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Mass Movement and Slope Safety: Paper 1
Mass Movement and Slope Safety: Paper 1
Ten items on the basics: slope conversion, the factor of safety, mass movement classes, infiltration, vegetation, Hong Kong man-made slopes and common works.
Direct answers Items 1-3: 57.7 per cent, 26.6 degrees, 1.5. Items 4-6: falls, slides, flows and creep; pore water pressure; root cohesion. Items 7-9: about sixty thousand slopes; three groups of works; the weak interface. Item 10: steeper slopes have larger driving forces.
01 Paper details (check answers afterwards)
| Item | Detail |
|---|---|
| Questions | 10 |
| Suggested time | 20 |
| Difficulty mix | Foundation 3 · Intermediate 3 · Challenge 3 · Error redo 1 |
| Chapter | Chapter: DSE Geography Mass Movement and Slope Safety |
| Level | Basics |
02 Questions (10 items)
- FoundationA slope rises at 30 degrees. What is its gradient expressed as a percentage (rise over run times 100)?
- FoundationA slope is written as 1:2 (one vertical to two horizontal). What angle is that?
- FoundationA slope has resisting force of 120 kN and driving force of 80 kN. What is the factor of safety?
- IntermediateWhat are the main classes of mass movement?
- IntermediateWhy are landslides especially common after prolonged heavy rain?
- IntermediateWhat role does vegetation play in slope stability?
- ChallengeRoughly how many man-made slopes are there in Hong Kong, and which body manages the risk?
- ChallengeWhat three groups of slope works are commonly used?
- ChallengeWhy does a weathered layer on a steep slope slide so readily along its base?
- Error redoError clinic: “Steeper slopes are safer because water drains faster.” What is wrong?
03 Answers and one-line notes
| # | Answer | One-line note |
|---|---|---|
| 1 | 57.7 per cent | The tangent of 30 degrees is about 0.577, so multiply by 100. |
| 2 | about 26.6 degrees | The tangent of the angle is 0.5, giving about 26.6 degrees. |
| 3 | 1.5 | One hundred twenty divided by eighty; only a ratio above one means resistance exceeds the driving force. |
| 4 | falls, slides, flows and creep | The classes follow the manner and speed of movement: falls are near free fall while creep is very slow. |
| 5 | infiltration raises pore water pressure, lowering effective stress and shear strength | The same soil body can be stable in the dry season and fail in the wet season; water pressure makes the difference. |
| 6 | roots add apparent cohesion near the surface and reduce raindrop impact and surface runoff | Roots reach only the shallow zone, so deep-seated slides still need engineering works. |
| 7 | about sixty thousand, handled by the Geotechnical Engineering Office under the Civil Engineering and Development Department | Registration, inspection and upgrading programmes all target these slopes. |
| 8 | drainage such as cut-off drains and drain pipes, structural support such as retaining walls and soil nails, and surface protection with vegetation | The three are usually combined; one measure alone rarely addresses every driving force. |
| 9 | the weathered material is loose and permeable, forming a weak interface with the more intact rock below | Water collects at that interface, letting the overlying material move as a mass. |
| 10 | wrong: a steeper slope has a larger downslope driving force, and fast drainage does not guarantee enough resistance | Safety depends on the ratio of resistance to driving force, not on drainage speed alone. |
04 What to do after marking
- After marking, redo only the wrong items and write down which step went wrong (formula, unit, or misread number).
- Repeat the same item two days later; move to the next paper only when both attempts are correct.
- Parents only need the answer and note columns; there is no need to explain every item.
Identify whether it is a fall, slide or flow before explaining causes.Tutor Registration →
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