1 Shallow Foundation Settlement. 2 Settlement Immediate Settlement: Occurs immediately after the...
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Transcript of 1 Shallow Foundation Settlement. 2 Settlement Immediate Settlement: Occurs immediately after the...
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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)________________________________________________________________For any of the above mentioned settlement calculations, we first need vertical stress increase in soil mass due to net load applied on the foundation
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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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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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Field Load Test
• Ultimate load, allowable load, and settlement can be determined from a
field load test (ASTM D-1194-72).
• The test plates are either square (12”or 18”) or circular (12” to 30”)