Foundation, Concrete and Earthquake Engineering

How do Fluctuating Loads Result Long-Term Foundation Settlement in Cohesionless Soil?

Dear reader in previous post we have learnt that cohesionless soil usually not susceptible to long-term settlement in foundation soil. But these have some exceptions; we, here, will discuss about influence of fluctuating loads on foundation settlement on cohesionless soil.

Say a storage tank like oil tanks which have numerous filling and emptying cycle over their life. Consider a foundation, soil sand but in loose state over which this cycles are done. What will happen? The loading unloading cycles result slow and gradual densification of sand.

Foundation Settlement of Wheat silo on sand
Thus long-term settlement is observed. These may happen in silos that are used for food grain, coal and raw materials for industrial production. Dear reader we will discuss about structural design of silo of both concrete and steel in our upcoming post.

The structures that impose low fluctuating loads on foundation, it is observed that after 30 years of construction settlement under footing may be of up to 1.5 times that of immediate after completion of structure.

The structures imposing heavy fluctuating loads, suffers up to 2.5 times that of immediate after completion of structure (post construction settlement)

The values provided above are upper limit of settlement, the actual value of settlement depend on following factors:

  1. Number of filling emptying cycles
  2. Magnitude of fluctuating load.
  3. Density of foundation soil (sand weather Loose or dense)

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