foundation system of burj al arab

Rainfall and Settlement Behavior of Foundation Soil, Loess (Part-2)

Dear reader in previous part we have learnt that rainfall infiltrates quickly into loess soil deposit due to its fractured structure. We know that horizontal permeability of loess soil is less than vertical permeability which is an exception in soil mechanics.

The moisture content of loess soil (in-situ) lies between (4-49)%. Now we are going to summarize some findings about loess that correlates moisture content, density and bearing capacity of this soil.

Bandyopadhyay (1983), Holland and Gibbs (1960):

Saturated loess soil under rainfall
They provided settlement relation with density:

-Settlement is suspected to be large when dry unit weight is less than 80 pcf

-Settlement is suspected to be small when dry unit weight is greater than 90 pcf

From this finding Bandyopadhyay concluded that such soils that have low in-situ densities and also low clay cementation are considered high consolidation and collapse susceptibility.

A dry loess soil may have bearing capacity more than 10 Ksf which may fall down to 0.5 Ksf under saturation.

Now some points about moisture and density correlation:

Holland and Gibbs:

At moisture content less than 10 percent, dry density reached its maximum value and as discussed above highest resistance against settlement is expected.

Moisture content (10-15) % ---soil shows moderate high strength

Moisture content around 20% ---strength decreased gradually

Moisture content > 20%----this moisture content is considered high for loess soil that leads to full consolidation under load.

Moisture content 35%---soil becomes saturated.

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