At first we will define both terms consolidation and compaction of soil. Consolidation is a process in which saturated soil is compressed due to steady and static pressure. Compaction is a process in which with the help of mechanical pressing air present in void of soil is expelled resulting closely packed soil structure. Compacted soil has better shear strength and hence better bearing capacity and stability of soil. Both terms are very important in foundation engineering.
Consolidation and compaction are totally different process. Though both process results a reduction in volume, it is important to know the difference between them. These are:
a. Compaction reduces volume of soil by rapid mechanical methods like tamping, rolling and vibration; whereas consolidation process reduces volume gradually by static, sustained loading.
b. Compaction decreases volume by expelling air from partially saturated or dry soil; whereas consolidation process reduces volume by squeezing out water from saturated soil. In compaction process water content is not altered.
c. Compaction is a human generated pressing method to produce high unit weight of soil. Thus increasing other properties to have better founding soil. In contrast, consolidation is natural process where volume of saturated soil mass reduced by static loads from the weight of building or other structures that is transferred to soil through a foundation system.