Unit 3 - Page 79 - 83

What is the primary cause of landslides in Hong Kong?

• Earthquakes

• Heavy rainfall and steep slopes

• Volcanic eruptions

• Mining activities

Answer explanation

Answer: B) Heavy rainfall and steep slopes
Explanation: Hong Kong has steep hills and gets a lot of rain during the wet season. When too much rain soaks into the soil, it becomes heavy and unstable, leading to landslides.
Example: Imagine pouring water into a pile of dry sand. The sand holds its shape at first, but if too much water is added, it collapses.

What is the purpose of "pinning" in landslide management?

• To attach vegetation to unstable slopes

• To stabilize slopes by using wire nets or concrete blocks

• To reinforce soil with synthetic fibers

• To plant trees along steep slopes

Answer explanation

Answer: B) To stabilize slopes by using wire nets or concrete blocks
Explanation: Pinning means attaching strong nets or concrete blocks to hold loose rocks in place, preventing them from falling.
Example: If you tie a net over a pile of loose bricks, they won’t scatter when shaken.

How does "netting" help reduce mass movements?

• It diverts water flow away from slopes

• It collects rock fragments and prevents rockfalls

• It adds concrete layers to steep slopes

• It regrades slopes to reduce their steepness

Answer explanation

Answer: B) It collects rock fragments and prevents rockfalls
Explanation: Netting catches small, loose rocks before they roll down a hill and cause damage.
Example: On mountain roads, you often see metal nets placed on slopes to stop falling rocks.

What does "grading" refer to in slope management?

• Smoothing the soil for agricultural purposes

• Strengthening soil by adding fibre materials

• Re-profiling slopes to make them more stable

• Installing drainage pipes in landslide-prone areas

Answer explanation

Answer: C) Re-profiling slopes to make them more stable
Explanation: Grading means changing the shape of a slope by making it less steep, so it is more stable.
Example: If you have a steep sandcastle, it falls easily, but if you flatten the sides, it holds better.

What is a "washout"?

• A rapid flow of water that removes soil and sediment

• A type of rockfall caused by erosion

• A process where soil compacts due to rainfall

• A technique used to stabilize slopes

Answer explanation

Answer: A) A rapid flow of water that removes soil and sediment
Explanation: A washout happens when fast-moving rainwater takes away soil, leaving a hole or trench.
Example: Have you seen a dirt path disappear after heavy rain? That’s a washout!

What are "greening techniques" used for in landslide management?

• To improve biodiversity on slopes

• To protect soil from erosion and increase slope stability

• To make slopes look more attractive

• To increase water flow on slopes

Answer explanation

Answer: B) To protect soil from erosion and increase slope stability
Explanation: Greening techniques use plants and grass to hold the soil together and prevent landslides.
Example: Planting grass on a slope stops rain from washing the soil away.

What is the benefit of using "long-rooting grass" on slopes?

• It adds decorative value to steep slopes

• It grows quickly and stabilizes slopes by reinforcing soil structure

• It absorbs excess rainfall, reducing landslides

• It increases erosion resistance but weakens over time

Answer explanation

Answer: B) It grows quickly and stabilizes slopes by reinforcing soil structure
Explanation: This type of grass has deep roots that act like anchors, making it harder for soil to slide.
Example: If you pull out a plant with short roots, the soil moves, but if the roots are deep, the soil stays firm.

The "fibre reinforced soil system" is designed to:

• Strengthen soil with polyester fibers for increased stability

• Provide an organic solution to soil degradation

• Prevent tree roots from penetrating deep into slopes

• Reduce water retention in soil

Answer explanation

Answer: A) Strengthen soil with polyester fibers for increased stability
Explanation: Synthetic fibers are mixed into the soil to hold it together like glue.
Example: Think of adding straw to mud bricks—they become stronger and less likely to break.

Why are steep slopes more prone to landslides?

• They are naturally unstable and easily affected by gravity

• They allow water to flow away quickly

• They contain denser soil, making them weaker

• They experience more sunlight, leading to soil dryness

Answer explanation

Answer: A) They are naturally unstable and easily affected by gravity
Explanation: The steeper a slope, the easier it is for soil and rocks to slide downhill.
Example: If you tilt a book upright, a toy car slides off quickly; if the book is flat, the car stays put.

Which of the following human activities contributes to landslides?

• Construction and excavation

• Planting trees on slopes

• Building underground tunnels

• Expanding green spaces

Answer explanation

Answer: A) Construction and excavation
Explanation: Digging and building on steep slopes removes natural support, making landslides more likely.
Example: Cutting a road into a hillside may weaken it, causing a landslide later.