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Mass Movement and Slope Safety Paper 4: Error Clinic
Mass Movement and Slope Safety Paper 4: Error Clinic
The same slope figures asked in new ways, aimed at the commonest calculation and concept errors.
Direct answers Answers and explanations for all ten questions
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 | Paper 4 (error clinic) |
02 Questions (10 items)
- FoundationA slope is written as 1:1.5 (vertical to horizontal). What is the angle?
- FoundationA slope has a driving force of 60 kN and shear resistance of 90 kN. What is the factor of safety?
- FoundationA rainstorm raises rainfall from 120 mm to 180 mm. What is the percentage increase?
- IntermediateInfiltration raises pore water pressure from 20 kPa to 35 kPa. What is the rise, and what happens to effective stress?
- IntermediateWhen the slope angle rises from 32 to 40 degrees, by what factor does the downslope gravity component (compared by tangent) grow?
- IntermediateA slope creeps 4 mm a year for 15 years. How far has it moved and why does it matter?
- ChallengeA slope has a driving force of 80 kN and the design requires a factor of safety of at least 1.5. What minimum resistance is needed?
- ChallengeA landslide body is 30 m long, 12 m wide and 2.5 m thick on average. What is its volume?
- ChallengeIf a slope is cut back from 35 to 25 degrees with resistance unchanged, by what factor does the factor of safety rise?
- Error redoError clinic: “The taller the retaining wall, the more stable the slope.” What is wrong?
03 Answers and one-line notes
| # | Answer | One-line note |
|---|---|---|
| 1 | about 33.7 degrees | tan theta = 1 / 1.5 = 0.667, and the inverse tangent gives 33.7 degrees; a larger ratio means a steeper slope. |
| 2 | 1.5 | FS equals resistance divided by driving force, 90 over 60; any value above one means the slope is stable for now. |
| 3 | 50.0 per cent | The extra 60 mm divided by the original 120 mm; heavier rain raises infiltration and pore water pressure. |
| 4 | a rise of 75.0 per cent; effective stress falls | Fifteen over twenty; the water pressure carries part of the load between grains, so shear strength drops. |
| 5 | about 1.34 times | The tangent of 40 degrees is 0.839 and of 32 degrees is 0.625; the ratio is 1.34, so a few extra degrees add a lot of driving force. |
| 6 | 60 mm; it is a warning sign before failure | Four times fifteen; slow creep often precedes collapse, showing as cracks and leaning poles. |
| 7 | 120.0 kN | Eighty times one point five; design works back from the required resistance instead of only checking that FS exceeds one. |
| 8 | 900 cubic metres | Thirty times twelve times two point five; volume drives the cost of clearance and how long a road stays shut. |
| 9 | about 1.5 times | The tangent of 35 degrees is 0.700 and of 25 degrees is 0.466, a ratio of 1.50; grading reduces driving force and is the commonest remedy. |
| 10 | wrong: a taller wall carries greater earth pressure, so foundations and drainage must be strengthened too | Stability is the ratio of resistance to driving force, and height alone adds no resistance; design must consider earth pressure, drainage and foundations. |
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.
After all four papers, copy the missed figures into your notes and revise only those in the week before the exam.Tutor Registration →
Questions and answers are written originally by the TutorZone team and are not taken from any school, publisher or examination authority paper. Every value is checked by computer.