Question

factors that influence consolidation characteristics of soil

Answer 1

Consolidation of soil is the process during which excess pore water is expelled out from a saturated clay mass due to application of external stress. Owing to the low permeability of clayey soils, consolidation is a time taking process and takes many years to complete. However consolidation causes a change in volume due to reduction in pore water or reduction in volume. The following are the consolidation characteristics which are required to measure the rate and amount of consolidation settlement :-

1) Coeffecient of compressibility : av = - ∆e/∆¶ where ∆e is change in void ratio and ∆¶ is change in vertical stress. Thus av is influenced by the type of soil structure and more dense the soil, lesser would be change in void ratio upon application of stress i.e. lesser would be it's compressibility.

2) Coeffecient of volume change : mv = av/(1+e) . Thus mv is influenced by the soil structure and the initial void ratio.

3) Coeffecient of consolidation : Cv = Tv d^2/ t where Tv is the time for given % of consolidation and is constant for all clays. d is length of drainage path and t is time period of consolidation. Thus Cv depends upon the permeability of soil because K= Cv* mv* Yw . It also depends upon the type of soil structure and the initial void ratio.

4) Compression Index : Cc = -∆e/(log((¶o + ∆¶)/¶o)). The type of soil structure. More the plasticity of clay more is Cc value. Also Cc value for stiff clay is higher than that of soft clays. Also the presence of organic matter results in an increase in Cc values.