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Compaction

Compaction. In-situ soils used as: Bases for the construction of highway pavements embankments or leveling material for construction projects Compacted to improve their density : M/V improves the soil’s strength lowers it’s permeability reduces future settlement. Compaction.

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Compaction

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  1. Compaction • In-situ soils used as: • Bases for the construction of highway pavements • embankments or leveling material for construction projects • Compacted to improve their density: M/V • improves the soil’s strength • lowers it’s permeability • reduces future settlement ENCI 579

  2. Compaction • Evaluation of density as a result of compactive efforts with rollers and other equipment • common quality control measurement on soils at construction sites • density of a compacted soil is measured and compared to a density goal previously determined in laboratory tests ENCI 579

  3. CompactionMaximum Dry Density • Maximum dry density must be established for each soil type • clay soil after compactive effort 2000 Kg/m3 • granular soil with no compactive effort may be well above this • Dry density of a soil fn (water content) ENCI 579

  4. CompactionMaximum Dry Density ENCI 579

  5. CompactionMaximum Dry Density Compaction Control Determine the maximum dry density for a particular soil under a certain compactive effort and the water content at which this density is reached. MD/V ENCI 579

  6. CompactionMaximum Dry Density ENCI 579

  7. CompactionMaximum Dry Density • Compaction Test • Moisture density test • Proctor test • soil is compacted into 10 cm diameter mold for material passes 4.75 mm sieve (15 cm mold for coarser material) • soil is placed in 3 layers • each layer compacted 25 blows with a 2.5 Kg hammer dropping 30 cm ( 56 blows) ENCI 579

  8. CompactionMaximum Dry Density • 25 blow/56 blow compactive efforts are the same and represent the compactive efforts of 1930 construction rollers • Compaction Test • sample of soil is mixed with water • mass of compacted sample is measured • water content determined • sample of soil is mixed with more water • repeated until density decreases ENCI 579

  9. CompactionMaximum Dry Density • Modified Compaction Test • Modified Moisture Density Test • Modified Proctor Test • Increased loading on our pavements • Increased compactive effort of equipment • Revised test of higher compactive effort is now often used • 4.5 Kg hammer, 45 cm drop, 5 layers • higher maximum dry density/lower w/c ENCI 579

  10. CompactionMaximum Dry Density *Volume of standard mold is 943.9 cm3 **Dry density = density/(1+w) ENCI 579

  11. CompactionMaximum Dry Density Zero Air Voids (ZAV) Curve • “the maximum theoretical density of a soil at various water contents” with no air left in the soil water mixture ZAV rD = rW 1/RD + W ENCI 579

  12. ENCI 579

  13. CompactionMaximum Dry Density • Maximum Dry Density of a soil is used in quality control • Specification requires a certain % of maximum dry density at optimum water content found by the compaction test for that particular soil • Ensures density • Reduces the compactive effort ENCI 579

  14. CompactionMaximum Dry Density ENCI 579

  15. CompactionMaximum Dry Density ENCI 579

  16. CompactionMaximum Dry Density Note: • If the soil was below optimum water content it may be necessary to add water by spraying • The most important factor required for successful compaction is having the correct water content ENCI 579

  17. CompactionField Density Tests • Sampling Methods • sample of compacted material taken • dry mass of the soil taken is determined • volume originally occupied by the sample is measured • field dry density = dry mass/volume of sample • Two sampling methods • balloon densometer • sand cone apparatus ENCI 579

  18. CompactionField Density Tests • Balloon densometer • Dry mass of the soil is determined • Volume of the sample hole is found by forcing a liquid filled balloon into the test hole • A rubber membrane allows the fluid to fill all the cavities of the hole • The volume of fluid required is measured • density calculated • water content determined ENCI 579

  19. CompactionField Density Tests • Sand Cone Apparatus • Dry mass of the soil is determined • Volume of the test hole is obtained from the mass of loose sand required to fill the hole • Sand is a uniform medium sand with a constant loose density • Volume=mass of sand / loose density of sand • density is calculated • water content determined ENCI 579

  20. CompactionMaximum Dry Density Example 3-4 Sand-Cone Apparatus: A sand cone holds 851.0 g. The loose density of the sand is 1.430 g/cm3 Field Test Results: Total weight of the soil 639.5 g Dry weight of the soil 547.9 g Initial weight of the sand-cone apparatus 4527.8g final weight of the sand-cone apparatus 3223.9g ENCI 579

  21. CompactionMaximum Dry Density Calculations: Mass of the sand used 4527.8g-3223.9g = 1303.9g Mass in test hole 1303.9g-851.0g = 452.9 g Volume of test hole 452.9 g = 316.7 cm3 1.430 g/cm3 Field dry density 547.9g/316.7 cm3 = 1.730 g/ cm3 Field water content 639.5-547.9 = 16.7% 547.9 ENCI 579

  22. CompactionField Density Tests • Nuclear Moisture-Density Gauge • Results are available within minutes • Increases equipment efficiency • Know that your construction methods are correct • Gamma rays are emitted into the soil • absorbed by the soil according to it’s density • rays that pass through the soil are measured by a detector • density is then calculated ENCI 579

  23. CompactionField Density Tests • Nuclear Moisture-Density Gauge • Neutron radiation emitted into the soil • neutrons loose energy when they collide with hydrogen atoms in the soil water • detector measures the amount of moderated neutrons • water content can be calculated • Direct transmission mode • Backscatter mode ENCI 579

  24. CompactionField Density Tests ENCI 579

  25. CompactionMaximum Dry Density • Corrected Maximum Dry Density • compaction test is usually done on materials finer than 4.75 mm • sample contains coarse grained sized particles • gravel in a soil composed mainly of fine grains can be compacted to 90% of their theoretical maximum density • assuming gravel RD=2.65 ENCI 579

  26. CompactionMaximum Dry Density Example Laboratory maximum density of a soil is 1900 kg/m3. Specifications require 95% compaction. In the filed, dry density of the soil is found to be 1810kg/m3. A visual check of the soil in the field indicates that it contains about 20% gravel sizes. (Scales can be used for a more accurate determination of the percentage of gravel.) Check for compaction. ENCI 579

  27. CompactionMaximum Dry Density Corrected maximum dry density is: 0.80 x 1900kg/m3 + 0.20 x (90% x 2.65 x 1000kg/m3 = 1520 kg/m3 + 477kg/m3 = 1997kg/m3 Percent compaction is 1810/1997 = 90.6% and is not acceptable ENCI 579

  28. CompactionOperation and Quality Control • Highway components that require compaction: • Subgrade (15-30cm) in depth, provides the foundation for the pavement structure • Fill material used to bring the soil surface up to the subgrade level (15-30 cm compacted lifts) • Backfill material • Layers in granular material used in pavement • Asphalt layers at the surface ENCI 579

  29. CompactionCompaction Equipment • Compaction Equipment • Consists of various types of rollers and tamping equipment • self propelled • compacting wheels equipped to vibrate • 1500-2500 cycles/minute for most soils and granular materials • smooth steel drums • drums with pads or “feet” • rubber tires ENCI 579

  30. CompactionCompaction Equipment • Vibratory Smooth Drum Rollers • one steel drum and rubber tired drive wheels • two steel drums one of which is the driver • effective for gravel, sand, silt soils • granular base courses and asphalt mixtures • mass of the drum is between 2-15 tonnes • utilized in layers from 0.5-1.0 meters in depth • usually require 3-5 passes to produce specified density ENCI 579

  31. CompactionCompaction Equipment • Vibratory Smooth Drum Rollers ENCI 579

  32. CompactionCompaction Equipment • Padded Wheel or “Sheep’s Foot” Rollers • pads on the rotating drum and may vibrate • effective in clay and silty clay soils • punching action breaks the clay’s bonds which resist rearrangement of the grain structure • pressure exerted by the pad 1000-5000 kpa depending on the size of the roller • utilized in layers of 15-30 cm in depth • usually require 3-5 passes to achieve density ENCI 579

  33. CompactionCompaction Equipment • Padded Wheel or “Sheep’s Foot” Rollers ENCI 579

  34. CompactionCompaction Equipment • Pneumatic Tire Rollers • 2-12 rubber tires on each axle • individual tires wobble or weave or move lower than adjacent tires to improve the kneading action • effective in clay and granular soils and asphalt mixtures can be kneaded and compacted • effective depths for soils or base courses is up to 15 cm (larger units of 40-50 tonnes 30 cm) ENCI 579

  35. CompactionCompaction Equipment • Pneumatic Tire Rollers ENCI 579

  36. CompactionCompaction Equipment • Smooth Drum Non-vibratory Rollers • used for finishing or sealing passes on soils and granular layers • final leveling passes on asphalt layers • Vibrating Plates or Tampers • used for trench backfills • around structures where larger equipment can’t operate • larger tamping equipment is usually attached to excavators or other equipment ENCI 579

  37. CompactionQuality Control • Determine which materials are to be sampled and tested • Frequency of the testing and type of tests to be performed on the material • Transportation authorities usually have specifications outlining these criteria • Moisture Density 1/ soil type (or 5000 m subgrade) • Field Compaction 4/500 m of each layer • Method Specification vs EPS Specifications ENCI 579

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