U.S. Department of Transportation
Federal Highway Administration
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Federal Highway Administration Research and Technology
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Publication Number: FHWA-HRT-07-052
Date: September 2007
The general method of compaction of Type 2 soils will be that of static loading (a modified version of the double plunger method). If testable thin-walled tubes are available, specimens shall not be recompacted.
Specimens shall be recompacted in a 71-mm (2.8-inch) diameter mold. The process is one of compacting a known weight of soil to a volume that is fixed by the dimensions of the mold assembly (mold shall be of a sufficient size to produce specimens 71 mm (2.8 inches) in diameter and 152 mm (6 inches) in height). A typical mold assembly is shown in Figure 6. As an alternative for soils lacking in cohesion, a mold with the membrane installed and held by vacuum, as in Appendix B, may be used. Several steps are required for static compaction as follows in the Procedures section of this appendix and as illustrated in Figures 7–11.
NOTE 21: Alternatively, the sample can be molded to 165 mm (6.5 inches) rather than 152 mm (6.0 inches) and then a miter box can be used to square the ends of the sample and reach the final testable length of 142 mm (5.6 inches). This tends to produce more consistently shaped (level) specimens.
This method covers the compaction of Type 2 soils for use in resilient modulus testing.
As shown in Figure 6.
NOTE 22: As an alternative for soils lacking in cohesion, a mold with the membrane installed and held by vacuum, as in Appendix B, may be used.
3.1 Five layers of equal weight shall be used to compact the specimens using this procedure. Determine the weight of wet soil, WL, to be used per layer where WL = Wt/5.
3.2 Place one of the spacer plugs into the specimen mold.
3.3 Place the weight of soil, WL, determined in step 3.1 into the specimen mold. Using a spatula, draw the soil away from the edge of the mold to form a slight mound in the center.
3.4 Insert the second plug and place the assembly in the static loading machine. Apply a small load. Adjust the position of the mold with respect to the soil weight, so that the distances from the mold ends to the respective spacer plug are equal. Soil pressure developed by the initial loading will serve to hold the mold in place. By having both spacer plugs reach the zero volume change simultaneously, more uniform layer densities are obtained.
Figure 6. Typical apparatus for static compaction of Type 2 materials.
Figure 7. Compaction of Type 2 soil, lift 1.
Figure 8. Compaction of Type 2 soil, lift 2.
Figure 9. Compaction of Type 2 soil, lift 3.
Figure 10. Compaction of Type 2 soil, lift 4.
Figure 11. Compaction of Type 2 soil, lift 5.
3.5 Slowly increase the load until the plugs rest firmly against the mold ends. Maintain this load for a period of not less than one minute. The amount of soil rebound depends on the rate of loading and load duration. The slower the rate of loading and the longer the load is maintained, the less the rebound (see Figure 7).
NOTE 23: To obtain uniform densities, extreme care must be taken to center the first soil layer exactly between the ends of the specimen mold. Checks and any necessary adjustments should be made after completion of steps 4 and 5.
NOTE 24: Use of compaction by measuring the plunge movements to determine that the desired volume has been reached for each layer is an acceptable alternative to the user of spacer plugs.
3.6 Decrease the load to zero and remove the assembly from the loading machine.
3.7 Remove the loading ram. Scarify the top surface of the compacted layer to a depth of 3.2 mm (1/8 inch) and put the weight of wet soil, WL, for the second layer in place and form a mound. Add a spacer plug of height shown in Figure 8.
3.8 Slowly increase the load until the plugs rest firmly against the top of the mold end. Maintain load for a period of not less than one minute (see Figure 8).
3.9 Remove the load and flip the mold over and remove the bottom plug keeping the top plug in place. Scarify the bottom surface of layer 1 and put the weight of wet soil, WL, for the third layer in place and form a mound. Add a spacer ring of height shown in Figure 9.
3.10 Place the assembly in the loading machine. Increase the load slowly until the spacer plugs firmly contact the ends of the specimen mold. Maintain this load for a period of not less than one minute.
3.11 Follow the steps presented in Figure 10 and 11 to compact the remaining two layers.
3.12 After compaction is completed, determine the moisture content of the remaining soil using LTPP Protocol P49. Record this value on LTPP Laboratory Data Form T46A.
3.13 Using the extrusion ram, press the compacted soil out of the specimen mold and into the extrusion mold. Extrusion should be done slowly to avoid impact loading the specimen.
3.14 Using the extrusion mold, carefully slide the specimen off the ram, onto a solid end platen. The platen should be circular with a diameter equal to that of the specimen and have a minimum thickness of 13 mm (0.5 in.). Platens shall be of a material which will not absorb soil moisture.
3.15 Determine the weight of the compacted specimen to the nearest gram. Measure the height and diameter to the nearest 0.25 mm (0.01 inch). Record these values on Worksheet T46.
3.16 Place a platen similar to the one used in step 3.13 on top of the specimen.
3.17 Using a vacuum membrane expander, place the membrane over the specimen. Carefully pull the ends of the membrane over the end platens. Secure the membrane to each platen using O-rings or other means to provide an airtight seal.
Proceed with Section 8.1 of this protocol.