Different methods are suggested to handle collapsible soil. In most problematic soils, it is the best way to remove all soils that can produce large foundation settlement and replaced by soil that is safe against settlement.
Does any soil type is safe? Same soil having in different state can be safe or unsafe. Say sand, cohesionless soil, is considered safe if they are in dense condition. Again sand having moisture and critical grading can suffer extensive settlement under vibration.
We know the vibration is usually considered from earthquake shaking, the settlement term is not perfect here it is better describe by liquefaction. We have published many posts about liquefaction in this blog; you can visit them from top menu and left menu.
A sand deposit that have no moisture or have relatively less moisture never subjected to liquefaction. So safe soil is relatively variable term depend on many factors. We use this term here as recompaction of sand is required to have a denser pack.
The collapse potential of collapsible soil can be reduced by using compaction grout. We know penetration of moisture result severe settlement in collapsible soil. So we can introduce water by flooding or forcing water to penetrate like providing wells to make the deposit collapse before foundation construction as the soil skeleton reach to equilibrium condition under this method.
Flooding techniques is also used in black cotton soil and effectiveness of this technique for both collapsible and expansive soil will be discussed in our upcoming posts. Dear reader we will learn about deep foundation and triggering mechanism of collapsible soil in next part of this topic; please stay with us.