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Clayton Group Servic Page3 Standard Operating Procedure SOP-12 - Unified Soil Classification System consistency (degree of adhesion between particles that can resist deformation or rupture) of soil. Consistency can be changed by adding or decreasing the amount of water in the soil. Soil passes from a solid state when dry to semisolid, plastic, and liquid as water is added. The water content at each of these states can be used to assist in classifying soils as used in the USCS. The boundary between the solid and semisolid states is the shrinkage limit, or the water content below which the soil volume is not reduced. The plastic limit (PL) is the boundary between the semisolid and plastic states, and the liquid limit (LL) is the boundary between the plastic and liquid states. These limits are based on the water content at which these boundaries occur. The plasticity index (PI) is defined as the range of water 'content at which soil remains plastic. PI equals the liquid limit (LL) minus the plastic limit (PL). ORGANIC SOILS Organic soils are classified first by estimating the percentage of ono -organic fines and sand. Typically, the organic matter is present in very fine particles, and an estimate of it is difficult. If organic matter makes up between 18% and 36% of the soil, the soil is an organic silt or organic clay depending on the nature of the inorganic constituents. If the soil contains between 36% and 90% organic matter, the soil is designated as muck or peaty muck (OL or OH). If more than 90% organic matter present, it is called peat (Pt). DUAL CLASSIFICATION (BOUNDARY SOILS) Commonly, soils have the characteristics of two soil types, a classification is used which incorporates both groups. Some general rules here are: 1. Soils that are between sand and gravel, use the coarser designation first (for instance, GC -SC if clay is present or GM -SM if silt is the finer constituent). 2. For coarse-grained soils where the fine constituent falls between 5% and 12%, use the coarser title first (GW, GP, SW, or SP) and the finer title second (GM, GC, SM, or SC). The result would be GW -GM, GW -GC, GP -GC, GP -GM, GP -GC, SW -SM, SW -SC, SP -SM, or SP -SC. 3. If the fines in a coarse-grained soil plot within the hatchured zone on the plasticity chart (attached), the coarser symbol is used first followed by the finer symbol (for instance (GM -GC, SM -SC). 4. For fine-grained soils that plot within the hatchured zone or along the A-line of the plasticity chart (attached), the coarser symbol comes first (for example ML -CL, MH - CH). S:\Ermr\Proj\SOPS\SOP- 12.doc