Soil classification systems

The U.S. Department of Agriculture (USDA) soil classification system was developed for use in describing soils in which plants grow.63-66 The USDA system is now universally accepted within the United States and it should be used to describe soils used in ET landfill covers. 

Clay is the most important component of soil liners because the clay fraction of the soil ensures low hydraulic conductivity. In the United States, however, there is some ambiguity in defining the term clay because two soil classification systems are widely used. One system, published by the American Society for Testing and Materials (ASTM), is used predominantly by civil engineers.18 The other, the U.S. Department of Agriculture s (USDA s) soil classification system, is used primarily by soil scientists, agronomists, and soil physicists.19... 

The distinction between various particle sizes differs between ASTM and USDA soil classification systems (see Table 26.2). In the ASTM system, for example, sand-sized particles are defined as those able to pass a No. 4 sieve but not able to pass a No. 200 sieve, fixing a grain size of between 0.075 and 4.74 mm. The USDA soil classification system specifies a grain size for sand between 0.050 and 2 mm. 

Surficial deposits at XY are dominated by tills and colluvium, which have been locally reworked by alluvial and glacio-fluvial processes (Figs. 1 2a). On the transect reported herein, the depth of overburden varies from negligible on mountain sides to at least 5 m thick in central parts of the till plain in central valley areas (unknown maximum thickness). In the section of the traverse the XY ore zone is c. 10 m thick, and occurs below c. 3 m of colluvial overburden (Fig. 2). Pedogenesis is generally restricted to minor to moderate horizonation that has produced predominantly brunisols (Canadian Soil Classification System, Agri-Canada 1998). 

Beinroth, F. H. 1975- Relationships between U.S. soil taxonomy, the Brazilian soil classification system, and FAO/UNESCO soil units. In Soil Management in Tropical America, eds. E. Bomemisza and A. Alvarado (North Carolina State Univ., Raleigh), pp. 92-108. 

FIGURE 3-2 The soil classification system adopted by the U.S. Department of Agriculture. The components sand, clay, and silt are defined in terms of particle size (see Table 3-3 later). It should be noted that other textural classifications also are in use. 

Approximate equivalents in the comprehensive soil classification system are Chernozem and Chestnut, Mollisol Serozem, Aridisol Gray Forest, Alfisol. 

Culminating a long-term international effort, the Soil Survey staff of the Soil Conservation Service (U S. Department of Agriculture) developed a Comprehensive Soil Classification System (CSCS) for world soils (Soil Survey Staff 1975). The CSCS defines soil classes strictly in terms of soil morphology, rather than based on soil genesis. A brief explanation of the 10 soil orders in the CSCS is given in Table 7.4 (see also Bodek et al. 1988). Their temporal relationships are considered in Fig. 7.6. 

TABLE 7.4 A simplified description of the 10 soil orders as defined in the Comprehensive Soil Classification System (CSCS)... 

The Unified Soil Classification System, Technical Memorandum No. 3-357, Volume 1, March 1953, Waterways Experiment Station, Vicksburg, MD. 

During field survey the soils were described according to the German soil classification system KA 4 (AG Boden, 1994), which allows the classification of natural and anthropogenic soils based on genetic and morphologic features. 

ASTM. D2487. Standard Practice for Classification of Soils for Engineering Purposes (Unified Soil Classification System). American Society for Testing and Materials, Philadelphia, PA, p. 12. ASTM. D4767. Standard Test Method for Consolidated Undrained Triaxial Compression Test for Cohesive Soil. American Society for Testing and Materials, Philadelphia, PA, p. 14. 

ASTM. 2011. Standard Practice for Classification of Soils for Engineering Purposes-D2487. Unified Soil Classification System. American Society for Testing and Materials, Philadelphia, PA. 

Wagner, A.A. 1957. The use of the unified soil classification system by the bureau of reclamation. Proceedings of the 4th International Conference on Soil Mechanics and Foundation Engineering (London), 1 125. 

The soil fractions as described in Section 1.2 along with the description of natural properties (such as origin, colour, shape, etc.) did not help engineers to easily recognise the soil s suitability for roadworks. As early as 1928, the AASHTO developed a soil classification system for highway engineering. The system has been revised several times, and the 1945 version formed the basis of the existing soil classification system by AASHTO. 

A necessity was also recognised, more than 60 years ago, for runway pavements where the construction had to be more meticulous because of heavier loads applied to the pavement. As a consequence, in the 1940s, Casagrande developed another classification system for airfields (Taylor 1948). It was then named as Unified Soil Classification System... 

Since then, other countries adopted or developed their own soil classification systems. 

In this book, the AASHTO, the ASTM, the European and the UK soil classification systems will be presented in brief. 

The AASHTO soil classification system considers coarse soil materials (boulders, cobbles, gravels and sands) as those in which >65% of their mass is retained on a 0.0075 mm sieve. Fine soil materials (silts and clays) are those in which >35% of their mass passes through a 0.075 mm sieve. 

The European soil classification system distinguishes very coarse materials (boulders and cobbles) as those in which most particles are retained on a 63 mm sieve, coarse materials (gravels and sands) as those in which most particles are retained on a 0.063 mm sieve and fine soil materials as those with low plasticity and are dilatant (silts) or those that are plastic and non-dilatant (clays). 

The basic UK soil classification system is similar to the ASTM classification system. 

The soil classification system is described in detail in AASHTO M 145 (2012). 

The analytical table of the USCS or ASTM soil classification system (ASTM D 2487 2011) is given in Table 1.8 (see also Figure 1.5). 

The European soil classification system distinguishes the following groups ... 

The basic UK soil classification system is based on and very similar to USCS. Details can be found in Dumbleton (1981). 

Dumbleton M..]. 9 i. TheBritish Soil Classification Systems for Engineering Furposes Its Development and Relation to Other Comparable Systems. TRRL Report LR 1030. Crowthorne, UK Transport Research Laboratory. 

---