A SHORT COURSE INSOIL AND ROCKSLOPE ENGINEERING

NOEL SIMONS, BRUCE MENZIES and MARCUS MATTHEWS

Published by Thomas Telford Publishing, Thomas Telford Ltd, 1 Heron Quay,

London E14 4JD.

URL: http://www.thomastelford.com

Distributors for Thomas Telford books are

USA: ASCE Press, 1801 Alexander Bell Drive, Reston, VA 20191-4400, USA

Japan: Maruzen Co. Ltd, Book Department, 310 Nihonbashi 2-chome, Chuo-ku,

Tokyo 103

Australia: DA Books and Journals, 648 Whitehorse Road, Mitcham 3132, Victoria

First published 2001

Reprinted 2005, 2007

A catalogue record for this book is available from the British Library

ISBN: 978-07277-2871-5

# Noel Simons, Bruce Menzies, Marcus Matthews and Thomas Telford Limited 2001.

All rights, including translation, reserved. Except as permitted by the Copyright,

Designs and Patents Act 1988, no part of this publication may be reproduced, stored in

a retrieval system or transmitted in any form or by any means, electronic, mechanical,

photocopying or otherwise, without the prior written permission of the Publishing

Director, Thomas Telford Publishing, Thomas Telford Ltd, 1 Heron Quay,

London E14 4JD.

This book is published on the understanding that the authors are solely responsible for

the statements made and opinions expressed in it and that its publication does not

necessarily imply that such statements and/or opinions are or reflect the views or

opinions of the publishers. While every effort has been made to ensure that the

statements made and the opinions expressed in this publication provide a safe and

accurate guide, no liability or responsibility can be accepted in this respect by the

authors or publishers.

Typeset by Academic Technical, BristolPrinted and bound in Great Britain by MPG Books, Bodmin

Cover photograph

Photograph of a landslide pushing over an apartment building in Kuala Lumpur, by kind

permission of Bruce Mitchell.

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Dedication

Professor Noel Simons FREng, 19312006

Noel Simons, who developed the University of Surrey into one of the UKs

leading centres of geotechnical learning and research, and who inspired

the Short Course Series of geotechnical books, died on August 10th

2006. He was aged 75.

He was not only a wonderful teacher, mentor, colleague and co-author,

but was also a dear friend. This book is dedicated to his memory.

viii

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= 20 kN/m3

su = 60 kN/m2

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Scale

12

3

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5

6

34

31

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10

17

C

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40 40 50 60 7030 3020 2010 100

02

0

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tan

n

tan F

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: degree

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05 m

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+55 m

1:1

1:1Depth of tensioncrack 05 m

Soft sensitive clay

Surcharge5 kPa

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(

Slip II (5 May 1957)

Slip I (24 April 1957)

N

16 April 1957

19 April 1957

23 April 1957

Date of excavation to 945 m O.D

Groundlevel+ 183 m O.D.

Excavated to 701 m O.D.by 14 April 1957

0 10 20 30 m

Scale

, * - )+

' - #$%&

! !

((

" .# 4 0

.6

,2 ,-

'

!

Originalground level

Excavation to 091 mon 1 April

Excavation to 701 mon 14 April

Excavation completed19 April

Note:Slip surfacesnor surveyed

BlueLondon clay

BrownLondon clay

Marsh clay

Clay fill

25 April2 p.m.

24 April9 p.m.

24 April5 p.m.

1:1

1:1

:1

366 m

183 m

1478

m

854

m

945 m

+533 m

+183 m

091 m

+091 m

823 m

O.D.

. ) - ) / # & $0 #

1 & )+ ' - #$%&

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BrownLondon clay

:1

Fill

Marsh claysu = 15 kPa

73

m

35

m2

7 m

85

m

Pw

Case

Londonclay

Strength for F = 10 suMeasured strength su

su in kPa

su / su

1 2 3 4 5527

958055

537

958056

508

1053048

594

1149052

685

1197057

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N

20

22

2330

25

28

29

26

24

2119

CBA

5

5

10

15

15

20

5

5

10

10

0 50 100 m

Scale

Vane testSoundingPiezometerSampling

Ovre Storgate

) 9! ) #$%,&

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' 4 ./ '

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5

5

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77

99

9

67

48

4

7

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10

10

1220

15

10

5

Reduced level+ 30 m

Dep

th: m

Sam

ple

No.

Soil type

Sandy rockFILLMediumSAND

Very soft to soft greysilty CLAYwith verythin seamsof silt andfine sand

Water content: %

20 30 40 50 2010 30 40 50 2010 302010 30 40 50

Boring 30

Salt content: g/lClay content: %Plasticity index: %

Unit weight: kN/m3

Shear strength: kPa

St.

Undisturbed

Remoulded

ClaySalt P.I.

St.

1510

5 Unconfined compression test,showing failure strain in %Cone testVane testSensitivity

Boring log for boring 30

% 9! ) #$%,&

"# $ " "#

+

0 )C !

( '

D ) "

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8 4 %$27'

,-. ,-3- 4

/

= 95

= 90

= 85

= 185

= 95

= 90

= 85

= 185

= 95

= 90

= 85

= 185G.W.L.

G.W.L.

G.W.L.

15

14

13

12

11

Fact

or o

f saf

ety

16

15

14

13

12

Fact

or o

f saf

ety

13

12

11

10 Fact

or o

f saf

ety

c : kPa, : kN/m3

Profile A

Profile B

+5

0

5

10

Elev

atio

n: m

Profile C

+5

0

5

10

Elev

atio

n: m

+5

0

5

10

15

Elev

atio

n: m

L.W.L. 10

L.W.L. 10

L.W.L. 10

Timber pilesat 1 m ccs

c = 1 = 32

c = 2 = 32

c = 3 = 32

c = 0 = 32

Slightly over-consolidated clayNormally-consolidated clay

c = 1 = 32

c = 3 = 32

c = 0 = 32

Slightly over-consolidated clayNormally-consolidated clay

Critical circle

Critical circle

Critical circle

c = 2 = 32

c = 1 = 32

c = 3 = 32

c = 4 = 32

c = 0 = 32

Slightly over-consolidated clay Normally-consolidated clay

c = 2 = 32

Profile after slip

0 " 9! )

#$%,&

"# $ " "#

++

0908

07

06 Fact

or o

f saf

ety

06

05

04 Fact

or o

f saf

ety

07

08

06

05 Fact

or o

f saf

ety

= 95

= 90

= 85

= 185

: kN/m3Profile A

+5

0

5

10

Elev

atio

n: m L.W.L. 10

Timber pilesat 1 m ccs

Critical circle

= 95

= 90

= 85

= 185

Profile C5

0

10

15

Elev

atio

n: m

L.W.L. 10

Critical circle

= 95

= 90

= 85

= 185

Profile B

0

5

10

15

Elev

atio

n: m

L.W.L. 10

Critical circle

Profile after slipProfile before slip

3025

2015

10 kPa

2015

10 kPa

20

25

30

1510 kPa

Undrained shear strength

6 # 8& 9! )#$%,&

! !

+,

15 19 255 9Borehole

25

20

15

10

50 1000

0 50 1000 50 100 1500 50 100 1500 50 100 2001500

5

Dep

th b

elow

gro

un

d su

rface

: m

Pore pressure: kPa

Measuredpore pressure

Level +74 +30 +225 +30 +28

$ *5 9! ) #$%,&

21 3

F = 101

F = 105Actual slip circlesafety factor 107

Critical slip circlesafety factor 100

30

20

10

2468

101214

0 4 8

4

12 16

8

20 m

Scale

Curves of equal pore pressure

12 16 metres of water

Measured pore pressure

02468

101214

metres

SectionNo.

Safety factorsc , analysis (Bishop 1955)

123

110100110

Weighted average safety factor for the whole slide F = 106

c = 10 kPa = 27

8 " ' ) #$%&

"# $ " "#

+$

( ,1:; = A C 0

0 )C

,11

,1=

!

%

9 7

( 1 = 5 1=

!

,-3-

" 1# &

4 .,, ' 1-

,1,

/ 5 '

7

4

1 " % #

" ./# 7

1

4'& * %27 L 8 9 7

5 ' 4 .,

G

,2 5

! ,-..

,2./

8 G

7

G

" ,67 /68 ,6 .6#

! !

+2

0

(

2/8 1 "#D 1 2 "# >

0 )C

,1 " 1-- ,,3 G

#

1/- " 4 .,#

G

21 3

0 5 10 m

Scale

SectionNo.

Safety factors = 0

123

097093135

10095

Actual slip circlesafety factor F = 117

Critical slip circlesafety factor F = 093

30

4050607080

70

80

60

50

40 kPa

20

10

Curves of equalshear strength

# 8& ' ) #$%&

"# $ " "#

+

!

G >

@ 5 ",-=#

0

0 5 10 15 m

Scale

Sandstone and shaleSandstone

Limestone

Fractured shaleLowercarboniferous

Boulderclay

Alluvial gravelRiver Lune

128

m

Typicalslip circle

Average inclinationof slope = 28

Boulder clay w = 12LL = 26PL = 13

Clay fraction = 25%

, ) ) )+

#$%&

60

60

40

20

200

0

Shea

r stre

ngth

: kPa

Effective pressure: kPa

w = 12LL = 26PL = 13

matrix

" %

$ % * &

! &

*

4

B

? 7 ,-,

,-3, 13. " 4

.,3# )

,/8

+

,-/

! ! &

7

&

75

50

25

0

cm Observations startedFailure after29 years

194119291912

Wall built

Forward movement of wall with time

North

BrownLondonClay

Blue London ClayLondon and North Western Railway

18361875

6 m

Ballast

2 ) 9 : 4 )+ #$00&

"# $ " "#

+%

&

! 0

4 .,.

(

! !

' * ,-== 8 0

: 0 H

4 +

&&0 '&9 '0 8 4%7'

7 + ,-/3

,-=

,-= 1=. ,-=. 1/ " 5

# > 4 .,/

'

8

) 7

,, E ,@

,-./

, 8

,-=. 1,. ,-

1 ,. "4 .,=#

150

125

100

75

50

25

00

c re

quire

d fo

r st

abilit

y: kP

a Wembley Hill

Uxbridge

Northolt

Wood Green

Upper HollowayKensal Green

Sudbury Hill

Mill Lane

Park Village East

10 20 30 40 50 60 70 80 90 100Age at failure: years

Analysis by circlesAnalysis by planesDenotes there is reason tobelieve point should bemoved in direction shown

; ' #$0&

! !

,)

7 & 31 .1

& "4 .,2# %

! 7 .=

.= 3( ,

,1 3 ( , &

.=

,1 11 4 .,2 +

1. 1. 4 .,-

CL

South

17 m

0 10 20 m

Scale

Hendon Motorway (M1)

North

Brown LondonClay

Blue London Clay4:1

1964

56

123

Piez.ru

1973 197512356

017022101105

+0090320809505

Mean ru values1973 (9yrs) = 0751975 (11yrs) = 062

% " )+ #$00&

11 m

Great Northern Railway

EastWest

Brown Londonclay

Blue London clay

4:1

3:1

3:1185018501956

54

12 9

8

11 10

Piez. ru

0061254

018021009

Piez. ru

03189

1110

034031032

Mean ru = 015

Mean ru = 032

Old SideNew Side

Piezometer readings 1975

Old Side (125 yrs)

New Side (19 yrs)

0 * )+ #$00&

"# $ " "#

,

! ! (

,8 1

18 17

7 (

,38 1

=8 1 ".1 #

7

(

,38 ,

04

02

02

04

0r u 20 40 60 80 100 120Time: years

6

4 .1

! 7

& A C A C

0 *

!

30

30 40 50 60

20

20

10

100

0

Shea

r stre

ngth

s: k

Pa

Effective pressure : kPa

West Acton Crews Hill

Grange Hill

Sudbury Hill Hadley Wood

First time slides, older than 45 years, depth 5 to 12 m

ru =035 03 025

c = 1 kPa = 20

$ " ' )+ #$00&

30

30 40 50 60

20

20

10

100

0

Shea

r stre

ngth

s: k

Pa

Effective pressure : kN/m2

Peak 38 m

m samples

Peak 250

mm dia. sa

mples

Back-anal

ysis first-sl

ides

= fully s

oftened

c 14

7 kPa

14 kPa

14 kPa

20

20

20

13

Residual

,8 " '

)+ #$00&

"# $ " "#

,+

0 7 8 0

7 ! ( ,8 1

A C

"* !#

,

! 7

&D

31 .1

' & 1 0 ",-=3#

>

7

( ,1 1 ,.8 1 .2

&

G

.2 & &

G

0 1 10 . : 09

!

",-31#

6 =>

' 3 )+ #$02&

E ( 0

, ,( ,

/ ( ,

,( ,

! !

,,

? "

! # ",-.1#

& " .1 #",-=1 #D

& $ % ;': 4'& %2,7 ,-. F! 0

9 0 )D

*

0 G "

) #

7 ? +

,-.1

,-.,

4 ,-. %

0

*

! )

,2 " 4 .,#

!

! />2

"4 .# "

,1# . ,=1 ,-.;.

1/

' /8 ,-8 % . /

,,8 . 5

!

4

"# $ " "#

,$

,-

/8 318 18

) "

#

,-8

NRiver Severn

B

E

F

GD

C

A

River bankafter slide

River bankbefore slide

Road before slide

Road after slide

Railway (maintained in position)

Approximateboundary ofmain slide

Secondary slide

0 50 100 m

Scale

Original positionof housePosition of houseafter slideHousedemolished

, * @+1 )+ #$%2&

Scarp ofmain slide

CoalportBeds

Fault

Probable limit ofweathering

Railway

1951 1952Road

183 m

Slip surfaceobserved

0 25 50 m

River Severn

Inclination of slope = 10

w = 21LL = 44 PL = 22

,, ) @+1 )+ #$%2&

! !

,2

& ,- - ,, - ! ,1 " 4 .#

+

F!

1/ " ,116

,1# <

,- ,,6

. 4 %27$ *

5

G

,. 1'

+

, 1

60

100

50

25

500

0

Shea

r stre

ngth

: kPa

Effective pressure: kPa

w = 21LL = 44PL = 22

1 ,.1

5

G

0

2. ,0 -.

G

& 2. -.

! &

G ,18 ,

2

- G 7 G

% &'( & *0 G

+

" #

&

!

10 4'& %2,7' ,-3- 7

0 E

0

" #

5 ! ,-./

" 4 .3#

,1 $ H>8

(

-8 28 &

,33 " "0 ,-/3# ,. 1# ' 7 , 0 E ,18 ,<

0 E ",-/-#

4 5 5C 5 0 5 9 ) @

"# $ " "#

,%

' !

% % &

' &

4 !

4

! &

" #

0

!

7 !

"

# F !

Typical slip circle

Piezometric line

Piezometric level

Piezometer

1900

Section after slip(surveyed 1956)

7 m

0 5 10 m

Scale

3:1

Brown LondonClay

w = 31LL = 82 PL = 28

Slip occurred after 49 years

Analysis of sectionafter slipc = 0 = 15

,2 ) ) = #$2$& )+

#$%2&

! !

$)

!

!

G

4

7

& 31 .1

"# $ " "#

$

!"

# ! $% #& '% ( ()

* (+ (+ ! ) (

,% (# #& # #+ #+ % -

%

% "

. ,%/ "

% "

0

0 1

%% % % %

2 %

%

% %

'

% %

' % % "

% % %

" 3 % % *

% % -

" %

4 % %

" %

2

% " 0 %%

% - % % %

2 % -

" % %

%

. %

% %

0

" % %-%

% 0 % "

%% " %

% - '

" %

5%-

% % 6 0

% %-

% -

" %7% 2

%- 68

" %

%

4 %

9

* 4% %

5% 8

% %

%

% %

0 % 8

%

2 %

8

" %

%

0

%

2

, : -

%

%

0 7%

% % %

! "

!

% % %

% %%

4 % %

% ;

) % 2 % %%

% % %

3 0

." )( " % "

3 "

" # 4

% %

9

5" % % %

9 5 0 9 - ? 3%

@

0 , %% 9 5

% 9 5 8 % % 5

% %% % )

2

% 8% 9 5

5 9 5

53

%

- % "

%

;% ? %% 9 5

"

! "# $ !

%% ! $ $ !

! ! $ ! & ! !

! "

.1 0 % %

0 % %%

% %

" % %

% % "3 -

A % " % %

% 6 % %

% 0

%

% -

%

% 7%"

%

2 B C ) >>

&>> " %

% %

. %

2 ' )) 8

4 ! 5

' * ,% %

' ! "" ! !

$ ! ! ! ! !!

$ %& #$ "! !!!

9 !% &> &>+ .-

4 5 ! ' % %

%

2 ) ( +>>

% " 4 +&

8 %

" %%% 9 -

% %7% %

2

% % % -

-3

0 %%

% 9 5

= #++ % -3 %

% 9 5

9 5 4 %

,

205

204412

180

190

200

220

230

250240

210

Toe

D

C

B

ABackscarp

0 10 20 30 40 50 mScale

BatterseaCourt

111 101102

104402403

103404

405

406

106105107

108

109110

112

401

Library

AC AB

AA

Lecturetheatres

413410411203

202 206408

407201

419

Trialdrain

250240

230

220

210

200

190

180

170

160

170

SurreyCourt

414

416415

417

N

Deep drainage trenches

( ! ) $ *

! "

(

4

;%

% %

9 % %

% ( ". 8 % % %

% 0" % 8

% %

% #) ".

2 ' ) %

D% )) . 2 -

% % %

%

2 ) "

>>>

E >>>

@8 %

E>> >>>

0 E)> >>>

0 E( >> E> >>>

7% % %

7%

" 9 5

% %

8% % % >

#) (

0 %

% %

%

% %-

2 %-

9 5 % % 3

P205 P201 P104 P107 P102

31

m

47

m

77

m

135

m81

m

16

m

04

m

182

m

104

m

Readings taken on4 January 1966prior to effects ofdrainage measures

# ,-% ! .

30

30

60

90

O.D.

m

Water levelin the Chalk

1820 1843 1878 1895 1911 1936

Drift and gravel

London Clay

Woolwich and Reading bedsThanet Sand

Chalk

/ ! !0 1 /

)"(*

! "

*

% %

%

%

% 9

!% (& 2

9

%

"

%

%%

2

3 0

' ) ; )( 3

- % 2 %

% - %

% % 8 % A

%

;% %

% 9

%

0 %

% %-

%

% % %-

% )

%

;% )#

-

5 % +>+

% % 2

%

% %

% &( 2

% )

+&F G 0

% %

1965 1966N D J F M A M J J A S O N D

0

1

2

3

Dep

th b

elow

gro

un

d su

rface

: m Piezometer P106Depth 61 m24 m from of drainDrains installedMarch / June 1966

LC

4 2

$ %& #$ "! !!!

+

% ;% )

%

+>+ %

;% )> %

%

% -

3

% 4

% *

% %%

=%

%

8 9

!%" (+

%

%

0 %

%

% %

19701969M A M J J A S O N D J F M A M J J

0

1

2

3

Dep

th b

elow

gro

un

d su

rface

: m Outside drained areaPiezometer CDepth unknown

Inside drained areaPiezometer 404Depth 57 m

5 % -% ,(6(

2

3

Dep

th b

elow

surfa

ce: m

1969 1970 1971 1972 1973 1974 1975 1976

Piezometer P404 21 m from centre line of drain

" 7 -% (6(

! "

*" ) % "

9 %

%

& %

0 % %

-%

6 % % % % 6

4 3 %

-

6

,% (# ! #+

' > >

> > &>

, 9 1 0 %

% ? = ,

% 9 4 5%

%%

I%/

2 D% #> J % J 5

= , % 9 "

% 0 %

% %

" % &) 0

% 0 % 8 >

0

&> ? 8 %

%

*" - %

%

;% #+

?

"

% 6

%

%

0

" %

8 % % % %

8 %

-

" 6 0 %

; )

" -

8 % + %

% 0 %

! "

!

9 %% .

% %

8 % > %

0 % 8 %

% 2 % %

% %

0 5 10 15 20 25 m

Scale

N

P10

P15

P14P13

P2

P6

P8P9

P7

P3(S)

P11(S)P12(D)

P4(D)

P1

I4 I5I8

I27

I14

I21

I12I10

I17

I2

3339 Victoria Crescent(under construction)

Existing rear retaining wall

Phase 2Counterfort drains

Lateral extentof slip

Y

X

Dow

nsl

ope

dire

ctio

nInclinometerreadingdirections

Lateral extentof slip

Phase 1 piles

Access RoadSite Boundary

Existing 3 storey block of flats

600 mm dia. bored pilecontaining 305 305 118 UCInclinometer and numberPiezometer and numberShallowDeep

(S)(D)

Note: Reinforced concrete retaining walls and associated works omitted for clarity

9 )""*

$ %& #$ "! !!!

'

4 %-% %

%%

2 >

2 % %

% % %7% % %

4 %

! #) 0 % %

% % 0

+ %

>

2

%

%

B %7% 0

% 8%

( -

%

P1 Piezometer tip and number

3339 Victoria Crescent

1

1

2

2

3

3

4

4

Flats

Access

Spur drain

Outline of counterfort

P1P10

P12P15

P9

P11

P4

P2P3P5P6

P7P8P13P14

Existing retaining wall

Original ground level

Final ground levelPost-slip ground level

Rows of piles

!! 9 )""*

! "

0 -

& % ;

% %

-

% &>

0 -- -

%%

0

% % 3 -

0

%

?

% %% 3

%

3 -

"

" , ." &>>> @%

&>>> C 9 &>>>

- - 4 8

%

. # 0 % 4# %%

%- ; 2 %

% 8% +> 0 %

%

% % % "

%

' % &

% %

0

% %%

" %

4

% % %-

% #> &>F %-

2 " -

%

2 % 8

" %

%

% % 0

% %

%

$ %& #$ "! !!!

%

%

" D &>>>

&>>>

: 0 %%

%

#K 0

( 0 )> >> %

0 7%"

%

%% 2

%

1% 7 ; 9 %

* '

-

4% "

%% 5

" % /

2 % % #)> .

%% @ 5 %

> .

%

% %

. %

%

% &> % 3 %

0

? 7% %

5

5%

0 9 @ 2 *

' ' 5% >

" %

/

%

%

%

0 %

" .

" % ? % 9

* ' ' 5% %

%

%

"

! "

(

0

" "

1

%% % 8

0 9

% %

; &>>> ! % %

I%/ % 3-

0

" %-

% -

9 @

5 0 %

7% % % % -

% % 0 ?

%

3-

8 % %

2 % % 7%

%% 1

0 % 7% 8% 6 %% ? % 8 %-

6 %

0 % 3 6 -3

%

4 % %3

%-

% 3

2 -

% %

% %

0 % % 3

2 % %

% - %

0 %

9 7%

% 9 -

" %

$ %& #$ "! !!!

)

;% ) %

; &>>> % %

% % .%

% %

%-

4 %

9

0 %

% %%

" 9 .

3%

; )+ 2

%

% ; )

#% % & %

% 1

6 % ; )) %

% %

0 10 m

Scale

Fish Bed

Grey Ledge

Table Ledge

Seacliff

Seawall

Beach

Mudslide

Loading at headfrom landslide above

1998 clifftop postion

1995 clifftop postion

Active slip surface observedapprox. 2 m above Grey Ledgein exposure above seawall

Denotes moving landslidePosition of shear surfaceconfirmed by inclinometeror visual observation

' % 1% 7 )666*

! "

*

45 40 35 30 25 20

Elevation mAOD

45 40 35 30 25 20

Elevation mAOD

45 40 35 30 25 20

Elevation mAOD

P2P3 P

6P4

P5

P1

Sect

ion

A

Sect

ion

D

Sect

ion

F

ND

rain

dril

led

to g

rou

nd

surfa

ce

Dra

in te

rmin

ates

with

in th

e gr

ou

nd

Not

e: dr

ain

leng

ths

and

posit

ions

are

pro

visi

onal

Birc

hi B

edEx

istin

g pi

ezo

me

ter.

(Prop

osed

addit

ional

piez

om

ete

rs n

ot s

how

n)

Prop

osed

loca

tions

of p

neum

atic

piez

om

ete

r

D

C

E

F

B

A

(,

1%7)%

/;;

9!.,7*

$ %& #$ "! !!!

(+

* 6

% % % ; )( ,%-

(# # #+

* % 3 %

% ,%-

(# % ;% )# % 8 4 3

2 %

3

%

2 % %

8 % % 2

% 3 %

# ; $.!- 7$ 9 ! / ; ;

*

Removal of soil

Toe, berm preferably free draining

? % $

! "

(

5 6

%

% " %

= % " %

2 % % 3

-

% ; )

4 - 8 %

% ;" * % @ ,

% % ; * *

7% * ; @8 3

J-! 4%

F F

Centre of slip circle

Removal of soil

Deep seated circular slip surface

4 % .

9! )"5' "5($*

Fills always advantageous

Fills always unfavourableFills adverse in

short term, butbeneficial in long term

Centre of rotation

Drained neutral point = mobilized

Undrained neutral point of landslide = , immediately under centre of rotation

5 ! ! 9! )"45*

$ %& #$ "! !!!

(

!

% '' 3 %% 3

2

%% %%

% %

" %% %

0 0 %

%% %

%

0 % %% % 5%

" " 5 ,"

! (( 2 #& 9? (( =

&>>> : &>>> D% ,% &>>>

(' %.-: 9 5 % - -

->

%

5 +( & 2

- % % -

% 8

4 %

%

;% )&>

% 0 6 %

@ & 4 %

-

0 - %-

% 5 !?%

)( 8

- % %

C 7%" 8

% + % %

0 4L % > " % B

B? 0 %

; )& -

; )&& 0 %

8

) ". 2

% !?% @ )

% -

7%"

0 -

%

> % ) % >

&& % >) 2 >

%

&>> &

C % 8

8 % % %

%

8

% %

0

+

-

% ! % % -

% % %

Cathode, can be a perforated tube

Original water table

Anode, usually a steel rod

Water flows from anode to cathode

6 %? .%

$ %& #$ "! !!!

('

% ; )&

%

4 -

%

0

'% 8

%

% (F

0 % % > >>> "*

+ 4 >>

8 % % &>>> ( "*

&& "

0

; )&+ %

% % % >>

% 4 &

%

Dep

th: m Descrip-

tion of soil

Water content: %

10 20 30 40

Unitweight:kN/m3

Shear strength: kPa

10 20

Sensi-tivity

Vertical effective stress: kPa

50 100Weath-eredcrust

5

Quickclay

10

15

wPw

w = Water contentwL = Liquid limitwP = Plastic limit

wL

193

196

200

195

195

Vane boring I50

80

80

7070

10

>100

>100

>100

Effective pressure

Vane boringUnconfined compression testCone test

Pre-consolidation pressure observed in consolidation test

! .% @ =A%

)"4*

! "

(

10+

8+

6+

4+

2+

1

3

5

7

9

Electrode row no:

N

+

B

P12P14P11

P13

P10P2 P4P1 P5

P3P6P8

P9P7

S1S2S3

S4

Brook

Excavation

BV7

V3V4V1V5V6

V2

I5

67

8910

1112

Section BB

S1

S4

S3

P6

P12

P13

P14

P7 P9

P11 P10 P1 P2P3

P4

P8

P5

0 5 10 m

Scale

Bedrock 28 m

Excavation

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Quick clay

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