landslide classification

8/13/2019 Landslide Classification

1/54

Varnes LandslideClassification


2/54

What is the purpose ofa classification?

To file material so it can be easily retrieved*

To organize thought To communicate*J.N. Hutchin so n, c. 2000

Our main need is for labels describing landslidetypes (typology)but the system must be flexible and adaptable tothe complexity of landslides


3/54

Typological classificationDivide phenomena into repeatingpatterns (types) characterized by

several descriptors.

Requirements:

1) Comprehensive definition2) Type examples3) References


4/54

Desirable qualities of atypological classification system:

1. Simple, not too many classes2. Respectful of previous usage

3. Flexible, with varying quality of data

4. Each class name to be supported by a

definition, examples and references


5/54

What to do with complex types?Suggestion: leave the decision to the user.

Rock avalancheRock slide

Dr. Rick Guthrie


6/54

Framework:

Pre-failure movementsPost-failure movements

Failureis the single most significantmovement episode.

Failureinvolves the first formation ofa rupture surface

It is up to the user to decide which.


7/54

PrincipalmovementtypesCruden andVarnes, 1996

(dates back toBalzer, 1875)


8/54

D.J. Varnes, 1978

33 types


9/54

Landslide classification (Varnes, 1978 ) Co de: RAP ID , SLOW ( IN MOST CASES)

B E D R O C K DEBRIS (80% sand and finer)

FALLS ROCK F A L L D E B R I S F A L L E A R T H F A L L

TOPPLES B LOCK TOP P L E

FLEXURAL TOPPLE

- B LOCK TOP P L E

SLIDES ROCK SLUMP

ROCK SL I DE

DEB R I S SL I DE E A R T H S L U MP

EARTH SLIDE

SPREADS ROCK SPREAD - EARTH SPREAD

F L O WS R O C K C R E E P

SLOPE SAGGING

DEBR I S F L OW

DEBR I S

A V A L A N C H E

SOIL CREEP

SOLIFLUCTION

WET SAND AN D SI L T

F L OW

RA PI D E A R T H F L OW

LOE SS F L OW

D R Y S A N D F L O W

E A R T H F L O W

C O MP L E X ROCK A V A L A NCH E

EARTH SLUMP-EARTHFLOW

Ref.: Varn es, D.J., 1978. Slope movem ent types and processes. In Landslides, Analysis and Control. Special

Report 176, Transportation Research Board, Washington, pp. 11-33.

Varnes Classification Type Names


10/54

Landslide velocity scale (Cruden and V arnes, 1996).

Velocity

class

Description Velocity

(mm/sec)

Typical

velocity

Human

response

7 Extremely Rapid N il

------------------------ 5x103 5 m/sec

6 Very Rapid N il

------------------------ 5x101 3 m/min

5 Rap id Evacuat ion

------------------------ 5x10 -1 1.8 m/hr

4 M oderate Evacuation

------------------------ 5x10-3

13 m/mo nth

3 Slow M aintenance

------------------------ 5x10-5

1.6 m/year

2 Very Slow M aintenance

------------------------ 5x10-7

16 mm /year

1 Extremely Slow N il

Ref.: Cruden, D.M. and Varnes, D.J., 1996. Landslide types and processes. In Landslides, Investigation and

Mitigation. Special Report 247, Transportat ion Research Board, Washington, pp. 36 -75.

Velocity scale


11/54

- Rock- Debris(more than 20% coarse*)

- Earth(less than 20% coarse*)* Gravel clasts and larger

1. Difficult to evaluate2. Little relevance to slide behaviour3. Incompatible with established systems

Material categories:


12/54

Suggested material classes


13/54


Geotechnicalclasses- plastic

- granular


14/54


Mixed materials- plastic- granular(Mixed grain sizes,

diluted by water)


15/54

Clay, silt, sand, gravel, boulders

How to simplify?Suggestion: use dominant componentwith emphasis on mechanicalbehaviour.

Example:plastic clayey silt > claylow plasticity clayey silt > silt

Geotechnical materials:


16/54


17/54

Supplementary terms, geomorphological

Do not use as primary names, because

there is insufficient correlation withlandslide behaviour.Example, Alluvial (could be gravel, silt, clay)


18/54

Some additional movement types:- Rotational/ translational/ compound slide(Hut ch inson , 1988)

- Block topple/ flexural topple(Goodman and Bray, 1976)

- Flow slide (Terzagh i, Casag rande, Meyerhof ..)

- Slope deformation creep?

- Rock collapse? (croulement, felssturz)

- Debris flood (e.g. Au litzsk i, 1970)


19/54

* Can be extremely rapid

Summary


20/54

Rock, ice fall

Detachment, fal l , ro l l ing and bouncing o f roc k o r ice

fragments. May o ccur s ingly or in clus ters, but there is l i t t le

dynam ic interact ion between the most mobi le moving

fragments, which interact mainly with th e substrate (path).

Fragment deformation is un important, although fragments

can break dur ing impacts. Usual ly o f l imi ted volum e.


21/54

Rock block

toppleChaco Canyon,

New Mexico

Forward rotat ion and over turn ing of roc k co lumns or

plates (one or many), separated by steeply-dipping

jo in ts . The rock is relat ively mass ive and ro tat ion oc-cu rs on wel l -def ined basal discon t inui t ies. Movement

may begin s low ly, bu t the last s tage of fai lure is

extremely rapid . Occurs at al l scales.


22/54

Multiple block topple

Czech Republic


23/54

Rock Flexural Topple

1980

1987

Bending and forw ard rotat ion of

a rock mass character ized by

very c losely-spaced, steeply

d ipp ing jo in ts or schis tose

part ings. The rock is relat ively

weak and fiss i le. There are nowel l-def ined basal dis continui t ies

that could al low for ro tat ion of

blocks around their bases. The

movement is general ly slow andtends to self-stabi l ize. However,

secondary rotat ional sl id ing may

develop in the hing e zone of the

topple. Occurs at large scale.

La Clapire, France


24/54

Rock rotational slide (rock slump)Sl id ing o f a mass of w eak rock on a cyl ind r ical or el lipso idal

rup ture surface which is no t stru ctural ly-contro l led. Li t t le

internal deformation. A large main scarp and back -t i l ted

bench at the head. Usual ly s low to moderately s low.


25/54

Rock translational (planar) slideSl id ing of a mass o f roc k on a planar rupture su rface. The

su rface may be s tepped forward. No internal deformation.

The sl ide head may be sepa-rating from stable rock along

a deep, vert ical tension c rack. Usual ly extremely rapid.


26/54

Rock wedge slideSlid ing of a mass o f rock on a rupture surface formed of

two planes w ith downslope-or iented intersect ion. No

internal deformation . Usual ly extremely rapid .


27/54

Rock compound slide

Scatter River, North-east British Columbia

(Hungr et al., 1984

Slid ing of a mass of roc k on a rupture sur face cons is t ing

of several planes, or a su rface of uneven curv ature, so that

mot ion is kinemat ical ly possib le only i f accompanied bysign i f icant internal distor t ion of the moving m ass. Horst-

and-graben features at the head and many secondary

shear su rfaces are typical . Parts o f the ruptu re sur face

may develop by shear ing through the rock. Slow o r rapid.


28/54

Compound sliding

Internal deformationrequired

Graben


29/54

Vaiont (1963)

A compound slide(Mencl, Hutchinson) non-circular


30/54

Rock irregular slide (rock collapse)

view

section

randomjoints

Sl id ing o f a rock mass on an irregu lar rupture surface

cons ist ing of a number of random ly-or iented jo ints,

separated by segments of intact rock (rock bridges).Occurs in strong rocks wi th non-sys temat ic structure.

Fai lure mechanism is very complex and often di f ficul t to

descr ibe. May includ e elements o f toppl ing. Often very

sudden and extremely rapid.


31/54

Clay, silt rotational slide (Soil slump)Slid ing o f a mass of (homogeneous and usu-ally cohesive)

so i l on a cyl ind r ical or ell ipsoidal rup ture su rface. Li t t le

internal deformat ion. Normally s low, bu t may be extremely

rapid in sensi t ive or co l laps ive soi ls.

rupture

surface


32/54

Clay, silt planar slideSlid ing o f a block o f cohesive so i l on an incl ined planar

rup ture surface, form ed by a weak layer (usual ly pre-sheared).

The head o f the s l ide mass separates from stable soi l along a

deep tens ion c rack (no active wedge). May be slow or rap id.

Panama Canal


33/54

Sand, Gravel,Debris slideSl iding o f a mass o f granu lar mater ial on a shal low, planar

su rface paral lel wi th the ground . Usual ly, the sl id ing massis a veneer of c ol luvium , weath-ered so i l , or py roc last ic

depos i ts rest ing on a stronger su bstrate. Many debr is

sl ides become f low -l ike after mov ing a short distance and

trans form into extremely rapid debr is ava-lanches.


34/54

Sl id ing o f a mass of so i l on arupture sur face cons is t ing of

several planes, or a su rface of

uneven cu rvature, so that

mot ion is k inemat ica lly po ssib le

only i f accompanied by

sign i f icant internal distor t ion of

the moving mass. Horst-and-

graben features at the head and

many secondary shear surfacesare observed. The basal

segment of the rupture surface

often fol lows a weak ho r izon in

the soi l strat igraphy

Clay, siltcompound slide


35/54

Rock slopespread

(or deformation?)Crest sagging in

s lopes formed from a

stro nger layer (caprock ) over weak rock.

Block s of the stronger

rock sp read and t i l t by

deformation of th e

under ly ing weak

mater ial, w ithout the

formation o f a def ined

rup ture surface.

Extremely s low.

Nemcok, 1982, Weak rocks

Initial stage, Mature stage, Final stage, Surficialmovements


36/54

Sand, silt liquefaction spreadExtremely rapid lateral spreading o f a series of so i l block s,

f loat ing on a layer of saturated (loose) granu lar so i l , l iquefied

by earthquake shaking o r spon taneous l iquefact ion.

TurnagainHeights Slide,1964


37/54

Sensitive clay spreadExtremely rapid lateral sp reading o f a series o f

coherent c lay b lock s, f loat ing on a layer of

remoulded sensit iv e clay.

St. Jude,Quebec, 2010


38/54

Rock avalancheExtremely rapid, massive, f low -l ike mo t ion of

fragmented roc k from a large rock sl ide or rock fal l .

Frank Slide,1903

Inverse sorting


39/54

Slow o r rapid f low -l ikemovement of loose dry,

moist o r saturated,

sor ted o r unsor ted

granu lar material,

w i thout excess pore-

pressure.

Dry (or non-liquefied)Sand, Silt, Gravel or

Debris Flow


40/54

Very rapid to extremely rapid f low of sorted or unsortedsaturated granular mater ia l on m oderate slopes, involv ing

excess pore-pressu re or l iquefact ion of mater ial

or ig inat ing from the lands l ide source. Usual ly or ig inates

as a mult ip le retrog ressiv e fai lure. Often under water.

Sand, Sil t , Debris flow slid e:


41/54

Very rapid to extremely rapid f low of

l iquef ied sensi t ive clay, due to remou lding

du ring a mu lt ip le retrogressive sl ide fai lure

at, or close to the orig inal water content .

(Photo: S.G. Evans)

Clay flow slide


42/54

Debris flow:Very rapid to extr emely

rap id surg ing f low of

saturated non-plast ic

debr is in a steepchannel. Strong

entrainment of mater ial

and water from the f low

path . (Plastic i ty Index

landslide classification

Documents