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Soil structures by compaction; DDL

Short answer

Compaction on dry side yields flocculated structure (random edge-to-face), while wet side yields dispersed (face-to-face). The double diffuse layer is the negative clay surface with an adjacent diffuse cloud of cations in pore water.

Describe the types of soil structures based on the compaction process. Also, define double diffuse layer in regard to clay minerals.

Soil structures based on compaction

  • Flocculated structure (dry side of OMC): particles remain in random edge-to-face contact because there is not enough water to separate them; high strength, high permeability, high swelling potential.
  • Dispersed structure (wet side of OMC): more water increases repulsion, so particles rotate and align face to face; lower strength, low permeability, more shrinkage and less swelling.
  • Compaction with higher energy at the same water content increases the orientation (dispersion).

Double diffuse layer (DDL)

Clay particles carry a negative charge on their surfaces. In water they attract positive ions (cations) and polar water molecules. Close to the particle the cations are held strongly (adsorbed layer), and further away the concentration decreases gradually with distance, forming a diffuse layer of ions. The negative particle surface together with this diffuse cloud of positive ions is called the double diffuse layer. Its thickness decreases as the salt concentration and the valence of the cations increase.

✓ Answer checked by Claude Opus 5.5 (high effort)

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