Shallow Foundation
Settlement
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Settlement
Immediate Settlement: Occurs immediately after the construction. This is
computed using elasticity theory (Important for Granular soil)
Primary Consolidation: Due to gradual dissipation of pore pressure induced by
external loading and consequently expulsion of water from the soil mass, hence
volume change. (Important for Inorganic clays)
Secondary Consolidation: Occurs at constant effective stress with volume
change due to rearrangement of particles. (Important for Organic soils)
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For any of the above mentioned settlement calculations, we first need
vertical stress increase in soil mass due to net load applied on the
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foundation
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Elastic Settlement
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Stress Due to a Concentrated Load
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Stress due to a Circularly Loaded
Area
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Distribution of Stress
(from a vertical line load)
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Stress below a Rectangular Area
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Stress Influence Chart
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Approximate methods
2:1 method
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Approximate methods
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Average Vertical Stress Increases
Due to a Rectangularly Loaded Area
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Average Vertical Stress Increases
Due to a Rectangularly Loaded Area
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Average Vertical Stress Increases
in a given layer
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Elastic settlement Based on the
Theory of Elasticity
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Elastic Settlement of Rectangular
footings
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Elastic Settlement on Saturated
Clay
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Multi-layer systems
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Elastic Settlement
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Elastic Settlement
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Elastic Settlement
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Elastic Settlement
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Elastic Settlement Using the Strain Influence
Factor: [Schmertman Method (1978)]
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Elastic Settlement Using the Strain Influence
Factor: [Schmertman Method (1978)]
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Elastic Settlement Using the Strain Influence Factor:
[Schmertman Method (1978)]
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Elastic Settlement Using the Strain Influence Factor:
[Schmertman Method (1978)]
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Elastic Settlement Using the Strain Influence Factor:
[Schmertman & Hartman Method (1978)]
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Procedure for Schmertman Method (1978)
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Procedure for Schmertman Method (1978)
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Procedure for Schmertman Method (1978)
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Procedure for Schmertman Method (1978)
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Notes on Schmertmann Method
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Notes Cont…
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Notes Cont…
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Elastic Settlement Using the Strain Influence
Factor: [Schmertman Method (1978)]
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Primary Consolidation
• Expulsion of water from soils accompanied by
increase in effective stress and strength
• Amount can be reasonably estimated based
on lab data, but rate is often poorly estimated
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Consolidation Settlement
• This method makes use of the results of the conventional
oedometer test where the consolidation parameters of the soil
are measured.
• To compute the stress changes within the soil mass. The
stress changes are computed using a Boussinesqtype
approach assuming elasticity.
• The important parameter for consolidation settlement
calculation is the net effective stress change in the soil.
• Usually the settlements are calculated for the soil divided into
a number of sub-layers and the final total settlement is the
sum of individual sub-layer settlements
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Consolidation Settlement
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Consolidation Settlement
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Consolidation Settlement
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Consolidation Settlement
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Consolidation Settlement
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Consolidation Settlement
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Consolidation Settlement
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Secondary Consolidation
• At the end of primary settlement, settlement
may continue to develop due to the plastic
deformation (creep) of the soil.
• The stage of consolidation is called secondary
consolidation.
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Secondary Compression Index
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Field Load Test
• Ultimate load, allowable
load, and settlement can
be determined from a
field load test (ASTM D1194-72).
• The test plates are either
square (12”or 18”) or
circular (12” to 30”)
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Allowable Bearing Capacity for
Sandy Soil based on Settlement
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Allowable Bearing Capacity for
Sandy Soil based on Settlement
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Reliability of Settlement
Computations
• The predication is quite satisfactorily in
general.
• The predication is better for inorganic,
insensitive clays than for others.
• The time rate of consolidation settlement
is not well-predicted.
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