Compaction helps the soil to be more resistant to
soaking up moisture from below.
Fills are built up in compacted layers. In
earthwork operations, these layers are called lifts.
Lifts are from 4 inches to 1 foot in depth, depending
upon the compaction necessary, compaction
equipment available, and material used for the fill.
The fill material must have the right amount of
moisture, referred to as optimum moisture content.
To obtain maximum compaction, wet the fill, when
necessary, before it is compacted. Compaction may be
obtained by using a pneumatic, tandem, or vibratory
There are three purposes for soil stabilization. The
first one is strength improvement. This increases the
strength of the existing soil to enhance its load-bearing
capacity. The second purpose is for dust control. This
is done to eliminate or alleviate dust, generated by the
operation of equipment and aircraft during dry
weather or in arid climates. The third purpose is soil
waterproofing, which is done to preserve the natural
or constructed strength of a soil by preventing the
entry of surface water.
There are two methods used to apply soil
stabilization materials. The first is the admix way.
This is used where it is necessary to combine two
different soils together for stabilization. This can be
done as follows:
. In-place mixing: accomplished by blending of
soil and stabilization materials on the jobsite.
. Off-site mixing: accomplished by using station-
ary mixing plants.
. Windrow mixing: accomplished by mixing the
materials using a grader.
The second way is the surface penetration
application, which is accomplished by placing a soil
treatment material directly to the existing ground
surface by spraying or other means of distribution.
Some of the additives used in soil stabilization are
cement, lime, bituminous products, and calcium
chloride. Cement-treated bases are the most
commonly used for the purpose of upgrading a poor
quality soil. Soil-cement is a mixture of pulverized
soil and measured amounts of portland cement and
water, compacted to a high density.
There are three types of soil-cement. The first type
is compacted soil-cement that contains sufficient
amounts of cement to harden the soil and enough
moisture for both compaction and hydration of the
cement. The second type is cement modified soil
which is an unhardened or semihardened mixture of
soil and cement. Only enough cement is used to
change the physical properties of the soil. The third is
plastic soil-cement. It is a hardened mixture of soil and
cement that contains at the time of placing, enough
water to produce a consistency similar to that of
plastering mortar. The three basic materials needed
when working with soil-cement are soil, portland
cement, and water. The soil can almost be any
combination of gravel, sand, silt, or clay.
Three major control factors when working with
soil-cement are as follows:
1. The proper cement content is needed. A rule of
thumb: use one 50-pound bag per square yard.
2. Proper moisture content. On a soil sample, a
firm cast should be made when squeezed in your hand
without squeezing out any water.
3. Adequate compaction. The principles of
compacting soil-cement are the same for compacting
the same soils without cement treatment. The
soil-cement mixture at optimum moisture content
should be compacted to maximum density and finished
immediately. Moisture loss by evaporation during
compaction, as indicated by the graying of the surface,
should be replaced with light applications of water.
Occasionally during compaction, the treated area
may yield under the compaction equipment. This may
be due to one or more of the following causes: (1) the
soil-cement mix is much wetter than optimum
moisture content, (2) the soil may be too wet and
unstable, and (3) the roller may be too heavy for the
soil. If the soil-cement mix is too damp, it should be
aerated by using the scarifier on the grader. After it
has dried to near optimum moisture content, then it is
TECHNIQUES OF EARTHWORK
Techniques of earthwork operations consist of
knowing the equipment needed and the operations of
pioneering, clearing, grubbing, stripping, draining,
and grading and excavating. These operations are
done primarily with heavy construction equipment,