consol1 - 53:030 Class Notes; C.C. Swan, University of Iowa...

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Period #15: Soil Compressibility and Consolidation (I) A. Motivation and Overview Our objective is now to understand how soils compress or consolidate with time after loads are placed on them. This a question of great importance when designing: a) foundations for all types of structures; b) landfills;or c) virtually anyother system that rests on soil. In studying the consolidation of soils there are two basic issues to be addressed: 1) Once a load is applied, how much settlement will occur? and 2) On what time scale will the settlement occur? A historic example of relevance is the Tower of Pisa. In this case, the builders did not understand either: how to compute soil settlements under structural loading; or how to compute the time scale on which settlements would occur. Consequently, over a time scale of centuries, the soil beneath this famous structure has developed very significant consolidation settlements. If unchecked, the structure would ultimately topple over. 1 53:030 Class Notes; C.C. Swan, University of Iowa
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B. Magnitude of Settlement/Consolidation in Soils Consider the following block diagram for a soil: For simplicity in treating the compression of soils, it isssumed that: a) the soil grains themselves are rigid and incompressible; and b) the change in volume of a soil is due to a re-arrangement of the soil grains, leading to a reduction of void volume. For most soils, these assumptions are quite valid. 2 53:030 Class Notes; C.C. Swan, University of Iowa Voids Solids V v or H v V s or H s V s + V v = V V v = eV s (1+e)V s = V V s = V/(1+e) H s + H v = H H v = eH s (1+e)H s = H H s = H/(1+e)
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53:030 Class Notes; C.C. Swan, University of Iowa When a soil is subjected to compressive stresses, there will be a reduction of volume. Most of the volume reduction comes from a reduction in void volume, as shown below. General Case
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consol1 - 53:030 Class Notes; C.C. Swan, University of Iowa...

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