What is a landslide?
wet soil soil layer rock layer
Landslide takes place when large masses of loose rocks and soil move downslope rapidly under gravity.

Types of landslide
Rapid movement of soil mass

Types of landslide
Rock fall

What are slopes?
Man-made slope Man-made slope
Natural slope

Conditions for landslides to occur in HK
1. Heavy rainfall
Ground surface
Ground surface
Soil spaces
Very little water
Some water in the soil spaces.
All soil spaces are filled with water.
All soil spaces are filled with water. Soil particles cannot hold together.
Heavy rainfall
Soil becomes saturated


After heavy rain, all soil spaces are filled with water. Soil becomes saturated.

Soil particles cannot hold together.

Conditions for landslides to occur in HK
2. Steep slopes
Hong Kong is hilly with many steep slopes.
The steeper the slope, the greater is the chance of landslide.

Conditions for landslides to occur in HK
3. Slope cutting and slope filling

Conditions for landslides to occur in HK
3. Slope cutting and slope filling
•
After people have cut a slope, the soil on the upper part of the cutting is no longer supported from below.
•
When the soil becomes saturated, the slope becomes unstable.

Conditions for landslides to occur in HK
4. Thick soil layer on slopes
Soil layer is thick that more soil will slide down slope.


In Hong Kong, the layer of soil is thick.

This is related to the hot and wet climate as well as the main type of rock in Hong Kong which is called granite.

High temperatures and high rainfall are favourable for weathering.

Granite has lots of joints that water can seep into the joints easily. That favours the breaking down of rocks’ minerals.

Conditions for landslides to occur in HK
5. Removal of vegetation
•
Without trees, there are no roots to bind the soil. There is also no organic matter to stick the soil together.

Conditions for landslides to occur in HK
6. Triggering action
A landslide may cause by a sudden shock.
piling explosion passing of heavy vehicles earthquake

Summary of the causes of landslide heavy rainfall buildings increase weight on slope thick soil layer on slope
Rock layer
Granite is easily weathered to form thick soil removal of vegetation slope cutting and slope filling

How can landslides affect us?

How can landslides affect us?
1. Loss of life

How can landslides affect us?
2. Property damage

How can landslides affect us?
3. Disruption of traffic

How can we prevent landslides?
1. Careful design of projects on slopes
Reduce slope angles as much as possible

How can we prevent landslides?
2. Stabilising slopes
Retaining wall and drainage channels are built to stabilize the slopes.
Preserve natural vegetation.

How can we prevent landslides?
3. Monitoring and maintaining slopes
The slope owners are responsible for the maintenance and safety of their slopes.

How can we prevent landslides?
4. Good farming practices
Contour ploughing
Building low walls