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7 BEFORE /' Compaction is required to attain a number of positive changes in a soil: The area available for water to flow through is reduced. AFTER The strength ofthe soil is increased because ofthe increased particle-to-particle contact. The properties of the soil become more predict- able. GURE 2.5-2 BREAKAGE CAUSES ADDITIONAL REDUCTION , VOIDS. The soil has increased resistance to erosion. Also note that the sand grain surfaces in contact with each other have increased after the applica- tion of additional pressure. Compaction is usually obtained by applying an impact force to the surface of the soil as shown in the example below. The soil used will contain equal parts of sand, silt, and clay. ".. .., .::~':~g;~.~( ~t' ..' *~ -~. .. . -- -"'--,-" ..- The soil provides more weight per volume (more solid particles). 2.5-1 PLACEMENT IN LA YERS - was used in order to obtain a uniformly dense material. Since placing the materials in layers requires a lot of work, is it necessary? Let us take a look at a compaction procedure similar to the one above; hov:::::ver, this time the con- tainer will not be fiUed in layers, but will be filled close to the top before the material is pounded with the tamping tool. .:.~ ~- ",' . ." : ;~~;:, "~'..~.~. ~~ '. , " ..:" '",-:,.-," "'; ...:; ," Co,,' .....,.... .-....- :. . ...:......; .....:. -": .....~. " ."':.~:"!... LOOSE STATE COMPACTION APPLIED a. b. COMPACTED MATERIAL c. a. b. -- -- -c:--- - d. FIGURE 2.5-3 THE COMPACTION PROCESS FIGURE 2.5-5 COMPACTION WITHOUT LAYERS ....... .... ~ . ',<i:: .... ..~.,'-~..-:...'i: .,;. -"..... .~. ... .....4.. "" .. b. .. .'-.~ "~ : ~ ~:.~'. ...~.: ,p.." -;.' . '~.' . , .". . :-'X~'V: d. AFTER COMPACTION ".''''':.- ,....... ...f..... .'.~ '.... ',." .~' . c. d. FIGURE 2.5-4 COMPACTION IN LAYERS In Figure 2.5-3 c, a tampingtoolis used to pound a 3-inch layer of soil with enough force to create an imprint about ~ inch deep. The pounding is continued until the entire surface of the sample has been compacted. (See Figure 2.5-3 d.) Now the soil layer that was 3 inches thick is only 2 ~ inches thick, although it contains the same amount of soil particles. Most of the air has been forced out of the soil sample. In order to fill the container with a soil of uniform density, successive 3-inch layers are placed, then compacted to a 2 ~-inch thickness, as shown in Figure 2.5-4. FIGURE 2.5-6 RESULT OF COMPACTION WITHOUT CON. TROLLED LAYERS. Figure 2.5-5d shows that only the upper por- tion of the material has become compacted, the middle portion shows only a small change from the loose state, and the bottom portion of the sample is unchanged from the loose ,state (Figure 2.5-5a). The primary reason for this is the way the impact from the tamping tool is transmitted throullh the wil.