Compaction

CompactionCompaction - Densification of soil by removing air voids using mechanical equipmentAs compaction increases, the following occurs:Strength increasespotential for settlement decreasespermeability decreasesIn soils compaction a function of water content

CompactionConsider 0% moisture - Only compact so muchAdd a little water - compacts betterA little more water - a little better compactionWhat is better compaction?More solid material (not water) in the same volumeIn other words - d increases with increasing moisture content - TO A POINT

CompactionAt some point (varies from soil to soil) Increasing moisture decreases d

CompactionCompaction curve plotted d vs. moisture contentThe peak of the curve is the maximum compaction(d max) and optimum moisture content under the specified energyThe energy in this case is the weight of the hammer and the height of the hammer drop

Compaction - Lab EquipmentStandard Proctor1/30 ft3 mold5.5 lb hammer12 drop3 layers of soil25 blows / layer

Compaction - Lab EquipmentModified Proctor1/30 ft3 mold10 lb hammer18 drop5 layers of soil25 blows / layer

Compaction - Lab Equipment

Compaction Project SpecsThe GE will provide compaction criteriaOther terms for compacted fill engineered fill controlled fillSpecs will refer to % Relative CompactionRelative to what?Proctor Test standard or modified

Compaction Project SpecsSoil will be compacted to 98% relative compaction as compared to a standard proctor test, ASTM D-698.

The soil moisture content will be +- 2% of optimum. (might say +2% or -1%)

Compaction Project Specs98% means the soil in the field should be 98% of the lab resultFor example, if the peak of the curve is at 100 pcf and 22% moistureThe field compaction must be at least 98 pcf and within the stated moisture range

Compaction Project SpecsThe moisture spec is sort of an additional check on the soilLooking at the curve, at any d there is a window of potential moisture contents.If the soil is too wet or too dry, it is unlikely it can achieve compactionIf the moisture is outside the range, something is probably not right

Compaction Project SpecsThe proctor could be wrong or the soil could have changed. It is up to the GE to determine if it is ok or not.Soils can vary dramatically, so at least one proctor should be run on every job. More than one needed if soils change.

Compaction Project SpecsIn Bowling Green, a standard proctor will on average be about 102 pcf at 22%MUST verify, cannot assume a value.I have seen 110 pcf to 85 pcf.

CompactionProctor Does Not Guarantee QualityIt only shows compaction relative to a lab test.Horse s____ can be compacted in the lab and you can test it in the fieldIf it passes compaction, it does not mean it is goodGE must determine 1st if the soil is acceptable as fill, then the compaction must pass

CompactionGenerally, the lower the PI and the higher the d the better the soil will be for compaction.Locally, if clay soils used as fill then some rock of the gravel size or slightly larger will make a better engineered fill.

Observing and Testing Compacted FillA qualified GE should be hired to properly observe and approve compactionThe GEs tools of testing fill:Observation of operationsSkill of the operatorDensity tests

Observing and Testing Compacted FillThe observations of the GE should include:Number of passes (compaction effort)Lift thicknessEquipment (compactor, blade)Soil properties, changes, type, moistureDirect contractor to work the soil as neededProofroll as neededTest results

Observing and Testing Compacted FillProblem:Too much moistureSolution:Work the soil (move the pile)AerateLet dryProblem:Low compactionSolution:More compaction effortMore passesThinner liftsfewer passes neededbetter productivity

Observing and Testing Compacted Fill

Observing and Testing Compacted FillProofrolling Looking for stability and no pumping

Compaction TestingMost common method is nuclear

Compaction TestingDensity test in the field determines the unit weight and moisture of the compacted fill.Compare the field data to labOther tests include sand cone and drive tubeDensity test alone does not tell you muchThe other 2 tools are neededObservation & operator (skill & equip)DENSITY TESTS DONT TELL YOU STRENGTH

Standard vs. Modified ProctorAs discussed, more energy moves the compaction curve up and to the leftThis decreases optimum moisture and increases dry unit weightThe standard was originally developed to simulate field compaction in the labThe modified was developed to simulate larger compaction effort for more serious loads and bigger equipment

Standard vs. Modified ProctorSO WHICH TO USE???To the untrained eye modified seems better as it will get you more solid material into the same volume thus it will reduce potential for settlement, etc.The trained eye will consider:What is neededWhat will workSoil typeGeographic conditionsCost

Standard vs. Modified ProctorIn BG, the building types most common:Low rise commercialBearing capacities 2000 to 3000 psfClaysClimate and precipitation keep soils below grade consistently moistStandard is the best choice in most cases here Why????

Standard vs. Modified ProctorWhile a modified will give you better strength do we need it?In a little league baseball dugout, would you spec 10000 psi concrete?Why or why notDont need it, thats whyFor most building cases would not specify modified (some you would which ones?) because you only need standard

Standard vs. Modified ProctorWhat is the harm in specifying modified?CostAlso should consider soils and local conditionsIn BG Standard will typically produce around 102 pcf at 22%Modified will typically produce around 108 at 16%

Standard vs. Modified ProctorBG soils in the summer (driest months) will have moistures around 22 to 24%With a lot of compaction effort, moistures might get down to 20%To meet a modified, will need to get down to 17 to 18% - Almost impossible to doIt can double or even triple time neededConsider the situation before choosing standard or modifiedLet the Geotech do it!!

Compaction EquipmentSheepsfoot CompactorSmooth DrumVibratoryRubber TireJumping JacksPlatesTrench Compactors

Compaction Equipment

Compaction EquipmentVibratory compactors most effective in cohesionless soilsCan help in clays, but not as muchSmooth drum for asphalt, DGA, finish grade in soils. Not good for initial compaction in soils.

Field Compaction OperationsPrimary Factors:EquipmentLift ThicknessSoil MoistureBook states intensity of pressure, which is equipment.

Field Compaction OperationsHeavier equipment is betterHowever - heavier must be translated to contact area (intensity of pressure)Track equipment - dozers, excavators, are heavy, but dont compactWhy?

Field Compaction OperationsBetter compaction comes from?1 -2 -3 -4 -etc.

Field Compaction OperationsThin lifts always betterEasier to compactFewer passes neededSome contractors think thin lifs slower, big thick lifts fasterNot true

Field Compaction OperationsImagine filling a holeIt will take X truck loadsWhether you place 2 foot lifts or 2 inch lifts, it is X truck loadsThinner lifts spread farther - less stop and reverse timeLess passes to compact 2 than 2Thin lifts almost compacted by truck or scraper

Chapter 5 problems:458

Have completed for next class for discussion and/or turn inHomework Exercises

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Compaction