Field Compaction Specification Allowable Moisture Range

1. Field Compaction Specification • Allowable Moisture Range

2. Soil Compaction • Moisture Density Relationship • Factors Affecting Compaction • Field Compaction Specification

3. Soil Compaction • Compaction: • The artificial process of densifying a soil mass by application of mechanical energy. • Decrease in Void Ratio • Increase in Dry Density or Unit Weight • Increase in Strength • Stiffness • Bearing capacity • Reduced Settlement • Decrease in compressibility • Decrease in Permeability • Compactive Effort • Mechanical energy consumed during compaction • removes air and reorients particle • Water provides lubrication

4. Moisture-Density Relationship • An unique relationship for a specific soil with a particular compactive effort: • Laboratory determination • Standard Proctor Test (AASHTO T 99) • Modified Proctor (AASHTO T 180) • Point of interest • Maximum Dry Density or Dry Unit Weight • Optimum Moisture Content (OMC) • Zero Air Void (ZAV) Line • Theoretical determination • Does not depend on compactive effort • No air voids • Maximum possible density at any moisture content

5. Moisture-Density Relationship • Factors • Soil type • Moisture content • Compaction Energy

6. Accuracy of MDD and OMC • Single Lab: • MDD 2.2 pcf • OMC 10% of mean • Multilab • MDD 4.5 pcf • OMC 15% of mean • OMC Lab1: 37% and Lab2: 43% • 15% of mean 40 is 6% OK – Muiltilab • At 40% OMC, it would be ±3% of mean

7. Accuracy of MDD and OMC • To Reduce variability • Replicate measurements: • For three replicate measurements: • Variability would be 1/√3

8. Influence of Moisture • Influence of Moisture • Coarse Soil – not significant • Eventually drains out • Fine Soil - significant • Increase in moisture • Reduce strength • Reduce stiffness • Decrease permeability up to OMC • Compressibility -

9. Moisture-Density Relationship Higher Compactive Effort With such a high MC, it will never be possible to achieve this density Zero- Air-Void-Line γdry Water Content, w (%)

10. Moisture-Density Relationship Higher Compactive Effort With such a high MC, density could only be achieved with higher compactive effort Zero- Air-Void-Line γdry Water Content, w (%)

11. Field Compaction Specification • Density Specification • Achieve a compacted field dry unit weight of 95 or 100% of the maximum dry unit weight determined in the lab by standard proctor test • Field Density • Sand Cone • Nuclear Density Gauge

12. Field Compaction Specification • Moisture Control – allowable range • Most agencies • Optimum ± x% (ex: 2 or 3%) • Or, Optimum ± x% point • VDOT • Optimum ± x% of optimum • (example: 20% of optimum) • Moisture Measurement • Nuclear moisture gauge • Repeated measurements – low variability

13. 20% of OMC vs 2% point • Both similar for OMC up to 10 -15% • Mostly coarse soils • Influence of moisture is minimum • High OMC • Fine Soil • Very sensitive to moisture • Significantly influences • Strength and stiffness

14. 20% of OMC vs 2% point • High OMC - example 40% • 20% of Optimum – range ±8% (32% to 48%) • Wide range • Close to 100% saturation or even more • High Compactive effort - Weaker soil • 2% point – range ±2% (38% to 42%) • Is it too restrictive? • What has historically been achieved in the field • Better quality subgrade