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    Chapter 8

    Compaction Using Standard Effort

    8.1 Purpose

    Soil placed as engineering ll (embankments, foundation pads, road bases) must be compacted to the se-

    lected density and water content to ensure the desired performance and engineering properties such as shearstrength, compressibility, or permeability. Also, foundation soils are often compacted to improve their en-gineering properties. Laboratory compaction tests provide the basis for determining the percent compactionand water content needed in the eld, and for controlling construction to assure that the target values areachieved.

    In a geotechnical laboratory you would prepare at least four (preferably ve) specimens with watercontents bracketing the estimated optimum water content. A specimen having a water content close tooptimum would be prepared rst by trial additions of water and mixing and then water contents for the restof the specimens would be selected to provide at least two specimens wet and two specimens dry of optimum,and water contents varying by about 2%, but no more than 4%. In this laboratory exercise each group in yoursection will compact one of the specimens at a specic water content, as directed by the laboratory instructor,and the results from all the groups will be combined later.

    The data, when plotted, represents a curvilinear relationship known as the compaction curve. The valuesof optimum water content and standard maximum dry unit weight are determined from the compaction curve.

    These test methods apply only to soils (materials) that have 20% or less by mass of particles retained onthe No.4 (4.75 mm) sieve.

    8.2 Standard Reference

    ASTM D 698 - Standard test methods for laboratory compaction characteristics of soil using standard effort(12,400 ft-lbf/ft 3 (600 kN-m/m 3 )).

    8.3 Required Materials and Equipment

    Mold - A cylindrical metal 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 f t 3 (944 14 cm 3 ).

    Rammer - with free fall of 12 0.05 in (304.8 1.3 mm) from the surface of the specimen. The massof the rammer is 5.5 0.02 lbm (2.5 0.01 kg).

    Sample extruder - A jack for extruding compacted specimens from the mold.

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    42 CVEN365 Laboratory Manual

    Balance - with 1 g readability.

    straight edge - for leveling off compacted sample

    mixing tools - for mixing the sample of soil with increments of water.

    8.4 Procedure

    8.4.1 Specimen preparation

    1. Obtain from your laboratory instructor a sample of the soil to be tested. You will need approximately2 kg.

    2. Without previously drying the sample, pass it through a No. 4 (4.7 mm) sieve. Determine the watercontent of the processed soil. See chapter 2 for the procedure.

    3. Double check the target water content for your specimen with the laboratory instructor.

    4. Calculate how much water should be added or subtracted from your sample to obtain the desired watercontent. Remember to account for the moisture already present in the sample and use the exact valuefor the mass of the soil, not the approximate number.

    5. To add water, spray it into the soil during mixing; to remove water, allow the soil to dry in air at ambienttemperature Mix the soil frequently during drying to maintain an even water content distribution.Thoroughly mix each specimen to ensure even distribution of water throughout and then place in aseparate covered container.

    8.4.2 Compaction

    1. Determine and record the mass of the mold or mold and base plate.

    2. Assemble and secure the mold and collar to the base plate. Place on the concrete oor of the laboratory,NOT on the counters.

    3. The specimen is compacted in 3 layers. Remember that after compaction the layers should be approx-imately equal in thickness and the last layer should extend above the top of the mold, but no more than14 in (6 mm). Place approximately 1/3 of the loose soil into the mold for each layer and spread into alayer of uniform thickness.

    4. Compact each layer with 25 blows. In operating the manual rammer, do not lift the guide sleeveduring the rammer upstroke. Hold the guide sleeve steady and within 5 o of vertical. Apply the blowsat a uniform rate of approximately 25 blows per minute and in such a manner as to provide complete,uniform coverage of the specimen surface. Usually this is achieved by moving the rammer along theperimeter of the mold and using 5 blows to cover the whole area. Then the pattern is repeated for 5times.

    5. After compaction of the rst two layers, trim any soil remaining on the mold walls or extending abovethe compacted surface and include it with the soil for the next layer. Before placing the next layer of soil scarify the surface of the compacted soil with a knife or other suitable tool to avoid separation of the layers at the joints later in the test.

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    8. Compaction Using Standard Effort 43

    6. If the third layer extends above the top of the mold by more than 14 in (6 mm) or below the top of thecompaction mold, the specimen should be discarded.

    7. Following compaction of the last layer, remove the collar and base plate from the mold. A knife maybe used to trim the soil adjacent to the collar to loosen the soil from the collar before removal to avoiddisrupting the soil below the top of the mold.

    8. Carefully trim the compacted specimen even with the top of the mold by means of the straightedgescraped across the top of the mold to form a plane surface even with the top of the mold. Initialtrimming of the specimen above the top of the mold with a knife may prevent the soil from tearingbelow the top of the mold. Fill any holes in the top surface with unused or trimmed soil from thespecimen, press in with the ngers, and again scrape the straightedge across the top of the mold.

    9. Determine and record the mass of the specimen and mold to the nearest gram.

    10. Remove the material from the mold using the sample extruder.

    11. Obtain a specimen for water content by using the whole specimen or a representative sample. Select a

    suitable container and record its weight.12. Weigh the container and the specimen.

    13. Place in the oven for 24 hours. If the entire specimen is used, break it up to facilitate drying.

    14. Record the weight of the oven dried specimen in the container.

    8.5 Calculations

    Post the following information as directed by the laboratory instructor: laboratory section (week day),group (color), date, mass of moist specimen in the mold, mass of mold, water content determination:

    mass of moist soil after compaction and can, mass of can, mass of oven dried specimen an can. Seesection 8.5 for a form to ll.

    Calculate the total unit weight of each specimen:

    t = M t g

    V m=

    (M sm M m )gV m

    (8.1)

    where:

    M t = mass of moist soilM sm = mass of the moist specimen and mold

    M m = mass of the moldV m = volume of the mold (944 cm3 )g = acceleration of gravity (9.807 m/ s2 )

    Calculate water content of each compacted specimen:

    w = M w gM s g

    = (M wsc M sc )

    (M sc Mc (8.2)

    where:

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    44 CVEN365 Laboratory Manual

    M w = mass of waterM s = mass of dry soilM wsc = mass of wet soil and canM sc = mass of dry soils and canM c = mass of canw = water content

    Calculate dry unit weight:

    d = t1 + w

    (8.3)

    Plot the values and draw the compaction curve as a smooth curve through the points (see example,Fig. 3). Plot dry unit weight to the nearest 0.1 lbf ft 3 , (0.2

    kNm 3 ) and water content to the nearest 0.1 %.

    From the compaction curve, determine the optimum water content and maximum dry unit weight.

    Plot the 100% saturation curve.

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    Chapter 9

    Measuring Suction with the Filter PaperMethod

    9.1 Purpose

    The lter paper method has long been used in soil science and engineering practice and it has recently beenaccepted as an adaptable test method for soil suction measurements because of its advantages over othersuction measurement devices. Basically, the lter paper comes to equilibrium with the soil either throughvapor (total suction measurement) or liquid (matric suction measurement) ow. At equilibrium, the suctionvalue of the lter paper and the soil will be equal. After equilibrium is established between the lter paperand the soil, the water content of the lter paper disc is measured. Then, by using lter paper water contentversus suction calibration curve, the corresponding suction value is found from the curve. This is the basicapproach suggested by ASTM Standard Test Method for Measurement of Soil Potential (Suction) UsingFilter Paper (ASTM D 5298). ASTM D 5298 employs a single calibration curve that has been used to inferboth total and matric suction measurements. The ASTM D 5298 calibration curve is a combination of both

    wetting and drying curves. Bulut (2001) demonstrates that the wetting and drying suction calibrationcurves do not match, an observation that was also made by Houston et al. (1994). In this test, the wettingcurve as shown in Figure 9.2 is used because the lter paper becomes wet during the test.

    9.2 Soil Suction Concept

    In general, porous materials have a fu