Collapsing Slopes Flashcards
What are the natural and human causes of landslides?
Heavy rainfall, steep relief, rock type, unfavourable human activities, natrual disasters (earthquakes etc)
What condition must be present for landslides to occur?
The shear stress is larger than the shear strength.
What is the relationship between rainfall and the likelihood of occurence of landslides？
The heavier the rainfall, the more likely landslides are going to occur. They form a positive relationship.
How does rainfall increase the risk of landslides?
Rainfall increases the weight of the soil and the pore water pressure, which increases shear stress. It also decreases the cohesion and friction, which decreases shear strength.
How is the steep relief related to the risk of landslides?
The steeper the slope, the more likely the rocks will move downslope.
How steep are the slopes in Hong Kong?
More than 65% of the slopes in Hong Kong are over 20 degrees in gradient.
Where can highlands and lowlands be found in Hong Kong?
Highlands are found in central, lantau island, and the eastern part of NT. Lowlands can be found in the reclaimed land on both sides of Victoria Harbour, and in the northwestern part of NT.
What is the most common type of rock in Hong Kong and what are its characteristics?
Granite. Granite is easily weathered and well-jointed.
How does the characteristics of Hong Kong and granite lead to a higher risk of landslides?
Hong Kong is hot and wet in summers, so rainwater may seep into the joints of the granite and break it down into weathered materials. This means that a thick layer of weathered materials will be formed on the top of the rocks. The cohesion among the loose particlaes decrease, which leads to a higher chance of landslides.
What are two unfavourable human activities in Hong Kong that may increase the risk of landslides?
Firstly, as Hong Kong is a densely populated place, people build houses and roads on many slopes. This increases the weight and shear stress of the slope, making it more likely for landslides to occur. Secondly, trees on slopes are cut down for wood or urban development, which reduces the vegetation on the slopes. This increases the risk of landslides as there are less roots of trees to hold loose soil in place.
Suggest an other factor for landslides to occur.
Earthquakes
What are the preventive measures to reduce the impacts of landslides?
Warning systems, education, government planning, regular inspection, and protecting slopes with engineering measures.
List all (8) engineering protecting measures to reduce the impact of landslides and how they work.
Drainage channels: drain rainwater Flexible barriers: to trap rock from falling down the slopes Gabion walls: to support soil slopes Weepholes: drain seeped-in rainwater Retaining walls: to support steep slopes Soil nails: to hold soil on slopes Shotcrete: to stabilize loose soil on the slope Reduce slope gradient
What is the name of the office that adives owners of need works for dangerpus private slopes?
Geotechnical engineering office
How should the government plan the land to reduce the impacts of landslides?
The built-up areas should be avoided on or near dangerous slopes.
