(i) Relative Compaction :– The dry density of soil in the fold expressed as a percentage the density of a soil after it has been subjected to a standard amount compaction.

(ii) Placement water Content :– The water content used in the field compaction is called the placement water content which may be equal to, lesser than or higher than the optimum water content.

Factors affecting Compaction :–

(1) Water content : →

(a) Proper control of moisture content in soil is necessary for achieving desired density.

(b) Maximum density with minimum compacting effort can be achieved by compaction of soil
near it's OMC.

(c) In the field, the natural moisture content (NMC) of soil is either less than OMC or above OMC.

(d) If with sprinkler attached to water tanker and mixed with soil by motor grade for uniform moisture content.

(e) When NMC of the soil is more than OMC, it is required to be dried by aeration to reach up to OMC.

(2) Amount of Compaction : →

(a) The amount of compaction greatly affects the maximum dry density and optimum water content of a given soil.

(b) The effect of increasing the compactive energy results in the increase of maximum dry density and reduction in OMC.

(c) However, the increase in maximum dry density does not have a linear relationship with increase of compactive effort.

(3) Method of compaction : →

(a) The density obtained during compaction for a given soil greatly depends on type of
compaction or the manner in which the compactive effort is applied.

(b) The various variables to this aspect are :

(i) Weight of the Compactive equipment

(ii) The manner or operation such aa dynamic or impact, static, kneading or rolling.

(iii) Time and area of contact between the compacting element and soil.

(4) Type of soil : →

(a) Normally, heavy days, clays and silts offer higher resistance to compaction where as sandy
soil and course grained or gravelly soils are amenable for easy compaction.

(b) The coarse grained soils yield higher densities in comparison to clays. A well graded file can
be compacted to higher density.

(5) Addition of Admixture : →

(a) The compaction properties/characteristics can be modified by a number of admixture other than soil material.

(b) There admixtures have special application in established soil construction.