Class 4 - Soil Compaction

Soil Mechanics Laboratory

Class 4

Determining Moisture-Unit Weight Relations of Soil(Compaction Test)Sources: Soil Mechanics Laboratory Manual, B. M. DAS (Chapters 6, 7)Matthew A. Dettman, P.E: http://www.wku.edu/~matthew.dettman/

Civil Engineering - Texas Tech University

Class OutlinesStandard Proctor Compaction TestEffect of Compaction EnergyModified Proctor Compaction Test Specification for Field Compaction


CompactionIn construction of highway embankments, earth dams and many other engineering structures, loose soils must be compacted to improve their strength by increasing their unit weightCompaction - Densification of soil by removing air voids using mechanical equipmentThe degree of compaction is measured in terms of its dry unit weight


Compaction EffectLoose soilCompacted soil


Compaction AdvantagesAs compaction increases, the following occurs:Increase soil strengthIncrease bearing capacity Decrease potential for settlementControl undesirable volume changes Reduction in hydraulic conductivity


Effect of Water on CompactionIn soils, compaction is a function of water contentWater added to the soil during compaction acts as a softening agent on the soil particlesConsider 0% moisture - only compacts so littleAdd a little water - compacts betterA little more water - a little better compactionEven more water soil begins to flowWhat is better compaction?The dry unit weight (gd) increases as the moisture content increases TO A POINTBeyond a certain moisture content, any increase in moisture content tends to reduce the dry unit weight


Relationship between Moisture Content and Dry DensityMoisture Content (%)Dry Density (pcf)


Compaction CurveCompaction curve plotted gd vs. wThe peak of the curve is the Maximum Compaction (gd max) at Optimum Moisture Content (wopt )


Standard Proctor Compaction TestThe standard was originally developed to simulate field compaction in the labPurpose: Find the optimum moisture content at which the maximum dry unit weight is attainedASTM D 698Equipments; Standard Proctor1/30 ft3 mold5.5 lb hammer12 drop3 layers of soil25 blows / layer


Compaction - Lab Equipment


ProcedureObtain 10 lbs of soil passing No. 4 sieveRecord the weight of the Proctor mold without the base and the (collar) extension, the volume of which is 1/30 ft3. Assemble the compaction apparatus. Place the soil in the mold in 3 layers and compact using 25 well distributed blows of the Proctor hammer. Detach the collar without disturbing the soil inside the mold Remove the base and determine the weight of the mold and compacted soil. Remove the compacted soil from the mold and take a sample (20-30 grams) of soil and find the moisture contentPlace the remainder of the molded soil into the pan, break it down, and thoroughly remix it with the other soil, plus 100 additional grams of water.


Compaction - Procedure12345


In your Report - ResultsPlot of dry unit weight vs moisture contentFind gd (max) and woptPlot Zero-Air-Void unit weight (only S=100%)


Standard Proctor TestModified Proctor Test


Effect of Compaction EnergyWith the development of heavy rollers and their uses in field compaction, the Standard Proctor Test was modified to better represent field compactionAs the compaction effort increases, the maximum dry unit weight of compaction increaseThe optimum moisture content decreases to some extend Compaction energy per unit volume


Effect of Compaction Energy (Cont.)


Modified Proctor TestThe modified was developed to simulate larger compaction effort for more serious loads and bigger equipmentASTM D 698Modified Proctor1/30 ft3 mold10 lb hammer18 drop5 layers of soil25 blows / layer


Specification for Field CompactionSpecifications will refer to % Relative CompactionRelative to what?Proctor Test standard or modified% Relative Compaction

If R > 100 +5% use Modified Proctor TestR ~ (90 100%)


Specification for Field CompactionSoil will be compacted to 98% relative compaction as compared to a standard proctor test, ASTM D-698The soil moisture content will be 2% of optimum. 98% 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 (20 ~24%)


Measurement of Field CompactionMost common methods areNuclear MethodSand Cone methodRubber Balloon method


Documents

Class 4 - Soil Compaction