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B.4 Typical Procedures B.4.1 Soil Classification ' Soils are typically logged in conjunction with advancing boreholes and sampling subsurface soils. Although the guideline focuses on classifying soil samples obtained from boreholes, this particular procedure also applies to soils and sediments collected using other techniques (e.g., post hole ' digger, scoop, Van Veen sampler, and backhoe). The USCS categorizes soils into 15 basic groups, each with distinct geologic and engineering ' properties. The following steps are required to classify a soil sample: 1. Observe basic properties and characteristics of the soil. These include grain-size grading and ' distribution and influence of moisture on fine-grained soil. 2. Assign the soil a USCS classification and denote it by the standard group name and symbol. ' 3. Provide a written description to differentiate between soils in the same group, if necessary. Many soils have characteristics that are not clearly associated with a specific soil group. These soils ' might be near the borderline between groups, based on either grain-size grading and distribution, or plasticity characteristics. In this case, assigning dual group names and symbols might be appropriate (e.g., GW/GC or ML/CL). The three basic soil groups are: ' 1. Coarse-Grained Soils — For soils in this group, more than half of the material is larger than No. 200 sieve (0.074 mm). 2. Fine-Grained Soils — For soils in this group, one half or more of the material is smaller than No. 200 sieve (0.074 mm). 3. Highly Organic Soils—This group includes soils with high organic content, such as peat. ' Note: No. 200 sieve is the smallest size that can be seen with the naked eye. ' B.4.2 Classification of Coarse-Grained Soils Coarse-grained soils are classified on the basis of: ' 1. Grain size and distribution ' 2. Quantity of fine-grained material (i.e., silt and clay) 3. Character of fine-grained material Soil Investigation Work Plan, Stockton Railyard 2 g.iadminasstVobs120031032777.16_union pacific-sfockton yaro109-reporfs19.09_reporfslwmk plan_soilboringlappendiceslapp_b_boreholelogging.doc