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33 ANNEX A-2 VIBRATORY COMPACTION 1. SCOPE 1.1 This method covers vibratory compaction procedures for use in resilient modulus testing of materials Type 1 and Type 2. 1.2 Split molds with an inside diameter of 152.4 mm (6 in) shall be used to prepare 305-mm (12-in) high test samples for all materials Type 1 or Type 2 having the maximum particle size (dmax) greater than 19 mm (3/4 in). All material greater than 25.4 mm (1 in) shall be scalped off prior to testing. Split molds with an inside diameter of 101.6 mm (4 in) shall be used to prepare 203.2-mm (8-in) high test samples for all materials Type 1 or Type 2 having the maximum particle size (dmax) less than 19 mm (3/4 in). 1.3 All specimens shall be compacted in 6 lifts in a split mold mounted on the base of the triaxial cell as shown in Figure A-2-1. 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 minimiz- ing particle breakage and damage to the sample mem- brane. Use a special compaction head on the final lift to ensure proper specimen alignment (Figure A-2-1 (b)). 2. APPARATUS 2.1 A split mold, with an inside diameter of 152 mm (6 in) having a minimum height of 381 mm (15 in) (or a suffi- cient height to allow guidance of the compaction head for the final lift) shall be used for all materials having the maximum particle size (dmax) greater than 19 mm (3/4 in). For materials having the maximum particle size (dmax) less than 19 mm (3/4 in), a split mold with an inside diameter of 101.6 mm (4 in) and a minimum height of 254 mm (10 in) may be used. 2.2 Vibratory Compaction Device â Vibratory compaction shall be provided using electric rotary or demolition hammers with a rated input of 750 to 1200 watts and capable of 1800 to 3000 blows per minute. 2.3 The compactor head shall be at least 25 mm (1 in) thick and have a diameter of not less than 146 mm (5.75 in) for the 6-in-diameter sample and 97 mm (3.83 in) for the 4-in-diameter sample. 3. PROCEDURE 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 inter- face with the cell constitutes a rigid joint. 3.2 Place the two 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 (0.01 in). 3.3 Remove the top platen and porous disc if used. Measure the thickness of the rubber membrane with a micrometer. 3.4 Place the rubber membrane over the bottom platen and lower porous disc. Secure the membrane to the bottom platen using an O-ring or other means to obtain an air- tight 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. During equipment calibration, ensure by indexing with a dial indicator that the top of the mold is parallel to the base of the triaxial cell. 3.6 Stretch the membrane tightly over the rim of the mold. Apply a vacuum to the mold sufficient to draw the mem- brane in contact with the mold. If wrinkles are present in the membrane, release the vacuum, adjust the mem- brane 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 (0.01 in) 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 an assumed value of height between 305 and 318 mm (12 and 12.5 in) for 152-mm (6-in) diameter specimens and between 203 and 216 mm (8 to 8.5 in) for 102-mm (4-in) diameter specimens. 3.9 Determine the mass 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-in) diameter specimens (specimen height of 305 mm (12 in)) 6 layers of 2 in per layer are required; for 102-mm (4-in) diameter specimens 6 layers of 33.9 mm (1.33 in) per layer shall be used. Determine the weight of the wet soil, WL, required for each layer. WL = Wt/6 where Wt = total weight of the specimen to produce appro- priate density. 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 the wet soil and the mixing pan.
34 3.13 Place the required 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 in Step 3.7 minus the thickness of the layered selected in Step 3.10. This may require removal and reinser- tion of the vibrator several times until the experience is gained in gauging the vibration time, which is re- quired. Use a small circular spirit level to assist in keeping each layer level. 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 about 6.4 mm (1/4 in). The measured dis- tance from the surface of the compacted layer to the rim of the mold is successively reduced by the layer thickness. The final surface should be a smooth plane parallel to the base of the triaxial cell. Use the special compaction head shown in Figure A-2-1 (b) for the final lift. As a final step, the top plate shall be placed Fig. A-2-1. Typical Apparatus for Vibratory Compaction
35 on the sample and seated firmly by vibrating with the compactor for about 10 seconds. If necessary, because of degradation of the first membrane, a second mem- brane can be applied to the sample at the conclusion of the compaction process. 3.16 When the compaction process is completed, determine the mass of the mixing pan and the excess soil. This mass subtracted from the mass determined in Step 3.12 is the mass of the wet soil used (mass of the speci- men). Verify the compaction water, Wc, of the excess soil using care in covering the pan of wetted soil dur- ing compaction to avoid drying and loss of moisture. The moisture content of this sample shall be conducted using T 265. Note 1 â As an alternative for soils lacking in cohesion, a mold with a membrane installed and held by vacuum may be used. 3.17 Store or prepare the specimen for testing according to Annex 1.
