- Geometric arrangement of soil particles with respect to one another is known as soil structure.
- Depending upon the particle size and mode of formation, the following types are found.
Single Grained Structure
- Found in coarse grained soils, like gravel, sand.
- The major cause for formation is gravitational force. Here the surface forces are negligible.
- Under the influence of gravitational forces, the grains will assume a particle to particle contact referred to as single grained structure.
- Single grained structure may be loose or dense as shown below.
- It is possible for fine sands or silts.
- Both gravitational force and surface force are responsible.
- Such a structure can support loads, only under static conditions.
- Under vibrations and shocks, the structure collapses and large deformations take place.
- This structure occurs in clays.
- Clay particles have a negative charge on surface and a positive charge on edges and flocculated structure occurs when there is an edge-to-face orientation.
- A flocculated structure is formed when there is a net attractive force between the particles.
- Soils with flocculent structure have a high void ratio and water content and, also have a low comprehensibility, a high permeability and high shear strength.
- A dispersed develops in clays that have been reworked or remolded.
- Remoulding converts ‘edge-to-face’ orientation to ‘faceto-face’ orientation.
- Dispersed structure is formed when there is a net repulsive force between particles.
- Have low shear strength, high compressibility and low permeability.
- A composite structure in the form of coarse grained skeleton or clay-matrix is formed when soil contains different types of soil particles.