04 detecting faults - pb

8/6/2019 04 Detecting Faults - PB

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Association of GeoTechnical &GeoEnvironmental Specialists (Hong Kong)

Technical Seminar 19th March 2011Hong Kong University

By: Pawel BarmutaSenior Associate

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Fault Zones & Their Influence onConstruction

Detecting Faults Ahead of the TunnelFace During Construction


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Marine Clay

CDG

Granite

44

Marine Clay

CDG

Granite


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Characteristic of fault zones in Hong Kong

Single or multiple shear plane

Fault gauge along shear plane

Intense fracturing in the vicinity of shear plane

High permeability

Faults are often followed by pervasive weathering

Abrupt, distinctive boundaries

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Examples of minor faults in Sandy Bay andCyberport shafts of HATS2 project

Even a narrow band of cohesion-lessmaterial may become a difficulty when withpresence of water under pressure


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Sub-vertical fault zonecontoured by the Geologist

on 10m diameter shaft facein Sandy Bay Shaft ofHATS2 C/2007/24 project


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Methods of Detecting the Weakness Zone: Vertical coring from surface

Directional drilling from surface

Horizontal (directional) coring from tunnel face

Logged percussion drilling from tunnel face

Percussion drilling from tunnel face with tele-viewing

Seismic refraction from surface

Seismic refraction from tunnel face

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Visual Logging of Percussion Probing:

Penetration Rate by use of e.g. 1m marks on the drillrods and measuring the drill time with a stop watch

Colour of flush

Content of fines (silt and clay fraction)

Lithology of chippings collected on sieve

Water flow rate

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Extremely Hazardous Environment:

Extreme noise from percussion drifters

Working between moving booms and close to rotatingtools

Poor ventilation

High temperature

Confined space

1212


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Sources of Uncertainties

Time lag between encountered geological

feature and flush appearance difficulty tolocate the feature and to determine its span

Effect of drilling pressures on Penetration

Rate can not be separated

Human factor in the observations and recordsdue to extremely hard working condition

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Seam of CDG factual position

Contentof fines

Probe depth

Peak on finescontent logcorresponding toseam of CDG


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On SSDS project tunnels AB and C the whole

alignment of 10.1 km was covered by probedrilling

The probe hole length was typically 50 m

Totally around 57 kmof probes weredrilled in 2 years and logged by Geologist

Reports from every probe drillings were timelyprepared and distributed by Geological Team

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Visual logging of percussion drilling is veryeffective and reliable tool to identify the

weakness zones ahead of the tunnel. It isrecommended for single cases inparticular.

Never do it again!

Lesson learned from HATS1 tunnels AB & C


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often can be found as MWD MeasuringWhen Drilling

AUTOMATED RECORDINGOF DRILLING PARAMETERS

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Parameters Logged Automatically on Drilling Machine

Hammer Pressure - PH

Torque Pressure - PTq

Thrust Pressure (Feed Pressure) - PTh

Instant Penetration Rate PR

Collar co-ordinates

Depth

Orientation (Vertical and Horizontal angle to tunnelaxis)

Water pressure

Current and Voltage


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Advantages of Analysis of Automatic Logs of PercussionDrilling

No disruption to production cycle the analysis iscarried out on logs of regular production drill holes(grout holes)

No problems with safety hazards There are nopersonnel present at the tunnel face when drilling

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Methods of Analysis:

Single parameter response

orVarious parameters response

that can be analyzed by:

Heuristic methods

Statistical methods


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Statistical Methods of Analysis:

Pattern recognition Each rock type leaves a statistically detectable specific

pattern of recorded pressures and penetration rate

Normalization of the data Eliminating from Penetration Rate the trends related to other

than rock properties factors detected statistically in therecords

(Presented first comprehensively byH. Schunnesson)

Results from both methods have to be calibrated against thefactual rock properties on site

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PR and PTq are the indicators of rockresistance

Systematic dependences between PTq,PTh, PTH, steel length and PR which are notrelated to rock properties have to bedetected and filtered out from PR and PTqrecord.


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Regression analysis

Records ofThTqHPRfrom the project

Normalization &scaling

Detecting systematicdependence

Th, Tq, PR vs. depth


Tq, PR vs. Th and H


Tq vs. PR

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Normalized PR and PTq parametersafter after scaling are dimensionless

and need to be calibrated againstfactual rock condition e.g.represented by Q- value or by rockgrade of decomposition


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Example of normalizationand scaling process

First step:

filtering out from the records allexcessive reading related to stoppages,collaring, changing drill bit and addingdrill rods


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Pressure [bar]

depth [m]

depth [m]

PR [m/min]

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Tq vs L (raw data from population)Tq [bar]

depth [m]28


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PR vs PH

y = 0.0175x - 0.5552

R2

= 0.8169

0

0.5

1

1.5

2

2.5

3

3.5

4

30 50 70 90 110 130 150 170 190

PH [bar]

PR [m/min]

PR vs PTh

y = 0.0004x2

- 0.0254x + 1.2851

R2

= 0.7693

0

0.5

1

1.5

2

2.5

3

3.5

4

20 30 40 50 60 70 80 90 100 110

PTh [bar]

PR [m/min]


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Tq vs Th

y = -0.0007x3

+ 0.1125x2

- 4.5571x + 99.652

R2

= 0.5157

0

20

40

60

80

100

120

140

20 30 40 50 60 70 80 90 100 110

PTh [bar]

PTq [bar]

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Geotechnicalinterpretation:

Higher torque

pressure is requiredwhen the tool

penetrates deeperinto the rock due to

higher thrustpressure

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No relationbetween PThand drill holedepth due to

computer

control of PTh

PTh vs depth

0

20

40

60

80

100

120

0 5 10 15 20

depth [m]

PTh [bar]

PR vs Tq

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

20 40 60 80 100 120

PTq [bar]

PR [m/min]


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The equation of regression line PR vs. PThand PR vs. PH are used to compensate eachraw PR measurement in a sample towardsaverage value of the population.

PR filtered of PH and PTh effect

0

0.5

1

1.5

2

2.5

3

3.5

0 5 10 15 20

Depth [m]

PR [m/min]

Raw data

PTh corrected

PTh and PH corrected


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In tunnel applications the statistical analysis has tobe first carried out on a large sample covering allrock condition expected along the tunnel i.e.provide appropriate MIN, MAX and regression lines

The trends of interdependence between PTq, PTh,PR, L & PH can be assumed machinery specific

hence used across projects

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Calibration of Probing Parameter

(Normalized and scaled PR) vs. mapped Q value5 m buffer

Q1 Q2

PR1PR2

PR3

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For tunneling purposes normalization andscaling should be based on initial largesample covering all kinds of rock condition

expected along the tunnel

InitialSample

Parameters fornormalization

& scaling

Application onsingle probe

hole


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Computers and software allow: Processing almost instantly large number of data

from numerous drill-holes

Provide unlimited options of presentation of theresults on 2D and 3D diagrams

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Rock module by BeverControl used on HATS2DC/2007/24

Cylindrical plane oflogged grout holesahead of the tunnelunfolded

Red color represents

weak rock. Potentialfault zone can becontoured by theGeologist

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Rock mass resistancereflects twodistinguished

lithological types ofrock:

Syenite - (Hard)

Shist - (Weak)

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Intensity of Jointing & FracturingWell represented by normalized Torque Pressure PTq

changes measured as Root Mean Square - RMS

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Rock Module byBever Controlused on HATS2DC/2007/24

Cylindrical planeof logged groutholes unfolded

Fracturingintensity isrepresented byRMS ofnormalized PTq

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Other Method of Analysis

of

Percussion Drilling Data

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Specific Energy Concept By R. Taele (Destruction Energy)

Definition: Specific Energy is the energy needed todisintegrate a unit volume of rock by drilling.

Specific Energy parameter reflects properties of

particular rock and drilling method

i.e. Is specific for rock and method.


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A drill hole face area

L drilled length (typically 100 mm)

L

A

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Espent = EH + ETq + EThE

spent= E

H+ E

Tq+ E

Th

EH energy spent due to hammer action

ETq energy spent due to torque action

ETh energy spent due to thrust action


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Energy spent to drill a section of drill holecan be calculated from discrete records ofpressures PTh, PTq and PH as well as fromrecords of electric current and voltage whendrilling.

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Specific Energy (SE)Parameter may also require corrections for:

Drill hole depth (string weight, wear of drill bit,

friction along string) systematic effect on SE

PTh, PTq and PR systematic effects on SE notrelated to variations of rock condition


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Specific Energy (SE)Contrary to normalized Penetration Rate andTorque Pressure, has physical meaning and

reportedly has good correlation to:

TBM performance Powder factor

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Summary 1 Visual logging of percussion probes is an efficient

tool for detecting bad ground condition ahead oftunnel face

2 Automated logging eliminates safety hazardsrelated to presence of staff at the tunnel face

3 Automated logging largely eliminates disruption toproduction cycle

4 Automated probing combined with data statisticalinterpretation provide reliable contouring ofweakness zones ahead of tunnel face


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5757

Granite

CDG

Marine Clay

5757

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Thank You.

04 detecting faults - pb

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