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Publication Number: FHWA-RD-07-052
Date: September 2007

Long Term Pavement Performance Project Laboratory Materials Testing and Handling Guide

Protocol P51
Test Method for Sieve Analysisof Subgrade Soils (SS01)

This LTPP protocol covers the determination of the gradation of subgrade soils by washed and dry sieve analyses. This protocol is based on: (1) the test standard AASHTO T27-88I (Sieve Analysis of Fine and Coarse Aggregates), and (2) the test standard AASHTO T11-85 (Amount of Material Finer Than 0.075 mm (No. 200 sieve) in Aggregate) collectively known as LTPP Test Designation SS01 for subgrade soils. The tests shall be carried out in accordance with these standards (AASHTO T27-88I and AASHTO T11-85), as modified herein. Those sections of the AASHTO standards included in this protocol by reference and without modifications shall be strictly followed. All other sections of this protocol shall be followed as herein written.

Determination of gradation using Protocol P51 shall be the first test to be performed on the bulk samples of the subgrade layer, after, (1) assigning the appropriate layer number and (2) determining the natural moisture content (Protocol P49) from jar samples for the subgrade layer. In addition, the combined bulk sample of the subgrade from each designated sampling area shall be described during the bulk sample handling in the laboratory and test sample preparation for the gradation (P51) and Atterberg Limits (Protocol P43) tests. These descriptions shall be later used for the classification and description of the sample (Protocol P52). The test results shall be reported separately for the test samples obtained from each designated sampling area.

The locations and sample numbers for P51 testing are as shown on the laboratory testing plans developed for each project.

When bulk samples of the subgrade layer are retrieved from BA1, BA2, BA3... type 12-inch (305-mm) diameter boreholes, these bulk samples are combined, prepared in accordance with AASHTO T87-86 and reduced to a representative test size in accordance with AASHTO T248-83. Because the bulk samples are combined, the Location Number of the sample should have an asterisk placed as the third digit. Similarly, the LTPP Sample Number should have an asterisk placed as the third and fourth digits.

The following definitions will be used throughout this protocol.

  1. Layer: That part of the pavement produced with similar material and placed with similar equipment and techniques. The material within a particular layer is assumed to be homogeneous. The subgrade layer may not conform to the above definition. Subgrade soils are prepared and compacted before the placement of subbase and/or base layers. For the SPS material sampling and testing program, the subgrade layer is considered to be representative of the subgrade soils within 12 inches (305 mm) below the top of the subgrade, unless otherwise indicated on field exploration logs (bore hole logs and/or test pit logs).
  2. Bulk Sample: That part of the pavement material that is removed from an unbound layer from the borehole(s) and the test pit at the designated locations. The bulk sample of each layer is shipped in one or more bag(s) to the participating laboratory. The material from one layer should never be mixed with the material from another layer even if there is less than the desired amount to perform the specified test.
  3. Test Sample: That part of the bulk sample of an unbound layer which is prepared and used for the specified test. The quantity of the test sample may be the same, but will usually be less than the bulk sample.


1.1 This method covers the determination of the particle size distribution in the test sample of fine and coarse aggregates by dry sieving the test sample of the subgrade soil according to AASHTO T27-88I, and as described in this protocol.

1.2 This method also covers the determination of the amount of material finer than a No. 200 (0.075-mm) sieve in the test sample of the subgrade soil by washing according to AASHTO T11-85, and as described in this protocol. Clay particles that are dispersed by the wash water, as well as water soluble materials, will be removed from the aggregate during the test.

1.3 As stated in Section 1.4 of AASHTO T27-88I.


2.1 AASHTO standards: As listed in Sections 2.1 of AASHTO T27-88I and AASHTO T11-85.
AASHTO T87-86 Dry Preparation of Disturbed Soil and Soil Aggregate Samples for Test.

2.2 ASTM Standards: As listed in Sections 2.2 of AASHTO T27-88I and AASHTO T11-85.
ASTM D2487-85 Classification of Soils for Engineering Purposes.

2.3 LTPP Protocols:
P43 Determination of Atterberg Limits.
P52 Classification and Description of Subgrade Soils.
P49 Determination of Natural Moisture Content.


3.1 As stated in Section 3.1 of AASHTO T11-85.

3.2 After completing the test according to Section 3.1 above, the test sample of dry aggregate is separated through a series of sieves of progressively smaller openings for determination of particle size distribution.


4.1 Material finer than the No. 200 (0.075-mm) sieve can be separated from larger particles much more efficiently and completely by wet sieving than through the use of dry sieving. Therefore, when accurate determinations of material finer than the No. 200 (0.075-mm) sieve in fine or coarse aggregate are desired, the AASHTO T11-85 method is used on the sample prior to dry sieving in accordance with AASHTO T27-88I. The results of the AASHTO T11-85 test are included in the calculations of AASHTO T27-88I. The total amount of material finer than the No. 200 (0.075-mm) sieve by washing from AASHTO T11-85 procedure plus that obtained from AASHTO T27-88I method by dry sieving the same sample is reported with the results of AASHTO T27-88I. Usually the amount of material finer than the No. 200 (0.075-mm) sieve obtained in the dry sieving process is a relatively small amount. If it is large, the efficiency of the washing operation should be checked. It could, also, be an indication of degradation of the aggregate.

4.2 The gradation results obtained by following the test procedures of this protocol (P51) and the Atterberg limits results (P43) shall be used for classification and description of subgrade soils (P52).


5.1 Balance - As required in Sections 5.1 of AASHTO T27-88I and AASHTO T11-85.

5.2 Sieves - As required in Section 5.1 of AASHTO T27-88I with the exception that the sieve sizes shall conform to Section 9.3.2 of Protocol P51.

5.3 Mechanical Sieve Shake - As required in Section 5.3 of AASHTO T27-88I.

5.4 Oven - As required in Section 5.4 of AASHTO T11-85.

5.5 Container - As required in Section 5.3 of AASHTO T11-85.


6.1 Assign the appropriate layer number to the bulk sample of the subgrade soil that is being tested. Weigh the total bulk sample received from the field for that layer. The bulk samples from different sampling areas shall be weighed separately. The following sections of this protocol refer to the combined bulk sample from one sampling area only. Combine the bulk samples if contained in more than one bag(s). Thoroughly mix the combined bulk sample and dry according to the procedure described in Section 4.1 of AASHTO T87-86.

6.2 Obtain the representative test sample according to the procedure described in Section 6.2 of AASHTO T27-88I.

6.3 Use the natural moisture content determined from the jar samples of the subgrade soil earlier on Form T49 according to Protocol P49 for the respective bulk sample location(s) to estimate the weight of the test sample when dry.

6.4 The approximate weight of the test sample shall conform to the weight requirement described in Section 6.4 of AASHTO T27-88I for aggregates with nominal maximum size of 2 inches (51 mm) or less for the total bulk sample weighing 150 lbs (68 kg) or more. The approximate weight of the test sample shall not exceed 50 lbs (23 kg) for larger nominal maximum size aggregates. The approximate weight of the test sample shall not exceed 40 lbs (18 kg) if the total bulk sample weighs 100 lbs (45 kg) or more, but less than 150 lbs (68 kg).

NOTE: The nominal maximum aggregate size is defined as the smallest sieve opening through which at least 95 percent of the aggregate passes. Delete Section 6.5 of AASHTO T27-88I.

6.5 Even if the weight of the test sample is less than the required minimum weight, the test shall be performed; however, this violation of the test standard AASHTO T27-88I shall be recorded as a standard comment code.


7.1 First test the sample by AASHTO T11-85 in conformity with Sections 7.1 to 7.5 of this protocol to determine the amount of material finer than the No. 200 (0.075-mm) sieve by washed sieving.

7.2 Dry the test sample to constant weight at a temperature of 110 ± 5°C (230 ± 9°F) and weigh to the nearest 0.1% of the weight of the sample. Designate this weight as "B".

7.3 As required in Section 7.3 of AASHTO T11-85, using the sieves listed in Section 9.3 of this protocol.

7.4 As required in Section 7.4 of AASHTO T11-85.

7.5 As required in Section 7.5 of AASHTO T11-85. Designate the dry weight of the washed sample to be "C". Weight of material finer than No. 200 (0.075-mm) sieve ("D") is calculated as the difference between "B" and "C". This completes the procedure using AASHTO T11-85.

7.6 Rest of the procedure involves AASHTO T27-88I. Commence dry sieving by using the AASHTO T27-88I procedure in conformity with Sections 7.6 to 7.13 of this protocol.

7.7 Nest the sieves in order of decreasing size of opening from top to bottom and place the dried test sample on the top sieve. Agitate the sieves by hand or by mechanical apparatus for a sufficient period, established by trial or checked by measurement on the actual test sample, to meet the criterion for adequacy of sieving described in Section 7.9 of this protocol.

7.8 As required in Section 7.3 of AASHTO T27-88I.

7.9 As required in Section 7.4 of AASHTO T27-88I.

7.10 The portion of the sample finer than the No. 4 (4.75-mm) sieve may require distribution on two or more sets of sieves to prevent overloading of individual sieves.

Follow Section 7.5 of AASHTO T27-88I.

7.11 As required in Section 7.6 of AASHTO T27-88I.

7.12 As required in Section 7.7 of AASHTO T27-88I.

7.13 Add the weight finer than the No 200 (0.075-mm) sieve determined by the AASHTO T11-85 procedures (according to Section 7.5 of this protocol) to the weight passing the No. 200 (0.075-mm) sieve determined by AASHTO T27-88I by dry sieving of the same sample performed according to Sections 7.6 to 7.12 of this protocol.


8.1 Calculate the amount of material passing the No. 200 (0.075-mm) sieve by washing as follows:

A = [(B-C)/B] x 100

where: A = percentage of material finer than a No. 200 (0.075-mm) sieve by washing,
B = original dry weight of test sample, as determined in Section 7.2 of this protocol,
C = dry weight of test sample after washing, as determined in Section 7.5 of this protocol.

8.2 Calculate percentages passing to the nearest 1% (for sieve sizes 3-in. [76-mm] to No. 80 [0.180-mm]), and to the nearest 0.1% for the No. 200 (0.075-mm) sieve on the basis of the total weight of the initial dry test sample (B) prior to the washed sieve analysis.

8.3 Include the weight (D) of material finer than the No. 200 (0.075-mm) sieve, as determined in Section 7.5 of this protocol in the sieve analysis calculation of Section 8.2 of this protocol.


The following information is to be recorded on Form T51.

9.1 Sample Identification shall include: Laboratory Identification Code, Region, State, State Code, SHRP ID, Layer Number, Field Set Number, Sample Area Number, Sample Location Number, LTPP Sample Number.

9.2 Test Identification shall include: LTPP Test Designation, LTPP Protocol Number, Laboratory Test Number, Test Date.

9.3 Test Results

Report the following:

9.3.1 Percent passing the No. 200 (0.075-mm) sieve by washing to the nearest 0.1 percent, as calculated in Section 8.1 of this protocol.

9.3.2 Gradation results based on Sections 8.2 and 8.3 of this protocol to the appropriate number of significant digits as follows:

Sieve Sizes Standard (mm) % Passing
3 in. (75.0) __ __ __.
2 in. (50.0) __ __ __.
1 ½ in. (37.5) __ __ __.
1 in. (25.0) __ __ __.
¾ in. (19.0) __ __ __.
½ in. (12.5) __ __ __.
3/8 in. (9.5) __ __ __.
#4 (4.75) __ __ __.
#10 (2.00) __ __ __.
#40 (0.425) __ __.
#80 (0.180) __ __.
#200 (0.075) __ __.__

9.3.3 Attach a cumulative particle size gradation curve such as shown in Figure 4 of ASTM D2487-85 with Form T51.

9.4 Comments shall include LTPP standard comment code(s), as shown in Section 4.3 of this Guide and any other note as needed. Additional codes for special comments that may be associated with the testing of bulk samples are:

Code Comment
61 Insufficient size of test sample because the quantity of the bulk sample was significantly less than that required for the tests.
62 Presence of roots and other organic material in the bulk sample retrieved from the field.
63 Presence of mica in the bulk sample retrieved from the field.
64 The bulk sample contained cobbles or large size aggregates (stone fragments passing the 12-in. [305-mm] sieve and retained on the 3-in. [76-mm] size sieve).
65 The test sample included shale chunks, claystone, mudstone, siltstone, and sandstone which convert into soils after field and/or laboratory processing (crushing, slacking, etc.)

In addition, record the weight of the test sample to the nearest 1 lb (0.45 kg) as per Section 7.1 of AASHTO T11-85 and the moisture content (Section 6.3 of Protocol P51) to the nearest 1%.

Use Form T51 (Test Sheet T51) to report the above information (Items 9.1 to 9.4).




LABORATORY PERFORMING TEST:______________________________________________________________


REGION _________________ STATE ___________________ STATE CODE __ __

EXPERIMENT NO _____ SHRP ID __ __ __ __

SAMPLED BY: ______________________________________________ FIELD SET NO. __

DATE SAMPLED: __ __-__ __-__ __ __ __


__ __ __ __ __ __
2. SAMPLING AREA NO. (SA-)__ ____ __
4. LOCATION NUMBER (Enter an asterisk as the third digit)__ __ ____ __ __
5. LTPP SAMPLE NUMBER (Enter an asterisk as third and fourth digit)__ __ __ ____ __ __ __
6. % PASSING #200 SIEVE BY WASHING (Section 9.3.1 of Protocol P51)__ __.____ __.__
7. GRADATION (Section 9.3.2 of Protocol P51) % PASSING SIEVE SIZE STANDARD (mm)
3 in. (75.0)__ __ __.__ __ __.
2 in. (50.0)__ __ __.__ __ __.
1 ½ in. (37.5)__ __ __.__ __ __.
1 in. (25.0)__ __ __.__ __ __.
¾ in. (19.0)__ __ __.__ __ __.
½ in. (12.5)__ __ __.__ __ __.
3/8 in. (9.5)__ __ __.__ __ __.
#4 (4.75)__ __ __.__ __ __.
#10 (2.00)__ __ __.__ __ __.
#40 (0.425)__ __.__ __.
#80 (0.180)__ __.__ __.
#200 (0.075)__ __.____ __.__
8. COMMENTS (Section 9.4 of Protocol P51)
      (a) CODE __ __ __ __ __ ____ __ __ __ __ __
__ __ __ __ __ __
      (b) NOTE ____________________________________
      (c) WEIGHT OF TEST SAMPLE, __ __ __.__ lb__ __ __.__ lb
9. TEST DATE__ __-__ __-__ __ __ ____ __-__ __-__ __ __ __



GENERAL REMARKS:___________________________________________________________________________


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