Compaction helps the soil to be more resistant tosoaking up moisture from below.Fills are built up in compacted layers. Inearthwork operations, these layers are called lifts.Lifts are from 4 inches to 1 foot in depth, dependingupon the compaction necessary, compactionequipment available, and material used for the fill.The fill material must have the right amount ofmoisture, referred to as optimum moisture content.To obtain maximum compaction, wet the fill, whennecessary, before it is compacted. Compaction may beobtained by using a pneumatic, tandem, or vibratoryroller.SOIL STABILIZATIONThere are three purposes for soil stabilization. Thefirst one is strength improvement. This increases thestrength of the existing soil to enhance its load-bearingcapacity. The second purpose is for dust control. Thisis done to eliminate or alleviate dust, generated by theoperation of equipment and aircraft during dryweather or in arid climates. The third purpose is soilwaterproofing, which is done to preserve the naturalor constructed strength of a soil by preventing theentry of surface water.There are two methods used to apply soilstabilization materials. The first is the admix way.This is used where it is necessary to combine twodifferent soils together for stabilization. This can bedone as follows:. In-place mixing: accomplished by blending ofsoil and stabilization materials on the jobsite.. Off-site mixing: accomplished by using station-ary mixing plants.. Windrow mixing: accomplished by mixing thematerials using a grader.The second way is the surface penetrationapplication, which is accomplished by placing a soiltreatment material directly to the existing groundsurface by spraying or other means of distribution.Some of the additives used in soil stabilization arecement, lime, bituminous products, and calciumchloride. Cement-treated bases are the mostcommonly used for the purpose of upgrading a poorquality soil. Soil-cement is a mixture of pulverizedsoil and measured amounts of portland cement andwater, compacted to a high density.There are three types of soil-cement. The first typeis compacted soil-cement that contains sufficientamounts of cement to harden the soil and enoughmoisture for both compaction and hydration of thecement. The second type is cement modified soilwhich is an unhardened or semihardened mixture ofsoil and cement. Only enough cement is used tochange the physical properties of the soil. The third isplastic soil-cement. It is a hardened mixture of soil andcement that contains at the time of placing, enoughwater to produce a consistency similar to that ofplastering mortar. The three basic materials neededwhen working with soil-cement are soil, portlandcement, and water. The soil can almost be anycombination of gravel, sand, silt, or clay.Three major control factors when working withsoil-cement are as follows:1. The proper cement content is needed. A rule ofthumb: use one 50-pound bag per square yard.2. Proper moisture content. On a soil sample, afirm cast should be made when squeezed in your handwithout squeezing out any water.3. Adequate compaction. The principles ofcompacting soil-cement are the same for compactingthe same soils without cement treatment. Thesoil-cement mixture at optimum moisture contentshould be compacted to maximum density and finishedimmediately. Moisture loss by evaporation duringcompaction, as indicated by the graying of the surface,should be replaced with light applications of water.Occasionally during compaction, the treated areamay yield under the compaction equipment. This maybe due to one or more of the following causes: (1) thesoil-cement mix is much wetter than optimummoisture content, (2) the soil may be too wet andunstable, and (3) the roller may be too heavy for thesoil. If the soil-cement mix is too damp, it should beaerated by using the scarifier on the grader. After ithas dried to near optimum moisture content, then it iscompacted.TECHNIQUES OF EARTHWORKOPERATIONSTechniques of earthwork operations consist ofknowing the equipment needed and the operations ofpioneering, clearing, grubbing, stripping, draining,and grading and excavating. These operations aredone primarily with heavy construction equipment,15-37
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