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适用范围：<p>For many cohesionless, free-draining soils, the maximum dry unit weight is one of the key components in evaluating the state of compactness of a given soil mass that is either naturally occurring or is constructed (fill).</p> <p>Soil placed as an engineered fill is compacted to a dense state to obtain satisfactory engineering properties such as shear strength, compressibility, permeability, or combinations thereof. Also, foundation soils are often compacted to improve their engineering properties. Laboratory compaction tests provide the basis for determining the percent compaction and water content needed at the time of compaction to achieve the required engineering properties, and for controlling construction to assure that the required unit weights and water contents are achieved.</p> <p>It is generally recognized that percent compaction is a good indicator of the state of compactness of a given soil mass. However, the engineering properties, such as strength, compressibility, and permeability of a given soil, compacted by various methods to a given state of compactness can vary considerably. Therefore, considerable engineering judgment must be used in relating the engineering properties of soil to the state of compactness.</p> <p>Experience indicates that the construction control aspects discussed in 5.2 are extremely difficult to implement or yield erroneous results when dealing with certain soils. 5.4.1, 5.4.2, and 5.4.3 describe typical problem soils, the problems encountered when dealing with such soils, and possible solutions to these problems.</p> <p><span class="italic"><span class="italic">Degradation</span>8212;</span>Soils containing particles that degrade during compaction are a problem, especially when more degradation occurs during laboratory compaction than field compaction, as is typical. Degradation typically occurs during the compaction of a granular-residual soil or aggregate. When degradation occurs, the maximum dry unit weight increases so that the laboratory maximum value is not representative of field conditions. Often, in these cases, the maximum dry unit weight is impossible to achieve in the field.</p> <p>One method to design and control the compaction of such soils is to use a test fill to determine the required degree of compaction and the method to obtain that compaction, followed by the use of a method specification to control the compaction. Components of a method specification typically contain the type and size of compaction equipment to be used, the lift thickness, and the number of passes.</p></p> <p class="desc"> <span class="smallcap">Note</span> 48212;Success in executing the compaction control of an earthwork project, especially when a method specification is used, is highly dependent upon the quality and experience of the <span class=''unicode''>x201C;</span>contractor<span class=''unicode''>x201D;</span> and <span class=''unicode''>x201C;</span>inspector.<span class=''unicode''>x201D;</span></p> <p><span class="italic"><span class="italic">Gap Graded</span>8212;</span>Gap-graded soils (soils containing many large particles with limited small particles) are a problem because the compacted soil will have larger voids than usual. To handle these large voids, standard test methods (laboratory or field) typically have to be modified using engineering judgment.</p> <p><span class="italic"><span class="italic">Gravelly Soils Possessing Low Angularity and High Percentage of Fines</span>8212;</span>Gravelly soils possessing low angularity and a high percentage of fines can lead to poor results for dry unit weight when using the wet/saturated method. However, when water contents at the time of compaction are near saturation with no free water, the dry unit weight achieved may result in a higher value than that from the dry method. Ultimately, during densification, the material may reach a saturated state. Therefore, for these soils, a water content of 1 o......<p......