Soil Stabilization

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.

way. Use this method where it is necessary to combine two different soils together for stabilization. Do this as follows:

• In-place mixing: blend soil and stabilization materials on the jobsite.
• Off-site mixing: use stationary mixing plants.
• Windrow mixing: mix 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 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 is cement modified soil which is an unhardened or semi-hardened 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 enough water at the time of placing 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 be almost any combination of gravel, sand, silt, or clay.

The 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. A soil sample, should make a firm cast 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. Compact the soil-cement mixture at optimum moisture content to maximum density and finish it 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 result from one or more of the following causes: (1) the soilcement 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, aerate it using the scarifier on the grader. After it has dried to near optimum moisture content, then compact it.