July 8, 2020

Soil Structure

Soil Structure  

  1. Geometric arrangement of soil particles with respect to  one another is known as soil structure.  
  2. Depending upon the particle size and mode of formation,  the following types are found.  

Single Grained Structure  

  1. Found in coarse grained soils, like gravel, sand.  
  2. The major cause for formation is gravitational force. Here  the surface forces are negligible.  
  3. Under the influence of gravitational forces, the grains will  assume a particle to particle contact referred to as single  grained structure.  
  4. Single grained structure may be loose or dense as shown  below. 

Honey-comb Structure 
  1. It is possible for fine sands or silts.  
  2. Both gravitational force and surface force are responsible.  
  3. Such a structure can support loads, only under static  conditions.  
  4. Under vibrations and shocks, the structure collapses and  large deformations take place. 
Flocculated Structure  
  1. This structure occurs in clays.  
  2. 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.  
  3. A flocculated structure is formed when there is a net  attractive force between the particles.  
  4. 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. 
Dispersed Structure 
  1. A dispersed develops in clays that have been reworked or  remolded. 
  2. Remoulding converts ‘edge-to-face’ orientation to ‘faceto-face’ orientation. 
  3. Dispersed structure is formed when there is a net repulsive force between particles.  
  4. Have low shear strength, high compressibility and low  permeability.  
Composite Structure  
  1. A composite structure in the form of coarse grained skeleton or clay-matrix is formed when soil contains different  types of soil particles. 

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