In highway and airport pavement engineering, identify the primary causes of depressions and undulations in flexible pavements.
Civil Engineering
Airport Engineering
Difficulty: Easy
Choose an option
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AImproper compaction of subgrade; impact of heavy wheel loads; punching effect (statements 1, 2, and 3 only).
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BFlexible gears are the main cause in service.
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COnly improper compaction of subgrade is responsible.
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DAll the listed causes are equally responsible, including “flexible gears”.
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EOnly impact of heavy wheel loads and punching effect (statements 2 and 3).
Answer
Correct Answer: Improper compaction of subgrade; impact of heavy wheel loads; punching effect (statements 1, 2, and 3 only).
Explanation
Introduction / Context:Service defects such as depressions and undulations in flexible pavements arise from structural and loading issues. This question distinguishes real engineering causes from a distractor term.
Given Data / Assumptions:
- Flexible pavement structure with subgrade, base, binder, and surface layers.
- Traffic includes heavy axle loads.
- “Flexible gears” appears as a non-standard term in pavement distress causes.
Concept / Approach:Depressions occur when support is inadequate (poor compaction or moisture weakening) and when repeated heavy loads induce plastic deformation or punching through weak spots. Correct diagnosis focuses on layer stiffness and load transfer.
Step-by-Step Solution:
1) Improper compaction of subgrade reduces bearing capacity, causing differential settlement and depressions under traffic.2) Impact of heavy wheel loads increases contact stresses, accelerating rutting and localized shear failure.3) Punching effect refers to high localized stresses that push through weak layers, creating bowls/undulations.4) “Flexible gears” is not a recognized cause of pavement distress; likely a distractor or misstatement.Verification / Alternative check:
Compare with standard distress mechanisms: rutting, shoving, consolidation of subgrade—each ties back to inadequate compaction and heavy loads.Why Other Options Are Wrong:
Options that include “flexible gears” as a cause are invalid because the term is unrelated to pavement mechanics.Single-cause options ignore the multifactor origin of undulations.Common Pitfalls:
Confusing “flexible pavements” with “flexible gears”; overlooking subgrade quality as a root cause.Final Answer:
Statements 1, 2, and 3 are correct; “flexible gears” is not a valid cause.