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the artificial alteration of soil properties for construction purposes without effecting a radical change in the soil’s physical or chemical state. Soil compaction consists in the reciprocal shifting of soil particles, as a result of which the number of contacts between particles per unit volume is increased; the increase is due to the redistribution of particles and to the penetration of smaller particles into the interstices between larger ones under the action of mechanical forces applied to the soil.
Soil compaction is used mainly to ensure prescribed soil density and thus to decrease the magnitude and unevenness of subsequent settling of beddings and earthworks. Soil compaction results in increased soil stability and decreased compressibility and filtering capacity. When water-saturated soils are compacted, water is squeezed through the interparticle pore space. The degree of soil compaction is measured by the density of the soil, that is, by the ratio of volume to weight of the soil with all moisture removed. Soil is conventionally termed compacted when this ratio is no less than 1.6 tons per m3.
Soil compaction is widely practiced in the construction of hydraulic engineering structures, roads and highways, railroads, and earthworks associated with the preparation of ground for urban construction. The technique is also used in filling in foundation pits and trenches after foundations are laid and in laying underground communications lines and pipelines. Soil compaction is especially effective in preparing beddings under buildings and structures erected on soils with nonuniform compressibility—fill, ground subject to subsidence, and water-saturated soils.
Soil may be compacted on the surface or to some given depth. Road rollers, compactors, and vibration plates are used for surface compaction. Deep compaction can be achieved through the use of vertical sand drains and piles and by means of the Vibroflotation process. Surface compaction is performed when the soil moisture level is optimum; if the natural moisture level is less than optimum, the soil is moistened prior to compaction. Probing and other subsurface exploration methods may be used to monitor the quality of soil compaction. Soil samples may also be taken from the compacted layer in order to test stability and deformation and filtration properties. (See alsoSOIL STABILIZATION.)
REFERENCENekliudov, M. K. Spravochnoe posobie po mekhanizirovannomu uplotneniiu gruntov. Moscow, 1965.
M. IU. ABELEV