Soils+Chap3 - SOIL IMPROVEMENT Soil Compaction Most sites...

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SOIL IMPROVEMENT Soil Compaction Most sites do not have suitable soil conditions to directly build on. Many projects require removal of soil from one place and its placement at another location. Some construction projects require mass grading, which may consist of cutting and removal of earth material from the hilltops and filling of the lower elevation areas and canyons in order to create level ground for housing developments and other structures. Some other projects are constructed mainly of earth materials including earth dams, levees, and embankments. Soil is the most abundant and in general, the most durable type of construction material. Soil is readily available at most sites or can be imported at relatively low cost. For buildings and earth structures to function properly, the supporting soils must be stabilized and have appropriate physical properties. The most common type of soil improvement is soil densification. This physical process reduces the volume of voids in soil and allows the solid particles into a denser state. Soil densification increases soil shear strength, decreases soil compressibility, and reduces the permeability of soil. In saturated soils, all voids are filled with water and for the densification to occur pore water has to escape from the soil mass. In saturated clay soils, the process of pore water migration due to construction loads can take several months to a few years and is referred to as soil consolidation and is discussed in chapter 6. In saturated granular soils, densification can take place quickly because of soil high drainage capacity. In partly saturated soils, where a good portion of the voids are occupied by air pockets, densification is readily achieved by forcing soil solids into a denser arrangement while compressing and forcing the air out of the soil mass. There are two categories of the soil densification process: surface compaction and deep ground densification. In surface compaction, soil from an excavated area is deposited at the project site in thin layers of no more than 0.2 m thick (known as lifts), then each layer is densified by heavy compaction equipment (e.g., a roller) moving over the deposited loose soil. This process is repeated until the final elevation is reached or the planned earth structure is shaped. The degree of compaction needed is site specific and depends on the project requirements and the specifications. The resulting compacted soil with the proper engineering properties is commonly referred to as engineered fill or structural fill. Soil compaction is usually the least expensive and by far the most widely used method of increasing the stability and supporting capacity of soils. The desirable features of a compacted fill can be achieved by proper selection of soil type and by appropriate fill placement. The two most desirable characteristics of a fill (high strength and low compressibility) are normally associated with high density or unit weight values that can be obtained with proper compaction. The quality of a compacted fill is examined by
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This note was uploaded on 05/22/2011 for the course CIVIL ENGI 171A taught by Professor Aryani during the Spring '11 term at CSU Sacramento.

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Soils+Chap3 - SOIL IMPROVEMENT Soil Compaction Most sites...

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