Consolidation-of the law of life: advanced consolidation manager

Spring analogy

The process of consolidation is often explained with an idealized system composed of a spring, a container with a hole in its cover, and water. In this system, the spring represents the compressibility or the structure itself of the soil, and the water which fills the container represents the pore water in the soil.

The container is completely filled with water, and the hole is closed. (Fully saturated soil)
A load is applied onto the cover, while the hole is still unopened. At this stage, only the water resists the applied load. (Development of excess pore water pressure)
As soon as the hole is opened, water starts to drain out through the hole and the spring shortens. (Drainage of excess pore water pressure)
After some time, the drainage of water no longer occurs. Now, the spring alone resists the applied load. (Full dissipation of excess pore water pressure. End of consolidation)
Primary consolidation

This method assumes consolidation occurs in only one-dimension. Laboratory data is used to construct a plot of strain or void ratio versus effective stress where the effective stress axis is on a logarithmic scale. The plot's slope is the compression index or recompression index. The equation for consolidation settlement of a normally consolidated soil can then be determined to be:

$\delta_c = \frac{ C_c }{ 1 + e_0 } H \log \left( \frac{ \sigma_{zf}' }{ \sigma_{z0}' } \right) \$

where

δ_c is the settlement due to consolidation.

C_c is the compression index.

e₀ is the initial void ratio.

H is the height of the soil.

σ_zf is the final vertical stress.

σ_z0 is the initial vertical stress.

C_c can be replaced by C_r (the recompression index) for use in overconsolidated soils where the final effective stress is less than the preconsolidation stress. When the final effective stress is greater than the preconsolidation stress, the two equations must be used in combination to model both the recompression portion and the virgin compression portion of the consolidation process, as follows:

$\delta_c = \frac{ C_r }{ 1 + e_0 } H \log \left( \frac{ \sigma_{zc}' }{ \sigma_{z0}' } \right) + \frac{ C_c }{ 1 + e_0 } H \log \left( \frac{ \sigma_{zf}' }{ \sigma_{zc}' } \right)\$

where σ_zc is the preconsolidation stress of the

Secondary compression

Secondary compression is the compression of soil that takes place after primary consolidation. Even after the reduction of hydrostatic pressure some compression of soil takes place at slow rate.this is known as secondary compression.Secondary compression is caused by creep, viscous behavior of the clay-water system, compression of organic matter, and other processes. In sand, settlement caused by secondary compression is negligible, but in peat, it is very significant. Due to secondary compression some of the highly viscous water between the points of contact is forced out.

Secondary compression is given by the formula

$S_s=\frac{H_0}{1+e_0} C_{a} \log \left( \frac {t} {t_{90} } \right) \$

Where H₀ is the height of the consolidating medium
e₀ is the initial void ratio
C_a is the secondary compression index
t is the length of time after consolidation considered
t₉₀ is the length of time for achieving 90% consolidation

Consolidation-of the law of life

Saturday 1 September 2012

advanced consolidation manager

Spring analogy

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