Investigation into the Compressibility of Different Types of Sand Fractions Using a Oedometer
|Published in:||Engineering Structures and Technologies, March 2011, n. 1, v. 3|
This work presents experimental tests on typical Baltic sea-shore sand along Klaipėda. The paper looks into changes in loaded soil void ratio when using different types of sand fractions in Klaipėda region. Three different types of sand fractions, including 1.18–0.6 mm, 0.6–0.425 mm and 0.425–0.3 mm were analyzed under laboratory conditions. In addition, one mixed sand fraction of diameter 1.18–0.3 mm was created from the equal parts (in mass) of these three different types of sand fractions. Soil usually consists of particles, water and air. An important basic parameter is void ratio e. The soil used under laboratory testing was air drained sand and water influence was not accounted. All tests on soil samples were recorded, because this is the only possible way of investigating the actual displacements versus time changes. Load increments were changed one minute later via the following loading steps: 0; 100; 200; 300; 400; 300; 200; 100; 0 kPa. Almost all displacements reached their final magnitudes in the first 5 seconds when load was increased; when unloaded, it took the first 3 seconds. When porosity is large, soil is called loosely packed. A laboratory test shows that maximum void ratio was in soil with 0,425–0,3 mm particle size where e = 0,840. The lowest maximum void ratio e = 0,714 was obtained for the mixed sand fraction and made 1,18–0,3 mm. The theoretical maximum soil void ratio can be e = 0,910, see Figure 3. This is the loosest packing of spherical particles that seems possible (minimum contact places between particle sizes are 4). Certainly, it is not stable: any small disturbance will make the assembly collapse. When using a very dense packing of spherical particles and the theoretical minimum soil void ratio of this assembly is e = 0,350, see Figure 4. This seems to be the major packing of a set of spherical particles (maximum contact places between particle sizes are 6). Minimum difference between the theoretical maximum void ratio and laboratory maximum void ratio was 0,07 in soil with particle sizes of 0,425–0,3 mm. Soil never consists of spherical particles and the values calculated above have no real meaning for actual soils. They may give a certain indication of what the void ratio of real soil may be. It can thus be expected that void ratio e may have a value somewhere in the range from 0,350 to 0,910. The results of the investigated sea-shore sand along Klaipėda confirms this statement. For Klaipėda sand, when loading it is better to show results of void ratio versus normal stress in lineral relationship (e = aσz + b), see Figure 10, and, when reloading to use semilogarithmic scale (e = alogσz + b), see Figure 11. In the general outline, one can make a conclusion that sand void ratio e decreases versus an increment in the size of soil fraction.
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