COMPACTION OF SOIL

1. COMPACTION OF SOIL • Definition: It is the process of bringing the soil particles close together to a dense state by the application of energy. • Purpose: • To improve the density of soil • To improve the shear strength of soil • To improve the bearing capacity of soil • To reduce the permeability of soil • To reduce the compressibility of soil • To reduce the shrinkage of soil • To reduce the frost susceptibility of soil

2. Compaction of soil is usually required when used as a fill The soil is commonly used as a fill material in the following cases. • To back fill an excavation e.g., for foundations. • To develop a made-up ground to support a structure. • As a sub-grade or sub-base for roads, railways or airfields • As an earth dam. • To raise the floor level to the required height in buildings. • As a back fill behind retaining walls. • To develop a site (residential, industrial, recreational etc.) in a difficult terrain (undulating topography) where substantial cutting and filling is involved.

3. FACTORS AFFECTING COMPACTION OF SOIL 1. Moisture Content Dry density ~ moisture content relationship

4. 2. Compaction Effort or Energy Dry density ~ moisture content curves for different compaction efforts

5. Compaction energyFor standard AASHTO test Compaction energyFor Modified AASHTO test CE = (5 layers)(25 blows)(10 lb weight)(1.5 ft drop) (1/30 ft3) = 56,250 ft-lb/ft3 (2693.3 kJ/m3)

6. Table: Specifications for Standard and Modified AASHTO Tests

8. 3. Soil Type A-4, A-5 A-6, A-7-6 Water Content (%) Dry density ~ moisture content curves for different soils

9. Method of Compaction • Kneading compaction • Static compaction • Dynamic compaction • Vibratory compaction • Admixture • Material added to the soil to improve its properties • Density will depend on the type and amount of admixture • Processing amount, • By thorough mixing of moisture in the soil higher dry density is achieved. Thorough mixing requires greater manipulation and curing time. • Energy distribution, • Uniform distribution of blows on each layer gives better compaction and higher dry density is obtained.

10. Standard AASHTO test equipment: (a) mould; (b) hammer

11. Where, W = weight of compacted sample in the mould V(m)= volume of the mould = 1/30 ft3 Where, m = moisture content Moisture-Dry density Curve

12. Where, • γzav= Zero air-void dry density • γw= density of water • e = void ratio • Gs= specific gravity of soil solids • For 100% saturation, e = mGs Where, m = moisture content

13. Modified proctor test apparatus (a) mould (b) hammer

14. COMPARISON OF AASHTO & MODIFIED AASHTO COMPACTION Table Comparison of AASHTO & modified AASHTO compaction

15. DETERMINATION OF FIELD DENSITY 1. Drive cylinder method 2. Sand cone method 3. Rubber balloon method 4. Nuclear density meter DRIVE CYLINDER METHOD Drive cylinder pushed into the soil and the surrounding soil excavated to take out the cylinder

16. Safest possible nuclear design as the source never leaves the meter. There is also automatic shielding when carried. • Faster testing time. • Larger samples tested: Using a new back scatter technology permits testing samples up to 20 times larger than direct transmission units. • The factory set density calibration to eliminate operator error. • The built-in brain and memory virtually eliminates need for special operator skills. The keyboard is used for all tests. The meter is factory calibrated for all materials. The following features speed up testing. • Separate systems take moisture and density reading simultaneously to cut time to half. • Immediate display of wet and dry densities. • Lab. densities can be entered and stored in memory bank. • Immediate display of relative compaction as a % of laboratory dry density. • Storage and display of previous contact, air gap, or moisture counts for subsequent reuse if new data is not needed. • No charts or tables. • No elaborate soil preparation or hole punching. • No field calibration.

17. MERITS AND DEMERITS OF THE FIELD DENSITY METHODS • The Drive Cylinder method is easy and quick. The cutting edge is easily damaged and need re-sharpening. This method is best suited for soft and cohesive soil. • The Sand-Cone method is relatively slow, but it can be used for any type of soil. • The Water-Displacement method is a lengthy process and it can only be used on cohesive soil. • The Rubber-Balloon method is easy and quick, but the results are not very reproducible owing to the difficulty of controlling the air pressure and ensuring that the balloon conforms to the shape of the hole. The method is not applicable to very stony soils. • The Nuclear Method is considerably faster to perform than the sand-cone and rubber-balloon methods. It has the disadvantage, however, of potential hazards to individuals handling radioactive materials.

18. FIELD COMPACTION • Commonly by use of rollers. • Type of roller depends on the type of soil and the degree of compaction required. • The roller may be self-propelled or towed. • The most common types of rollers are: • Smooth-wheel roller • Pneumatic rubber-tired roller • Sheep-foot roller • Vibratory roller • 5. Grid roller

19. Advantages of the Improved Design of the SAKAI Rollers The following features of the improved design of the SAKAI (JAPAN) road rollers give smooth steady rolling and excellent maneuverability for high-class compaction work. These features ensure high performance capabilities. The rollers with these features provide better, economical and more effective compaction. • Equal drum diameter • 2. Centre-pin steering • 3. Independent steering for front and rear drums (axles) • 4. All wheels driven

20. VIBRATORY ROLLERS • Smooth drum-and-tire type vibratory roller • Pad-foot drum-and-tire type vibratory roller • Double-drum type vibratory roller • All-drum drive and vibration vibratory roller • Tractor towed vibratory roller • f. Hand-guided vibratory roller

21. COMPACTING CAPABILITY OF ROLLER The amount of material (weight or volume) compacted to the specified density by a given roller per unit time is known as the capability of roller. It depends on the following factors. 1. Working width (W) 2. Speed of roller (S) 3. Number of passes (N) 4. Thickness of layer (D) Asphalt Compaction Theoretical capability = Soil Compaction Theoretical capability =

22. FACTORS AFFECTING FIELD COMPACTION Following are the factors, which affect the field compaction. 1. Type of the compacting equipment 2. Field moisture content 3. Number of passes of the compacting equipment 4. Thickness of the lift (layer) 5. Speed of the compacting equipment 6. Soil type Relation between dry density and number of roller passes

23. Table: General Guide to Selection of AASHTO Groups Based on Anticipated Embankment Performance

24. Table: Compaction Characteristics and Ratings of the Unified Soil Classification (USC) Groups

25. Table: Compaction Characteristics and Ratings of the Unified Soil Classification (USC) Groups

26. SPECIFICATIONS FOR FIELD COMPACTION Where, R = relative compaction For granular soil the term relative density as defined below is commonly used Where, Dr = Relative density Where Ro =

27. Dry density m4 m1 m2 m3 Moisture Content, m Fig: Most economical compaction condition

28. Fig: Effect of compaction on structure of cohesive soil

29. Compacted dry of optimum Void ratio, e Compacted wet of optimum Compacted dry of optimum Pressure (natural scale) Low-pressure consolidation Fig: Effect of compaction on compressibility of clayey soil Compacted wet of optimum Void ratio, e Pressure (log scale) High-pressure consolidation Fig: Effect of compaction on compressibility of clayey soil

30. Fig: Effect of compaction on the strength of clayey soils Fig: Qualitative stress-strain curves for clay compacted on dry & wet sides of optimum and tested at moulding moisture content as well as after soaking to produce saturation.