Believing on the importance of soil in any project, there are variousvalues need to be check for sub-soil that will hold the whole structure. Thevalues are the internal friction angle and cohesion which need to be foundedusing different field and laboratory tests. These values will give indicationabout how the soil is strong in facing loads due to different sources like thestructure loads or filling loads. However, to start any project, the soil characteristic must be computeusing different soil laboratory tests.
Then, the geotechnical report will beready for the responsible engineer to decide if stabilization of soil is neededor not. In fact, these works are concentrate on the bearing capacity of soilwhether it can carry the loads from the structure and foundations or not. Ifthe site location cannot be change and the soil capacity cannot resist theload, then stabilization of soil is needed. Otherwise the site need to bechanged before design process and this issue need to be checked for the newsite also.
Stabilization is a process applied on soil to improve its capacity inresisting loads by enhancing the physical properties of it. The stabilizationhas different effect on the soil and its strength which can be done usingvarious methods. One of them is mechanical stabilization and the other ischemical method. In both methods, there can be different results on soilimprovement which depend on the percentage of chemicals or effort done usingmechanical equipment.
1 Effect of various binders onstabilized soil 1:Stabilization of softsoils by deep mixing with binders is the most frequently used method of groundimprovement. The binders react with water to form cementitious compositematerials. The most common binders employed are cement and lime, but a varietyof other binders may also be used for stabilization of soils.
This sectioncontains a summary of the performance of lime, cement, fly ash and blastfurnace slag. 1.1 Cement: Its considered as primarystabilizing agent or hydraulic binder because it can be used alone to bringabout the stabilizing action required. Hydration process is a process underwhich cement reaction takes place. The process starts when cement is mixed withwater and other components for a desired application resulting into hardening phenomena.
The hardening (setting) of cement will enclose soil as glue, but it will notchange the structure of soil.This process can be affected by: presence of foreign matters or impurities water-cement ratio curing temperature presence of additives specific surface of the mixture. Depending on factor(s)involved, the ultimate effect on setting and gain in strength of cementstabilized soil may vary.However, Cementstabilized soils have the following improved properties: decreased cohesiveness (Plasticity) decreased volume expansion or compressibility increased strength 1.2 Lime: The two primary types oflime used in construction today are quicklime (calcium oxide) and hydrated lime(calcium hydroxide). Heating limestoneat elevated temperatures produces quicklime and the addition of water toquicklime produces hydrated lime. For soil stabilization with lime, soilconditions and mineralogical properties have a significant effect on thelong-term strength gain. Introduction of calcium hydroxide increases the pH,causing the silica and alumina in the clay particles to become soluble andinteract with the calcium in a pozzolanic reaction.
A pozzolanic reaction between silica oralumina in the clay particles and calcium from the lime can form a cementedstructure that increases the strength of the stabilized soil. 1.3 Fly Ash: Fly ash is an industrialby product generated at coal-fired electricity generating power plants thatcontains silica, alumina, and calcium-based minerals. it has littlecementitious properties compared to lime and cement. Most of the fly ashesbelong to secondary binders; these binders cannot produce the desired effect ontheir own. However, in the presence of a small amount of activator, it canreact chemically to form cementitious compound that contributes to improvedstrength of soft soil. Fly ashes are readily available, cheaper andenvironmental friendly. 1.
4 Blast Furnace Slags: These are the by-productin pig iron production. The chemical compositions are similar to that of cement.It is however, not cementitious compound by itself, but it possesses latenthydraulic properties which upon addition of lime or alkaline material thehydraulic properties can develop. Itemized slag inthree forms, namely: 1. Air-cooledslag :Hot slag after leaving the blast furnace may be slowly cooled in openair, resulting into crystallized slag which can be crushed and used asaggregate.2. Granulated or Pelletised slag: The granulated blast furnace slag is a result of use of water duringquenching process, while, the use of air in the process of quenching may resultinto formation of pelletised slag.3.
Expandedslag :Under certain conditions, steam produced during cooling of hot slag maygive rise to expanded slag. 2 stabilizationsMethodsThe main purpose of thesoil stabilizations is to make the soil incompressible and impermeable.Impermeability can by supported mainly by chemical methods of stabilization,but incompressibility can be achieved mainly by mechanical methods ofstabilization.First, themechanical methods of stabilization will be explain, and then the chemicalmethods. 2.1 Mechanical Methods of Soil Stabilizations:These methodsof soil stabilization include physical measures for soil improvement. The mostcommon mechanical methods are: A-Compression Method.
B-Drainage Method.The mostcommon mechanical method is compression method, so it will be explained first. 2.1.1 Compression Method:It is themost obvious and simple way of increasing the stability and supporting capacityof soil (improving the physical properties of soil).
Soil compaction is theprocess of increasing the unit weight of soil by forcing solids into a tighterstate and reducing air. The compaction will reduce the voids in the soil andthus will increase the strength of the soil, which means having higher bearingcapacity. By compacting the soil, the air volume will decreases until a pointwhich more compaction cannot apply to prevent damaging the grain structure. In the field,there are four different mechanisms of compression: vibration, impact, kneadingand pressure. These different types of compaction are found in two principletypes of force: static and vibratory.
Static compaction uses deadweight of themachine as downward force on the soil surface. To change the intensity ofcompaction force, weight of the machine has to be decreased or increased.Static compression is limited to upper soil layers. Vibratory compaction usesengine-driven mechanism for applying downward force in addition to themachine’s static weight.Different types of compaction are best suited for different soil typesand conditions.
This is because of the underlying density and moisture thatdifferent soil types are able to retain. Soil types are classified in threesoil groups, with consideration to grain sizes.These types are: Cohesive: In cohesive soils, such as clay, the particles contain characteristics that make them easily stick together so compaction can be achieved by high impact, which forces the air out of the particles, pushing them together. Granular: granular soils include sand, gravel, and other particles that typically range in size from 0.
003 to 0.08 inches (0.008 to 0.2 cm). Because granular soils have good water-draining properties, they are able to obtain high density when fully dry or saturated. Granular is best compacted by shaking or vibrating the particles. Any type of vibratory equipment is best suited for this type. Depending on the type of granular soil, different degrees of vibration are required.
Granular and Cohesive: often, soils are a mixture of both granular and cohesive, requiring more precise compaction equipment. Equipment should be chosen on the basis of the soil in the mix that is present in the highest percentage. Some materials, such as asphalt, require both vibration and static pressure to be compacted effectively.
Machinery uses frequency and amplitude to apply a force for compaction. Frequency is the measure of the speed of the eccentric shaft rotation, or of the jumping of the machine, quantifiable by vibrations per minute (vpm). Amplitude measures the maximum movement of a vibrating body from its axis in one directionFrom SoilMechanics Course (CENG341), we took our results about the compaction experimentfor normal hammer using different water content, and then plot the values andget the max dry density of the soil with the optimum water content should beused to compact the soil in order to get high strength. Here are theresults and plot:No.
of blows: 27, No. of layers: 3, Wt of hammer =2.5kg Mold dimensions: D=10.1cm, H=11.638cmMold Volume=?(10.1)2(11.638)/4=932.42 cm3 Table 1 Density Calculations for 2.
5 kg Rammer Method Determination No. 1 2 3 4 Wt of mold+ compacted soil (g) 6006 6055 6115 6135 Wt of mold (g) 4326 Wt of compacted soil (g) 1680 1729 1789 1809 Wet density ? (g/cm3) 1.802 1.
85 1.92 1.94 Dry density ?d (g/cm3) 1.66 1.65 1.
67 1.64 Table 2 Water Content Determination for 2.5 kg Rammer Method Determination No. 1 2 3 4 Container No.
A-1 A-2 A-3 A-4 Wt container + wet soil (g) 110.49 103.96 85.78 131.45 Wt container + dry soil (g) 102.
34 93.91 75.68 112.27 Wt water, Ww (g) 8.15 10.
05 10.1 19.18 Wt container (g) 9.32 9.30 8.88 9.
33 Wt dry soil, Ws (g) 93.02 84.61 66.8 102.94 Water content w% 8.76% 11.88% 15.12% 18.
63% Sample of calculation:Wt of compacted soil=(Wt of mold+ compacted soil)–(Wt of mold)=6006 –4326= 1680gWet density= Wt of compacted soil / volume of mold= 1680/932.42= 1.802g/cm3Dry density= wet density /(1+w)= 1.802/(1+0.0876)= 1.66 g/cm3Wt water, Ww =(Wt container + wet soil)–(Wt container + drysoil)=110.49–102.
34=8.15gWt dry soil, Ws=(Wt container + dry soil)–(Wt container)=102.34 –9.32=93.02gWater content W%= (Ww/Ws)*100= (8.15/93.02)*100= 8.76%Zero Air Voids : ?d = Gs/(1+wGs) Table 3 Calculation of Zero Air Voids for 2.
5kg Rammer Method Water content W 8.76 11.88 15.
12 18.63 Dry density ?d 2.15 2.015 1.89 1.77 Figure 1 Water Content vs Dry Density for 2.
5 kg Rammer Method After plotting watercontent vs dry density of the soil sample and the zero air void sample thevalue of the maximum water content is calculated using the derivative of thecurve equation: Y= -0.0005×2+0.0119x+1.5882 , Y?= -0.0005(2)x+0.0119, , Y?= 0 0= – 0.
001x+0.0119 so x=11.9%= 12% ofwater content to get the maximum dry density equal Y= -0.0005×2+0.0119x+1.
5882 = -0.0005(12)2+0.0119(12) +1.5882 =1.
66g/cm3 witherror equal (1.66 – 1.67)/1.
66= 0.006 where the 1.67 is the experimental drydensity.Compaction Energy CE= No.of blows*Wt of hammer*Hdrop / volume =(27*3*2.5*0.3)/(9.
3242*10-4)=65153 kJAccording toGraph-1,While the water content at the beginning increased the dry density ofthe soil is increased too and that’s because the water is lubricating the soilgrains so it be easier to compact, after reach the maximum density a drop on itwill occur and that’s happened because when add more and more water the samplewill resist the compaction because of the huge amount of water and the water isincompressible fluid.2.1.
2 Drainage Method:Drainage involves underground systems ofpipes and pumps to extract excessive water from soil. Common drainage methodsare well-point systems, deep-well drainage, vacuum dewatering, dewatering byelectro-osmosis, etc.A well pointsystem consists of a number of well points spaced along a trench or around anexcavation site, all connected to a common header which is attached to one ormore well point pumps. Well point assemblies-made up of a well point, screen,riser pipe, and swing joint with tuning-are generally installed by jetting.They provide for entry of water into the system by creation of a partialvacuum. The water is then pumped off through the header pipe. A well point pumpis a combination of two pumps, one of which pumps water from the header and theother of which is a vacuum pump to remove air which enters the system.
Controlof air is important, as excessive air causes cavitation which reduces pump efficiency.The dewatering pumps used are normally designed specifically for the dewateringfunction. They are available in sizes from 4″ to 10″ with handling capacity upto 500m3/hour. 2.
2 Chemical Methods ofStabilizations of Soil 4: There are many chemicalscan be used for chemical stabilization. The type of chemical can be selecteddepend on the soil type and condition of construction site. For example, Limeis not good stabilizer for silts, granular materials and soils with sulphatecontents greater than 0.3 percent. Actually, lime is helpful material forclay-bearing and highly cohesive soil whereas fly ash is being used forgranular or poorly cohesive soil.
Manymaterials can be used like, lime , cement, fly ash and asphalt. these materialcan improve strength, compressibility, hydraulic conductivity, swellingpotential and volume change properties with different results depending on thetype of material ant its action with soil. 2.2.1 Soil Stabilization with Lime:Lime is a white causticalkaline substance consisting of calcium oxide “CaO”, which is obtained byheating limestone and which combines with water with the production of muchheat. It is very effective chemical in modifying high plastic clayey soil whichcan be used alone or by mixing it with another chemical component like cement,fly ash or bitumen. It is used mainly for stabilizing subgrade.
Lime stabilization will be done by changing the nature of adsorbedlayer and providing pozzolanic action. As a result, the high plasticity indexof the soil will be reduced. Also, the optimum water content will be increasedand decreasing in the maximum compacted density of the soil. Therefore, lesscompaction will lead to the maximum compacted density. It found that lime canincrease the soil strength and durability when it added to the soil as ( Fig. )shows. There is an advisable percentage of lime to gain that good improvementfrom it, from 5-8% for plastic soil. 2.
2.2 Soil Stabilization with Cement 5:The soil stabilized with cement is known as soil cement which done dueto cementing action. Cementing is the result of chemical reactions of cementwith siliceous soil during hydration reaction.
There are some factor affectingsoil-cement such as nature of soil content, conditions of mixing, compaction,curing and admixtures used. In addition, depending on the soil type, the amountof cement will differ as follow:Gravels – 5 to 10% Sands – 7 to 12% Silts – 12 to 15%, and Clays – 12 – 20%In general , Cement stabilization give better strength and improvequality of soil. Other additives can be mixed with cement to enhance the soillike Lime, calcium chloride, sodium carbonate, sodium sulphate and fly ash. Infact, the type of cement which used for stabilization usually is ordinaryPortland cement. calculation of required cement amount is discussed following:If the layer of soil having surface area of A (m2), thickness H (cm)and dry density rd (tonnes/m3), has to be stabilized with p percentage ofcement by weight on the basis of dry soil, cement mixture will be =100*P/(100+p)and, the amount of cementrequired for soil stabilization is given byAmount of cementrequired, in tonnes = 2.
2.3 Soil Stabilization with Bitumen: Asphalt is a dark bituminoussubstance that is found in natural beds and is also obtained as a residue inpetroleum refining and that consists chiefly of hydrocarbons. Asphalts and tarsare bituminous materials which are used for stabilization of soil. Thisstabilization method can be defined as the treatment of naturally occurringneoplastic or moderately plastic soil with liquid asphalt at normaltemperatures to improve the load-bearing qualities of the soil.That Bituminous materialscan impart cohesion and reduced water absorption when added to a soil. 3 Stabilization Tools:There are many machinesand tools can be used in stabilization. Choosing the approperiate machinedepends on the method adopted, type of the soil and the soil area to beadjusted.
Here the tools will be classified according to the method used: 3.1.1 Machines for Mechanical Methods 6: 1. Rammers: Rammers areused for compacting small areas by providing impact load to the soil. Thisequipment is light and can be hand or machine operated. The base size of rammerscan be 15cm x 15cm or 20cm x 20cm or more.Figure 8 RAMMERS 2.
Vibrating Plate Compactors: Vibratingplate compactors are used for compaction of coarse soils with 4 to 8% fines.These equipments are used for small areas. The usual weights of these machinesvary from 100 kg to 2 tonne with plate areas between 0.
16 m2 and 1.6 m2.Figure 9 Vibrating PlateCompactors 3. SmoothWheeled Rollers:a. Static smooth wheeled rollers.b. Vibrating smooth wheeled rollers.The most suitable soils for these roller type are well graded sand, gravel,crushed rock, asphalt etc.
where crushing is required. These are used on soilswhich does not require great pressure for compaction. These rollers aregenerally used for finishing the upper surface of the soil. These roller arenot used for compaction of uniform sands.In case of vibrating smooth wheeled rollers, the drums are made to vibrate byemploying rotating or reciprocating mass.4.
Sheepsfoot Roller: Sheepsfootrollers are used for compacting fine grained soils such as heavy clays andsilty clays. Sheepsfoot rollers are used for compaction of soils in dams,embankments, subgrade layers in pavements and rail road construction projects.5. PneumaticTyred Rollers: Pneumatic tyred rollers are also called as rubbertyred rollers. These rollers are used for compaction of coarse grained soilswith some fines.
These rollers are least suitable for uniform coarse soils androcks. Generally pneumatic tyred rollers are used in pavement subgrade worksboth earthwork and bituminous works. Pneumatic rollers have wheels on bothaxles. These wheels are staggered for compaction of soil layers with uniformpressure throughout the width of the roller.6.
Grid Rollers: Grid rollersare used for compaction of weathered rocks, well graded coarse soils. Theserollers are not suitable for clayey soils, silty clays and uniform soils. Themain use of these rollers are in subgrade and sub-base in road constructions.
As the name suggests, these rollers have a cylindrical heavy steel surfaceconsisting of a network of steel bars forming a grid with squire holes. Theweight of this roller can be increased by ballasting with concrete blocks. 3.1.2 Machines for Chemical Methods 7: Here are some steps thatexplain which machines should be used in this method:1. Pulverize thearea to be stabilized2. Uniformlyspread stabilizing material3. Blend withthe Asphalt Zipper machine4.
Thenhomogenous mixture will appear5. Reshape6. Compact7. Pave Figures below shows themachines with steps clearly: 4 CONCLUSIONThe consideration of soilproperties is very important stage before any other stages can take place inthe projects. If the geotechnical engineer found the soil is weak, which havelow bearing capacity and cannot resist the loads coming from the structure,then as a solution for that soil stabilizations can made. After checking theeffects of various binders on stabilized soil, two main methods can do to makethe soil stabilized.
The most common binders employed are cement and lime, buta variety of other binders may also be used for stabilization of soils such asfly ash and blast furnace slag. The main purpose of the stabilizations is tomake the soil incompressible and impermeable. Impermeability can by supportedmainly by chemical methods of stabilization, but incompressibility can beachieved mainly by mechanical methods of stabilization. For the mechanicalmethods, there are two common sub methods, the first one is compression orcompacting method and the other is drainage method. The compaction caneffectively improve the strength of the soil, but to do that an optimum watervolume should be spread on the surface of the soil to be as lubrication agentto ease the compaction. Also, each type of soil has its own way to compactusing different machines. The proper machine should be used to get the maximumpossible soil strength.
The effective stress of the soil will be decreasedwhile the ground water table increased, so to solve this issue the drainagemethod will be useful to remove the water from the site where the structuresshould build. The other method of soil stabilization is the chemical methodswhich have many ways to do it, but the three more used ways explained in this reportlike chemical stabilization using lime, cement and bitumen. Both methods,mechanical and chemical are effective, but they need to be made by the propermachine or equipment by the exact procedure as explained in this report.Finally, the site of the project will have a high bearing capacity soil afterit stabilized. Therefore, it can resist the applied load coming from thestructure without bearing failure or excessive settlement.