Reduction in volume of soil primarily due to squeezing out of water from the voids is called
- Aprimary consolidationCorrect
- Bsecondary consolidation
- Cplastic flow
- Dshrinkage
Solution
Concept
Primary consolidation is the volume decrease caused by water slowly flowing out of the voids as excess pore pressure dissipates.
Step-by-step solution
1. When load acts on saturated clay, excess pore water pressure develops. 2. Water slowly flows out of the voids, and the load shifts to the soil grains. 3. The volume decrease due to this expulsion of water is called primary consolidation. 4. Secondary consolidation happens after this, due to plastic readjustment (creep) of the soil grains. 5. Answer is (A).
Explanation
In saturated clay, the soil becomes smaller mainly because water is squeezed out of the pores over time. This process is called primary consolidation and is explained by Terzaghi's theory. Secondary consolidation comes later and is due to creep of the soil skeleton.
Why the other options are wrong
B: Secondary consolidation is due to plastic readjustment of grains after excess pore pressure is gone. C: Plastic flow is a deformation of the soil structure, not expulsion of water. D: Shrinkage is volume loss due to drying (evaporation), not due to load.
Shortcut
Water squeezed out means primary. Grains creeping means secondary.
Common mistake
Confusing consolidation (water squeezed out by load) with shrinkage (water lost by drying).
Correct answer: A) primary consolidation