.7 Very High

17.7 High

Unlike SAT, for a soft ground soil type, SGAT provides a range of abrasivity values.

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CONCLUSIONS

• Advantage: Improves the accuracy of characterizing ground conditions for soft-ground machine tunnelling

• Advantage: The ability of the SGAT to more accurately and quantitatively measure the abrasiveness of sedimentary deposits and soils, in conditions closely simulating the conditions of density and moisture content in which they will be excavated by a TBM, makes it potentially a far superior tool.

• The widely accepted SAT (Soil Abrasion Test) may continue to be used for broad classification purposes, if sample quantities and testing budgets are limited.

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FUTURE PLAN

•After characterizing the PSD and the soil mineralogy of the small submitted samples, it may be possible by mixing calculated proportions of the several “commercial” sands to construct analogue materials in masses large enough for significant testing at many densities and moisture contents, to bracket the full range of expected variability in-situ.

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FUTURE PLAN

• Planned work at BRTS will enable the injection of different conditioning agents into the test chamber, to quantify the reductions in abrasiveness that may be achieved by appropriate soil conditioning.

• The consequent changes in torque/thrust and power will also show how optimum TBM operating parameters for a particular soil might result from the appropriate soil conditioning agents.

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Typical EPBM in section, showing where conditioning agents may be introduced

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Thank you

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