Chapter 4 Laboratory Compaction Characteristics of Soil Using Standard Effort 4.1 Objective and Significance Optimal engineering properties such as shear strength, compressibility, or permeability can be achieved by compacting engineering fill

used for road bases, foundation pads, levees, and other applications. Foundation bearing soils are often compacted to improve their engineering properties. Laboratory compaction tests provide the basis for determining the percent compaction and required water content to achieve the desired engineering properties, and for controlling construction quality to assure the compaction and water content are achieved. Standard laboratory tests on engineered fill require te st samples to be prepared at some water content and unit weight. Geotechnical engineers commonly first determine the optimum water content (w) and maximum dry unit weight (m) using a compaction test. In a geotechnical laboratory, you would prepare four or five samples with different water contents which bracket the estimated optimal water content. Each water content should vary by approximately 2% and no more than 4%. The results from each group will be posted on Canvas. The test method only applies to soils with 20% or less by mass of particles retained on the No. 4 (4.75 mm) sieve. 4.2 Standard Reference ASTM D 698 Standard Test Methods for Laboratory Compaction Characteristics of Soil Using Standard Effort (12,400 ft-lbffe (600 kN-m/m¹)) Required Materials and Equipment . 4 in Mold - a mold having a 4.000+ 0.016 in (101.6 ± 0.4 mm) average inside diameter, a height of 4.584 +0.018 in (116.4 ±0.5 mm) and a volume of 0.0333 0.0005 ft (943.0 14 cm³). 4.2.1 20/n. Rammer 31.9 68 • Sample extruder • Balance with 1-g readability Approximately 2 kg of material • Maxing tools Cup for measuring water content 4.2.2 Specimen preparation 1. Obtain approximately 2 kg of air dried soil. You may be told the current water content of the soil write it down. 2. Double check your target water content for your specimen 3. Calculate how much water should be added to your sample to obtain the desired water con tent. Remember, there is some water naturally in the soil already. 4. To add the water, squirt it into the soil during mixing. Thoroughly mix the specimen to ensure even distribution of water throughout 4.2.3 Procedure 1. Determine and record the mass of the mold and base plate 2. Assemble and secure the mold and collar to the base plate. Place it on the floor, do NOT compact on the counters 3. Compact the soil in three layers. The total amount of soil used shall be such that the third compacted layer slightly extends into the collar, but does not extend more than approximately 1/4 in (6 mm) above the top of the mold. Prior to compaction, place the loose soil into the mold and spread into a layer of uniform thickness. 4. Compact each layer with 25 blows of the rammer following the compaction pattern shown in Figure 1. In operating the rammer, take care to avoid raising the guide sleeve while lifting the rammer Apply the blows at a uniform rate of about 25 blows/min and in such a manner to as to provide uniform coverage of the specimen 5. Before placing the next layer of soil, scarify the surface of the compacted soil with a spatula or other suitable tool to avoid separation of the layers at the joints later in the test. 6. Following compaction of the last layer, remove the collar from the mold. A spatula may be used to trim the soil adjacent to the collar to loosen the soil from the collar to avoid disrupting the soil below the top of the mold Figure 4.1: Rammer pattern for compaction in 4 in mold 7. Carefully trim the compacted specimen even with the top of the mold by means of a straight edge scraped across the top of the mold to form a plane surface even with the top of the mold. Initial trimming of the specimen above the top of the mold may prevent the soil from being below the top of the mold. Fill any holes in the top surface with unused or trimmed soil from the specimen. Press the soil in the holes with your fingers and again scrape the straightedge across the top of the mold 8. Determine and record the mass of the specimen and mold to the nearest g. If the soil is ver wet or very dry, soil may be lost when removing the mold from the base plate. In this case you may leave the base plate attached to record the final mass, however remember to accoun for this when determining the mass of the sample. 9. Remove the material from the mold. Obuain a specimen for the water content using either the whole specimen (preferred method) or a representative portion. When the entire specimen used, break it up to facilitate drying Otherwise, obtain a representative portion of the thre layers, removing enough material from the specimen to report the water content to 0.1%. W will use the representative portion method due to the size of our oven 10. Select a suitable container and record its weight. 11. Weigh the container and the specimen. 12. Place the specimen in the oven for 24 hours. Make sure your specimen is clearly labeled 13. Return and obtain the mass of your sample container. 4.2.4 Calculations Each group must post the following information on Canvas * Group • Team name . Target water contents • Mass of saturated specimen in the mold/nFigure 4.2: Example of a compaction curve with required information . Mass of mold . Mass of saturated soil after compaction and container weight • Mass of can . Mass of oven dried specimen and can Calculate the total unit weight of each specimen as M₁9 V₂ 4- (4.1) where M, - mass of moist soil g=acceleration of gravity (9.81 m/s²) V-volume of mold You will also need to calculate the water content of each compacted specimen and the correspond ing dry unit weigh PAV (4.2) where is the dry unit weight and is the actual water content of the sample (not the target water content). Plot the dry unit weight and water content. Draw the compaction curve as a smooth curve through the points following the example in Figure 2. Plot the 100% saturation curve also known as the zero air voids line. You will have to pick water content values higher than what you measured in the lab. You may assume the specific gravity, G, of the soil is 2.7. If the zero air voids line crosses the compaction curve (not possible) adjust the assumed specific gravity. Remember to report your assumptions in Lab Report 2. Determine and we from your compaction curve. Label these on your compaction curve. 4.3 Data sheet Compaction test Target water con tent (%) 15 18 21 24 Jal P Lit 27 Water content Mass of mold (kg) Mass of moist specimen + mold 5318-5 7381-4 5318.5 7352.0 5318-5 5318.5 5318-5 2062-9 2033.5 7328-2 2009-7 7259-1 1940.6 7209.0 1890.5 Mass of moist specimen (kg) Target water content (%) 15 18 21 24 27 Name of can Mass of can (g) 31.9 323 21-6 14.8 14.4 Mass of wet soil can (g) 4.4 118.4 86.3 68.4 66.0 Mass of dry soil can (g) Mass of water (g) 82-4 108-1 76-9 60-457-2 7.5 10.8 9.4 8 8.8 SO-5 75-8 55.3 45.642-8 14.9 14-2 17.0 17.5 20.6 Mass of dry soil (g) Water content (%) 4.4 Lab Report 2 For the report include the following in addition to your data sheets and other material outline the rubric: Natural soil water content • Compaction curve with zero air voids line on figure • Maximum dry unit weight • Optimum water content