U.S. Department of Transportation
Federal Highway Administration
1200 New Jersey Avenue, SE
Washington, DC 20590
Federal Highway Administration Research and Technology
Coordinating, Developing, and Delivering Highway Transportation Innovations
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Publication Number: FHWA-HRT-07-052
Date: September 2007
Type 1 soils will be recompacted using a 152-mm (6.0-inch) split mold and vibratory compaction. Split molds with an inside diameter of 152 mm (6 inches) shall be used to prepare 305-mm (12-inch) high test samples for all Type 1 materials with nominal particle sizes less than or equal to 37.5 mm (1.5 inches). If 10 percent or less of a Type 1 sample is retained on the 37.5-mm (1.5-inch) sieve, the material greater than the 37.5-mm (1.5-inch) sieve shall be scalped off prior to testing. If more than 10 percent of the sample is retained on the 37.5-mm (1.5-inch) sieve, the material shall not be tested and the material shall be stored until further notice. Instructions concerning the testing of these materials will be issued at a later date.
Cohesionless soils shall be compacted in 6 lifts in a split mold mounted on the base of the triaxial cell as shown in Figure 5. Compaction forces are generated by a vibratory impact hammer without kneading action powered by air or electricity and of sufficient size to provide the required laboratory densities while minimizing damage to the sample membrane.
This method covers the compaction of Type 1 soils for use in resilient modulus testing.
2.1 A split mold, with an inside diameter of 152 mm (6 inches) having a minimum height of 381 mm (15 inches) (or sufficient height to allow guidance of the compaction head for the final lift).
2.2 Vibratory Compaction Device Vibratory compaction shall be provided using electric rotary or demolition hammers. The specifications for the hammers are listed below:
|Rated watts input:||750 – 1,250 watts|
|Blows per minute:||1,800 – 3,000|
The compactor head shall be at least 13-mm (0.5-inch) thick and have a diameter of not less than 146 mm (5.75 in.).
NOTE 20: The vibratory compaction device shall be approved by the FHWA COTR prior to the initiation of the testing program.
3.1 For removable platens, tighten the bottom platen into place on the triaxial cell base. It is essential that an airtight seal is obtained and that the bottom platen interface constitutes a rigid body since calculations of strain assume zero movement of the bottom platen under load.
Figure 5. Typical apparatus for vibratory compaction of Type 1 unbound materials.
3.2 Place the paper filters, two bronze discs/porous stones and the top platen on the bottom platen. Determine the total height of the top and bottom platens and stones to the nearest 0.25 mm (0.1 inch).
3.3 Remove the top platen and bronze disc/porous stone. Measure the thickness of the rubber membrane with a micrometer.
3.4 Place the rubber membrane over the bottom platen, lower bronze disc/porous stone and paper filters. Secure the membrane to the bottom platen using an O-ring or other means to obtain an airtight seal.
3.5 Place the split mold around the bottom platen and draw the membrane up through the mold. Tighten the split mold firmly in place. Exercise care to avoid pinching the membrane.
3.6 Stretch the membrane tightly over the rim of the mold. Apply a vacuum to the mold sufficient to draw the membrane on contact. If wrinkles are present in the membrane, release the vacuum, adjust the membrane, and reapply the vacuum. The use of a porous plastic forming jacket liner helps to ensure that the membrane fits smoothly inside the mold. The vacuum is maintained throughout the compaction procedure.
3.7 Measure, to the nearest 0.25 mm (0.1 inch), the inside diameter of the membrane lined mold and the distance between the top of the lower porous stone and the top of the mold.
3.8 Determine the volume, V, of the specimen to be prepared using the diameter determined in step 3.7 and a value of height between 305 and 318 mm (12 and 12.5 inches).
3.9 Determine the weight of material, at the prepared water content, to be compacted into the volume, V, to obtain the desired density.
3.10 For 152-mm (6-inch) diameter specimens (specimen height of 305 mm (12 inches)) 6 layers of 2 inches (51 mm) per layer are required for the compaction process. Determine the weight of wet soil, WL, required for each layer.
3.11 Place the total required weight of soil for all lifts, Wad, into a mixing pan. Add the required amount of water, Waw, and mix thoroughly.
3.12 Determine the weight of wet soil and the mixing pan.
3.13 Place the amount of wet soil, WL, into the mold. Avoid spillage. Using a spatula, draw soil away from the inside edge of the mold to form a small mound at the center.
3.14 Insert the vibrator head and vibrate the soil until the distance from the surface of the compacted layer to the rim of the mold is equal to the distance measured up in step 3.7 minus the thickness of the layer selected in step 3.10. This may require removal and reinsertion of the vibrator several times until experience is gained in gaging the vibration time which is required.
3.15 Repeat steps 3.13 and 3.14 for each new layer after first scarifying the top surface of the previous layer to a depth of 6.4 mm (¼ inch). The measured distance from the surface of the compacted layer to the rim of the mold is successively reduced by the layer thickness selected in step 3.10. The final surface shall be a smooth horizontal plane. As a recommended final step where porous bronze discs are used, the top plate shall be placed on the sample and seated with the vibrator head. If necessary, due to degradation of the first membrane, a second membrane can be applied to the sample at the conclusion of the compaction process.
3.16 When the compaction process is completed, weight the mixing pan and the excess soil. This weight subtracted from the weight determined in step 3.12 is the weight of the wet soil used (weight of specimen). Verify the compaction water content, Wc, of the excess soil using care in covering the pan of the wetted soil during compaction to avoid drying and loss of moisture. The moisture content of this sample shall be conducted using LTPP Protocol P49.
Proceed with section 8.2 of this protocol.