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1、Shallow Foundation Settlement1SettlementImmediate 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(孔压消散） induced by external loading and consequently expulsi
2、on of water（脱水） 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（有机质土）)_For any of the above mentioned settlement calculations, we fi
3、rst need vertical stress increase in soil mass due to net load applied on the foundation23与时间有关的沉降4Elastic Settlement5Stress Due to a Concentrated Load6Stress due to a Circularly Loaded Area7Distribution of Stress(from a vertical line load)89Stress below a Rectangular Area10Stress Influence Chart112
4、:1 methodApproximate methods12Approximate methods13Average Vertical Stress IncreasesDue to a Rectangularly Loaded Area14Average Vertical Stress IncreasesDue to a Rectangularly Loaded Area15Average Vertical Stress Increasesin a given layer16Elastic settlement Based on theTheory of Elasticity17Elastic
5、 Settlement of Rectangular footings18Elastic Settlement on Saturated Clay1920Multi-layer systems212223Elastic Settlement24Elastic Settlement25Elastic Settlement26Elastic Settlement（静力触探试验）（扁铲试验）（标准贯入试验）27282930Elastic Settlement Using the Strain Influence Factor: Schmertman Method (1978)This is a se
6、miempirical method . q Z(1):Effective stress at a depth of z1 before construction of the foundation .31Elastic Settlement Using the Strain Influence Factor: Schmertman Method (1978)32Elastic Settlement Using the Strain Influence Factor: Schmertman Method (1978)33Elastic Settlement Using the Strain I
7、nfluence Factor: Schmertman & Hartman Method (1978)34轴对称平面应变35Procedure for Schmertman Method (1978)插值36Procedure for Schmertman Method (1978)37Procedure for Schmertman Method (1978)38Procedure for Schmertman Method (1978)39Notes on Schmertmann Method40Notes Cont41Notes Cont42Elastic Settlement Usin
8、g the Strain Influence Factor: Schmertman Method (1978)434445464748495051Primary ConsolidationExpulsion of water from soils accompanied by increase in effective stress and strengthAmount can be reasonably estimated based on lab data, but rate is often poorly estimated52Consolidation SettlementThis m
9、ethod makes use of the results of the conventional oedometer test（固结试验） 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 cons
10、olidation 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 settlements53Consolidation Settlement54Consolidation Settlement55C
11、onsolidation Settlement56Consolidation Settlement57Consolidation Settlement58Consolidation Settlement59Consolidation Settlement60Secondary ConsolidationAt the end of primary settlement, settlement may continue to develop due to the plastic deformation (creep) of the soil.The stage of consolidation i
12、s called secondary consolidation.61Secondary Compression Index62Field Load TestUltimate 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”)63Allowable Bearing Capacity forSandy Soil base
13、d on Settlement64Allowable Bearing Capacity forSandy Soil based on Settlement65Reliability of SettlementComputationsThe 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.66
