CHAPTER 6 COMPACTION

Omitted Sections 6.6, 6.7, 6.8

 In practice, the at a given site are often less than desirable for the intended purpose. They may be:  Weak (strength)  Highly compressible  Have a high permeability Solution Relocate the project Articulate design for structure members Stabilize or improve the properties of the soil The third alternative may be in most cases the most economical alternative. There are different techniques for improvement of soils (This subject is covered in details in CE 486 “Improvement of Geotechnical Materials”). We will consider in this course only compaction. SOIL COMPACTION

 Compaction is also very important when soil is used as an engineering material, that is the structure itself is made of soil.

Ex. .Earth dams .Highways .Airfields .etc.

Definition Compaction is the densification of soils by removal of air through the application of mechanical energy.

The degree of compaction is measured in terms of its dry unit weight. SOIL COMPACTION

Increases unit weight

Increases

Increases

Increases stability of slopes of embankments

Decreases settlement of structures SOIL COMPACTION

You remember -graded

reduced Air Air Compaction Water Water

Solid Solid SOIL COMPACTION

General Principle The degree of compaction of soil is measured by its dry unit weight. When water is added during compaction it acts as a softening agent on the soil particles.

gd(max) When the moisture content is Soil Solid gradually increased, the weight of the soil solids in a unit water volume gradually increases.

Soil Solid

 Optimum moisture content (OMC) isgthe at which the maximum dry unit weight d (max) is attained. SOIL COMPACTION

Soil Solid

water

Soil Solid SOIL COMPACTION

Types of Compaction Methods in the Laboratory •Impact or dynamic (The most common type) •Kneading •Static  The laboratory test generally used to obtain the maximum dry unit weight of compaction and the optimum moisture content is called the Proctor compaction test.  It is named after R. R. Proctor (1933) (engineer in LA). He established that compaction is a function of: 1.Moisture Content 2.Compactive Effort 3.Soil Type  There are two methods or tests:  Standard Proctor test (ASTM D-698 & AASHTO T-99)  Modified Proctor test (ASTM D-1557 & AASHTO T-180) Standard Proctor Test

• Mold 1/30 ft3 in volume • 3 layers • 25 blows • 5.5 lb hammer • 12 inch drop

Mold Hammer

The procedure for the standard Proctor test is elaborated in ASTM Test Designation D-698 (ASTM, 2007) and AASHTO Test Designation T-99 (AASHTO, 1982). Standard Proctor Test Standard Proctor Test

Process of Compaction  Several samples are mixed at different water contents  Compact according to the compaction test (standard or modified). W g moist  Vmold W = Weight of compacted soil in the mold 3 Vmold = Volume of the mold = (1/30 ft )  For each test find the moisture content of the compacted soil.  The dry unit weight is given by g g  moist d 1 w

 Plot g d vs. w

 From the plot, find OMC and g d (max) Standard Proctor Test

 In order to avoid a large number of compaction tests, it is desirable to begin the first test at a moisture content that is about 4 to 5% below the approximate optimum moisture content. Standard Proctor Test

REMARKS

1. Each data point on the curve represent a single compaction test.

2. Four or five tests are required

3. The curve is unique for: - A given soil type - Method of compaction - (constant) compactive effort

4. gd(max) is only a maximum for a specific compactive effort and method of compaction. This does not necessarily reflect the maximum dry unit weight that can be obtained in the field. 5. Typical OMC are between 10% and 20%. Outside maximum range 5% to 40%. Standard Proctor Test

6. Increasing the compactive effort tends to increase the maximum dry density, as expected, but also decrease the OMC. (This is why the curve never be to the right of zero curve). 7. In practice less amount of water is used but higher compactive effort or vise versa.

8. For soils gd(max) tends to decrease as plasticity increases.

9. The approximation to field is not exact because the lab. test is a dynamic impact type, whereas field compaction is essentially a kneading-type compaction.

10. In the field, compactive effort is the number of passes or “coverage” of the roller of a certain type and weight on a given volume of soil. Standard Proctor Test

Theoretical g d(max)

The maximumg d (max)is obtained when no air in the voids (i.e. s =100%) G g  s g d 1 e w

but wGs  se for S 100% e  wGs G g g  s g  w z av w 1 1 wGs  w Gs

Where gzav = zero air void unit weight.

 The relationship between gzav and w can be obtained as shown in the figure across.  Compaction curve is always to the left of the zero-air-void curve. No matter how much water is added, the soil never becomes completely saturated by compaction. Standard Proctor Test

To obtain the variation of gzav with moisture content, use the following procedure:

Under no circumstances should any part of the compaction curve lie to the right of the zero-air-void curve. FACTORS AFFECTING COMPACTION

Besides moisture content, other important factors that affect compaction are: 1) Soil type; 2) Compaction effort.

1. Effect of Soil Type

 Grain Size Distribution  Shape of the soil grains

 Gs  Amount of clay minerals  Type of clay minerals

Fine grain soil needs more water to reach optimum. FACTORS AFFECTING COMPACTION

Effect of Soil type and gradation

Fine grain soil needs more water to reach optimum. FACTORS AFFECTING COMPACTION

Effect of Soil type and gradation Gs g w g  g  Typical Values z av w 1 1 wGs  w 3 Gs g d (max)(kN/m ) OMC (%)

Well graded SW 22 7

Sandy clay SC 19 12

Poorly graded sand SP 18 15

Low plasticity clay CL 18 15

Non plastic ML 17 17

High plasticity clay CH 15 25

 Gs is constant, therefore increasing maximum dry unit weight is associated with decreasing optimum moisture contents.

 Do not use typical values for design as soil is highly variable. FACTORS AFFECTING COMPACTION

Compaction Curves Encountered in Soils •The bell-shaped compaction curve is typical for most clayey soils.

Typical

•Some curves have more than one peak others have no peak. FACTORS AFFECTING COMPACTION

2. Effect of Compaction Effort

Standard Proctor

For the standard Proctor test

• The standard Proctor mold and hammer were used to obtain these compaction curves. • For all cases the number of layers was equal to 3. g Compaction effort dmax

wopt. EXAMPLE 6.1

TEXT IN SI UNITS EXAMPLE 6.1

TEXT IN SI UNITS EXAMPLE 6.1

TEXT IN SI UNITS EXAMPLE EXAMPLE Example (2nd Midterm Exam Fall 40-41)

If you are checking the field compaction of a layer of soil and the compaction curve for the soil is shown in Figure 1. From the specifications, the dry density of the compacted soil should be at least 95% of the maximum value and within ± 1% of the optimum water content. When you did the sand cone test, the volume of the soil excavated was 1153 cm3. It weighed 2209 grams wet and 1875 grams dry. a. What is the compacted dry density? b. What is the field water content? c. What is the relative compaction? d. Does the test meet the specifications (explain)? e. If it does not meet, what should be done to improve the compaction so that it will meet the specifications? f. What is the degree of saturation of the field sample? g. If the sample were saturated at constant density, what would be the water content? Modified Proctor Test

Modified Proctor Test (ASTM D-1557, AASHTO T-180)

 With the development of heavy rollers (also requirements of heavy aircrafts and trucks) and their use in field compaction, the standard Proctor test was modified for better representation of the field conditions. This is sometimes referred to as modified Proctor test.

•Mold 1/30 ft3 in volume (same as for standard test) •5 layers •25 blows (same as for standard test) •10 lb hammer •18 inch drop

 Developed in WWII by U.S. Army Corps of Engineers to better represent the compaction required for airfield to support heavy aircraft. Modified Proctor Test

Modified Proctor Standard Proctor Test Test

Layer 5 Layer 4 Layer 3 Drop = 457.2 mm Layer 2 (18 in) Layer 1

Drop = 304.8 mm (12 in)

hammer hammer = 2.5 kg (5.5 lb) = 4.54 kg (10 lb) Modified Proctor Test

Standard Modified Proctor Proctor Test Test Volume of mold 944 cm3 944 cm3

# of layers 3 5 Mass of hammer 2.5 kg 4.54 kg Drop of hammer 30.5 cm 45.7 cm # of hammer blows 25 25 Compaction Energy for Unit Volume of Soil

 Standard Proctor Test

(25)(3)5.5(1) E  12375 ft -lb/ft 3  592.5 kN  m/ m3  600 kN  m/ m3 (1/ 30)

 Modified Proctor Test

(25)(5)10(1.5) E   56250 ft -lb/ft 3  2693.3 kN  m/ m3  2700 kN  m/ m3 (1/ 30)

. Because it increases compactive effort, the modified Proctor test results in an increase of the maximum dry unit weight of the soil, and this is accompanied by decrease in the optimum moisture content.

. Note: In the field, compactive effort is the number of passes of the roller of a certain type and weight on a given volume of soil. SOIL COMPACTION FIELD COMPACTION FIELD COMPACTION

Most of the compaction in the field is done by means of ROLLERS.

The most common types are:

1. Smooth-wheel rollers (smooth-drum rollers)

2. Pneumatic rubber-tired rollers

3. Sheepsfoot rollers

4. Vibratory rollers FIELD COMPACTION

1. Smooth-wheel rollers (smooth-drum roller) Proof rolling subgrades Finishing operation of fills with sandy &clayey soils Provide 100% coverage Contact pressure 310 – 380 kN/m2 Not suitable for producing high g for thicker layers FIELD COMPACTION

2.Pneumatic rubber-tired rollers

Heavily loaded with several rows of tires

Tires are closely spaced 4 -6 in a row

Provide 70-80% coverage

Contact pressure 600 – 700 kN/m2

Combination of pressure and kneading FIELD COMPACTION

3.Sheepsfoot rollers

Drums with a large number of projections

Area of each projection 25 – 85 cm2

Most effective in compacting clayey soils

Contact pressure 1400 – 7000 kN/m2 FIELD COMPACTION

4.Vibratory rollers  Efficient in compacting granular soils  Vibrators can be attached to smooth-wheel, pneumatic rubber-tired, or sheepsfoot rollers to provide vibratory effects to the soil.

Figure 6.20 Principles of vibratory rollers FIELD COMPACTION

Handheld vibratory Handheld vibratory plates can be used for effective compaction of granular soils over a limited area. FACTORS AFFECTINGFIELD COMPACTION

There are several factors that must be considered to achieve the desired unit weight of compaction in the field:

Soil type

Moisture content

 Thickness of lift

 Intensity of pressure

 Area over which the pressure is applied

No. of roller passes FIELD COMPACTION

Compaction of Silty Clay FIELD COMPACTION

Vibratory Compaction of Sand FIELD COMPACTION

In most cases, about 10 to 15 roller passes Lack of confining pressure yield the maximum dry unit weight towards the surface economically attainable.

Relationship between dry unit weight Relationship between dry unit weight, and number of passes number of passes, and depth. SPECIFICATIONS FOR FIELD COMPACTION

. Usually it is required for the contractor to achieve a compacted field dry unit weight of say 90 to 95% of the maximum dry unit weight determined in the laboratory by either the standard or modified Proctor test (Recall previous examples).

Relative compaction, R (a)

. For granular soils, specifications can be expressed in terms of relative density. Applicable if the soil (b) contains less than 12% fines (passing No. 200 sieve) From (a) and (b)

where FIELD COMPACTION

Dividing by

R

1 R FIELD COMPACTION

Solve for R

. Approximate formula for granular soils EXAMPLE 6.8 Determination of Field Unit Weight of Compaction

We know that both relative compaction or relative density are both needed for determination of dry density in the field.

Common Methods: 1. Sand cone method

2. Rubber balloon method

3. Nuclear method Sand cone method

1. Sand cone method (ASTM Designation D-1556)

 Filling the jar with very uniform dry Ottawa sand

 W1 = weight of the jar, the cone, and the sand filling the jar

 Excavating a small hole in the area where the soil has been compacted

 W2 = weight of the moist soil excavated from the hole.

 W3 = the dry weight of the soil = Recall  = moisture content  = Ww/Ws Sand cone method

 The cone with the sand-filled jar attached to it is inverted and placed over the hole.

 W4 = combined weight of the jar, the cone, and the remaining sand filling the jar.

 W5 = weight of sand to fill both the hole and cone

 V = the volume of the excavated hole

Wc= weight of sand to fill the cone only

g d (sand)  dry unit weight of Ottawa sand used

 The dry unit weight of compaction made in the field is determined as W g  3 d ( field ) V Field Density Test Field Density Test EXAMPLE 6.9

Proctor test

Sand Cone Test EXAMPLE 6.9 EXAMPLE 6.9 EXAMPLE 6.10

Proctor test

Sand Cone Test Proctor test EXAMPLE 6.10

Sand Cone Test RUBBER BALLOON METHOD

2. Rubber Balloon Method (ASTM Designation D-2167) Similar to sand cone method except that the volume of the hole is determined by introducing into it a rubber balloon filled with water from a calibrated vessel.

Determine weight of dry soil Determine volume of the hole (can be read directly) Determine dry unit weight Nuclear Method

3. Nuclear Method (ASTM D6938 - 15 ) . Nuclear density meter (Densometer) o Dense soil absorbs more radiation than loose soil. o Measures the weight of wet soil per unit volume and the weight of water present in a unit volume of soil. o The dry unit weight of compacted soil can be determined by subtracting the weight of water from the moist unit weight of soil.

Operates either in drilled holes or on ground surface Uses radioactive isotope source (Gamma rays) Measure weight of wet soil per unit volume It also measure weight of water per unit volume Determine the dry unit weight of soil Special Compaction Techniques Special Compaction Techniques

Vibroflotation

A technique for in situ densification of thick layers of loose granular soil deposits. Special Compaction Techniques Special Compaction Techniques GSD and compaction by vibrflotation

The most suitable for compaction by The rate of probe Vibroflotation. penetration may be slow and may prove uneconomical in the long run. Difficult to compact

Lower limit of grain-size distribution for which compaction by vibroflotation is effective. Special Compaction Techniques

RATING BACKFILL (Brown , 1977)

SN = Suitability No. for rating backfill where D50, D20, and D10 are the diameters (in mm) through which, respectively, 50, 20, and 10% of the material passes.

The smaller the value of SN, the more desirable the backfill material. Special Compaction Techniques

Typical patterns of Vibroflot probe spacings for a column

Compaction over a large area EXAMPLE 6.11 Special Compaction Techniques

Dynamic Compaction Densification of granular soil deposits Dropping a heavy weight on the ground at regular intervals Weight of hammer 80-360 kN Hammer drop 7.5-30.5 m

Degree of compaction depends on: Weight of hammer Height of hammer drop Spacing of locations at which the hammer is dropped Special Compaction Techniques

Blasting

 Compaction (up to a relative density of 80%) up to a depth of about 18 m over a large area can easily be achieved.  Usually the explosive charges are placed at a depth of about two-thirds of the thickness of the soil layer desired to be compacted. THE END