session 1 instrumentation and monitoringcliffs.lboro.ac.uk/downloads/workshop...

Climate impact forecasting for slopes: are we getting the story right?

The fourth themed CLIFFS workshop, 3 July 2007

Holywell Conference Centre, Loughborough University

Session 1

Instrumentation and monitoring

Andrew Ridley

Geotechnical bservations

www.geo-observations.com

The presence of vegetation can lead to seasonal

effects that can give serviceability problems.

Numerical analysis also suggests that these seasonal

variations of pore water pressure can lead to stability

problems (Kovacevic et al. 2001).

The stability and serviceability of embankments in clay

The effect of cycling the suction at the surface on

the stability of a clay fill embankment

(after Kovacevic, Potts & Vaughan 2001)

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Deep standpipe to investigate underlying

ground water

Piezometers capable of measuring positive and negative

pore water pressures

Inclinometers to detect lateral movement

Extensometers to detect vertical movement

Instrumentation for investigating the stability of embankments

-10.0

-5.0

0.0

5.0

10.0

15.0

Displacement (mm)

0.68m

0.85m1.90m

3.00m

3.96m

-40

-30

-20

-10

0

10

Displacement (mm)

0.14m

0.64m

1.14m

1.64m

Vertical displacement at toe

Outward displacement at toe

-10.0

-8.0

-6.0

-4.0

-2.0

0.0

2.0

09-Mar-06 11-Apr-06 14-May-06 16-Jun-06 19-Jul-06 21-Aug-06 23-Sep-06 26-Oct-06 28-Nov-06 31-Dec-06 02-Feb-07

piezometric head (m)

0

2

4

6

8

10

12

Daily Rainfall (mm)

PWP at 0.64mbgl

-30

-20

-10

0

10


Displacement (mm)

-10

0

10

20

30

Displacement (mm)

1.51m

1.48m

1.90m

2.48m

4.09m

Vertical displacement at the top of the slope

Outward displacement at the top of the slope

At the top of the slope vertical displacements are greater than outward displacements

Scale

2m - Section

20mm - Deflection

40mm - Settlement

Summary of pore water pressures and displacements at the toe of an embankment

Scale

2m - Section

20mm - Deflection

40mm - Settlement

Summary of pore water pressures and displacements at the top of an embankment

Unloading will cause a reduction in the pore water

pressures, which may become negative.

The stability of cut slopes in clay

Negative pore pressures will improve stability.


In some cases swelling due to the increase of pwp

will cause softening in the soil near the toe of the

slope, a plastic zone will develop and failure may

occur in a slope that was otherwise stable in the

static sense.

The effect of increasing pore water pressure on

the stability of a cut slope in clay

(after Potts, Kovacevic & Vaughan 1997)

Design charts to assess the potential for failure (after

Ellis and O’Brien, 2007)


Instrumentation for investigating the stability of cut slopes

Piezometers capable of measuring positive and negative

pore water pressures to assess the profiles relative to the

long term equilibrium

Inclinometers at the toe for

detecting shear zones

1

3.8

10 20 30 40 50 60

horizontal distance from barrier (m)

-4

-2

0

2

4

6

8

10

12

14

elevation (m)

Tree Line

5

6

3

1

2

7

8

Long term equilibrium conditions

Weathered brown

London Clay

Unweathered blue

London Clay

-8 -6 -4 -2 0 2 4 6

2

4

6

8

10

Pore pressures measured in a highway cutting with surface vegetation

9 years after construction

1

3.8

10 20 30 40 50 60


-4

-2

0

2

4

6

8

10

12

14

elevation (m)

-8 -6 -4 -2 0 2 4 6

Tree Line



1

3.8

10 20 30 40 50 60


-4

-2

0

2

4

6

8

10

12

14

elevation (m)

-8 -6 -4 -2 0 2 4 6

2

4

6

8

10

12

14

-8 -6 -4 -2 0 2 4 6

-8 -6 -4 -2 0 2 4 6

Tree Line

-8 -6 -4 -2 0 2 4 6



10mm Inclinometer

Deformation

2m - Slope

1

3

~ 5m

Displacements in a failed cut slope in Gault Clay

Pore water pressures can be positive or negative.

Deformations near the top of the slope are

principally vertical.Displacements near the toe are principally

lateral.

Embankments

Cuttings

Pore water pressures will initially be negative and

will, in time, become positive. Displacements will begin at the toe.

Displacements in the upper part of the slope

will occur suddenly and with little warning.

SUMMARY

Piezometers that can measure positive and

negative pore water pressures.Extensometers at the top of the slope.

Inclinometers and extensometers near the toe

of the slope.

Embankments

Cuttings

Analysis to identify if the slope is susceptible to

progressive failure.Piezometers that can measure positive and

negative pore water pressures.

SUMMARY

Inclinometers in the lower part of the slope.

Porous

Filter

Valve

Pressure

Sensor

Hydraulic

pipes

Data

Logger

5 cm

GeO flushable piezometers

for pore water pressures

(positive and negative)

PVC stemO'ring seals here

Epoxy seal here1 bar ceramic filter

Flushing

system

Electrical cable

Pressure Sensor

Borehole

Borehole

Piezometer Stem

Cement / Bentonite

Grout

Borehole

Piezometer Stem

Cement / Bentonite

Grout

Borehole

GeO piezometer sensor

and valve

Piezometer Stem

Insitu calibration

check using known

head of water

Open the valve to check calibration

Remove the sensor and valve to check zero and repair

Inclinometers

Manually read or real-time data logging?

Displacements are initially small and slow to develop.

Manually read is normally adequate but perform

baseline readings with two probes so displacements

(if they exist) can be verified.

In-place sensors can be used if displacement is

detected and it is rapid. Sensors only required above,

on and below the shear plane.

Absolute shape of inclinometer casing

Profile of casing in plane parallel to the track(positive values lie to the right when facing the track)

0

1

2

3

4

5

6

-900 -750 -600 -450 -300 -150 0 150 300 450 600 750 900

cumulative deviation relative to bottom of casing (mm)

depth below top of casing (m)

13-Apr-05

Profile of casing in plane perpendicular to the track (positive values lie closer to the track)

0

1

2

3

4

5

6

-900 -750 -600 -450 -300 -150 0 150 300 450 600 750 900



13-Apr-05

24cm

24cm

Site Location : Pound Green Embankment

Inclinometer : BH32

Stickup : 24cm

: ArupClient

110°

+

+

T R A C K

Probe DI1090

Probe DI1090

Movement in plane perpendicular to the track(positive values indicate movement towards the track)

0

1

2

3

4

5

6

-5 -4 -3 -2 -1 0 1 2 3 4 5

cumulative displacement relative to baseline readings (mm)


13-Apr-06

Movement in plane parallel to the track(positive values indicate movement to the right when facing the track)

0

1

2

3

4

5

6

-5 -4 -3 -2 -1 0 1 2 3 4 5



13-Apr-06

(x = 0 axis represents profile on 13-04-05)

Displacement relative to base set of readings


Inclinometer : BH32

Stickup : 24cm

: ArupClient

24cm

24cm

Broken lines indicate the range of random error


110°

+

+

T R A C K

Probe DI1090

Probe DI1090

Baseline reading probe 1090 – run 1 Baseline reading probe 1090 – run 2

Absolute shape of inclinometer casing

Profile of casing in plane parallel to the track(positive values lie to the right when facing the track)

0

1

2

3

4

5

6

-900 -750 -600 -450 -300 -150 0 150 300 450 600 750 900



13-Apr-05

Profile of casing in plane perpendicular to the track (positive values lie closer to the track)

0

1

2

3

4

5

6

-900 -750 -600 -450 -300 -150 0 150 300 450 600 750 900



13-Apr-05

24cm

24cm


Inclinometer : BH32

Stickup : 24cm

: ArupClient

110°

+

+

T R A C K

Probe DI1179

Probe DI1179


0

1

2

3

4

5

6

-5 -4 -3 -2 -1 0 1 2 3 4 5



13-Apr-06


0

1

2

3

4

5

6

-5 -4 -3 -2 -1 0 1 2 3 4 5



13-Apr-06




Inclinometer : BH32

Stickup : 24cm

: ArupClient

24cm

24cm



110°

+

+

T R A C K

Probe DI1179

Probe DI1179

Baseline reading probe 1179 – run 1 Baseline reading probe 1179 – run 2


0

1

2

3

4

5

6

-14 -12 -10 -8 -6 -4 -2 0 2 4 6 8 10 12



09-May-06

13-Jun-06

07-Jul-06

04-Aug-06

14-Sep-06

13-Oct-06

15-Nov-06


0

1

2

3

4

5

6

-14 -12 -10 -8 -6 -4 -2 0 2 4 6 8 10 12



09-May-06

13-Jun-06

07-Jul-06

04-Aug-06

14-Sep-06

13-Oct-06

15-Nov-06




Inclinometer : BH32

Stickup : 24cm

: ArupClient

24cm

24cm



110°

+

+

T R A C K

Probe DI1090

Probe DI1090

Readings to Nov 2006 – probe 1090


0

1

2

3

4

5

6

-14 -12 -10 -8 -6 -4 -2 0 2 4 6 8 10 12



15-Nov-06


0

1

2

3

4

5

6

-14 -12 -10 -8 -6 -4 -2 0 2 4 6 8 10 12



15-Nov-06




Inclinometer : BH32

Stickup : 24cm

: ArupClient

24cm

24cm



110°

+

+

T R A C K

Probe DI1179

Probe DI1179

Reading in Nov 2006 – probe 1179


0

1

2

3

4

5

6

-14 -12 -10 -8 -6 -4 -2 0 2 4 6 8 10 12



Probe 1179

Probe 1090


0

1

2

3

4

5

6

-14 -12 -10 -8 -6 -4 -2 0 2 4 6 8 10 12



Probe 1179

Probe 1090




Inclinometer : BH32

Stickup : 24cm

: ArupClient

24cm

24cm



110°

+

+

T R A C K

Nov 06

Nov 06

Comparison of displacements with probe 1090 and probe 1179 – Apr 06 to Nov 06

Movement in plane perpendicular to the M25 Motorway.(positive values indicate movement towards the motorway)

0

2

4

6

8

10

12

14

16

18

20

-14 -13 -12 -11 -10 -9 -8 -7 -6 -5 -4 -3 -2 -1 0 1 2 3

displacement (mm)

depth (m)

pre Apr 04

05-Apr-04

13-Apr-04

19-Apr-04

26-Apr-04

Movement in plane parallel to the M25 Motorway.

(positive values indicate movement to the right when facing the motorway)

0

2

4

6

8

10

12

14

16

18

20

-14 -13 -12 -11 -10 -9 -8 -7 -6 -5 -4 -3 -2 -1 0 1 2 3

displacement (mm)

depth (m)

pre Apr 04

05-Apr-04

13-Apr-04

19-Apr-04

26-Apr-04



Site location : M25 - Junction 6 - Godstone

Inclinometer : BH4-06

Stick-up : + 35 cm

Client : Mouchel Parkman / Highways Agency

M25

+

+

348o

35cm

35cm

range of random error

range of random error

Displacement in the plane perpendicular to the motorway(positive values indicate movement towards the motorway)

Displacement in the plane parallel to the motorway(positive values indicate movement to right when facing the motorway)

Manual readings to identify where the shear surface is

-12.0

-10.0

-8.0

-6.0

-4.0

-2.0

0.0

2.0

14/03/2003 13/05/2003 12/07/2003 10/09/2003 09/11/2003 08/01/2004 08/03/2004 07/05/2004

Cumulative displacement (m

m)

5.65m

6.15m

6.65m

7.15m

Displacement verses time to assess the speed of movement

Figure B1 Location of inplace sensors

Site location: M25 - Junction 6 - Godstone

Inclinometer: BH4-06

Length of casing: 20m

Stick-up: + 35 cm

Client: Mouchel Parkman / Highways Agency

Profile of casing in plane parallel to the M25 Motorway.

(positive values to the right when facing the motorway)

5.00

5.50

6.00

6.50

7.00

7.50

8.00

8.50

9.00

0 50 100 150 200 250 300Cumulative deviation (mm)


Profile of casing in plane perpendicular to the M25 Motorway.

(positive values lie closer to the motorway)

5.00

5.50

6.00

6.50

7.00

7.50

8.00

8.50

9.00

0 50 100 150 200 250 300

Cumulative deviation (mm)


#1

#5

#4

#3

#2

#1

#2

#3

#4

#5

M25

+

+

348o

Profile of casing in plane perpendicular to the motorway

(positive values lie closer to the motorway)

Profile of casing in plane parallel to the motorway

(positive values lie to the right when facing the motorway)

Place sensors above, on and below the shear plane

Displacement predominantly on the shear plane

Insertion tool

Spider Magnet

Flush access pipe

Insertion tool is used to push

the magnet to the required

depth. Sprung legs bend and

rest on borehole wall during

insertion

Insertion tool is pulled to

embed sprung legs into the

wall of the borehole

Insertion tool is withdrawn

leaving magnet in place

Borehole

GeO Magnet Extensometers for vertical movement

-10.0

0.0

10.0

20.0

30.0


Settlement (m

m)

0.695 1.290 1.521 2.073 2.605 3.114 3.452 4.168 4.484 5.027 5.459 6.372

7.404 8.771

Site location: Pound Green Embankment

Extensometer: BH21

Client: Arup

Geotechnical bservations

www.geo-observations.com

Thank you

session 1 instrumentation and monitoringcliffs.lboro.ac.uk/downloads/workshop...

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