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Sabrina

Sabrina. Patricia. Fiona. Karen. “ St. Francis’ Canossian College has the threat of experiencing mass wasting in the future. Do you agree?. What is mass wasting? What is landslide?.

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Sabrina

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  1. Sabrina Patricia Fiona Karen “St. Francis’ Canossian College has the threat of experiencing mass wasting in the future. Do you agree?

  2. What is mass wasting?What is landslide? • Mass wasting is the geomorphic process by which soil, regolith, and rock move downslope under the force of gravity. • Landslide is a kind of fast movement by rocks and soils of all sizes collapse through either sliding or slumping along a curved surface. The landslide in 2000.

  3. Did SFCC experienced landslides before? • occurred on 24 August 2000 • involving unregistered fill on the hillside adjacent to No. 2B Bowen Road on Hong Kong Island. • Debris with an estimated volume of 120 m3, • transported downstream for a long distance beyond the landslide site (up to about 250 m on plan) to reach Hong Kong Park below Kennedy Road. • To reach also our school!!!!!!!!

  4. Physical FactorsThe potential shear threats of slopes near our school Steep gradient • Larger gravitational force • force>resistance • stress Steep slope

  5. The distribution of rainfall The rainfall distribution in 2000 The rainfall intensity is the highest in August in 2000, therefore it is one of the reasons of the occurrence of landslide.

  6. Human factorLack of maintenance of the drainage system • According to the Civic Engineering and Development department, there has been no maintenance work done on the slopes on Kennedy Road other than the two below.

  7. Large Population Large population densely populated (as there are many residential buildings) More pressure to the slope system Stress There are many students in our school.

  8. Different type of land use nearby Residential land use Uphill and downhill sides: Roads, residential buildings, school…etc. • Many land use = many human activities • much pressure to the slope • Stress Transport land use

  9. The rainfall intensity of Wanchai is not high comparing to that in the eastern part of Kowloon

  10. Potential shear strength – Physical Factor Distribution of rainfall It is not usual for Wanchai to have prolonged heavy rainfall. light rainfall would not add weight to slopes or create lubrication effect  Strength

  11. Human FactorSubsurface drainage system Surface and subsurface drainage system were built on the slope can drain water from the slope surface or soil

  12. can effectively reduce the rising rate of pore water pressure in the soil after rainstorm. less pressure to the slope strength

  13. Measures • Done by the Civil Engineering and Development Department • Aim: increase the strength and reduce the stress of the soil on slopes

  14. 1. Covering slopes with impermeable layers • Protect slope surface with masonry walls (a kind of impermeable layer of covering) • water cannot percolate into rocks and both physical and chemical weathering could not take place. • maintain the stability of slope • There would not be regolith Taken on Kennedy Road

  15. 2. Afforestation • Planting vegetation cover • grass can help to bind the soil with their long and dense roots, producing a “woven mat” covering the slope • less likely to be washed away

  16. 3. Removing large trees since densely vegetated area added pressure and weight to the slope • The government removed large tress from steep slopes

  17. 4. Put up warning signs • People would learn to avoid slopes on rainy days • Minimize destruction of landslide • Fewer casualties

  18. Do SFCC has the threat of experiencing mass wasting in the future?

  19. Does SFCC has the threat of experiencing mass wasting in the future? • The chance is low. • Potential strength> potential stress • The management of slope is updated and comprehensive. • But mass wasting is still possible, if given that a sudden stress is caused to the slopes.

  20. Physical FactorRainfall intensity • The nature is dynamic. • In summer, there might be chances of prolonged heavy rain to occur as the summer monsoon brought moisture from the south (sea) to inland. • creates lubrication effect • trigger landslide

  21. Human FactorLack of maintenance Lack of maintenance surface and subsurface drainage system blocked water trap inside the permeable layers Subsurface water increases weight of the soil mass water acts as lubricant, reducing frictional resistance and increasing mobility of flow. Raises water table, increases pore water pressure, more stress

  22. Also, there are several reasons that might trigger landslide.

  23. Also, there are several reasons that might trigger landslide. Our school

  24. Ｗｈｅｒｅ　ａｒｅ　ｔｈｅ　ｈｏｌｅｓ？

  25. Reflection • 1. Although the government has carried out several measures to deal with the landslide problem on Kennedy road, no one could promise the safety of our slopes. • Our earth is dynamic, hazards could occur any time. • So in summer, watch out! • Also, to be a responsible citizen, don’t throw rubbish into the drainage system, or you might be the one who trigger landslides!

  26. Thank you !

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