7 Standard Vs. Modified Proctor Compaction A small soil sample is taken from the jobsite. A standard weight is dropped several times on the soil. The material weighed and then oven dried for 12 hours in order to evaluate water content .The Proctor, or Modified Proctor Test, determines the maximum density of a soil needed for a specific job site. The test first determines the maximum density achievable for the materials and uses this figure as a reference. Secondly, it tests the effects of moisture on soil density. The soil reference value is expressed as a percentage of density. These values are determined before any compaction takes place to develop the compaction specifications. Modified Proctor values are higher because they take into account higher densities needed foe certain typed of construction projects. Test methods are similar for both tests.Modified ProctorStandard Proctor
8 Moisture-Density Curve Zero Air Voids LineS = 100%Dry side of optimumwoptWet side of optimumdry side of optimum As the water content increases, the particles develop larger and larger water films around them, which tend to “lubricate” the particles and make them easier to be moved about and reoriented into a denser configuration.At wopt:The density is at the maximum, and it does not increase any further.Above wopt (wet side of optimum):Water starts to replace soil particles in the mold, and since w << s the dry density starts to decrease.Test1234wgtgdgZAV
10 Factors affecting Compaction Compactive EffortMoisture ContentSoil Type
11 Compactive Effort gd max wopt Zero air void Water content w (%) Dry density gd (Mg/m3)Dry density d (lb/ft3)Line of optimumsModified ProctorStandard ProctorHoltz and Kovacs, 1981gd maxwoptOptimum water content is typically slightly less than the plastic limit.The line of optimum moisture contents is usually around 85% saturation
12 Soil Type Grain size distribution. Shape of soil grains. Specific gravity of soil solids.Amount and type of clay minerals.
13 Constant compaction energy Soil Type (cont’d)Dry DensitySand, some finesZero air voids linegd maxOMCSand double peak moisture density curves because of capillary riseClayMoisture contentConstant compaction energy
14 Check Point Method Check Point Method wopt Line of optimums 100% saturation1 point Proctor testKnown compaction curves A, B, CField check point X (it should be on the dry side of optimum)AY (No)Dry density, gdgd maxBXXMMCwoptHoltz and Kovacs, 1981Water content w %
15 Relative CompactionCorrelation between relative compaction (R.C.) and the relative density DrTypical required R.C. = 90% ~ 100%
20 Smooth-wheel roller (drum) 100% coverage under the wheelAll soil types except for rocky soils.Contact pressure up to 380 kPaCompactive effort: static weightMost common use is for proof-rolling subgrades and compacting asphalt pavement.Holtz and Kovacs, 1981
21 Sheepsfoot Rollers 8% ~ 12 % coverage Best for clayey soils. Contact pressure from 1400 to 7000 kPaCompactive effort: static weight and kneading.
22 Pad Roller About 40% coverage Best for compacting fine-grained soils (silt and clay).Contact pressure is from 1400 to 8400 kPaCompactive effort: static weight and kneading.
23 Pneumatic Rollers 80% coverage under the wheel. Bet for Granular and fine-grained soils.Contact pressure up to 700 kPa.Compactive effort: static weight and kneading.
24 Grid Rollers About 40% coverage Contact pressure is from 1400 to 8400 kPaBest for compacting fine-grained soils (silt and clay).Compactive effort: static weight and kneading.
25 Vibratory Compactors Compactive effort: static weight and vibration. Suitable for granular soils
26 Compaction Type Vs. Soil Type MaterialsVibrating Sheepsfoot RollersStatic Sheepsfoot Grid Roller ScraperVibrating Plate Compactor Vibrating Roller Vibrating SheepsfootScraper Rubber-tired Roller Loader Grid RollerLift ThicknessImpactPressure (with kneading)VibrationKneading (with pressure)Gravel12+PoorNoGoodVery GoodSand10+/-ExcellentSilt6+/-Clay
27 Compaction Difficulty Vs. Soil Type Fill MaterialsPermeabilityFoundation SupportPavement SubgradeExpansiveCompaction DifficultyGravelVery HighExcellentNoVery EasySandMediumGoodEasySiltMedium LowPoorSomeClayNone+ModerateDifficultVery DifficultOrganicLowVery PoorNot Acceptable
28 Nondestructive Testing: Field DensityDestructive Testing:Sand ConeCore CutterRubber BalloonNondestructive Testing:Nuclear Density
29 Standard Sand with known Gs Sand Cone TestW1Standard Sand with known GsW2W1= mass of sand cone before testW2 = mass of sand cone after testW3 = mass of sand filling cone and hole(W3 = W1-W2)W4 = mass of sand filling the cone = gsand*VconeW5 = mass of sand filling the hole = W3-W4Vhole = W5 / gsandW6 = mass of soil extracted from the wholew = moisture content of soilW4W5
30 Sand Cone Test Procedure A small hole (6" x 6" deep) is dug in the compacted material to be tested. The soil is removed and weighed, then dried and weighed again to determine its moisture content. The specific volume of the hole is determined by filling it with calibrated dry sand from a jar and cone device. The dry weight of the soil removed is divided by the volume of sand needed to fill the hole. This gives the density of the compacted soil.
31 Suitable for cohesive soils only Core CutterStatic LoadSuitable for cohesive soils only5 in4 in
33 Nuclear DensityNuclear Density meters are a quick and fairly accurate way of determining density and moisture content. The meter uses a radioactive isotope source (Cesium 137) at the soil surface (backscatter) or from a probe placed into the soil (direct transmission). The isotope source gives off photons (usually Gamma rays) which radiate back to the mater's detectors on the bottom of the unit. Dense soil absorbs more radiation than loose soil and the readings reflect overall density. Water content can also be read, all within a few minutes.