10 Compressibility of Soil A stress increase caused by thc construction of foundationsor other loacls comprcsses soil layers. The compression is caused by (a) deformation of soil particles. (b) reloca- tions of soil particles, and (c) expulsion of water or air from thc void sperct;s. In gcn- eral, the soil settlementcaused by loads may be divided into three brcladcatcgorics: l. Immediutesettlemcnt (or elastic settlemcnt). which is causcdby thc elasticde- formation of dry soil and of moist and saturated soils without any change in the moisture content.Immcdiatc settlement calculations are gcnerally based on equationsderived from the thcory of elasticity. 2. Primarv consolidation settlement, which is the result of a volume changein saturated cohesive soilsbecause of expulsion ol'thc water that occupies the void spaces. 3. Secondury consoliclatkntsettlemanL which is observcd in saturatcd cohesive soilsand is the resultof the plastic adjustment of soil fabrics. It is an additional form of compression that occursat constanteffective strcss. This chapter presents the fundamcntal principlcs for cstimating thc immcdiate and consolidationsettlemenls of soil laycrs under supcrimposed loaclings. The total settlementof a foundation can then be given as 57:S,+S.+S, where Sr : total settlement S,. : primary consolidationsettlement ,S. : secondary consolidationsettlemcnt S,, : immediate scttlement When foundations are constructed on very compressibleclays, the consolidation settlementcan be several times greater than the immediate scttlement. IMMEDIATE SETTLEMENT Contact Pressureand Settlement Profile Immediate, or elastic, settlementof foundations (S") occursdirectly after the appli- cation of a load, without a changein the moisture content of the soil. The masnitude 10.1
Compressibility of Soil
Jun 29, 2023
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