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• Chandan Blee

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Cohesion of Soil Cohesive soils are clay type soils. Cohesion is the force that holds together molecules or like particles within a soil. Cohesion, c, is usually determined in the laboratory from the Direct Shear Test. Unconfined Compressive Strength, Suc, can be determined in the laboratory using the Triaxial Test or the Unconfined Compressive Strength Test. There are also correlations for Suc with shear strength as estimated from the field using Vane Shear Tests c = Suc/2 Where: c = cohesion, kN/m2 (lb/ft2), and Suc = unconfined compressive strength, kN/m2 (lb/ft2).

Guide for Consistency of Fine-Grained Soil, NAVFAC 7.02 SPT Penetration Estimated (blows/ foot) Consistency Suc (tons/ft2) 30

Very Soft Soft Medium Stiff Very Stiff Hard

4

Empirical Values for Consistency of Cohesive Soil, (from Foundation Analysis, Bowels) SPT Penetration Estimated (blows/ foot) Consistency Suc (kips/ft2) 0-2 2-4 4-8 8 - 16 16 - 32 >32

Very Soft Soft Medium Stiff Very Stiff Hard

0 - 0.5 0.5 - 1.0 1.0 - 2.0 2.0 - 4.0 4.0 - 8.0 >8

Typical Strength Characteristics (from Lindeburg, Civil Engineering Reference Manual for the PE Exam, 8th ed.) USCS Soil c, as compacted c, saturated 2 2 Group (lb/ft ) (lb/ft ) GW GP GM GC SW SP SM SM-SC SC ML ML-CL CL OL MH CH

0 0 1050 1050 1550 1400 1350 1800 1500 2150

0 0 420 300 230 190 460 270 420 230