Foundation Engineering, Inc.Professional Geotechnical Services COMMON SOIL DESCRIPTION TERMS <br />EXPLORATION LOG KEY <br />Explanation of Common Terms Used in Soil Descriptions <br />Field Identification Cohesive Soils Granular Soils <br />SPT*Su** (tsf)Term SPT*Term <br />Easily penetrated several inches by fist.0 - 2 < 0.125 Very Soft 0 - 4 Very Loose <br />Easily penetrated several inches by thumb.2 - 4 0.125 - 0.25 Soft 4 - 10 Loose <br />Can be penetrated several inches by thumb with <br />moderate effort.4 - 8 0.25 - 0.50 Medium Stiff 10 - 30 Medium Dense <br />Readily indented by thumb but penetrated only with <br />great effort.8 - 15 0.50 - 1.0 Stiff 30 - 50 Dense <br />Readily indented by thumbnail.15 - 30 1.0 - 2.0 <br />Very Stiff > 50 Very Dense <br />Indented with difficulty by thumbnail.> 30 > 2.0 Hard <br />Term Soil Moisture Field Description <br />Dry Absence of moisture. Dusty. Dry to the touch. <br />Damp Soil has moisture. Cohesive soils are below plastic limit and usually moldable. <br />Moist Grains appear darkened, but no visible water. Silt/clay will clump. Sand will bulk. Soils are often at or near plastic <br />limit. <br />Wet <br />Visible water on larger grain surfaces. Sand and cohesionless silt exhibit dilatancy. Cohesive soil can be readily <br />remolded. Soil leaves wetness on the hand when squeezed. Soil is wetter than the optimum moisture content and <br />above the plastic limit. <br />Term PI Plasticity Field Test <br />Non-plastic 0 - 3 Cannot be rolled into a thread at any moisture. <br />Low Plasticity 3 - 15 Can be rolled into a thread with some difficulty. <br />Medium Plasticity 15 - 30 Easily rolled into thread. <br />High Plasticity > 30 Easily rolled and re-rolled into thread. <br />Term Soil Structure Criteria <br />Stratified Alternating layers at least ¼ inch thick. <br />Laminated Alternating layers less than ¼ inch thick. <br />Fissured Contains shears and partings along <br />planes of weakness. <br />Slickensided Partings appear glossy or striated. <br />Blocky Breaks along surfaces into smaller lumps <br />or blocks. Slickensides may be visible. <br />Lensed Contains pockets of different soils. <br />Term Soil Cementation Criteria <br />Weak Breaks under light finger pressure. <br />Moderate Breaks under hard finger pressure. <br />Strong Will not break with finger pressure. <br />* SPT N-value in blows per foot (bpf) <br />** Undrained shear strength