5 rock%2520mass%2520damage%2520assessment final

7/31/2019 5 Rock%2520Mass%2520Damage%2520Assessment FINAL

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Rock mass damage assessmentRock mass damage assessment

Methods and applicationsMethods and applications


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Rock Mass Damage

Engineering perspective:damage is any change in

a material property which degrades the materialsperformance. (Brown et al 1994)

Geotechnical perspective:fracturing ordiscontinuity generation, extension ordegradation, or any irreversible deformation

such as the shearing and opening ofdiscontinuities, which causes deterioration ofthe rock mass strength (Li 1993).


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Large basal fault

Jointing sub-parallel to fault plane

Zone of Rock Cracking

Zone of Joint Cracking

Zone of Rock Bridge

Potential Failure Plane

80% Charge, 20% Air

Presplit

Blast Damage AssessmentOpen pits

(Bye, 2006)


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Damage assessment - Underground


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Damage assessment methods recenttechnologies

Technology Quantity observed or measured

3D Digital image mapping Excavation profile; overbreak

Ground Penetrating Radar(GPR)

Depth of damage. Non-destructive method that uses electromagneticradiation in the microwave band (UHF/VHF frequencies) of the radio

spectrum, and detects the reflected signals from subsurface structuresGround Probe Radar Measure and monitor the stability of rock walls (sub mm accuracy)

3D digital photogrammetry(SiroVision)

High-precision 3D images used for the mapping and analysis of rockmass surfaces.

Crack monitors Measures crack displacementLaser Scanner Pre and post blast wall displacement (30 mm accuracy)

Downhole imaging Pre and post blast fracture mapping

Impulse response technique(CSM)

Depth of damage


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Slope Monitoring Techniques

Technology Precision WallCoverage

Update Rate Range Deployment Allweather

SSR

Laser

(Prisms)

Laser(Prismless)

Extenso-meters

GPS ~ 10s cm DiscretePoints

~ secs n/a Difficult Yes

Photogram-metry

~ 1s cm BroadArea

~ mins < 150 m Moderate No

0.2 mm BroadArea

~ mins 450 m(1 km)

Easy Yes

~ 1s cm Discrete

Points

Twice Daily < 2 km Difficult No

~ 10s cm BroadArea

~ secs < 200 m Moderate

~ 1s mm DiscretePoints

~ secs n/a

No

YesDifficult


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Direct methods - observations

Borehole surveys

Half barrels


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Downhole imaging

(courtesy Wellfield Services Limitada)


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Subsurface damage

A B

Section A-B

9.2 m

distance f rom damage tonearest fully coupled blasthole

damage inspectionboreholes (1m apart)

1 m

Chapter 11, LOP, 2007)


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Direct methods profile measurements

Reflectorless distance measurementsystems

Desired profile

Measured profile

Major structures

Photo: LeicaTMS Total Station


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Direct method of overbreak measurement in undergroundenvironments - cavity monitoring system (CMS)

Developed by Noranda and Optechsystem s Canada.

CMS


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Direct methods profile measurements with 3Ddigital imaging

Courtesy MD Robotics


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Indirect methods - seismic tomography

Electronic Detonators Vs Pyrotechnic (After Ichijo et al, 1994)


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Seismic monitoring relative reduction in Vp

ASP Blastronics, 2006


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GPR technology - Underground


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GPR technology Open pit

Codelco IM2, 2006


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Impulse response techniquePetr, 2005


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Ground Probe Radar

(Bye, 2006)


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RIEGL Laser Scanner

(Bye, 2006)

3D di it l h t t


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3D digital photogrammetrySiroVision


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Other instrumentation - crack monitors

Addressing blasting complaints

Eight month history of displacement andcrack displacement showing greatest change

width to correlate with the most intense andlongest drop in humidity in April

Dowding and Siebert, 2000

D A t f Vib ti


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Damage Assessment from VibrationMonitoring

Uphole Geophone Schematic

Triaxial Geophone

PVC Pipe

Grout Bleeding Hose

Grout Pumping hose

Plug

Vertical

Geophone

Radial

Geophone

Transverse

Geophone

Data

Cable

Example of commercial data


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Example of commercial dataacquisition systems

Instantel

Texcel


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Terminology on vibrations

Peak particle velocity (PPV)refers to the peak

vibration velocity measured in a given transducer (e.g.radial, transverse or vertical)

Attenuationrefers to the diminishing of intensity of a

wave front as it progresses through a media

Vector sumis the resultant of the magnitude to thethree orthogonal components coincident with time

Peak vector sumis the resultant of the peakmagnitude of each orthogonal component not

coincident with time

Types of wave motion Body


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Types of wave motion Bodywaves

Compressional wave (P-wave). The particle motion is

parallel to the direction of the wave propagation

Propagationdirection

Particlemotion

Types of wave motion Body


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Types of wave motion Bodywaves

Shear waves (s-waves) the particles generally move

transversely to the direction of the wave propagation

Particlemotion


Types of wave motion surface


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Types of wave motion surfacewaves

At interfaces (Ground and air,

ground and joints) differenttype of surface waves aredeveloped. The most

important is the Rayleighwave (R-wave)

Particlemotion


Indirect methods Near field peak


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Indirect methods Near field peakparticle velocity (PPV) monitoring

Station 1

Leading TunnelLagging Tunnel

Observation Holes

(diamond drilled)

0.5-0.8m from geophone

holes

Geophone hole A

Geophone hole B

Plan View

Vibration measurements Equipment


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Vibration measurements Equipmentrequirements

Fit for use sensors

Good and consistent coupling

Data capturing and reporting

Monitoring system with auto-trigger level capabilities

Adequate calibration

Ideally, the monitoring system should be self reliant, thatis have long life battery or permanent power

Damage assessment - PPV


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Damage assessment PPVbased monitoring

Damage assessment - PPV


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Damage assessment PPVbased monitoring

Damage assessment - PPV based


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Damage assessment PPV basedmonitoring


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Best practice is to use a combination of directand indirect methods to infer damage

Combination of borehole surveys with vibrationsExtensometers with seismics

O di i i


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Open discussion session

Local experience on rock mass damage assessment

Use of PPV based criteria Can it be used for structurally controlled damage ?

Single versus a range of values

PPV relation to strain

Intact rock versus rock mass

Quantifying the impact of damage Surface stability

Rock reinforcement and support Mechanisms of damage (gas versus stress induced)

5 rock%2520mass%2520damage%2520assessment final

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