SOIL SETTLEMENTS: PART 1 - INTRO

Causes of soil settlement

In engineering calculation, it is accepted that settlement due to applied pressure is composed of 3 parts:

1. Distortion because of elastic stresses (Se)

2. Primary consolidation due to squeezing out of pore water (Sc)

3. Secondary compression due to creep in soil structure (Ss)

Is consolidation only time-dependent?

Primary consolidation in sand happens immediately after loading due to its high permeability. In contrast to clay, primary consolidation takes a long time to complete. Secondary compression will take some time for all types of soil. It's not years but decades.

What is the most important part?

Distortion settlement is negligible in both sand and clay. Primary consolidation plays the most crucial role in settlement analysis. Secondary compression can be significant in clay.

How can we compute primary consolidation?

Primary consolidation is computed by the e-log p curve. The Cc and Cr coefficients value must be obtained from the 1D consolidation test (valid for clayey soils only). From the test curve, the pre-consolidation stress can be found, and then the total consolidation settlement is calculated from

Ref.

DP Coduto, Foundation Design: Principles and Practices, 2nd ed., Prentice Hall, 2001