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ENV-3A1Y: Natural Hazards: 2006 - 7

Landslide Hazards

N.K. Tovey

Н.К.Тови

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

14,607 days ago today

Exactly 40 years ago next Saturday

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• Lecture 1: Wednesday Week 42

– Introduction

• Landslides as a Hazard and their consequences

• background to why they occur

• Lecture 2: Thursday Week 4 12 – 13 EF 1.01

– Types of Landslide

• Lecture 3: Thursday Week 4 14 - 15

– Landslide Warning systems

• Lecture 4: Wednesday Week 5 09 – 10 EF 1.01

– Landslide and Slope Management

• Field Excursion: Thursday Week 5 12 – 17

• Bring Field Clothing and a packed lunch

ENV-3A1Y: Natural Hazards: 2006 - 7

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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: Natural Hazards: 2006 - 7

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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

ENV-3A1Y: Natural Hazards: 2006 - 7

Failure of slope above Po Shan Road in June 1972

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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: Natural Hazards: 2006 - 7

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ENV-3A1Y: Natural Hazards: 2006 - 7

14607 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

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

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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: Natural Hazards: 2006 - 7

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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 =

ENV-3A1Y: Natural Hazards: 2006 - 7

Fs > 1 stable But is it?

Fs = 1 just stable Fs < 1 unstable

But is it?

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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

Geochemistry