Rock Engineering Practice & Design · Rock Mechanics Rock Mechanics. Although the slides have been...

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Lecture Lecture 13:13:InstrumentationInstrumentationInstrumentationInstrumentationPlanning & DesignPlanning & Design

1 of 42 Erik Eberhardt – UBC Geological Engineering ISRM Edition

Author’s Note:Author’s Note:The lecture slides provided here are taken from the course “Geotechnical Engineering Practice”, which is part of the 4th year Geological Engineering program at the University of British Columbia (V C d ) Th k i i d (Vancouver, Canada). The course covers rock engineering and geotechnical design methodologies, building on those already taken by the students covering Introductory Rock Mechanics and Advanced Rock Mechanics Rock Mechanics.

Although the slides have been modified in part to add context, they of course are missing the detailed narrative that accompanies any l l d h h l lecture. It is also recognized that these lectures summarize, reproduce and build on the work of others for which gratitude is extended. Where possible, efforts have been made to acknowledge th v ri us s urc s ith list f r f r nc s b in pr vid d t th the various sources, with a list of references being provided at the end of each lecture.

Errors, omissions, comments, etc., can be forwarded to the


Errors, omissions, comments, etc., can be forwarded to the author at: [email protected]

Instrumentation & MonitoringInstrumentation & MonitoringThe use of geotechnical instrumentation is not merely the selection of instruments but a comprehensive step-by-step engineering process beginning with a definition of the objective and ending with implementation of the data implementation of the data.

Engineering objectives typically encountered in soil and rock engineering projects have g g p jled to the design and commercial marketingof numerous instrument types, measuring for example:

• temperature

• deformation

easing

bi

lity

• groundwater/pore pressures

• total stress in soil and stress change in rock

decr

ere

liab


change in rock

Field InstrumentationField InstrumentationGeotechnical engineering projects often present the ultimate measurement challenge, in part because of their initial lack of definitionand the sheer scale of the problem. The measurement problem usually requires information ranging from a coarse scale down to a fine scale and requires information ranging from a coarse scale down to a fine scale and involving a number of instrumentation techniques.

Th lti t l i t l t th The ultimate goal is to select the most sensitive measurement parameters with respect to theproject objectives, e.g. the ones project objectives, e.g. the ones that will change significantly at the onset of failure. However, because of physical limitations and economic c nstr ints ll p r meters c nn t constraints, all parameters cannot be measured with equal ease and success.


Franklin (1977)

Planning and DesignPlanning and Design

Adequate planning is required before proceeding, and these plans should be logical and comprehensive – from defining the bj i l i h h objectives to planning how the measurement

data will be implemented. The ‘red bible’

(Dunnicliff 1993).

1. Define the project conditions.

The steps through which planning should proceed include:

p j

… these might include project type and layout, geology and structure, engineering properties of materials, engineering properties of materials, groundwater conditions, status of nearby structures or other facilities, environmental conditions, and planned construction method


and planned construction method.

Planning and DesignPlanning and Design2. Predict mechanisms that control behaviour.… may involve one or more working hypotheses based on a comprehensive knowledge

of the project conditions.

dt (2

008)Existing

FractureFracture Initiation

Surface/SubsurfaceDisplacements

Mi i i E i i

Eber

hard

Pore Pressures(fracture permeability)

Microseismic Emissions

Where brittle fracture mechanisms contribute significantly to rock mass deformation and failure, microseismic monitoring may form an integral part


microseismic monitoring may form an integral part of the monitoring strategy.

Planning and DesignPlanning and Design3. Define the geotechnical

questions that need to be answered.

i j … every instrument on a project should be selected and placed to assist in answering a specific question: if there is no question, h h ld b i ithere should be no instrumentation.

Monitoring serves a number of important functions including:functions, including:

(i) Investigative Monitoring: To provide an understanding of the rock mass behaviour and thus enable appropriate actions to be pp pimplemented.

(ii) Predictive Monitoring: To provide a warning of a change in behaviour and thus enable the possibility of limiting damage or


Imrie et al. (1992)enable the possibility of limiting damage or intervening to prevent failure.

Planning and DesignPlanning and Design4 D fi th f th i t t ti4. Define the purpose of the instrumentation.… Peck (1984) stated that, “The legitimate uses of instrumentation are so many,

and the questions that instruments and observation can answer so vital, that we should not risk discrediting their value by using them improperly or should not risk discrediting their value by using them improperly or unnecessarily.”

… monitoring the performance of a waste barrier system designed to prevent the


g p y g ppolluting of a major aquifer from a chemical waste dump in Switzerland.


5. Select the parameters to be monitored.… Parameters include pore water pressure, joint water pressure, total stress,

stress change, deformation, load and strain in structural members, and gtemperature.

… high precision joint water pressure measurements at the Bedretto tunnel adit, Switzerland.


Planning and DesignPlanning and Design6. Predict magnitudes of change.… Predictions are necessary so that the required instrument ranges and required

instrument sensitivities or accuracies can be selected.

… 1999 Eibelschrofen rockfall in f fthe Austrian alps. Post-failure monitoring of the slope

included the installation of a fibre-optic extensometer capable of measuring displacements on the scale


measuring displacements on the scale of m. Was this practical?

Planning and DesignPlanning and DesignBurland et al. (2001)

7. Devise remedial action.… Inherent in the use of

instrumentation for construction i th b l t it purposes is the absolute necessity

for deciding in advance, a positive means for solving any problem that may be disclosed by the results of th b ti nthe observation.


Planning and DesignPlanning and Design8. Assign tasks for design, construction and operation phases.… Instrumentation specialists may be employees of the owner or the design

consultant or may be consultants with special expertise in geotechnical h k f h h h instrumentation. When assigning tasks for monitoring, the party with the

greatest vested interest in the data should be given direct line responsibility for producing it accurately.


Planning and DesignPlanning and Design9. Select Instruments.… When selecting instruments, the overriding desirable feature is reliability!

Inherent in reliability is maximum simplicity.

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ty

• Optical

• Mechanical

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complex

it M chan ca

• Hydraulic

• Pneumatic

• Electrical

Instruments should be: … reliable, rugged and capable of functioning for long periods of time without repair or replacement;… capable of responding rapidly and precisely to changes so


that a true picture of events can be maintained at all times.


10. Select instrument locations.… The selection of instrument locations should reflect predicted behaviour and p

should be compatible with the method of analysis that will later be used when interpreting the data.

… instrumentation layout at the Randa Rockslide Laboratory in the Swiss Alps.

Willenberg et al. (2008b)


W llenberg et al. ( 008b)


11. Account for factors that may influence measured data.

… Details of each instrument installation should be recorded, because local or unusual conditions often influence measured variables.

12. Establish procedures for ensuring reading correctness.

… When reading an instrument, one should be able to answer the question: Is the instrument functioning correctly? The answer can sometimes be provided by answer can sometimes be provided by visual observations, duplication of instruments, data consistency or through the use of instruments that internally check their own correct functioning.

Dunnicliff (1993)


ch c th r own corr ct funct on ng.

Planning and DesignPlanning and Design13. List the specific purpose of each instrument.… It is useful to question whether all planned instruments are justified. If no

viable purpose can be found for a planned instrument, it should be deleted.

14. Prepare budget.… A budget should be prepared for all

instrumentation-related tasks to ensure sufficient funds are indeed available. A frequent error in budget preparation is to underestimate the duration of the project and the real data collection and processing costs.

15. Prepare instrument procurement specifications.15. Prepare instrument procurement specifications.… There are several competing instrumentation manufacturers, each offering

products designed for similar geotechnical purposes. Be aware of an instrument’s capabilities (and limitations), as well as those of competing products.


Instruments should be purchased from established manufacturers.


16. Plan installation, regular calibration & maintenance.

… Installation procedures should be … Installation procedures should be planned well in advance of scheduled installation dates. The step-by-step procedures should include a detailed list of required include a detailed list of required materials and tools, and installation record sheets for documenting factors that may influence measured data.influence measured data.

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… schematic diagram of the borehole instrumentation and installation design developed for the Randa Rockslide Laboratory in Switzerland


EberLaboratory in Switzerland.

Planning and DesignPlanning and Design17. Plan data collection, processing, presentation, interpretation, reporting

and implementation.… The effort required for these tasks should not be underestimated. Many

consulting firms have files filled with large quantities of partially processed and undigested data because sufficient time/funds were not available for these tasks.


Instrumentation Instrumentation –– Geodetic MonitoringGeodetic MonitoringGeodetic monitoring provides a means to measure the magnitude and rate of horizontal and vertical ground movements. Methods are well established and are often entirely well established, and are often entirely adequate for performance monitoring.

Advantages: automated (total station), inexpensive, versatile.Accuracy: typically ±2mm + 2 ppm x D mm over 3000 m

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Geodetic Monitoring Geodetic Monitoring -- BenchmarksBenchmarks

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Measurement accuracy (and reliability) is controlled by the characteristics of reference

lson

& M

ikkecharacteristics of reference

datums and measuring points. Checks are required to make sure these datums are located on stable ground


Wion stable ground.

Instrumentation Instrumentation –– Global Positioning SystemsGlobal Positioning Systems

… satellite measurements and base-stations at known locations are used to provide simultaneous corrections and refinements to the computed locations of one or several differential global positioning system (DGPS) g p g ystations positioned on the slide body.

Advantages: automated, economical (especially over large areas).S iti it b tt th 1 i id l diti


Sensitivity: better than 1 cm in ideal conditions

Instrumentation Instrumentation –– CrackmetersCrackmeters

… used to measure and monitor the opening of surface fractures and tension crackstension cracks.

Advantages: simple, ideally suited for early warning systems.Sensitivity:

Instrumentation Instrumentation –– Convergence IndicatorsConvergence IndicatorsConvergence is one of the most frequently made underground measurements. Made between two or more fixed points around the excavation perimeter, repeat monitoring provides rates of convergence changes in monitoring provides rates of convergence, changes in rate and total convergence values.

Ad t : i l i i d b t i Advantages: simple, inexpensive and robust in anunderground environment.

Sensitivity:

Borehole Instrumentation Borehole Instrumentation –– InclinometersInclinometers

Inclinometers monitor differential subsurface deformations by means of a probe that measures changes in inclination along the length of a borehole.

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Advantages: can detect and monitor complex slope deformations and displacements along multiple shear planes.

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p g p pSensitivity: ±10 arc seconds (±0.05mm/m)

Inclinometer CasingInclinometer Casing


Inclinometer InstallationInclinometer Installation


Inclinometer Inclinometer MeasurementsMeasurements


Bonzanigo et al. (2007)

Borehole Instrumentation Borehole Instrumentation –– ExtensometersExtensometers

… extensometers measure the relative change in position between several fixed points.

Advantages: simple to install, inexpensive, can measure larger slope displacements than inclinometers.

Accuracy: ±0.01 mm/m


Borehole Instrumentation Borehole Instrumentation –– TDRTDR

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Time Domain Reflectometry (TDR) - uses characteristics of returned electrical pulses to determine the amount of strain, or the existence

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of a rupture, in a coaxial cable.

Borehole Instrumentation Borehole Instrumentation -- PiezometersPiezometers

Vibrating wire piezometers consist of a diaphragm, which when deflected by pore

b d b pressures,can be measured by an electrical transducer. These have the advantage of a negligible time lag and being a negligible time lag and being extremely sensitive.


Emerging Technologies Emerging Technologies –– Fiber Fiber OpticesOptices

Fiber-Optics - light that is launched into and confined to the fiber core Fiber Optics light that is launched into and confined to the fiber core propagates along the length of the fiber unperturbed unless acted upon by an external influence. Any disturbance of the fiber alters the guided light which can then be related to the magnitude of the disturbing influence.


Case History: Investigative Slope MonitoringCase History: Investigative Slope Monitoring

current instabilitycurrent instability1991 Randa Rockslide


Courtesy - H.Willenberg

Case History: Investigative Slope MonitoringCase History: Investigative Slope Monitoringbrass rings for brass rings for electromagnetic

induction extensometer

brass rings for brass rings for electromagnetic

induction extensometer

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Geological investigations

Geophysical investigations

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Geological investigations

Geophysical investigations

3-D geological model

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Geotechnical Mi i i

Kinematics of the rockslide

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Numerical modelling

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Frequency content of attenuated microseismicsignals suggest the presence of large open


fractures, deep (>100 m) below surface.

Case History: Investigative Slope MonitoringCase History: Investigative Slope MonitoringInt t d d t m d l: P b bilit d nsit f n ti ns Integrated data model: Probability density functions (PDF) of microseismic event locations, and relative displacement rates of ongoing block movements.

Kinematic model defined by the


Willenberg et al. (2008b) Kinematic model defined by the collective measurements.

Case History: Investigative Slope MonitoringCase History: Investigative Slope MonitoringMonitoring data provides a key means to constrain numerical models. At the same time, numerical modelling provides an ideal means to g psupport and/or refute interpretations drawn from investigative monitoring, as well as to explore possible future behaviour.

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Lecture ReferencesLecture ReferencesBonzanigo L Eberhardt E & Loew S (2007) Long term investigation of a deep seated creepingBonzanigo, L, Eberhardt, E & Loew, S (2007). Long-term investigation of a deep-seated creepinglandslide in crystalline rock – Part 1: Geological and hydromechanical factors controlling the CampoVallemaggia landslide. Canadian Geotechnical Journal 44(10): 1157-1180.

Brady, BHG & Brown, ET (2006). Rock Mechanics for Underground Mining (3rd Edition). Chapman &Hall: LondonHall: London.

Burland JB, Standing JR & Jardine FM (2001). Building Response to Tunnelling - Case Studies fromConstruction of the Jubilee Line Extension, London. Thomas Telford: London.

Dowding, CH & Huang, FC (1994). Early detection of rock movement with time domainDowd ng, H & Huang, F ( 99 ). Early detect on of rock movement w th t me doma nreflectometry. Journal of Geotechnical Engineering, ASCE 120(8): 1413–1427.

Dunnicliff, J (1993). Geotechnical Instrumentation for Monitoring Field Performance. John Wiley &Sons: New York.

Eb h d E (2008) T Ni h C di G h i l C ll i Th l f d dEberhardt, E (2008). Twenty-Ninth Canadian Geotechnical Colloquium: The role of advancednumerical methods and geotechnical field measurements in understanding complex deep-seated rockslope failure mechanisms. Canadian Geotechnical Journal 45(4): 484-510.

Eberhardt, E., Spillmann, T., Maurer, H., Willenberg, H., Loew, S. & Stead, D. (2004). TheR d R k lid L b E bli hi b i l d d il i bili h i i i lRanda Rockslide Laboratory: Establishing brittle and ductile instability mechanisms using numericalmodelling and microseismicity. In Proc., 9th International Symposium on Landslides, Rio de Janeiro.A.A. Balkema: Leiden, pp. 481-487.

Franklin, JA (1977). Some practical considerations in the planning of field instrumentation. InP di f h I i l i Fi ld M i R k M h i Z i h A A


Proceedings of the International Symposium on Field Measurements in Rock Mechanics, Zurich. A.A.Balkema: Rotterdam, pp. 3-13.

Lecture ReferencesLecture ReferencesImrie, AS, Moore, DP & Energen, EG (1992). Performance and maintenance of the drainage systemat Downie Slide. In Proceedings, Sixth International Symposium on Landslides, Christchurch. A.A.Balkema: Rotterdam, pp. 751-757.

Peck, RB (1984). Observation and instrumentation, some elementary considerations, 1983 postscript.In Judgement in Geotechnical Engineering: The Professional Legacy of Ralph B. Peck. Wiley: New York,pp. 128-130.

Willenberg, H, Loew, S, Eberhardt, E, Evans, KF, Spillmann, T, Heincke, B, Maurer, H &Green, AG (2008a). Internal structure and deformation of an unstable crystalline rock mass aboveRanda (Switzerland): Part I - Internal structure from integrated geological and geophysicalinvestigations. Engineering Geology 101(1-2): 1-14.

Willenberg, H, Evans, KF, Eberhardt, E, Spillmann, T & Loew, S (2008b). Internal structure anddeformation of an unstable crystalline rock mass above Randa (Switzerland): Part II – Three-dimensional deformation patterns. Engineering Geology 101(1-2): 15-32.

Wilson, SD & Mikkelsen, PE (1978). Field instrumentation. In Landslides: Analysis and Control -Special Report 176. National Research Council: Washington, D.C., pp. 112-138.


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