Soil Classification Methods PDF

Soil Classification Geofisika Teknik dan Lingkungan Early Development of Soil Classification C.F. Marbut strongly emphasized that the classification of soils should be based on morphology instead of on theories of soil genesis, because theories are both ephemeral and dynamic. He perhaps o...

Soil Classification Geofisika Teknik dan Lingkungan Early Development of Soil Classification C.F. Marbut strongly emphasized that the classification of soils should be based on morphology instead of on theories of soil genesis, because theories are both ephemeral and dynamic. He perhaps overemphasized this point because some scientists assumed that soils had certain characteristics without ever actually examining them. Marbut stressed that examination of the soils themselves was essential in developing a system of soil classification and in making usable soil maps. However, Marbut's work reveals his personal understanding of the contributions of geology to soil science. His soil classification of 1935 relied heavily on the concept of a "normal soil,” the product of equilibrium on a landscape where downward erosion keeps pace with soil formation. Continued work in soil classification by the U.S. Department of Agriculture (USDA) culminated in the release of a new system published in the 1938 Yearbook of Agriculture in the chapter "Soil Classification" (Baldwin et al., 1938). Early Development of Soil Classification In both the early classification developed by Marbut and the later 1938 classification developed by USDA, the classes were described mainly in qualitative terms. Because the central concept of each class was described but the limits between classes were not, some soils seemed to be members of more than one class. The classes were not defined in quantitative terms that would permit consistent application of the system by different scientists. Neither system definitely linked the classes of its higher categories, which were largely influenced by the genetic concepts initiated by the Russian soil scientists, to the soil series and their subdivisions that were used in soil mapping in the United States. Both systems reflected the concepts and theories of soil genesis of the time, which were themselves predominantly qualitative in character. Modification of the 1938 system in 1949 corrected some deficiencies but also illustrated the need for a reappraisal of concepts and principles. One continuing problem was that a scientist required knowledge about the genesis of the soil to classify it. This information was often lacking or was disagreed upon by soil surveyors. It was determined that a new classification system was required, one that could be applied consistently by an increasingly large and varied cadre of soil surveyors Soil Classification Methods The soil classification methods were developed step by step with different ideas In early days soil was classified depending on its composition and their weight related to total mass. Then soil was classified depending on texture which was finally developed to triangular classification diagram method. But Geo technicians found that this method is more suitable for agriculture than Geo technical engineering. Finally, Sir Arthur Casagrande, classified the soil depending on size distribution and consistence of soil particles. With some development such as considering the mechanical properties of soil to the method of Airfield Classification System by Arthur Casagrande, the British soil classification system was introduced. Soil Classification Methods Soil classification systems can be divided into two main groups, one for engineering purposes and another for soil science. For engineering purposes, the following are the most used classification systems (Das 2009): USDA USCS AASHTO (United States Department (Unified Soil Classification (American Association of of Agriculture) System) State Highway and Transportation Officials) Based on particle size Based on particle size Based on particle size distribution distribution, liquid limit, soil distribution and soil plasticity, and organic matter plasticity concentrations Commonly used because Widely used by geotechnical Used mostly by state and of its simplicity engineers county highway departments 1. USDA Soil Classification One of the most widely used soil classification systems, the USDA textural classification, which the USDA adopted in 1938 (USDA 1987), is based solely on grain size distribution In agriculture, textural classification is used to determine crop suitability and to approximate the soil’s response to environmental and management conditions, such as drought or calcium requirements The following are the primary classifications: Sand—particle sizes from 2.0 to 0.05 mm in diameter Silt—particles sizes from 0.05 to 0.002 mm in diameter Clay—particles smaller than 0.002 mm in diameter This is further refined for a total of 12 classes. The classes are often displayed on what is known as the USDA triangle 1. USDA Soil Classification 2. USCS Soil Classification The most used soil classification system among engineers is USCS. It was originally developed by Casagrande (1948) for use in the airfield construction works undertaken by the Army Corps of Engineers during World War II This system classifies soils into two broad categories: a. Coarse-grained soils that are gravelly and sandy in nature with less than 50% passing through the No. 200 sieve. The group symbol start with a prefix of G or S. G stands for gravel or gravelly soil, and S for sand or sandy soil. b. Fine-grained soils are with 50% or more passing through the No. 200 sieve. The group symbols start with prefixes of M, which stands for inorganic silt, C for inorganic clay, or O for organic silts and clays. The symbol Pt is used for peat, muck, or other highly organic soils 2. USCS Soil Classification This system also uses other symbols as:  W—well graded  P—poorly graded  L—low plasticity (liquid limit less than 50)  H—high plasticity (liquid limit more than 50) For proper classification according to this system, some or all of the following information must be known: a. Percent of gravel—that is, the fraction passing the 76.2-mm sieve and retained on the No. 4 sieve (4.75-mm opening) b. Percent of sand—that is, the fraction passing the No. 4 sieve (4.75- mm opening) and retained on the No. 200 sieve (0.075-mm opening) c. Percent of silt and clay—that is, the fraction finer than the No. 200 sieve (0.075-mm opening) d. Uniformity coefficient (Cu) and the Coefficient of gradation (Cc) e. Liquid limit and plasticity index of the portion of soil passing the No. 40 sieve Pass sieve no.200 50% Pass sieve no.200 ≥ 50% Pass sieve no.200 ≥ 50% Untuk klasifikasi tanah berbutir halus dan fraksi halus dari tanah berbutir kasar Cu = koefisien keseragaman Cc = koefisien kelengkungan Diameter butiran Dimana 60% dari total butiran lolos / lebih kecil dari diameter tersebut Diameter butiran Dimana 30% dari total butiran lolos / lebih kecil dari diameter tersebut Diameter butiran Dimana 10% dari total butiran lolos / lebih kecil dari diameter tersebut 3. AASHTO Soil Classification The ASSHTO system is used mostly by state and county highway departments Soil is classified into seven major groups: A-1 through A-7 Soils classified under categories A-1, A-2, and A-3 are granular materials of which 35% or less of the particles pass through the No. 200 sieve Soils of which more than 35% of the particles pass through the No. 200 sieve are classified using categories A-4, A-5, A-6, and A-7. These soils are mostly silt and clay-type materials 3. AASHTO Soil Classification This classification system is based on the following criteria: Grain size: Gravel : fraction passing the 75-mm sieve and retained on the No. 10 (2- mm) U.S. sieve Sand : fraction passing the No. 10 (2-mm) U.S. sieve and retained on the No. 200 (0.075-mm) U.S. sieve Silt and clay : fraction passing the No. 200 U.S. sieve Plasticity: The term silty is applied when the fine fractions of the soil have a plasticity index of 10 or less. The term clayey is applied when the fine fractions have a plasticity index of 11 or more. If cobbles and boulders (size larger than 75 mm) are encountered, they are excluded from the portion of the soil sample from which classification is made. However, the percentage of such material is recorded. Summary