Soil settlement part 1

Soil deformation

When a soil mass is subjected to loading, such as loads due to embankment, soil settlement occurs. Regarding the time of soil deformation, settlements can be divided into 2 categories including elastic settlement and soil consolidation. Short term settlement occurs immediately after loading in all kinds of soils. Consolidation is a phenomenon that happens only for saturated and nearly saturated soils.

On the other hand, soil settlement can also be categorized into elastic and plastic settlements based on a structural point of view. Elastic deformation is reversible by unloading, while plastic deformation causes a permanent settlement. A brief summary of different technical terms has been categorized below:

  • Short term settlement
    • elastic settlement
    • non-elastic settlement due to air going out of soil
    • non-linear settlement due to water immediately going out of soil
  • long term settlement

2-1 primarily consolidation

2-2 secondary consolidation

For most of geotechnical projects we need to calculate the amount of elastic settlements as well as primary and secondary consolidations.

Soil consolidation

One-dimensional consolidation is divided into three steps including  initial compression, primary consolidation, and secondary consolidation. Since the compressibility of pore water is trivial, the amount of initial one-dimensional compression of saturated clay is negligible. Primary consolidation is usually identified by a  S-shaped curve to compare settlement vs. log time.  And finally soil secondary consolidation, also known as soil creep, happens over a long period of time.

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