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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
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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
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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
Detecting systematicdependence
Tq, PR vs. Th and H
Detecting systematicdependence
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.