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Questions and Answers
What is the primary difference between settlement and subsidence in the context of ground engineering?
What is the primary difference between settlement and subsidence in the context of ground engineering?
- Settlement always results in catastrophic failure, while subsidence is a gradual process.
- Settlement is the downward movement of a structure due to compression of underlying soil, while subsidence is a failure resulting in loss of the ability to support loads. (correct)
- Settlement refers to the collapse of ground due to natural properties, while subsidence is due to compression from external loads.
- There is no significant difference; the terms are interchangeable in all contexts.
Which geological condition would pose the highest risk for regional settlement and subsidence, based on consolidation?
Which geological condition would pose the highest risk for regional settlement and subsidence, based on consolidation?
- Extensive deposits of granular soil with high permeability.
- Regions with thick layers of well-drained sandy soils.
- Highly populated areas underlain by extensive clay soils. (correct)
- Areas underlain by solid rock formations with minimal fracturing.
Which factor most significantly influences the potential for subsidence in areas with soluble rock?
Which factor most significantly influences the potential for subsidence in areas with soluble rock?
- The density and compaction of overlying soil layers.
- The absence of bedding planes and fractures in the rock.
- The rate of water flow and chemical composition of groundwater. (correct)
- The presence of uniform loading from surface structures.
What is the most likely cause of ground subsidence in areas with a history of longwall mining?
What is the most likely cause of ground subsidence in areas with a history of longwall mining?
Which of the following scenarios would most likely lead to differential settlement?
Which of the following scenarios would most likely lead to differential settlement?
How do expansive clays contribute to geohazards, and what primary mechanism is involved?
How do expansive clays contribute to geohazards, and what primary mechanism is involved?
What is the role of porosity in clay soils regarding their potential for compression and settlement?
What is the role of porosity in clay soils regarding their potential for compression and settlement?
Why is organic soil (e.g., peat) generally avoided for construction purposes?
Why is organic soil (e.g., peat) generally avoided for construction purposes?
How might climate change exacerbate the risk of geohazards associated with expansive clays?
How might climate change exacerbate the risk of geohazards associated with expansive clays?
What is the significance of identifying rock type on a geological map in the context of subsidence?
What is the significance of identifying rock type on a geological map in the context of subsidence?
Flashcards
Settlement
Settlement
Downward movement of a structure due to compression of underlying ground material, usually clay soils.
Subsidence
Subsidence
Failure/collapse in the ground, losing the ability to support loads, often due to natural ground properties.
Settlement risk: Granular soil
Settlement risk: Granular soil
Granular soils such as sand or gravel usually do not pose a great risk, but loose sand can create instability.
Clay soils
Clay soils
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Montmorillonite
Montmorillonite
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Subsidence in soluble rock
Subsidence in soluble rock
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Sinkhole
Sinkhole
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Longwall mining
Longwall mining
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Study Notes
- Subsidence and settlement are key concepts in ground engineering
'Settlement' vs. 'Subsidence'
- Settlement refers to the downward movement of a structure because of compression in the underlying soil, typically due to imposed loads
- The ground retains some load-bearing capacity during settlement
- Settlement often stems from the consolidation of clay soils
- Settlement can manifest uniformly or differentially due to factors like uneven loading or soil composition changes
- Subsidence indicates a failure in the ground, losing its ability to support loads
- Often a consequence of the ground's natural characteristics rather than external loads, though external factors can be triggers
- Ground material may displace into underground macrovoids (e.g., caves) or microvoids (e.g., voids in clay-based soils)
- Subsidence in solid rock requires a shear failure
- Geological maps help identify subsidence potential based on rock type
Settlement Potential by Ground Material
- Rock: Generally low settlement risk, but not immune to subsidence
- Granular soil (sand or gravel): Typically low concern for settlement, but loose sand and flooding can be destabilizing
- Cohesive soil (clay): Primary soil type prone to settlement
- Organic soil (peat): High void ratio makes it generally unsuitable for construction unless deep foundation piles are used
- Made ground (artificial soil and fill): Direct building is possible with low organic content after settling, but landfill settlement is hard to predict
Settlement in Clay Soils
- Clay soils are most prone to settlement due to consolidation
- High porosity and deformable clay mineral grains contribute to high compression potential under load
- Heavily populated regions with clay soils experience regional settlement and subsidence due to consolidation
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