Dear reader we were discussing about long-term settlement of foundation supported on cohesionless soil. At first we will discuss about collapsible soil.
Our concern is collapsible soils that are cohesionless. We have learnt earlier in this blog that collapsible soil suffer large settlement when water infiltrates through the soil under no or small compressive load.
In most cases soil deposit are stratified and different layer, as usual, may have different degree of settlement, here we use the term collapse potential as discussed in our previous post-about collapse potential of collapsible soil.
Total settlement of multiple collapsible layers of soil is derived by adding collapse value of different layers.
Seismic shaking due to seismic waves traveling through soil layers or along ground surface, may also result densification of cohesionless soil, provided that the soil layer must be in saturated condition and be in loose conditions. This phenomenon is known as liquefaction we have discussed many posts about cause, potential, triggering and mitigation of liquefaction susceptible soil in previous post.
Another source of such settlement is vibration from machinery. Let us consider a machine like printing press supported on foundation soil of this type, here also loose sand is more susceptible. The densification of loose deposit is done slowly by vibration and this is also a long-term settlement.
Fluctuation of loads
These types of cases occur when loading and unloading of material results fluctuation of loads on cohesionless soil. Dear reader in our last part we have discussed this elaborately, please read this post for more clarification.