Soil Mechanics: Cohesion and Stresses

Cohesion:

it is the force of attractioon between the particles binding them togeth er. cohesion is present in clays and silts but is n ormally absent in sands and gravels.Cohesio n (C), is a measure of the forces that cement particles of soils

Angle of Repose determ ined by:

·        Particle size (hig her for large particles)

·        Particle shape (higher for angular shapes)

·        Shear strength (h igher for higher shear strength)

Stresses:

Gravity generates stresses (force per unit area) in the ground at different points. Stress on a plane at a given point is viewed in terms of two components:

1 Normal stress (?): acts normal to the plane and tend s to compress soil grains towards each oth er (volume change)

2Shear stress (?): a cts tangential to the plane and tends to slide grains relative to each other (distortion and ulti mately sliding failure)

3Factors Influenci ng Shear Strength:

The shearing strength is affected by:

·        Soil composition: mineralogy, grain size and grain size distribution, shape of particles, pore fl uid type and content, ions on grain and in pore fluid.

·        Initial state: State can be describe by terms such as: loose, dense, over-consolidated, no rmally consolidated, stiff, soft, etc.

·        Structure: Refers to the arrangement of particles within the soil mass; the manner in whic h the particles are packed or distributed. Feaatures such as layers, voids, pockets, cementation, etc, are part of the structure.

4 Formulation of Shear Strength of Soil:

·        In reality, a com plete shear strength formulation would acco unt for all previously stated factors.

Soil behavior is quite complex due to the possible variables s tated.