Page 1

GDT 108

A. Scope

For a complete list of GDTs, see the Table of Contents.

Use this test method to determine the bearing value of limerock bases when compacted in the Laboratory with a 10 lb

(4.5 kg) rammer dropped from a height of 18 in (450 mm). Moistures vary from dry to the wet side of optimum. This

compaction procedure modifies AASHTO T 180 D.

B. Apparatus

The apparatus consists of the following:

1. Molds: Use cylindrical metal molds with an internal diameter of 6.00 in, ± 0.026 in (150 mm,± 0.66 mm) and a

height of 7.00 in, ± 0.016 in (7 mm, ± 0.41 mm) Figure 108-1.

2. The molds will have a detachable collar assembly approximately 2.0 in (50 mm) high to help prepare compacted

specimens of soil-water mixtures of desired height and volume. Molds may be “split,” consisting of 2 half-round

sections, or a section of pipe split along 1 element that can be securely locked in place to form a cylinder. The mold

and collar assembly must be constructed so it can be fastened firmly to a detachable base plate.

3. Spacer Disc: Use a metal disc 5-15/16 in, ± 1/32 in (150.81 mm, ± 0.79 mm) diameter and 2.416 in, ± 0.01 in (61.4

mm, ± 0.25 mm) high Figure 108-2

4. Insert this as a false bottom in the cylinder mold during compaction. This would give the compacted sample a

thinckness of 4.584 in (116 mm).

5. Rammer: Use either a manual or a mechanical rammer.

a. Manual Rammer: Ensure the contact face is flat and circular with a wear tolerance of 0.005 in (0.125 mm) and a

diameter of 2.000 in, ± 0.005 in (50 mm, ± 0.125 mm), weighing 10.00 lbs, ± 0.02 lbs (4.5 kg, ± 0.01 kg). The

rammer must be able to control the height of drop from 18.0 in, ± 0.06 in (450 mm, ± 1.5 mm) above the soil.

b. Mechanical Rammer: Ensure the contact face is flat and circular with a wear tolerance of 0.005 in (0.125 mm)

and a diameter of 2.000 in, ± 0.005 in (50 mm, ± 0.125 mm), weighing 10.00 lbs, ± 0.02 lbs (4.5 kg, ± 0.01 kg).

The rammer must be able to control the height of drop from 18.0 in, ± 0.06 in (450 mm, ± 1.5 mm) above the

soil. The rammer must provide uniform and complete coverage of the specimen surface.

c. Rammer Face: Use a circular face, but you may also use a sector face rammer if the area of the rammer face is

the same as the circular face and if the report indicates the type of face used (see Figure 108-3).

NOTE: Calibrate the mechanical rammer with several soil types and adjust the weight of the rammer if

necessary to give the same moisture density as the manually operated hammer.

6. Surcharge Weights: Use 1 annular metal weight with a center hole 2-1/8 in (53.975mm) diameter and several slotted

or split metal weights, all 5-7/8 in (149.225 mm) diameter and each weighing 5 lbs, ± 0.10 lbs (2.27 kg, ± 0.04 kg)

(see Figure 108-2)

NOTE: When using split weights, the mass of the pair shall be 5 lbs, ± 0.10 lbs (2.27 kg, ± 0.04 kg).

7. Penetration Piston: Use a circular metal piston that has a diameter of 1.954 in, ± 0.005 in (49.632 mm, ± 0.125 mm)

and is at least 4 in (100 mm) long.

8. Loading Device: Use a compression-type apparatus that can apply a uniformly increasing load up to 10,000 lbs (44

482 kN) at a rate of 0.05 in (1.25 mm) per minute. Use it to force the penetration piston into the specimen.

9. Apparatus for Measuring Expansion: Use a swell plate with adjustable stem and a tripod support for a dial indicator.

The swell plate is made of metal, 5-7/8 in (149.225 mm) diameter and is perforated with 1/16 in (1.56 mm) diameter

holes. The tripod used to support the dial indicator is arranged to fit the mold extension collar (see Figure 108-3).

10. Indicators: Use 2 dial indicators. Each indicator has a 1 in (25 mm) throw and read to 0.001 in (0.025 mm).

11. Balance: Use a balance sensitive to 0.1 g for samples weighing approximately 110 g or less. For larger samples, the

balance must be sensitive to within 0.1 percent of the sample weight.

12. Drying Oven: Use a thermostatically controlled drying oven capable of maintaining a temperature of 230 °F, + 9 °F

(100 °C, + 5 °C).

GDT 108

Page 2

13. Straightedge: Use a steel straightedge 12 in (300 mm) long. It must have one beveled edge and at least one

longitudinal surface (used for final trimming) that is flat within 0.1% along the length used for trimming.

14. Sieves: Use 2 in, 3/4 in, and No. 4 (50 mm, 19 mm, and 4.75 mm) sieves that conform to the requirements of the

Specifications for Sieves for Testing Purposes (AASHTO M 92 801).

15. Mixing Tools: Use mixing pans, a spoon, a trowel, a spatula, etc., or a suitable mechanical device to thoroughly mix

the soil sample with increments of water.

16. Soak Tank: Use a rectangular tank approximately 26 in (650 mm) wide, 60 in long (1500 mm), and 10 in (250 mm)

deep. A smaller tank may be used if quantity of tests or laboratory space is not large enough to accommodate the

suggested size.

The tank must have raised ridges or other devices in the bottom, placed in such a manner to allow the water free

access to the bottom of the mold. The tank must have an overflow placed so that the height of water in the tank

remains within ± 1/4 in (6 mm) of the same elevation as the top of the soil sample in the mold.

C. Sample Size and Preparation

1. If the soil is damp when received from the field, dry it until friable under a trowel. Dry the soil in air or with a drying

apparatus that does not exceed 140 °F (60 °C).

2. For limerock materials used for base or stabilizers, pass the entire sample through a crusher set at a maximum

opening of 3/4 in (19 mm) (with an under-tolerance of 1/8 in (3 mm)). You may also crush the entire limerock

sample before drying it in step 1.

3. Pass the soil through the 2 in, 3/4 in, and No. 4 (50 mm, 19 mm, and 4.75 mm) sieves.

a. Thoroughly break up the aggregations without reducing the natural size of the individual particles.

b. Break down any clay or silt aggregations until they pass through a No. 4 (4.75 mm) sieve.

4. Record the percentages retained on each sieve.

For limerock materials, pass the material through a No. 4 (4.75 mm) sieve and record the percent retained.

5. For other soils, discard the material retained on the 2 in (50 mm) sieve.

6. Weigh the material retained on the 3/4 in (19 mm) sieve.

7. Remove this material from the soil and replace it with an equal weight of material passing the 3/4 in (19 mm) sieve

and retained on the No. 4 (4.75 mm) sieve.

8. Separate the material into at least 4 (preferably 5) portions, weighing approximately 12 lbs (5 kg) each. Make sure

the material is representative of the total.

D. Procedures

1. Immediately prior to compacting the material, remix the sample and take a representative sample to determine

moisture content.

2. Weigh the sample immediately and record the weight on Form 108a.

3. Dry the sample in an oven at 230 °F, ± 9 °F (110 °C, ± 5 °C) for at least 12 hours, or to a constant weight to

determine the moisture content.

The sample must weigh at least 1.1 lbs (500 g).

4. Insert the spacer disc into the bottom of the 7 in (125 mm) mold.

5. Add a specimen formed by compacting the prepared soil in the 6 in (150 mm) diameter mold (with collar attached).

a. During compaction, rest the mold on a uniform rigid foundation, such as a cube of concrete weighing not less

than 200 lbs (91 kg).

b. Compact the material in 5 equal layers to give a total compacted depth of about 5 in (125 mm).

c. Compact each layer with 56 uniformly distributed blows from the rammer, dropping free from a height of 18 in,

± 1/16 in (450 mm, ± 1.5 mm) above the expected compacted layer (if using a stationary mounted rammer).

6. After compacting the samples, remove the extension collar.

7. Carefully trim the compacted soil with the straight edge to be even with the top of the mold.

8. Patch any holes in the surface with smaller size material passing a No. 4 (4.75 mm) sieve.

9. Remove the base plate and the spacer disc.

GDT 108

Page 3

10. Place a coarse filter paper (No. 4 (4.75 mm), 15 cm) on the top and bottom of the compacted sample.

11. Invert the mold and reattach it to the base plate.

12. Weigh the mold and compacted sample and record the weight on the test form.

13. Repeat the above procedure for each increment of moisture content using samples prepared as described in

Sample Size and Preparation.

14. Compact at least 4 (preferably 5) specimens at varying moisture contents.

a. Begin approximately 4 percent below the optimum moisture content.

b. Increase the moisture until exceeding the optimum moisture content.

15. Determine the moisture-density relationship.

a. For each trial, calculate the moisture content to the nearest 0.1 percent and the dry unit weight of the soil to the

nearest 0.1 lb/ft3 (1 kg/m

3) as follows:

M = A - B x 100 ; and

B - C

W = Z__

m + 100

where:

m = percentage of moisture in the specimen based on oven-dry weight of soil

A = weight of container and wet soil

B = weight of container and dry soil

C = weight of container

W = dry unit weight in pounds per cubic foot of compacted soil (kilograms per cubic meter)

Z = wet unit weight in pounds per cubic foot of compacted soil (kilograms per cubic meter)

b. Plot the oven-dry unit weights of the soil in pounds per cubic foot (kilograms per cubic meter) (densities). The

weights are ordinates and the corresponding moisture contents as abscissas (lower curve, Figure 108-4).

c. Fit the best smooth curve through these points, usually a convex curve.

d. The coordinates of the peak of the curve are the optimum moisture content and the maximum dry density of the

soil, respectively.

16. Soaking

a. After compacting, place a surcharge of approximately 2-1/2 lbs (1 kg) (weight of a swell plate) on top of each

sample before placing it in the soak tank.

b. Place the compacted specimens in a soaking tank. Ensure that the height of water remains within 1/4 in (6 mm)

of the top of soil the sample in the mold. Leave the plate in place during the soaking and draining period.

c. Soak the sample for 48 hours, ± 4 hours.

d. If you observe any swelling or bulking, add more surcharge weights, not exceeding a total of 15 lbs (7 kg) for

embankment.

e. Resoak the specimen.

17. Draining

a. Remove the specimen from the soaking tank.

b. Allow the specimen to drain on a level surface for 15 minutes, ± 2 minutes.

c. Remove the swell plate and run the penetration test immediately.

18. Penetration Test

a. Apply a surcharge of 15 and 20 lbs (7 and 9 kg) to the stabilized subgrade and embankment specimens,

respectively. Do not use a surcharge weight on base materials.

When using a manually operated machine, add a seating load of 10 lbs (4.5 kg) to the specimen with the

required surcharge weights.

GDT 108

Page 4

Note: When using automatic recording equipment, you do not need the 10 lb (4.5 kg) seating load. Zero the

recording pen on the chart paper before applying the load.

b. Zero the deflection and load gauges.

c. Apply the load through the piston at a constant rate of approximately 0.05 in (1.25 mm) per minute.

d. Record load readings for each 0.01 in (0.25 mm) penetration. Take readings at 0.01in (0.25 mm) up to 0.2 in (5

mm) and 0.225 (5.7 mm), 0.25 in (6.3 mm), 0.275 in (7 mm), and 0.3 in (7.6 mm). See Form 108a and Figure

108-5.

Note: Form 108a is a suggested form sheet to record the necessary data obtained from a test specimen when

using compression-type loading devices.

e. Record each unit load, in pounds per square inch (kilopascals), by first dividing the incremental load by 3 in²

(0.001935 m²).

f. Plot this unit load as the ordinate of a graph. Plot the penetration, in millimetersinches, as the abscissa.

g. Draw a smooth curve through the plotted points (see Figure 108-6). (Machines equipped with load-deflection

recorders plot the curve automatically.)

1) Most machines with attached recorders show the load in pounds (kilograms) rather than in pounds per

square inch (kilopascals). Since the cross-sectional area of the piston is a constant, you can easily convert

the load scale to a pressure scale by dividing the load in pounds (kilograms) by 3 in² (0.001935 m²).

2) As an alternative, you can determine the corrected unit load by reading the load in pounds (kilograms) at

0.1 inch (2.5 mm) penetration on the corrected curve and dividing it by 3 in² (0.001935 m²).

E. Calculations

1. Load-Penetration Relationship

The curve will usually be convex upwards although the initial portion of the curve may be concave upwards (the

concavity may be due to surface irregularities) (see Figure 108-7).

a. Apply a correction by drawing a tangent to the curve at the point of greatest slope.

b. The corrected curve then becomes the tangent plus the convex position of the original curve. Move the original

curve with the origin moved to the point where the tangent intersects the horizontal axis.

2. Establishing Limerock Bearing Ratio (LBR) of Material

a. Divide the corrected unit load obtained at 0.1 in (2 mm) penetration by 800 psi (5.5 MPa), the standard strength

of limerock.

b. Multiply this ratio by 100 to get the LBR in percent.

c. Collect the LBR values for each compacted sample.

d. Plot an LBR vs. moisture content curve.

e. Determine the maximum LBR value in the same way you obtained the maximum density from a moisture-

density curve (see Figure 108-4). Use this procedure whenever you need to establish an LBR value for a

material.

f. In cases where you test a material only to check for compliance to a specified minimum LBR value, test the two

samples nearest optimum moisture.

1) If both samples satisfy the minimum LBR requirements, report the material as satisfying the Specification

and discard the remainder of the samples.

2) If either sample fails to meet the minimum specified LBR value, then create the full LBR curve as described

above.

F. Report

1. Report the test results on Form 108a. The report should include:

A plot of the moisture-density curve with the maximum dry density and optimum moisture content

(see Figure 108-4).

A semi-log plot of the LBR-moisture curve with the maximum LBR value.

GDT 108

Page 5

NOTE: Dimensions for the following figures are given in English units only. Use conversion factors if metric units

are desired.

(Nominal)1/16” Holes inBase Plate

Base

(Nominal) 10”

(Nominal)2-1/2”

Cylinder Mold

Spacer Disc

(Nominal) 5-15/16”

(Nominal) 6-1/2”

7.00 ± 0.2

(Mold Height)

6” ± .0.20

2.416” ± 0.03”

LBR Mold

(NOT TO SCALE)

Figure 108-1

GDT 108

Page 6

NOT TO SCALESURCHARGE WEIGHTS

(Nominal Dimensions)

2-1/8”

5-7/8”

2-1/8”

5-7/8”

Thickness (t) to Give

5 Pounds(t) (t)

SPACER

2.4

16 ±

0.0

3”

Gripping Slot

5-15/16” ± 1/32”Metal Disc

Items Used in Testing MoldedSoil Specimens for the LBR

Figure 108-2

GDT 108

Page 7

RAMMER (not to scale)

(Both surface areas equal)42.5°

2.9

R

1” R

PLAN

Circular Pie-Shaped

ELEVATION

SWELL PLATE (not to scale)

5-7/8”1/4”

5-1/2”

3/8”

Items Used in Testing Molded Soil Specimens for the LBR

Figure 108-3

GDT 108

Page 8

116

115

114

113

112

111

110

5 7 9 11 13 15

Figure 108-4

FORM 108a

Department of Transportation

State of Georgia

Office of Materials and Research

(DOT-108)

GDT 108

Page 9

Unconsolidated Limerock Base

Theoretical Density and Limerock Bearing Ratio (LBR)

(Florida Method FM-5-515) (Modified)

Project: County: Lab No.:

Material Source: Date Compacted/Tested:

Mold. No.

Target Moisture%

Wt. Wet MatÕl &

Mold

Wt. Mold

Wt. Wet Material

Constant (454 x

0.0751)

Wet Unit Wt.

Dry Unit

L.B.R.

Actual Moisture

Cup No.

Wet Wt. Material

Dry Wt. Material

% Moisture

Penetration Test (3 in.2 Piston)

Test 1 Test 2 Test 3 Test 4 Test 5

Penetration (in.) Load Stress

(psi)

Load Stress

(psi)

Load Stress

(psi)

Load Stress

(psi)

Load Stress

(psi)

.025

.050

.075

.100

.125

.150

.175

.200

.300

GDT 108

Page 10

Figure 108-5

GDT 108

Page 11

.000 .050 .100 .150 .200 .250 .300

Penetration in Inches

2000

1800

1600

1400

1200

1000

800

600

400

200

0

SOIL SUPPORT GRAPH

Lab No. 30961

Test #3

CBR @ 0.1” = 760 = 760

CBR @ 0.2” = 1040 = 69.3SSV (from Chart) =

760/800 = LBR 95.0

Figure 108-6

GDT 108

Page 12

STRESS VS PENETRATION

0

200

400

600

800

1000

1200

1400

1600

1800

2000

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35

INCHES

PS

I

Figure 108-7