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ENV-3A1Y/ENVF3A1Y: Natural Hazards:

2009 - 10Landslide Hazards

N.K. Tovey

Н.К.Тови

Landslide on Main Highway at km 365 west of Sao Paulo: August 2002

Lecture 2 Lecture 3 Lecture 4Lecture 1

15,699 days ago today

43 years ago next Wednesday

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• Lecture 1: Wednesday Week 4 09 – 10 Lab A– Introduction

• Landslides as a Hazard and their consequences• background to why they occur

• Lecture 2: Thursday Week 4 12 – 12:50 CD Annexe 0.01• Types of Landslide

• Lecture 3: Wednesday Week 5 09 – 10 CD Annexe 0.01 [ but may be in Lab A depending on how things goes in Week 1]

• Landslide Warning systems

• Lecture 4: Thursday Week 5 12 – 12:50 CD Annexe 0.01– Landslide and Slope Management

– Field Excursion: Week 4 or Week 5 starting at 12:55– from bus stop [watch email for details]

• Bring Field Clothing and a packed lunch – meet at CD annexe Bus Stop

ENV-3A1Y/ENVF3A1Y: Natural Hazards: 2009 - 10

New Book Published October 20081 Enduring Landslides and Floods in the Caribbean

Region by Angella Cropper1

Landslides2 Modelling Landslides in Tropical Environments by

Keith Tovey15

3 Planning for Hillside Terrains by Deborah Thomas and Senwan M. J. Baban

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4 Developing a GIS-based Landslide Susceptibility Map for Tropical Mountainous Environments by Serwan M. J. Baban and Kamal Sant

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5 Using Contemporary Geo-imaging Technologies for Landslide Investigations in Tropical Environments by Raid Al-Tahir and Vernon Singhroy

81

Floods6 Using GIS for Flood Management and Mitigation in

Trinidad and Tobago by Bheshem Ramlal107

7 Using GIS for Flood Risk Assessment and Flood Sensitivity Maps for a Watershed in Trinidad and Tobago by Serwan M. J. Baban and Ronnie Kantasingh

124

8 A New Examination of Floods in the Region: Debris Floods and Debris Flows in the Caribbean by Rafi Ahmad

141

9 Mapping Flood-prone Areas: A Geoinformatics Approach by Serwan M. J. Baban and Francis Cannisus

157

Geohazards Management10 Developing a Proactive Approach to Geohazards

Management in Trinidad and Tobago by Serwan M. J. Baban

181

11 Issues in Flood Risk Management by Andrew Fox 192

12 Recognizing and Managing Unstable Slopes in Trinidad and Tobago by Serwan M. J. Baban and John B. Ritter

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13 Developing Early "Warning Systems for Managing Geohazards in the Caribbean by Serwan M. J. Baban and Kelly Aliasgar

225

14 Beyond Humanitarianism: Building Resilient Communities, Revisiting the Development Dialogue by Jeremy Collymore

244

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• Aims of the course

• An introduction to Landslide Hazard Management

• Factor of Safety

• the causes

• Why they occur

• Can we predict them

• the consequences

• The types of landslide

• Landslide Warning –

• Development of the Hong Kong System and what was learnt

• Strategic Planning for the future

• Slope management

ENV-3A1Y/ENVF3A1Y: Natural Hazards: 2009 - 10

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Landslides as a Hazard• Grossly Under Represented as a

Hazard

• Often treated as a secondary issue

• e.g Rain Storm Disasters of 18th June 1972 in Hong Kong

• 2 major landslides each killing over 60 people

• No one was killed by drowning/flooding or as a result of the typhonn.

Failure of slope above Po Shan Road in June 1972

ENV-3A1Y/ENVF3A1Y: Natural Hazards: 2009 - 10

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Landslides associated with• Heavy Rain (Tropical Cyclones)

– ~ 500+ landslides affected man in Hong Kong 28th May to 2nd June 1982.

– As a result of NKT’s actions Yuen Mo village ceased to exist.

• Earthquakes– Cause liquefaction and rise of pore pressures

• Volcanic Eruptions

ENV-3A1Y/ENVF3A1Y: Natural Hazards: 2009 - 10

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15699 days ago today at 09:15

N K Tovey a second year PhD student was listening to a lecture by Andrew Schofield.

• Theme of lecture was Landslide Hazards

At 09:15 he turned his attention to a landslide disaster which had occurred a few year earlier in Belgium.

A colliery tip collapsed killing around 20 people in the village.

• At precisely the time he was speaking about the disaster

>>>>>>>>>>>>>>>>>>>>>

ENV-3A1Y/ENVF3A1Y: Natural Hazards: 2009 - 10

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• Aberfan: 21st October 1966

• Tip 7 collapsed, engulfed Pantglas School and parts of the village killing 144 mostly children

ENV-3A1Y/ENVF3A1Y: Natural Hazards: 2009 - 10

Main Manchester – Sheffield Road (A625)

Alternative route – only suitable for light vehicles – gradient of 1 in 4

Landslides: Removing the Consequence

Manchester

1 km

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• Geotechnics – the discipline needed for detailed analysis

• "the application of the laws of mechanics and hydraulics to the mechanical problems relating to soils and rocks"

• Factor of Safety (Fs):

Forces resisting landslide movement arising from the inherent strength of the soil.

Forces trying to cause failure(i.e. the mobilizing forces).

Fs =

Fs > 1 stable But is it?

Fs = 1 just stable Fs < 1 unstable

But is it?

ENV-3A1Y/ENVF3A1Y: Natural Hazards: 2009 - 10

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berms

Heave at toe

Landslide in man made Cut Slope at km 365 west of Sao Paolo - August 2002

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berms

Steep scar to rotational failure

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Landslide

Consequence

Remedial Measures

Remove ConsequenceSafe at the moment

Cost

Build

Landslide Warning

No Danger Temporarily Safe

Design

LandslidePreventive Measures

Stability Assessment Slope Profile

GeologyErosion/DepositionGlaciationWeatheringGeochemistry

Cut / Fill SlopesConstructionDrainage Pumping

Man’s Influence (Agriculture /Development)

Earthquakes

Material Properties (Shear Strength)

Ground Loading(Consolidation)

Slope Management

Hydrology (rainfall)

Ground Water

Surface Water

GIS

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N

S

=WN

S

W

Relationship between mobilizing & resisting forces

Force (S) required to move block is proportional to Normal Force (N)

On a slope

N depends on weight and N = W cos

S also depends on weight and N = W sin

S1

N1

S2

N2

S3

N3

N

S

W

W

Normal Force

Shear Force