1

Grasberg, 2003

Slope Monitoring

Types of slope instruments

Displacement monitoring devicesPrecise surveysDifferential global positioning systems (DGPS)Space-borne and terrestrial SAR Interferometry

Strain monitoring devicesSurface extensometersBorehole extensometersBorehole inclinometersTiltmetersTime domain reflectometry (TDR)

Pore-pressure measurementsPiezometers and monitoring wellsTensiometersTDR moisture gauges

MicroseismicityGeophones

2

Displacement monitoring1) “Total Station”: Electronic Distance Measurement

(“EDM”) + Theodolite

2) “DGPS” Differential Global Positioning System:Base station+measuring stations Target prism

Britannia Mine, B.C. Disturbed Area

PR #104

PR #102

PR #100

3

PR #100

PR #104

PR #102

“East Block”

East Block, failure model

0 50 100 150 200 250 300 350 400

1000

1050

1100

1150

1200

1250

1300

1350

1400

ELE

VA

TIO

N (m

)

Toppling(schematic)

Tensioncracks

102

100

300,000 m3

0 50 100 150 200 250 300 350 400

1000

1050

1100

1150

1200

1250

1300

1350

1400

ELE

VA

TIO

N (m

)

Toppling(schematic)

Tensioncracks

102

100

4

MonitoringJane Basin Slope

26-Jul-02 30-Aug-04

04-Jan-9506-Jan-92

05-Aug-93

25-Nov-92

20-Jul-92

-0.15

-0.10

-0.05

0.00

0.05

0.10

0.15

0.20

0.25

0.30

Jan-92 Jan-93 Jan-94 Jan-95 Jan-96 Jan-97 Jan-98 Jan-99 Jan-00 Jan-01 Jan-02 Jan-03 Jan-04 Jan-05 Jan-06

Date

Del

ta T

otal

Mov

emen

t (m

)PR100

PR101

PR102

PR103

PR104

Coal Mine Waste Dumps

5

Wire extensometer

With data logger

Borehole extensometer (Slope Indicator, Ltd.)

6

Surface rod extensometer (“crackmeter”)

Vibrating wire displacement gauge (or a vernier for manual readings or a linear transducer) accuracy

7

Borehole inclinometer (“Slope Indicator”)

Some inclinometer applications (Slope Indicator, Ltd.)

8

Time domain reflectometry (TDR)

Synthetic aperture radar interferometry (SAR)

9

Piezometers

▼ 1) Observation well (open) –not a piezometer

2) Pneumatic piezometer

3) Standipe(Casagrande) piezometer

4) Electric piezometer(Vibrating Wire)

SEAL

SAND PACK

MEMBRANE

AIR

Piezometercomparison

10

Slope Indicator multi-point vibrating wire

piezometer

Grasberg, 2003

Monitoring Interpretation

11

Chuquicamata Mine, Chile, 1968

Movement vector F-2

Micro-seismic events/day

Chuquicamata Mine, Chile, 1968

Movement vector F-2

Micro-seismic events/day

12

Inverse Velocity Method (Fukuzono, 1985)Normal

Inverse

Inverse Velocity Method, more examples

“La Clapiere”France

PredictionReal

Tripp Mine: slow failure

13

Inverse Velocity Method, another example

18-Jul-01 25-Jul-01 1-Aug-01 8-Aug-01 15-Aug-01 22-Aug-01 29-Aug-01DATE

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

INV

ER

SE

VE

LOC

ITY

(day

s/cm

)

45 40 35 30 25 20 15 10 5 0TIME BEFORE FAILURE (DAYS)

0

5

10

15

20

25

30

35

VE

LOC

ITY

(cm

/day

)45 40 35 30 25 20 15 10 5 0

TIME BEFORE FAILURE (DAYS)

Regression coeffiecient (R2) = 99%for all inverse-velocity fits

Predicted velocity curves (basedon inverse-velocity fits) comparedwith actual velocity data

18 million m3 pit slope failure prediction (Rose and Hungr, 2006)

14

Use of inverse velocity to monitor stabilization progress (Rose and Hungr, 2006)

1-May-02 16-May-02 31-May-02 15-Jun-02 30-Jun-02 16-Jul-02 31-Jul-02 15-Aug-02DATE

0

0.5

1

1.5

2

INV

ER

SE

VE

LOC

ITY

(day

s/cm

)

105 100 95 90 85 80 75 70 65 60 55 50 45 40 35 30 25 20 15 10 5 0TIME BEFORE FAILURE (DAYS)

Buttress and OffloadRemedial Measures

Stabilization of Slope Displacements

Regression Coeffiecient (R2) = 96 to 99%for all Inverse-Velocity Fits.

Pats FaultMidnight Fault

Carlin waxy silt unit

100mScale

Two faults and a pre-sheared silt layer, 3 million m3

Total Displacement?

ValPola rock avalanche, 1986

100 m pre-historic movement

New crack

15

Small rock slides

Libby Dam, Montana, 1971

Prediction not feasible

Purpose of monitoring

1) Movement detection, failure prediction

2) Vector solutions, interpretation of failure mechanism

(Cruden, 1986)

Predicted rupture surface