2012GeomechLecture1 (3)

2012GeomechLecture1 (3) - Compaction Objectives Compaction...

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Unformatted text preview: Compaction Objectives Compaction • Many types of earth construction, such as dams, retaining walls, highways, and airport, require man-placed soil, or fill. To compact a soil, that is, to place it in a dense state. • The dense state is achieved through the reduction of the air voids in the soil, with little or no reduction in the water content. This process must not be confused with consolidation, in which water is squeezed out under the action of a continuous static load. Objectives: (1) Decrease future settlements (2) Increase shear strength (3) Decrease permeability (From Lambe, 1991; Head, 1992) General Compaction Methods Coarse-grained soils Fine-grained soils • Hand-operated vibration plates • Motorized vibratory rollers • Rubber-tired equipment • Free-falling weight; dynamic compaction (low frequency vibration, 4~10 Hz) • Falling weight and hammers • Kneading compactors • Static loading and press • Hand-operated tampers • Sheepsfoot rollers • Rubber-tired rollers Laboratory Field Vibration • Vibrating hammer (BS) (Holtz and Kovacs, 1981; Head, Kneading Elephants and Compaction Heavy Weight Question? Soils under elephants are not always well compacted. Why? What is compaction? A simple ground improvement technique, where the soil is densified through external compactive effort. + water = Compactive effort Compaction Curve Water content Dry density ( ρ d ) optimum water content ρ d, max Soil grains densely packed- good strength and stiffness- low permeability Compaction Curve What happens to the relative quantities of the three phases with addition of water ? Water content Dry density ( ρ d ) soil water air difficult to expel all air lowest void ratio and highest dry density at optimum w Zero Air Void Curve All compaction points should lie to the left of ZAV curve- corresponds to 100% saturation Water content Dry density ( ρ d ) Zero air void curve (S=100%) s w s d wG G + = 1 : Eq ρ ρ S<100% S>100% (impossible) Effect of Compactive Effort Increasing compactive effort results in: E 1 E 2 (>E 1 ) Lower optimum water content Higher maximum dry density Water content Dry density ( ρ d ) Compaction and Clay Fabric Higher water content or lower compactive effort gives more dispersed fabric. more dispersed fabric more dispersed fabric Water content Dry density ( ρ d ) Line of Optimum Compaction Water content Dry density ( ρ d ) Compaction curves for different efforts Line of optimum Laboratory Compaction Origin The fundamentals of compaction of fine-grained soils are relatively new. R.R. Proctor in the early 1930s was building dams for the old Bureau of Waterworks and Supply in Los Angeles, and he developed the principles of compaction in a series of articles in Engineering News-Record. In his honor, the standard laboratory compaction test which he developed is commonly called the Proctor test ....
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2012GeomechLecture1 (3) - Compaction Objectives Compaction...

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