LABORATORY COMPACTION TEST Application

Transcription

1 1 LABORATORY COMPACTION TEST Application Compaction of soil is probably one of the largest contributors to the site ork economy; in other ors-it is important. Large sums of money are spent on it every ay. Soil is a very flexible an inexpensive construction material. It can be manipulate to prouce a material ith a ie range of properties. Control of compaction in the fiel permits civil engineers to engineer a soil to prouce a material ith properties that are optimize for a project. Compaction is efine as the reuction in soil voi ratio by expulsion of air from the vois. In contrast, the consoliation process is the reuction of voi ratio by expulsion of ater from the vois. These to processes are similar in that they result in a ecrease in voi ratio. Compaction occurs instantly ith application of a force. Consoliation is a timeepenent process that can take many years to complete after a loa is applie to soil. Because compaction involves reucing the voi ratio ithout changing the moisture content, the egree of saturation ill increase. Soil is compacte to improve the folloing soil properties an aspects of strengtheformation behaviors: Improve shear strength Reuce compressibility Decrease permeability Reuce shrink/sell potential Reuce liquefaction potential Reuce compression ue to etting The behavior of a soil uring compaction an after compaction epens on: soil type (fine vs. coarse graine) compaction moisture conition metho of compaction A variety of methos an machinery are use to compact soil. Compaction of Fine-Graine Soils When fine-graine soils are compacte they isplay a strong epenency on compaction moisture content. Proctor (1933) escribe this behavior through the concept of the "moisture unit eight relationship ". This is also loosely (an unfortunately all too commonly) referre to as the moisture-ensity relationship even though the "ensity" is actually unit eight.

2 It as foun that, for any given amount of energy expene in compacting the soil, there existe an optimum moisture here the ry ensity as greatest. This relationship is shon in Figure 1 (from Hilf, Chapter 8. Compacte Fill, Founation Engineering Hanbook, Fang, Eitor, 1991). 2 Figure 1 Moisture unit eight relationships for a soil using to compaction efforts. The tests shon on Figure 1 are the result of to Proctor compaction tests on one soil. In these tests, soil is compacte by a series of blos of a stanar hammer in cylinrical mols that have a knon stanar volume. The hammers are esigne to provie a knon, repeatable input energy. Table 1 provies the etails of each test. The complete moisture unit eight relationship is obtaine by compacting soil at a series of ifferent moisture contents (but using the same effort each time). A smooth curve beteen the points is ran an the maximum ry unit eight an optimum ater content are etermine for a soil at that compaction effort. The maximum ry unit eight is the peak point on the curve an the optimum moisture content is the ater content corresponing to that peak ry unit eight. Test Stanar Proctor (ASTM D 698) Moifie Proctor (ASTM D 1557) Table 1. Details of Stanar an Moifie Proctor Tests. Mol* Volume No. of Layers Blos/ layer Hammer Weight Drop Height Energy Input 1/30 ft lb 12 in 12,400 ft lb/ft 3 1/30 ft lb 18 in 56,000 ft lb/ft 3 *4.0 iameter x 4.6 tall mol The influence of stanar effort vs. moifie effort on the moisture-ensity relationship is shon in Figure 1. Note as the compaction effort is increase, the maximum ensity increases an the optimum moisture content ecreases. The ifferences in the tests are in the amount of energy transmitte to the soil ith each hammer blo an are shon belo.

3 To the left of optimum moisture the soil is referre to as on the ry sie. Similarly, points to the right of optimum (higher moisture contents) are referre to as on the et sie. 3 Relative compaction is typically use as an inex to compare the fiel ensity ith the laboratory ensity. Relative compaction is efine as: Relative Compaction: RC 100%,max (1) Where, fiel ensity measure in the fiel, max Proctor maximum ry ensity obtaine from a Proctor Test. This is expresse as a percentage. Note: Relative compaction is base on ry unit eights. RC greater than 100% is possible. The Zero Air Vois Line The zero air vois (ZAV) line is the combination of moisture an ensity that prouce complete saturation of the soil or the obtaine hen there is no air in the voi spaces. The compaction curve theoretically oes not cross this line but becomes parallel to it. Remember that the values of ater content, et unit eight, an specific gravity are not constant throughout the soil. There coul also be variability in the test results. Variability can result in points on the compaction curve above the ZAV line (S>100%). These ata points shoul not be thron out. Basic eight volume relationships are use to evelop an equation for the ZAV line. Recall that: W V Ws V + V s v Gs Vs V + ev s s Gs 1+ e Since S 1 if the saturation is equal to 100 percent, the relationship: G s e can be substitute into the above equation to yiel the final equation for the ZAV line: GS (2) 1 + G S Note that G s an are constants for a given soil. Therefore the ZAV line is a linear function of ater content. To ra the ZAV line, simply enter values of an compute the corresponing value of.

4 LABORATORY PROCEDURE (Moifie Proctor) 4 Equipment Compaction mol US Sieve # 4 Moifie Proctor Hammer Balance sensitive to 0.01 lb Balance sensitive to 0.1 g Large flat pan Jack Steel straight ege Moisture cans Drying oven Plastic squeeze bottle ith ater Proceure 1. Obtain approximately 5 lbs. of unrie soil passing the No. 4 sieve for each test being performe. A minimum of 5 tests is require, 6 is preferre. 2. A enough ater to each test sample to bring the ater content ithin range of optimum. Test samples shoul be prepare in approximately 2% increments. First trial ater content might be 4%. 3. Determine the eight (W 1 ) an volume (V) of the Proctor compaction mol or ith base plate (o not measure the extension). Use the scale sensitive to 0.1 lb. to etermine the eight of the mol. 4. Determine the eight (W tin ) of the moisture tins. Use the scale sensitive to.01 g to etermine these eights. 5. Assemble an secure the mol an extension to the base plate. Make sure that the apparatus is place on a rigi founation (i.e., concrete slab). This is important not only for safety reasons, but to ensure that the compaction effort is applie to the soil an not the founation. 6. Compact the first test specimen in the mol in five equal layers. a. For the first layer, fill the mol about one thir ith loose soil. b. Compact the lift ith 25 blos of the compaction hammer. Make sure that the hammer is kept vertical an the guie sleeve is not lifte. Also, take care to evenly istribute the blos over the entire mol. c. Score the top of the layer ith a metal spatula.. For the secon layer, fill up to to thir level of the mol. e. Repeat steps b an c. f. For the final layer, fill to about the mipoint or higher of the extension. This layer is important because after compaction, the top of the layer must be equal to or above the top of the mol. If it is not the test must be one over. g. Repeat step b. 7. Remove the extension an base plate. 8. With the steel straight ege level off the sample so it is even ith the top an bottom of the mol. Take care not to create ivots in the sample uring this process.

5 9. Determine the eight (W 2 ) of the soil an mol or plus base plate (not the extension). Use scale sensitive to 0.1 lb. to etermine this eight. 10. With the ai of the extruer, remove the sample from the mol. 11. Collect a sample of soil from the center of the compacte soil an place it in the moisture tin. 12. Determine the eight (W tin+soil ) of the moisture tin an soil. 13. Place the moisture tin an soil in the oven over night to ry. 14. Repeat steps 5 through 13 for each of the remaining test specimens. 15. Determine the eight (W tin+ry soil ) of the tin an ry soil for each test specimen. 5 Calculations Moisture Content Moist Unit Weight Dry Unit Weight Weight of ater Moisture c ontent, or Weight of ry sample Wtin+ soil Wtin+ rysoil 100 (3) Wtin+ rysoil Wtin eight of moist soil Moist unit eight, or volume of mol W2 W1 (4) V eight of ry soil Dry unit eight, or volume of mol (5) Plot the compaction curve, vs.. Dra a best-fit curve, using a French curve so the curve is smooth. Determine the optimum ater content an maximum ry unit eight from the curve. Plot the zero air vois curve on the same plot as the compaction curve. Use a French curve an plot at least 4 points to get the general shape of the curve. Plot the Zero Air Vois Curve: Gs (6) Gs

6 California State University, Fullerton Department of Civil an Environmental Engineering Soil Mechanics Laboratory Moifie 6