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Soil gradation is a classification of a coarse-grained soil that ranks the soil based on the different particle sizes contained in the soil.〔Holtz, R. and Kovacs, W. (1981), ''An Introduction to Geotechnical Engineering'', Prentice-Hall, Inc. ISBN 0-13-484394-0〕 Soil gradation is an important aspect of soil mechanics and geotechnical engineering because it is an indicator of other engineering properties such as compressibility, shear strength, and hydraulic conductivity. In a design, the gradation of the in situ or on site soil often controls the design and ground water drainage of the site. A poorly graded soil will have better drainage than a well graded soil.〔"(ASTM D6913 - 04(2009) )".''ASTM International''. ASTM International. 1996-2009. October 13, 2009.〕 Soil is graded as either well graded or poorly graded.〔“(Soil Gradation )”. ''Integrated Publishing''. Integrated Publishing. 2003-2007. October 13, 2009.〕 ref Dr.B.C PUNMIA- Soil Mechanics and Khanna civil engineering hand book ,Delhi. Soil gradation is determined by analyzing the results of a sieve analysis 〔“(Sieve Analysis and Particle Analysis )”. ''Grand Solution Manual''. SJ Soft Technologies. 2008. October 13, 2009.〕 〔“(Sieve Analysis )”. ''Integrated Publishing''. Integrated Publishing. 2003-2007. October 13, 2009.〕 or a hydrometer analysis.〔 The process for grading a soil is in accordance with either the Unified Soil Classification System or the AASHTO Soil Classification System. Gradation of a soil is determined by reading the grain size distribution curve produced from the results of laboratory tests on the soil. Gradation of a soil can also be determined by calculating the coefficient of uniformity, Cu, and the coefficient of curvature, Cc, of the soil and comparing the calculated values with published gradation limits.〔〔Coduto, Donald P. Foundation Design Principles and Practices (2nd Edition). 02nd ed. Upper Saddle River: Prentice Hall, 2000. Print. ISBN 0-13-589706-8〕 == Soil Gradations == Soil gradation is a classification of the particle size distribution of a soil. Coarse-grained soils, mainly gravels or sands, are graded as either well graded or poorly graded. Poorly graded soils are further divided into uniformly-graded or gap-graded soils. Fine-grained soils, mainly silts and clays, are classified according to their Atterberg limits.〔〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Soil gradation」の詳細全文を読む スポンサード リンク
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