07 - Stress Distribution & Settlement Continued.pdf

07 - Stress Distribution & Settlement Continued.pdf -...

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Daniel Rosenbalm, Ph.D., P.E. Geotechnical Services Manager CEE 452 Foundations
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Components of Settlement Volume Change (Compression) 1-Dimensional consolidation, d c Due to pore water pressure dissipation (“drained” settlement) Distortion (Shear) Undrained settlement, d d Lateral spreading c d d d d
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Settlement Computation Footings on a uniform layer of sand Elasticity theory Immediate or distortion settlement Footings on clay Elasticity theory for undrained distortion (shear) settlement Consolidation theory for drained settlement (volume change)
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Settlement Calculation on Clays
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Consolidation Settlement Using Elastic Stresses Classical Approach Consolidation settlement of cohesive soil layer at depth beneath footing Gets added to immediate (undrained) settlement P Gravel Normally Consolidated Clay Rock
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Consolidation Settlement Using Elastic Stresses 1. Evaluate initial vertical stress Geostatic stress, s z0 (plus any existing building loads) 2. Calculate vertical stress change at representative points using theory of elasticity Ds z 3. Calculate final vertical stress 4. Calculate vertical strain and settlement at center line due to Ds z using consolidation equations 5. Adjust for foundation rigidity
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Consolidation Settlement 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 1.2 10 100 1000 C r C c s c (s z ) 0 (s z ) f e s v r c = S log + log C r H 1+ e o C c H 1+ e c s c (s z ) o (s z ) f s c
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Adjustment for Foundation Rigidity r = r c x r where: r c = consolidation settlement r = rigidity factor (r < 1)
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Rigidity Factor, r Perfectly flexible load, e.g. Steel tanks, earth fill: r = 1 Perfectly rigid foundation, e.g. Concrete footing: r = 0.85 Intermediate foundations, e.g. Mat foundations: r = 0.9 Note: DO NOT use the 1H:2V projection method for stress increment with this approach
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Reason for Flexibility Factor Infinite Stresses Under Rigid Corners
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