# Objectives Be able to use basic volume weight equations

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Objectives Be able to use basic volume weight equations
Understand principal of soil compaction. Explain how the compaction test is used in design and quality control Be able to perform basic compaction test (LAB EXERCISE) plot compaction data and evaluate for accuracy Understand procedure for Atterberg Limit Tests (LAB EXERCISE)

Review of Compaction Principles
Compaction Tests are not suitable for soils with more than 30 % by weight of the sample being larger than a ¾” sieve. Compaction tests are not usually performed on soils with 12 % or fewer fines

Review of Compaction Principles
Relative Density testing is used for clean sands and gravels – covered later in class Standard Procedures for testing are available for soils with some gravel (less than the maximum allowable content)

Principle of compaction
Theory developed by R.R. Proctor in 1930’s in California Three Factors determine the density that results from soil compaction

Proctor Developed Principle
Three variables determine the density of a compacted soil The energy used in compaction The water content of the soil The properties of the soil

State Diagram Dry Density, pcf 100 % saturation curve Water content, %

State Diagram Dry Density, pcf Water content, %

Energy Used in Compaction
Assume you have some clay soil that is at a water content of 16 percent. Look at the effect different compaction energy has on the density of the soil. Energy expressed as number of passes of a sheepsfoot roller on a lift of soil

At this water content, energy has a large effect on compacted density
10 passes of equipment Dry Density, pcf 4 passes of equipment 3 passes of equipment 2 passes of equipment 1 pass of equipment Water content, %

At this point, the sample has had most of its air driven out by the compaction
10 passes of equipment Dry Density, pcf 100 % saturation line Water content, %

At a lower water content, energy has little effect on the compacted density of a clay soil
Dry Density, pcf 10 passes of equipment 4 passes of equipment 3 passes of equipment 2 passes of equipment 1 pass of equipment Water content, %

Compacting at low water contents
At low water contents, insufficient water is available to lubricate the particles and allow them to be rearranged into a dense structure. The frictional resistance of dry particles is high

At a very high water content, energy has little effect on the compacted density of a clay soil because the water is incompressible and takes the applied force without densifying the soil Dry Density, pcf 10 passes of equipment 4 passes of equipment 3 passes of equipment This results in a term called pumping 2 passes of equipment 1 pass of equipment Water content, %

Compacting Very Wet Soil
At this point, few air pockets remain – compaction forces are carried by water in soil which is incompressible

Water has Zero Shear Strength

Water has Zero Shear Strength

Effect of Water Content
Now examine the effect of just changing the water content on a clay soil, using the same energy each time the soil is compacted. For example, assume soil is spread and compacted with 4 passes of a sheepsfoot roller each time. Examine using State Diagram

Effect of Water Content
Dry density, pcf 99.0 pcf Sample 1 compacted at 12 % water – Dry Density is 99.0 pcf 12 % Water content, %

Effect of Water Content
Dry density, pcf Sample 2 compacted at 14 % water – Dry Density is pcf 104.5pcf 14 % Water content, %

Effect of Water Content
Dry density, pcf 105.5pcf Sample 3 compacted at 16 % water – Dry Density is pcf 16 % Water content, %

Effect of Water Content
Dry density, pcf Sample 4 compacted at 18 % water – Dry Density is 98.5 pcf 98.5 pcf Water content, % 18 %

Effect of Water Content @ constant energy
Dry density, pcf Maximum dry density, pcf Optimum water content, % Water content, %

Now, perform the same test at a different (Higher energy) on the soil
Dry density, pcf 10 passes of sheepsfoot roller 4 passes of sheepsfoot roller Water content, %

Effect of Soil Type on Curves
Dry density, pcf Plastic Clay Soils have Low Values of Maximum Dry Density 80-95 pcf Water content, %

Effect of Soil Type on Curves
Dry density, pcf 20-40 % Plastic Clay Soils have high values for optimum water content (20-40 %) Water content, %

Effect of Soil Type on Curves
Dry density, pcf Plastic Clay Soils have a Flat Curve for Lower Energies Density Water content, %

Effect of Soil Type on Curves
Dry density, pcf pcf Sandy Soils with Lower PI’s have High Values of Maximum Dry Density Water content, %

Effect of Soil Type on Curves
Dry density, pcf Sandy Soils with Lower PI’s have Low Values of Optimum Water Content 8-15 % Water content, %

Effect of Soil Type on Curves
Dry density, pcf Sandy Soils have a Steep Curve – Short distance from plastic to liquid states of consistency Water content, %

Summary Lower PI – Sandier Soils in this Region 110-135
Dry density, pcf Intermediate PI Soils in this Region 95-120 Higher PI – Clayey Soils in this Region 75-95 Water content, %

Lower PI – Sandier Soils in this Region
Summary Lower PI – Sandier Soils in this Region 8-14 Dry density, pcf Intermediate PI Soils in this Region Higher PI – Clayey Soils in this Region 20-40 12-20 Water content, %

Family of Curves (Covered Later)

Zero air voids curve not parallel to line of optimums at upper end
Family of Curves Zero air voids curve not parallel to line of optimums at upper end gd, dry density, pcf Line of Optimums water content, %

Proctor’s principle of compaction
Using a standard energy, if a series of specimens of a soil are compacted at increasing water contents, the resultant dry density of the specimens will vary. The density will increase to a peak value, then decrease.

Principle of Compaction
A plot of the dry density versus the water content from a compaction test will be parabolic in shape. The peak of the curve is termed the maximum dry density, and the water content at which the peak occurs is the optimum water content.

Standard Proctor Energies
Several standard energies are used for laboratory compaction tests Standard – 12,400 ft-lbs/ft3 Modified – 56,000 ft-lbs/ft3 California – 20,300 ft-lbs/ft3

Standard Proctor Compaction Test Summary
5.5 # hammer Uses 5.5 pound hammer dropped 12 inches mold filled in 3 lifts 25 blows of hammer per lift Total energy is 12,400 ft-lbs/ft3 12”drop 3 lifts

Modified Proctor Compaction Test Summary
10 # hammer Uses 10 pound hammer dropped 12 inches mold filled in 5 lifts 25 blows of hammer per lift Total energy is 12,400 ft-lbs/ft3 18”drop 5 lifts

Proctor Compaction Test Summary
Several Standard molds are used depending on maximum particle size in sample 4”diameter mold (1/30 ft3) used for soils with low gravel contents Method A for soils with < 20 % gravel Method B for soils with > 20 % gravel and < 20 % larger than 3/8”

Proctor Compaction Test Summary
Several Standard molds are used depending on maximum particle size in sample 6”diameter mold (1/13.33 ft3) used for soils with significant gravel contents More than 20 % gravel larger than 3/8” Must have less than 30 % larger than 3/4”

Proctor Compaction Test Summary
Standardized tests are not available for soils with more than 30 percent by weight of the total sample being larger than 3/4”in diameter gravels ASTM Compaction Test Methods are D698A D1557A D698B D1557B D698C D1557C

Proctor Compaction Test Summary
Prepare 4 to 5 specimens at increasing water contents about 2 % apart. Example - prepared samples at 14, 16, 18, and 20 percent. Use range of moistures based on feel and experience.

Proctor Compaction Test Summary
Hammer Then, compact each sample into a steel mold with standard procedures Cured soil Compaction mold

Proctor Compaction Test Summary
Then, strike off excess soil so the mold has a known volume of soil.

Proctor Compaction Test Summary
For each sample, measure the weight and the water content of the soil in the mold The mold volume and weight are pre-measured. Don’t assume nominal volume of 1/30 ft3 or 1/13.33 ft3 Calculate moist density Calculate dry density Plot dry density and water content for each point

Class Problem Calculate Moist density, dry density

Class Problem Mold wt = 4.26 #, Mold Vol. = ft3

Class Problem Calculate Moist density, dry density
Plot curve of dry density versus water content Determine Maximum dry density and optimum water content

Set Up Plot – Form SCS-352 110 { 5 pounds 90

Make each vertical division equal to 1 percent water content
Set Up Plot – Form SCS-352 Make each vertical division equal to 1 percent water content

Class Problem Calculate Moist density, dry density
Plot curve of dry density versus water content Determine Maximum dry density and optimum water content Plot zero air voids ( 100 % saturation curve assuming specific gravity = 2.68

Zero Air Voids Curve After you plot a compaction test, plotting a zero air voids curve is very important. This curve is also called the 100 % saturation curve This curve shows for a range of dry density values what the saturated water content is for any given value

Assume 3 values of gd and calculate wsat%
Compaction Problem Zero air void equation Assume 3 values of gd and calculate wsat%

Assumed dry density = 105 pcf
Unit wt. water = 62.4 Assumed dry density = 105 pcf assumed Gs = 2.70 95 % Saturation Curve 100 % Saturation Curve 75 % Saturation Curve wsat(%) = 22.1(%)

Zero Air Voids Curve

Plotted Class Problem

Zero Air Voids Curve The 100 % saturation curve is used to judge the reliability of the compaction curve and of field measurements of compacted soil density and water content Compacted soils for NRCS specifications are usually at a degree of saturation of about 75 to 95 percent

95 % Saturation Curve 75 % Saturation Curve 100 % Saturation Curve

Review of Compaction Evaluating Compaction Tests
Standard requirements - spread in water content about 2 % and at least two points above and below optimum Typical shape - soil type ?

Compaction Problem Other given information:
LL = 47, PI = 30, classified as CL soil Gs = 2.68

Evaluating compaction test
2.7 % 2.7 % 2.1 % Are points about two percent apart ?

Evaluating compaction test
Are two points below and 2 above optimum ?

Review of Compaction Optimum w% = 21.0  Optimum water content about 80 % saturated water content ? - Acceptable range is 75-95 % sat = 21.0÷23.6=89% 102.5 pcf

Plotted Class Problem wopt/wsat = 21.0/23.6 = 89 %  pcf = (62.4/ /2.68) * 100 = 23.6 %

Check a point on wet side at 98 pcf, w % on curve is 24.3%
Review of Compaction Wet side parallel to saturation curve at  90 % saturation ? % Sat = 24.3 ÷ 26.4 = 92.0 % gd, pcf Check a point on wet side at 98 pcf, w % on curve is 24.3% w, %

Plotted Class Problem wopt/wsat = 24.3/26.6 = 91 % 
pcf = (62.4/ /2.70) * 100 = 26.6 %

dmax = 130.3 - 0.82 *LL + 0.3*PI wopt = 6.77 + 0.43 * LL - 0.21 * PI
Review of Compaction Evaluating Compaction Tests Typical value for fine-grained soils compared to Navdocks equations dmax = *LL + 0.3*PI wopt = * LL * PI

Review of Compaction Evaluating Compaction Tests
Typical value for fine-grained soils compared to Navdocks equations dmax = * *30 = pcf OK - test value was pcf wopt = * * 30 = 19.6 % OK Test value was 21.0 %

Purposes of compaction
Soils are compacted to improve the engineering properties over those of loosely placed soils. The engineering properties are affected both by the density to which the soil is compacted and the water content at which it is compacted

Role of compaction tests in earth fill projects
Samples are obtained in site investigation and sent to laboratory for testing Soils are tested to determine reference density - as well as other index properties Engineering properties are measured by testing at a percentage of the reference test density. For example, a shear test might be performed at 95 percent of the Standard Proctor maximum dry density of the soil.

Role of compaction tests in earth fill projects
The engineering properties are used in analyses to determine a suitable design For example, the shear strength is used in a slope stability analyses If the engineering properties allow a satisfactory design, then the degree of compaction is used in a contract specification.

Role of compaction tests in earth fill projects
If an unsatisfactory design results, the soil is re-tested at a different degree of compaction to obtain better engineering properties The design is re-analyzed and the process repeated until a final satisfactory degree of compaction is decided Then the degree of compaction is used in a contract specification.

Role of compaction tests in earth fill projects
Quality control processes are used to ensure that the earth fill is compacted to the degree of compaction specified, within a range of specified water contents Field compaction tests are performed to assure that the proper reference density is being used

Compaction Tests as Used in Design of an Earth Fill

Example of Process Sample obtained to determine suitability as clay liner Sample Sent to Laboratory Laboratory performs Standard Proctor Test A Permeability Test is performed at 95 % of maximum Standard Proctor Dry Density

Example of Process The sample is remolded at 2 percent wet of optimum (for this sample, 85 % saturated) The permeability test measures an acceptably low permeability A recommendation is given to the field office that compaction to this combination of density and water content results in acceptably low permeability

Example of Process During construction, measurements of dry density and water content are made during construction. If the degree of compaction and percent saturation are equal to or better than specified, the liner is judged to have a low permeability and is considered acceptable.

Class Problem 2 A compaction test measures a maximum dry density of pcf and an optimum water content of 18.0 %. The soil has an estimated Gs value of 2.68 A contract requires compaction to 95 % of maximum dry density at a water content of optimum or greater

Class Problem 2 A field test measures a moist density of pcf and a water content of 23.4 % Does the compacted fill meet the contract requirement ? Use the values given for measured moist density and water content, calculate the dry density Assume a Gs value of 2.68 and compute a wsat value

Class Problem Compare the reported compaction water content to theoretical saturated water content Compacted soils are commonly in the range of percent saturated What do the results tell you about the reliability of the field data? What would you look for to explain any problems?

Conclusions of Class Problem
The measured data appears to have problems. Possible errors are in the measurement of the dry density, the water content, or the specific gravity value used in computations Recommend investigating most probable causes