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Section Two

Section Two. Collapsing slopes. wet soil. soil layer. rock layer. What is a landslide?. 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?.

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Section Two

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  1. Section Two Collapsing slopes

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

  3. Types of landslide Rapid movement of soil mass

  4. Types of landslide Rock fall

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

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

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

  8. 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.

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

  10. 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.

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

  12. 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.

  13. 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.

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

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

  16. How can landslides affect us?

  17. How can landslides affect us? 1. Loss of life

  18. How can landslides affect us? 2. Property damage

  19. How can landslides affect us? 3. Disruption of traffic

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

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

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

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

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