SHEAR STRENGTH

Shear strength of soil is its ability to resist sliding along internal surface within mass. The force causing this type of sliding is called shear force and the resistance offered just before failure per unit area is termed shear strength. * Natural slopes of hillsides, slopes of earth dam, slopes of a cut and bearing capacity of soil depend upon the shearing strength. * Shear strength is mainly due to 1. Internal friction due to interlocking of particles and friction between individual particles of their contact surfaces. 2. Cohesion, which is due to interparticle forces which tend to hold the particles in soil mass. * Coulomb’s equation for shear strength is t = c + s tan f where s = Normal stress on the failure plane c = Cohesion f = Angle of internal friction * Angle of internal friction depends upon 1. Shape of particles 2. Surface roughness 3. Type of interlocking 4. Lateral pressure 5. State of packing The angle of internal friction is 25° to 30° for loose sand and 32° to 37° fo