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Soil Compaction

Soil Compaction. COSC 323: Soils in Construction. Question. The contractor, during construction of the soil embankment, conducted a sand-cone in-place density test to determine whether the required compaction was achieved. The following data were obtained during the test:

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Soil Compaction

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  1. Soil Compaction COSC 323: Soils in Construction

  2. Question • The contractor, during construction of the soil embankment, conducted a sand-cone in-place density test to determine whether the required compaction was achieved. The following data were obtained during the test: • Weight of sand used to fill test hole and funnel of sand-cone device = 845 g. • Weight of sand to fill funnel = 323g. • Unit weigh of sand = 100 lb/ft3 • Weigh of wet soil from test hole = 600g • Moisture content of soil from test hole = 17%. • Based on the contract, the contractor is supposed to attain the 95% compaction. Will you approve the contractor’s work?

  3. Compaction • Compaction – expelling air from the void space • Consolidation – extrusion of water • Effects of compaction • Increase soil’s shear strength • Decrease in future settlement of the soil • Decrease in its permeability • How to quantify – use dry unit weight of soil

  4. Compaction • What does water do for compaction? • Lubricant • Too much water  lesser density • Optimum moisture content(=maximum dry unit weight)  best compaction • How to use maximum dry unit weight? • Target unit weight at the job site • Need to know how much the soil can be compacted.

  5. Compaction Test • ASTM D 698 • Standard Proctor Compaction Test • Hammer: 5.5 lb • Drop Height: 12in • ASTM D 1557 • Modified Proctor Compaction Test • Hammer: 10 lb • Drop Height: 18in • For higher value of dry unit weight

  6. Compaction Test • Dry out soil sample • Add water to the soil sample • Compact the soil sample in the compaction mold • Measure wet unit weight (g) • Measure moisture content (w) • Calculate dry unit weight • Repeat 4 times with different moisture contents

  7. Proctor Curve

  8. Example • Condition • The combined weight of a mold and the specimen of compacted soil it contains is 9.0 lb. • The mold’s volume is 1/35ft3 • The mold’s weight is 4.35 lb. • The specimen’s water content is 12%. • What is dry unit weight of the specimen?

  9. Example • A set of laboratory compaction test data and results is tabulated as follows. Determine the soil’s maximum dry unit weight and optimum moisture content.

  10. What affects Compaction? • Moisture content • Compaction effort • Compaction energy per unit volume (function of number of blows per layer) • For the stand proctor test: 12,400 ft-lb/ft3 • For the modified proctor test: 56,000 ft-lb/ft3 • Type of soil • Grain size distribution • Specific gravity of solids • Type and amount of clay materials

  11. Compaction

  12. Facts about Compaction • Maximum dry unit weight • Min: Organic soils (60lb/ft3) • Max: Well-graded granular material (145 lb/ft3) • Optimum moisture contents • Min: Granular material (5%) • Max: Elastic silts and clays (35%) • Higher optimum moisture contents = Lower dry unit weight

  13. Field Compaction • Compacted in layers • 8 in. loose horizontal layer  compacted to a thickness of 6 in. • Sprinkling or drying to control moisture content • Scarifying to provide bonding between layers. • Equipments • Tempers – Limited in scope and compacting ability • Rollers • Smooth wheel roller, Sheepsfoot roller, Pneumatic roller, Vibratory roller

  14. Field Compaction • Smooth wheel roller • Provide a smooth finished grade • Used for paving

  15. Field Compaction • Sheepsfoot roller • Greater compaction pressure • Effective for compacting fine-grained soil

  16. Field Compaction • Pneumatic roller • Effective for compacting clayey soil and silty soils

  17. Field Compaction • Vibratory roller • Effective for compacting granular materials: clean sands and gravels

  18. Dynamic Compaction • When • Existing surface or near-surface soil is poor with regard to foundation support • For which soil? • Both cohesive and cohesionless soils • How • Drop a very heavy (2~20 tons) weight onto the soil from a relatively great height (20 ~ 100 ft) • Dropping weight randomly?  a closely spaced grid pattern is selected.

  19. Dynamic Compaction

  20. Dynamic Compaction • How deep soil will be affected? • Approximate depth of influence of dynamic compaction (D)

  21. Dynamic Compaction • How many drops do we need? • Typically 5~10 drops • Additional drops beyond 10 drops improves little • What about craters? • Need to be backfilled and compacted by other means

  22. In-Place Soil Unit Weight Test • Destructive testing method • Sand-cone • Rubber-balloon methods • Nondestructive method • Nuclear moisture-density apparatus • Soil unit weight is inversely proportional to the amount of radiation that reaches the detector. • Speedy Moisture Tester

  23. In-Place Test: Sand-cone method

  24. Example • During construction of a soil embankment, a sand-cone in-place unit weight test was performed in the field. • Weight of sand used to fill test hole and funnel of sand-cone device = 867g • Weigh of sand to fill funnel = 319g • Unit weigh of sand = 98.0 lb/ft3 • Weigh of wet soil from the test hole = 747g • Moisture content of soil from test hole = 13.7%

  25. Example 4-3

  26. In-Place Test: Rubber-balloon

  27. In-Place Test: Nuclear Apparatus Nuclear moisture-density apparatus

  28. Field Control of Compaction • Required percent of compaction the required in-place dry unit weight = ----------------------------------------------------- x 100% the maximum laboratory dry unit weight • Minimum number of field unit weight tests required. • Maximum thickness of loose lifts (layers) • Methods to obtain maximum dry unit weight • Methods to determine in-place unit weight

  29. Example • Given • Soil from a borrow pit to be used for construction of an embankment gave the following laboratory results when subjected to the ASTM D 698 Standard Proctor test • Maximum dry unit weight = 118.5 lb/ft3 • Optimum moisture content = 12.5% • The contractor, during construction of the soil embankment, achieved the following • Dry unit weight reached by field compaction = 117.8 lb/ft3 • Actual water content = 13.7% • Required • Percent of compaction achieved by the contractor

  30. Example • Solution

  31. Example • Given • A borrow pit’s soil is being used as earth fill at a construction project. • The in situ dry unit weight of the borrow pit soil was determined to be 17.18 kN/m3 • The soil at the construction site is to be compacted to a dry unit weight of 18.90 kN/m3 • The construction project requires 15,000m3 of compacted soil fill. • Required • Volume of soil required to be excavated from the borrow pit to provide the necessary volume of compacted fill.

  32. Example • Solution

  33. Example • Given • The in situ void ratio of a borrow pit’s oil is 0.72. • The borrow pit soil is to be excavated and transported to fill a construction site where it will be compacted to a void ratio of 0.42. • The construction project requires 10,000 m3 of compacted soil fill. • Required • Volume of soil that must be excavated from the borrow pit to provide the required volume of fill

  34. Example • Solution

  35. Example • Solution

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