Expected Damage From Displacement of Slow Moving Slides

Landslides (2011) 8:117–131DOI 10.1007/s10346-010-0227-7Received: 27 March 2009Accepted: 12 May 2010Published online: 16 June 2010© Springer-Verlag 2010

Mohamed Farouk Mansour I Norbert R. Morgenstern I C. Derek Martin

Expected damage from displacement of slow-movingslides

Abstract Facilities such as buildings, highways, railways, bridges,dams and pipelines often are built on natural slopes where the riskof landslides is not low. The vulnerability of these facilities to slow-moving slides has sometimes been underestimated, although thevelocity of some classes of slow slides is uncontrollable. More than50 cases of slow slides were compiled from the literature for thisstudy. Some statistics about the movement trigger(s), the methodsused to measure displacement, the material forming the rupturesurface and the type of the vulnerable facilities are presented. It isshown that the expected degree of damage to urban settlements,highways, bridges and dams can be related to the slide velocity oraccumulating displacement. Buildings and residential houses maytolerate higher slide velocities and total displacements than otherfacilities before experiencing serious damage. Movements as low as100mmmay severely damage bridges, but such low rates may causeonly moderate damage to urban communities. The relationshipbetween movement and the expected extent of damage should beuseful to geotechnical engineers who deal with different classes ofslow slides and will help in the choice of appropriate mitigationmeasures based on preliminary estimates of movement rates.

Keywords Slow-moving slides . landslide-induced damage .

damage description . landslide velocity . vulnerability to slides

IntroductionVulnerability is the degree of loss for a given element at riskresulting from the occurrence of a natural phenomenon such as alandslide. It is usually expressed as a value ranging from zero toone. Vulnerability is one of two factors used to evaluate the specificrisk. The other element is the natural hazard. Natural hazard isdefined as the probability of occurrence of a potentially damagingphenomenon, such as a landslide, within a certain period of timeand a specific area. Specific risk is mathematically expressed as theproduct of the hazard and the vulnerability (Varnes 1984).

The vulnerability to a landslide can be assessed by comparingthe value of the resulting damage to the actual value of thevulnerable facility (Remondo et al. 2004). The steadily increasingpopulation throughout the world has led to a considerable rise inurban development in landslide-prone areas. Urban landslides aretriggered mainly by seasonal hydrological, environmental andanthropogenic changes, such as rainfall, earthquakes and humanactivities. The adverse effects of urban landsliding have been mademore severe by uncontrolled population growth in hillside areas insome countries. Therefore, the risks arising from urban develop-ment in landslide-prone areas are increasing despite the progressin the application of mitigation measures.

Landslide movement types fall into five main categories: fall,topple, spread, flow and slide. While this paper focuses on slides, thefive main categories will be defined briefly to illustrate the generaldifferences between them. A fall occurs when the shear resistancealong a surface inside a steep slope becomes very low or zero, so soilor rock descends through the air by falling. The velocity of this kind

of landslides is very rapid to extremely rapid. Falls may occur as freefall, bouncing or rolling. A topple is the rotation of a soil or rockmass around an axis that lies below the center of gravity of thedisplaced material. Toppling could occur due to the weight ofmaterials upslope of the displaced soil or rock, or due to waterbuilding up in cracks in the soil or rock mass. Topples can beextremely slow or extremely rapid. Spread is the extension, andhence fracturing, of a cohesive soil, accompanied by subsidence overan underlying softer material. Flows are rapid movements in whichthe shear surfaces are closely spaced and not preserved. Thedistribution of velocity within the moving mass is similar to that ofa viscous liquid. The basal detachment surface of a flow is thick. Aslide, in contrast, is the downslope movement of soil or rock onrupture surfaces that are relatively thinner than those of flows andwhere intense shear strain has taken place (Cruden and Varnes 1996).

While the losses resulting from rapid landslides such as debrisflows, mud flows and rock falls are the highest and most severe,slow-moving slides also have adverse effects on affected facilities.The accumulation of slow movement can lead in some cases to totaldisruption of the serviceability of these facilities. Loss of life mayresult as well. Slow slides fall into three classes (Cruden and Varnes1996):

– Extremely slowly moving slides: this class includes slidesmoving at rates ranging from 0 to 16 mm/year.

– Very slow-moving slides: this class includes slides moving atrates ranging from 16 mm/year to 1.6 m/year.

– Slow-moving slides: this class includes slides moving at ratesranging from 1.6 to 160 m/year (∼13.3 m/month).

This study used the available literature to describe the damageto different facilities caused by the different classes of slow slides.The vulnerable infrastructure includes urban and suburbansettlements, highways and railways, bridges, dams and lifelinessuch as pipelines. The main information required from each of thereviewed cases is the movement rate and the extent of damagecaused. The different attributes of the reviewed cases, such as themethod used to measure the movement, the type of materialscontrolling the movement and the likely trigger(s) of movement,were highlighted, and some elementary statistics were calculated.

The analysis allows the typical (or expected) extent ofdamage to be related to the rate (or more usually the amount)of movement. Separate analyses are made for each class of thesurveyed infrastructure. The damage extent is not vulner-ability, but case histories rarely document the original value ofthe vulnerable facility and the cost of repairing the damage.The extent of damage resulting from slides of a certain velocityis the most common information mentioned in the cases cited.

Characteristics of slow-moving slidesMore than 50 cases of slow-moving slides were reviewed in thestudy. The cases cover instabilities in many countries in the world:

Landslides 8 & (2011) 117

Technical Note

Table1Summaryof

thereviewed

cases

Case

number

Reference

Materialhostingthe

rupturesurface

Displacement

measurementmethod

Movem

entrate

(mm/year)

Durationof

monitoring

Trigger

Vulnerablefacility

1Lim

itedandEdmonton

(1992)

Preglacialclays

andclay

shale

Inclinometers

143months(one

SIwas

installedfor7

years)

–TownofPeaceRiver,Alberta,

Canada

2Clifton

etal.(1986)

Clay

shale

Inclinometers

108

1–1.5years

Rivererosion

Regina

beachin

Saskatchew

an,Canada

3Clem

entinoet

al.

(2008)

Presheared

bentonitic

clayshaleand

sandstone

Inclinometers

35During2001

Water

pondingon

the

slope

Highway

eastof

thetownof

DraytoninAlberta,Canada

4Hayley(1968)

Clay

shale

Inclinometersandsurface

monum

ents

100

5months

Rivererosion

Highway

49andtheLittle

Smokybridge

inAlberta,

Canada

5BrookerandPeck

(1993)

Clay

shale

Personalestim

ates

90–120

2years

Toeerosion,precipitation

andhorizontalforces

from

thebridge

anchor

PeaceRiversuspension

Bridge

andawater

pipeline,British

Columbia,

Canada

6Moore

etal.(2006)

Clay


monum

ents

10–14

Recent

monitoring

lasted

4years

Reservoirlevel

fluctuations

and

rainfall

Mica

Dam,British

Columbia,

Canada

7BrookerandPeck

(1993)

Clay

shale

Inclinometers

100

5years

Rainfall

Oilw

ellcasing,Sw

anHills,

Alberta,Canada

8Barlow(2000)

Clay

shale

Geom

orphologicevidence

188

Notindicated

Stream

incision

Pipeline,FortMcM

urray,

Canada

9Esser(2000)

Plastic

lacustrineclay

Inclinometer

306

5years

Constructionactivities

Residentialcom

plex

inOhio,

USA

10BrookerandPeck

(1993)

Clay

shale

–100

13years

Bridge

construction

TheBism

arck

Bridge

across

theMissouriRiver,USA

11Bressaniet

al.(2008)

Interface

between

overlying

colluviu

mandclayeysiltstone

Inclinometers

34(upto

80)

22months

Rainfall

Urbanslope

inSantaCruz

doSul,Brazil

12Ibadango

etal.(2005)

Sedimentaryrocks

DifferentialG

PS6,000

2months


Urbansettlem

entson

the

elongatedvalleyof

the

Lojabasin

inEcuador

13Jworchan

etal.(2008)

Colluviu

mandinterface

betweenresidualsoils

andbedrock

Inclinometers

125months

Rainfall

Aslope

proposed

for

residentialdevelopmentin

theWestPennantHills,

Sydney,A

ustralia

14GillonandSaul(1996)

Sandysiltclaygouge

Aerialsurveydata

180

42years

Rainfall

ClydeDam,N

ewZealand

15Cascinietal.(2008b)

Quaternarydeposits

DifferentialSynthetic

Aperture

Radar

Interferometry(D-InSAR)

55years

Rainfall

A489km

2nextto

Liri-

Garigliano

andVolturno

RiversinItaly(urban

developm

ent)

16Wasow

skietal.(2008)

Clay

PersistentScatterers

Interferometry

84years

Rainfallandconstruction

activity

Casalnuovo

Monterotaro

and

Pietramontecorvinotowns

inItaly

Technical Note

Landslides 8 & (2011)118

Table1

(continued)

Case

number

Reference

Materialhostingthe

rupturesurface

Displacement

measurementmethod

Movem

entrate

(mm/year)

Durationof

monitoring

Trigger

Vulnerablefacility

17Calcaterra

etal.(2008)

Rock

PermanentScatterers

Synthetic

ApertureRadar

Interferometry(PS-

InSAR)

and

inclinometers

169years

Rainfall

Buildings

oftheMoiodella

Civitellavillage

inSalerno,

Italy

18Buccoliniand

Sciarra

(1996)

Marlyclays


monum

ents

19–26

15months

Rainfall

Dwellinghouses

anda

highway

intheAbruzzo

region,Italy

19Spizzichinoet

al.

(2004)

Clay

Airphotos

4,000

25years

Rainfallandhuman

activity

Cragovillage

inItaly

20Cascinietal.(2008a)

Softenedclay

Inclinometers

442.5years

Rainfall

Amajor

road

andtheRome-

Florencerailw

ay

21Ceccucciet

al.(2008)

Quaternarydepositsand

dislocatedbedrock

Inclinometers

659years

Rainfall

Collapseof

along

stretchof

anationalroad,theSerre

LaVoutelandslide,N

orth

WestItaly

22D’Eliaet

al.(2000)

Interface

betweenweak

andcompetent

rock

Inclinometers

132

3months

Rainfall

TheIoniccoast,Italy

23Catalano

etal.(2000)

Clay

Inclinometers

127

11years

Reservoirfilling

Trinita

Dam,Italy

24Catalano

etal.(2000)

Softenedclaylayer

Topographicmonum

ents

110

Inferredto

be1year

Reservoirfilling

CasanuovaDam,Italy

25BartonandMcCosker

(2000)

Rock

Inclinometers

1216

years

Rainfall

CoastalcliffinAftonDown,

UK

26Fortet

al.(2000b)

–Inclinometersandsurface

surveying

911year

Coastalerosionand

rainfall

Seaw

allstructures,roads

and

footpathsinthetownof

LymeRegis,UK

27Fortet

al.(2000a)

Stiff,fissured

overconsolidated

Bartonclay

Surface

surveying

861

3.5years

Toeerosionandrainfall

Buildings

ontopof

acliffat

Barton-on-Sea

shorein

Hampshire,U

K

28BeaumontandForth

(1996)

Glacialdeposits

ofsands

andgravelsoverlying

boulderclay

Inclinometers

13.8

4months

Miningactivities

Wideningof

arailw

ayem

bankmentinthe

countyof

Durham

,UK,in

orderto

constructanew

duallane

carriagew

ay

29LeeandClark(2000)

Glacialtill

Surface

surveying

560

2and4years(both

periods

confirm

edthesamerate)

Rainfallanderosion

Coastalcliffinstabilitiesalong

theScarboroughCoast,UK

affected

aroad

30NicholandLowman

(2000)

Interface

betweentill

andmudstones

and

siltstones

–600–6,000

Inferredby

authorsto

be1month

Rainfall

TheA5

Trunkroad

between

London

andDublin,U

K

31Carson

andFisher

(1991)

Bentoniticlayers

–23

13years

Riverdowncutting

Anancientbridge

inthecounty

ofShropshire,England

32Bonnardet

al.(2008)

Clay

shale

Surface

surveying

techniques

10Notindicated

–TriesenandTriesenberg

villagesineastern

Switzerland

33Bonnardet

al.(2000)

–Surface

surveyingand

inclinometers

6032

yearsforsurface

surveying

Rainfall

Polmengo

bridge

nearFaido,

Switzerland


Table1

(continued)

Case

number

Reference

Materialhostingthe

rupturesurface

Displacement

measurementmethod

Movem

entrate

(mm/year)

Durationof

monitoring

Trigger

Vulnerablefacility

34Blikra(2008)

Rock

Extensom

eters,GPS,total

stationand

inclinometers

30–100

(upto

365)

Ranged

frommorethan

ayearto10

years

Seasonalchanges(mostly

rainfall)

TheAknesrockslide

inNorway

may

generate

tsunam

isthat

killed

peoplebefore

35Oppikoferet

al.(2008)

Rock

TLS

60–70(upto

200)

1year

Rainfall,earthquakes,

miningoperations

and

snow

melt

TheAknesrockslide

inNorway

may

generate

tsunam

isthat

killed

peoplebefore

36Mihalinec

andOrtolan

(2008)

Clay

Comparison

oftopographic

maps

152–300

Over

33years

Rainfall

Urbancommunities

inZagreb,Croatia

37Lokin

etal.(1996)

Weathered

marlyclay

Inclinometers

102.5yearsand13

years

Toeerosion

SLOBOD

Abridge

inNoviSad,

Yugoslavia

38Bunza(2000)

Gravelandsilt

Extensom

eters

922years+4months

Rainfall,snow

meltand

erosion

Tiefenbach

village

near

Oberstdorf,

Germany

39Kalteziotis

etal.(1993)

–Inclinometers

13–19

Notindicated

–Thenationalroadfrom

Athens

toSounion

40Topaland

Akin(2008)

Interface

betweenclayey

layersandclaystone

Inclinometers

–Notindicated

Toeerosion

PipelinebetweenTurkey

and

Greece

41Fuchsbergerand

Mauerhofer(1996)

Shaley

graphite

Inclinometers

590

65days


Amotorway

intheAustrian

Alps

42Wanget

al.(2008)

Colluviu

mGPSandextensom

eters

180

3years

Rainfallandreservoir

levelfluctuations

Village

locatedon

theslope

oftheShuping

landslide,China

43Zhou

(2000)

Soilrock

interface

–2,000(a

maximum

ofmorethan

4,000)

53days

–SichuancityinChina

44Sunet

al.(2000)

Volcanicsaprolite

Airp

hotosandtopographic

maps

450

20years

Rainfall

Aroadsidecutslope

aboveLai

Ping

Road,Sha

Tin,China

45Wuet

al.(2008)

Coalbedswith

sandstones

andmudstones

Inclinometers

573years

Undergroundcoalmining

Hancheng

power

station,

China

46Baietal.(2008)

Finegrainedmaterial

–730

135days

Reservoirfilling

Lijiaxia

hydropow

erstation,

China

47Fujisaw

aet

al.(2007)

Earth

slide

Extensom

etersand

inclinometers

9,100

2months

Rainfall

Buildings

andwater

service

pipescollapsed

andapart

ofahighway

heaved

inJapan

48Maloneet

al.(2008)

Rock

Totalstationand

photogrammetric

surveys

7,000

3years

Rainfall

Newhighway

inMalaysia

49Kang

etal.(2000)

Incompetent

shales

–240

3yearsand9months

Bridge

construction

TheSugock

Bridge

inAndong,Korea

50Chandler

andBroise

(2000)

Sandysiltandclayeysilt

colluviu

mAirphotos

5,600

16years

Rainfall

Major

railw

aycorridorfrom

Colombo

toBodalla,Sri

Lanka

rupturesurface

measurementmethod

(mm/year)

monitoring

Technical Note


Canada, USA, Brazil, Ecuador, Australia, New Zealand, Italy,United Kingdom, Switzerland, Norway, Croatia, Yugoslavia,Germany, Greece, Austria, Turkey, China, Japan, Malaysia, Koreaand Sri Lanka. Some of the surveyed slides affect more than oneclass of facility, e.g., urban areas and highways or highways andother infrastructure. The reviewed cases are listed in Table 1. Eachgroup of slides occurring in the same country are groupedtogether. The order of countries is the same as mentioned earlierin this paragraph.

In addition to the rate of movement and the extent ofdamage, information regarding the method of displacement

measurement, the nature of the slide material and the maintrigger(s) of movement is presented. These attributes aresummarized in Table 1. The statistics presented are intended tobe helpful to geotechnical engineers dealing with slow-movingslides.

Displacement measurementThe methods used to measure the displacement play an importantrole in defining the mechanisms and the movement behaviour ofslow and extremely slow slides. A major issue when dealing with

Table 2 Advantages and disadvantages of different methods of measuring displacement

Instrumentation type Advantages Disadvantages

Manual inclinometers - Can measure displacements as low as a fractionof a millimeter.

- Slope indicator casings are broken at cumulativedisplacements of about 130 mm. Therefore, thelifetime is short in very slow and slow slides.

- Temporal resolution can be improved by increasingthe frequency of measurements, i.e., every day or less.

- Measure the displacement versus time at a single point.Thus, there is no spatial coverage for large sites. Hence,the technique is not economically feasible for large sites.

- Highly frequent monitoring of manual inclinometers isexpensive for remote sites in terms of a technician wages.

In-place Inclinometers - Overcome the temporal resolution drawback of manualinclinometers. The sensor is connected to a data-loggerthat records the displacements at intervals as shortas required.

- The location of the rupture surface should bedetermined before the installation of the in-placeinclinometers. Therefore, a slope indicator casingshould be installed first.

- Have the same drawback of the low spatial coverage asmanual inclinometers.

Extensometers - Measure the displacement by measuring the openingof cracks

- Do not measure large displacements and, hence, notsuitable for measuring displacements of slow slides or theupper range of very slow slides.

- Do not require deep installations - Measure the displacement at discrete points and, hence,do not provide good spatial coverage for large sites.

- Measure surface displacements rather than thedisplacement at the rupture surface elevation.

- Unable to determine the location of the rupture surface.

Remote techniques (InSAR, DInSAR,TLS, etc.)

- Suitable for measuring relatively large displacements (slowand the upper range of very slow movements), whichcannot be captured by inclinometers or extensometers.

- May not be able to capture extremely slow movementsover the monitoring interval, which is around a month.

- Overcome the spatial resolution drawback of the previoustechniques by providing coverage to large sites as long asreflective objects are present or installed at strategiclocations across the site.

- No coherence is expected to occur if no reflective surfacesexist or are installed.

- Measure the surface displacement rather than themovement of the rupture surface.


Surface surveying - Suitable for measuring relatively large displacements (slowand the upper range of very slow movements), whichcannot be captured by inclinometers or extensometers.

- Extremely slow movements may fall below the accuracyof the measuring instruments (total station).

- Overcome the spatial resolution drawback of inclinometersand extensometers by providing coverage to large sites aslong as surface targets are installed at strategic locationsacross the site.


- The installation of surface targets for surveying is lessexpensive than installing corner reflectors for satelliteimagery.


Geomorphologic evidence - Very useful in quantifying long-term movements thatoccurred over many years and where there is no othermethod of measuring the movement.

- Cannot account for very slow or extremely slowmovements because of the small scale of air photos.




very slow or extremely slow slides is the low frequency of datarecording; hence, the trends of movement variation over timeoften are not clear. This hinders accurately determining therelative effects of different causal factors on movement. Inaddition, the movement rate is sometimes considered constant,while in fact it is not. Extremely and very slow movements consistof a viscous or creep component that is responsible for thepersistence of movement during periods without pore-pressurechange. The literature suggests that the slow movements ofshallow slides are affected mainly by changes in hydrologicalboundary conditions, while the viscous soil properties contributeto a large percentage of the movement of deep-seated slides(Picarelli and Russo 2004).

About 45 cases indicate the method of displacement measure-ment. Some of the surveyed slides were monitored using morethan one type of measurement. The methods used includedinclinometers, extensometers, remote techniques such as Syn-thetic Aperture Radar Interferometry (InSAR) and Terrestrial

Laser Scanning (TLS), surface surveying and geomorphologicevidence. A brief summary of the advantages and the drawbacksof each method is provided in Table 2. Inclinometers were used torecord movement in about 60% of the reported cases. However,because of the shearing-off of inclinometer casings when displace-ments reach around 130 mm, inclinometers were not used tomeasure the displacements of slides moving at rates of more than590 mm/year. In the upper range of very slow slides and in therange of slow slides, other methods, such as surface surveying,remote techniques, and geomorphologic evidence, become moreuseful to determine larger displacements over longer periods oftime. The lower precision of these methods may not allow them tobe used to accurately detect extremely slow movements. Remotetechniques such as InSAR and TLS were used in only 9% of thestudied slides. These techniques have been developed recently,and reliance on them should increase in the future as they providecoverage of large areas and overcome some of the disadvantagesof inclinometers. However, the increased application of in situ

Geomorphologic evidence, 13%

Remotetechniques, 9%

Surfacesurveying, 31%

Inclinometer, 58%

Extensometers, 9%

Fig. 1 Percentages of differentmethods of displacementmeasurement

Weak Rock, 27%

Rock, 10%

Soil, 53%

Interface, 12%Fig. 2 Percentages of differentmaterial types in the rupture surface

Technical Note


inclinometers can overcome the present issue of eventual loss ofaccess to the shearing zone. Figure 1 shows the percentages of useof each of inclinometers, surface surveying, remote techniques,extensometers and geomorphology in measuring the displace-ments of slow slides. The sum of the percentages of the differentmethods is more than 100% because more than one method ofdisplacement measurement was used in some of the surveyedcases.

Materials of the rupture surfaceOnly 48 of the studied cases explicitly state the type of thematerial in the rupture surface. More than half of these slides(52%) have rupture surfaces in soil materials, mainly clays and

silts. About 27% of the surveyed cases have rupture surfaces inweak rocks such as clay shales. The rupture surfaces run along theinterface between the soil and the underlying rock in 13% of thereviewed cases, and the rest have rupture surfaces in rockmaterials. The sum of the percentages is slightly higher than100% because one case (#4) involves more than one material typein the rupture surface.

Comparison across the cases suggests that the usuallyexpected hazards from rocky slopes are rock falls and topplingrather than sliding on a well-defined rupture surface. More thanhalf of the studied cases have their rupture surfaces in soil ratherthan rock. This observation, however, does not necessarilyindicate that sliding is the dominant mode of failure of earth

Mining activities,6%

Stream incision,23%

Rainfall, 64%

Anthropogenicactivities, 19%

Reservoir fillingand fluctuations,

11%

Earthquakes, 2%Snow melt, 4%

Fig. 3 Percentages of differenttriggers of movement

LinearInfrastructure, 9%

Dams, 11%

Railways, 5%

Highways, 23%

Urbansettlements, 40%

Bridges, 12%

Fig. 4 Percentages of citation ofdifferent vulnerable facilities in thereviewed literature


Table 3 Summary of the case histories on the damage extent of urban communities due to slow-moving slides

Casenumber

Location Amount of damage Movement rate(mm/year)

Soil type Remarks

15 Italy No exact statement of damage butcould be minor

5 Quaternary deposits overlyingupper Miocene bedrock

16 Italy Cracks in buildings 8 – Cracks might be from buildingssubsidence

32 Switzerland Minor damage to village housesand infrastructure

10 Clay shales Development in the village is notaffected by slope movements

13 Australia Cracks in an embankment withinthe site in addition to somebent trees

12 Colluvium over residual soilsoverlying bedrock

25 UnitedKingdom

It is considered that there could be athreat to a coastal road in a town

12 Well jointed rock with noshear surfaces

1 Peace Rivertown,Canada

Removal of a portion of a streetand structural distress to somehouses

14 Glacial deposits overlyingpreglacial lake clays overclay shale

17 Italy Open cracks, wall disjunction andbadly working casings

16.2 Authors classified this damage as lightto moderate

18 Italy Damage to dwelling houses 26 Marly clay

34 Norway Minor damages could occur toresidential settlements and towns

30–100 Rock A wide-scale study.

A warning system was designed wherethe recorded rate lies in the greenrange (safe and no damagesexpected)

11 Brazil Cracked pavements in streets anddamages to houses

80 Interface between colluviumand clayey siltstone

26 UnitedKingdom

Cracks in roads and footpaths of atown and damage to seawallstructures

91 –

38 Germany The slides threatens a village bydebris flow

92 Gravel and silt

2 Reginabeach,Canada

Rupture of service utilities, groundcracking. No damage toconcrete sidewalk

108 Bentonitic clay shales The study concluded that 100 mm/yearis enough to break a municipalwater line

42 China Cracks in roads and houses of aresidential settlement on aslope

170–240 – The toe is the Three Gorges Damreservoir but the study is about thedamage to the residential settlementson the slope

36 Croatia Houses suffered damage (notspecified)

150–300 Clay

35 Norway Minor to moderate damage mayoccur to residential settlements

200–365 Rock

9 USA Cracks in houses 306 Plastic lacustrine clay

Walls buckling

Bending of doors and windows

Damage of the rear wall of a garageby downslope movement

27 UnitedKingdom

Movement led to major slopefailures below a hotel building

861 Stiff, fissured overconsolidatedBarton clay

43 China Cracks in a slope within aresidential complex

2000(a maximumof more than4,000)

Soil rock interface Because of the implementation of awarning system, the buildings wereevacuated and no life losses tookplaceSevere damage to the backwall of

a building

19 Italy Severe damage to Crago villagebuildings

4,000 –

12 Ecuador Parts of some houses of the city ofLoja were separated by 1 m in2 months

6000 –

47 Japan Collapse of a car repair factory 9,100 –

Technical Note


slopes. Figure 2 shows the percentages of slides having theirrupture surfaces in soil, rock and weak rock and at the interfacebetween soils and rocks.

Trigger(s) of movementSome of the cases have more than one identified movementtrigger, although the majority have a single identified trigger.

Forty-seven cases report the trigger(s) of the slow movement ofslides. Rainfall is the main trigger in 64% of the reviewed slides.This finding suggests that designing and installing drainagemeasures are important for facilities constructed in heavy-rainfallareas. Toe erosion and human activities are the triggers (or one ofthe triggers) of movement in about 42% of the surveyed slides.Reservoir filling and seasonal fluctuations in reservoir levels seem

Table 4 Summary of the case histories on the damage extent of highways and railways due to slow-moving slides

Casenumber


Soil type Remarks

28 United Kingdom Cracks in road pavement 13.8 Glacial deposits overlyingboulder clay

Road needed re-pavementevery 3 or 4 years

39 Greece Cracks in the pavement of amajor highway

13–19 –

18 Italy Traffic disruption to a highway 26 Marly clay

3 Alberta, Canada Cracks in a highway thatneeded patching once ortwice a year

35 Presheared bentonitic clayshale over sandstone

20 Italy Damage not specified 44 Softened clay A previous reactivation caused lotsof damage and has interrupted amajor road and highway

4 Alberta, Canada Cracks in highway 49 Minimum of 15and up to 100

Till overlying preglacial lakeclay and clay shale

Patching performed once ayear

21 Italy Damage not specified but notsevere

65 Quaternary deposits inaddition to dislocatedbedrock

A previous reactivation led to thecollapse of a long stretch of anational road

22 Italy Undefined threat to a road anda railway

132 Intensely fissured clay shaleand limestone over abedrock

44 China No quantification of damagereported

450 Volcanic saprolite overcompetent bedrock

Severe rainstorm events cause roadblocking

29 United Kingdom No damage reported to acoastal road

560 Sedimentary rocks overlainby glacial till

This rate was recorded afterremedial measures havebeen installed

41 Austria Development of large fissuresand failures in the cut slopesof a motorway

590 Intensely sheared shaleygraphite layer

A major traffic disruptionexpected if no drainagemeasures were adopted

30 United kingdom Traffic obstruction of a trunkroad

600–6000 Glacial till overlying asequence of mudstonesand siltstones

Breach of the boundarybetween the road and therear garden of a residentialproperty

50 Sri Lanka Severe disruption to a railwaycorridor

5,600 Sandy silt and clayey siltcolluvium

48 Malaysia Disruption to a highwayconstruction

7,000 Rock (schist)

47 Japan Upheaval of a part of ahighway

9,100 –


Table 5 Summary of the case histories on the damage extent of bridges due to slow-moving slides

Case number Location Amount of damage Movement rate(mm/year)

Soil type Remarks

37 Yugoslavia No actual damage to the SLOBODA bridge,but there is a threat.

10 Weathered marly clay

Mitigation plans are set for probabledistress in the future

31 United Kingdom Continuous movement of abutment and piers 23 –

33 Switzerland Numerous cracks in the abutment of a bridgecaused by a very high flood

60 –

5 British Columbia,Canada

Displacement of one of the Peace River suspensionbridge anchors led to the bridge collapse

90–120 Clay shale

4 Alberta, Canada The Little Smoky bridge south pier needscontinuous extension to accommodatemovements

100 Till overlying clay shale

10 USA The Bismarck bridge pier needs continuousextension to accommodate movements

100 Clay shale

49 Korea Bridge suffered severe deformations 240 Alternating competentsandstones and incompetentshales

Table 6 Summary of the case histories on the damage extent of dams due to slow-moving slides

Casenumber


Soil type Remarks


Minor or no damage to Mica Dam 10–14 Rock slide moving on thin claygouges

45 China Serious damage to the Hancheng powerstation structures

57 –

24 Italy Fissures and cracks observed in Casanuovadam

110 Softened clay layer

23 Italy Damage to the electric cabin and theguardian’s house of Trinita Dam

127 Highly permeable formation overa weathered clay formation

No damages to the dam

14 New Zealand Slide volume is enough to block the Clydedam reservoir

180 Planar rock slide moving overslickensided sandy silt claygouge

The slide-generated waves are expectedto be higher than the free board

46 China Failure of localized disintegrated looseslide mass on the surface of the slope

730 Fine-grained material with a claypercentage sometimes morethan 90%

Slide-generated waves may endanger thehydropower station

Table 7 Summary of the case histories on the damage extent of linear infrastructure due to slow-moving slides

Case number Location Amount of damage Movement rate (mm/year) Soil type Remarks

7 Alberta, Canada Bending of oil well casing(Swan Hills Oil Field)

100 –


Break down of a pipeline 90–120 Clay shale

8 Fort McMurray, AB,Canada

Displacement of pipelines 188 Glacial deposits overlying Cretaceoussedimentary clay shale over oil sands

47 Japan Rupture to a water service pipe 9,100

Technical Note


to affect slopes that lie upstream of dams, as these factors triggerthe movement of about 11% of the studied cases. Other triggerssuch as earthquakes, snowmelt and mining activities are respon-sible together for the sliding in about 12% of the reviewed cases.Figure 3 shows the percentages of the contribution of differenttriggers to slow-slide movements.

Classes of vulnerable facilitiesThe vulnerable facilities include the five categories mentionedabove: urban and suburban settlements, highways and railways,bridges, dams and linear infrastructure. In 40% of the reviewedcases, the vulnerable facilities are urban and suburban commun-ities. This high proportion is expected due to the direct threatposed to human life when towns are built close to natural moving

slopes. The vulnerabilities of highways and railways are docu-mented in 23% and 5% of the studied cases, respectively. Highwayand railway hazards can be life-threatening to travellers. The levelof threat is, however, less than that to urban communities.Figure 4 shows the relative citations of the different types ofvulnerable facilities among the studied cases.

Damage extentTwenty-two of the reviewed cases described the extent of damageto urban and suburban communities. The cases are sorted inascending order of the slide velocities, starting from a measuredrate of 5 mm/year up to 9 m/year. The case numbers in Table 3 arelinked to Table 1. Table 3 presents a summary of these cases,focusing on the extent of damage resulting from slides with

Strain

Time(a) (b)

Prim

aryLog (Time)

Log (Strain Rate)

Secondary

Ter

tiary

Primary

Secondary

Tertia

ry

Fig. 5 Primary, secondary and tertiary creep stages from a typical triaxial test shown on both: (a) arithmetic and (b) logarithmic scales (Modified after Augustesen et al.2004)

Table 8 Damage expected from slow-moving slides to urban communities versusmovement rate

Movement rate(mm/year)

Extent of Damage

0–10 - Minor or no damage

10–100 - Cracks in streets, footpaths and nearby embankments

- General signs of distress like bent trees

- House walls disjunction and badly working casings

- May cause damage to small dwelling houses

100–300 - Cracks are wide to the extent that houses start to suffera noticeable damage

- Rupture of service utilities

300–800 - House walls buckling, bending of doors and windowsand various damages in houses

800–4,000 - Severe damage and failures to slopes or retainingwalls supporting buildings

- If no warning system is implemented, human lossesmay occur

>4,000 - Complete collapse of buildings

Table 9 Damage expected from slow-moving slides to highways versus move-ment rate


Extent of damage

0–10 - Minor or no damage

10–100 - Cracks start to appear

- Developed cracks need patching once or may be twicea year

- Needs re-pavement once every 3 or 4 years

- May cause traffic disruption

100–160 - Wider cracks in pavements

- Need patching at intervals less than 1 year

160–1600 - Development of large fissures in embankment slopes

- Failure may occur to embankment slopes

- A major traffic disruption is expected if no drainagemeasures were implemented

>1600 - Severe collapse to the highway or the railway

- Traffic obstruction

- May lead to life losses


different velocities. All of the cases are compiled to qualitativelyrelate the expected damage to urban communities resulting fromslow-moving slides. The relationship describes the expectedincrease in damage to urban communities from increasing slidevelocities (or slide displacements) within the ranges of slow, veryslow and extremely slow slides. The qualitative relationship ispresented in Table 8 and graphically in Fig. 6.

Tables 4, 5, 6, 7 similarly summarize the extent of damageresulting from slides moving at different rates that adversely affecthighways and railways, bridges, dams and linear infrastructure,respectively. Table 4 indicates that only cases 22 and 50 documentdamage to railways. Hence, it is considered that the availableinformation about the vulnerability of railways to slow-movingslides is not enough to develop a general description of the expecteddegree of damage to railways. Therefore, Tables 9, 10, 11 show thequalitative expected extents of damage from different slide velocitiesfor highways, bridges and dams, respectively. Unlike the casesdescribing urban-community damage, the cases summarized inTables 9, 10, 11 do not reveal a wide spectrum ofmovement rates. Thedamage extents for highways, bridges and dams show that theexpected extents of damage occur at different limits of movement.

Pipelines and water-reticulation pipes are examples of linearinfrastructure. Only four cases are available with sufficient data, asshown in Table 7. A fifth one has a qualitative description of the threatposed by a slow-moving earth slide to a pipeline. The limited numberof available cases makes it difficult to relate the extent of damage topipelines and water service pipes by the movement of slow-movingslides.

DiscussionThe study presents simple statistics about the different attributesof slow-moving slides. In addition, it relates qualitative damageextents or damage descriptions to annual movement rate (or total

Table 10 Damage expected from slow-moving slides to bridges versus movementrate


Extent of damage

0-10 - Minor or no damage

10–30 - Movement of piers and abutments take placebut cracks may be very small

- Mitigation plans should be set for probablefuture distress

30–100 - Numerous cracks start to appear

- There is a continuous need to extend the bridgepiers and abutments to accommodatemovements

>100 - Deformations become severe and pose a realthreat to the bridge safety

- Suspension bridges may collapse if the bridgeanchors lied in the movement zone

Table 11 Damage expected from slow-moving slides to dams versus movementrates


Extent of Damage

0–16 - No reported damage

16–160 - Serious damage to hydropower structures

- Fissures and cracks may be observed in earth androck fill dams

>160 - Failure of loose masses on the slope surface andhence the reservoir may be blocked

- Slide-generated waves may overtop the dam crest

1 10 100 1,000 10,000 100,000 1,000,000

160

m/y

r

Minor

Moderate

Major

Severe

Urban Communities

Highways

Bridges

Dams

Urban Communities

Highways

Bridges

Dams

Urban Communities

Highways

Bridges

Dams

Urban Communities

Highways

Bridges

Dams

Movement Rate (mm/yr)

Deg

ree

of D

amag

e

Fig. 6 Schematic representation of the expected extent of damage versus movement rate for various forms of infrastructure. Green color indicates minor damage,orange indicates moderate damage, yellow indicates major damage, and red indicates severe damage

Technical Note


displacement). It should be noted, however, that the damagedescriptions corresponding to every movement-rate range isbased only on the shown range. The extent of damage willbecome more severe if proper mitigation measures are notapplied promptly to prevent the movement accumulating. Forexample, minor or no damage would result from a movement rateof 5 mm/year if the proper mitigation strategies are applied in atimely manner. However, if there has been no attempt to arrestthe movement for 10 years, for example, the cumulative move-ment may become around 50 mm. This movement magnitude willbring the resulting damage to a higher level, which may bedestructive in some cases. Therefore, it is the cumulativedisplacement that ultimately controls the extent of damage ratherthan the annual movement rate.

Another problem is associated with extremely slow move-ments. Extremely slow slides are often considered as moving at aconstant rate, unless a comprehensive program of monitoring thedisplacement over very short intervals is implemented. While thisconstant-rate movement is considered a creep displacement, thestrain–time curve in a creep test in a triaxial apparatus shows thatthe strain rate decreases, remains constant and then increasesuntil failure during the primary, secondary and tertiary creepstages, as shown in Fig. 5. The laboratory creep behaviour impliesthat creeping landslides may change to be extremely rapid afterlong periods of observed decreasing movement rate. Theevolution of catastrophic movements from creep displacementsis a quite complex mechanism. Petley and Allison (1997)mentioned some basic patterns that control the relationshipbetween creep and catastrophic movements. Creep may continuefor long periods of time during which the displacement rate isessentially constant, but may show minor fluctuations due tosmall changes in the water table. Another pattern is incrementalcreep, in which pore pressure changes and/or seismic events maycause changes in the rate of displacement. Deep-seated slides maysimilarly undergo short periods of creep followed by suddenfailure. Finally, a deep-seated slide may undergo long-term creepdisplacements followed by a sudden failure.

Schuster and Highland (2007) have pointed out the adverseeffects of landslides on the natural environment in general. Theirstudy discussed the vulnerability of each of the mountain andvalley systems, i.e., the earth’s surface morphology, the rivers andstreams in terms of water quality, forests and grasslands, and thenative wildlife to landslides. Our study investigates a specificaspect of the issue by highlighting the vulnerability of differentkinds of facilities to a particular type of landslides—slow-movingslides. Based on the outcomes of this study, we agree with theconclusions of Schuster and Highland (2007) that typical risk-management strategies, including (1) restricting development inlandslide-prone areas, (2) implementing building codes, (3)design of physical mitigation works and (4) developing andinstalling landslide-monitoring and warning systems, could beadopted to reduce the impacts from these types of landslides.

ConclusionsThe paper has reviewed about 50 cases relating to the vulner-ability of different kinds of facilities to extremely slow, very slowand slow-moving slides. The results indicate the types oflandslides and their associated ranges in movement rates; whattypes of equipment are routinely used to monitor these types of

landslide; the movement triggers; and the impacts. This literaturesurvey allowed us to relate qualitative expected extent of damageto movement rate for urban communities, highways, bridges anddams threatened by extremely slow, very slow and slow-movingslides. The extent of damage to each of the studied facilities iscategorized into minor, moderate, major and severe. Thetabulated relationships shown in Tables 8, 9, 10, 11 are shownschematically in Fig. 6, which reveals that buildings andresidential houses may tolerate higher slide velocities and totaldisplacements than the other facilities before experiencing seriousdamage. Bridges are the least tolerant facilities, for movementrates as low as 100 mm/year may severely damage bridges withina year, whereas such low rates may cause only moderate damageto urban communities.

Slow landslides can, however, become rapid landslides ifconditions change. For creeping landslides, however, it is usuallythe cumulative total displacements that cause problems toinfrastructure and housing.

The study has an important practical significance for geo-technical engineers as it provides a way of assessing the likelyextent of damage based on preliminary estimates of movementrates. Hence, the proper field investigation program can beplanned, and the appropriate remedial measures can be imple-mented. In addition, alarm systems can be designed based on themeasured movement rates in the field.

AcknowledgmentsThe authors would like to thank the Natural Science andEngineering Research Council of Canada for providing thefinancial support of the project.

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Expected Damage From Displacement of Slow Moving Slides