1、Standard Specification for Classification of Soils and Soil-Aggregate Mixtures for Highway Construction Purposes AASHTO Designation: M 145-91 (2012) American Association of State Highway and Transportation Officials 444 North Capitol Street N.W., Suite 249 Washington, D.C. 20001TS-1b M 145-1 AASHTO
2、Standard Specification for Classification of Soils and Soil-Aggregate Mixtures for Highway Construction Purposes AASHTO Designation: M 145-91 (2012) 1. SCOPE 1.1. This recommended practice describes a procedure for classifying soils into seven groups based on laboratory determination of particle siz
3、e distribution, liquid limit, and plasticity index. Evaluation of soils within each group is made by means of a “group index,” which is a value calculated from an empirical formula. The group classification, including group index, should be useful in determining the relative quality of the soil mate
4、rial for use in earthwork structures, particularly embankments, subgrades, subbases, and bases. However, for the detailed design of important structures, additional data concerning strength or performance characteristics of the soil under field conditions will usually be required. 1.2. The values st
5、ated in SI units are to be regarded as the standard. 2. REFERENCED DOCUMENTS 2.1. AASHTO Standards: R 58, Dry Preparation of Disturbed Soil and Soil-Aggregate Samples for Test T 11, Materials Finer Than 75-m (No. 200) Sieve in Mineral Aggregates by Washing T 27, Sieve Analysis of Fine and Coarse Agg
6、regates T 88, Particle Size Analysis of Soils T 89, Determining the Liquid Limit of Soils T 90, Determining the Plastic Limit and Plasticity Index of Soils T 146, Wet Preparation of Disturbed Soil Samples for Test 2.2. ASTM Standard: D1140, Standard Test Methods for Amount of Material in Soils Finer
7、 than No. 200 (75-m) Sieve Note 1Either T 88, or T 11 and T 27, or ASTM D1140 will be used to determine the particle size distribution of soils or soil-aggregate mixtures as a basis for classification. 3. CLASSIFICATION 3.1. The classification is made by using the test limits and group index values
8、shown in Table 1. If a more detailed classification is desired, a further subdivision of the groups shown in Table 1 may be made. An example of the classification with subgroups such as those shown in Table 1 may be made. An example of the classification with such subgroups is shown in Table 2. The
9、liquid limit and plasticity index ranges for the A-4, A-5, A-6, and A-7 soil groups are shown graphically in Figure 2. 2015 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.Table 1Classification of Soils and S
10、oil-Aggregate Mixtures General Classification Granular Materials (35 Percent or Less Passing 75 m) Silt-Clay Materials (More Than 35 Percent Passing 75 m) Group Classification A-1 A-3aA-2 A-4 A-5 A-6 A-7 Sieve analysis, percent passing: 2.00 mm (No. 10) 0.425 mm (No. 40) 50 max 51 min 75 m (No. 200)
11、 25 max 10 max 35 max 36 min 36 min 36 min 36 min Characteristics of fraction passing 0.425 mm (No. 40): Liquid limit 40 max 41 min 40 max 41 min Plasticity index 6 max Nonplastic (NP) b 10 max 10 max 11 min 11 min General rating as subgrade Excellent to Good Fair to Poor aThe placing of A-3 before
12、A-2 is necessary in the “left to right elimination process” and does not indicate superiority of A-3 over A-2. bSee Table 2 for values. Table 2Classification of Soils and Soil-Aggregate Mixtures General Classification Granular Materials (35 Percent or Less Passing 75 m) Silt-Clay Materials (More Tha
13、n 35 Percent Passing 75 m) Group Classification A-1 A-2 A-7 A-1-a A-1-b A-3 A-2-4 A-2-5 A-2-6 A-2-7 A-4 A-5 A-6 A-7-5, A-7-6 Sieve analysis, percent passing: 2.00 mm (No. 10) 50 max 0.425 mm (No. 40) 30 max 50 max 51 min 75 m (No. 200) 15 max 25 max 10 max 35 max 35 max 35 max 35 max 36 min 36 min 3
14、6 min 36 min Characteristics of fraction passing 0.425 mm (No. 40): Liquid limit 40 max 41 min 40 max 41 min 40 max 41 min 40 max 41 min Plasticity index 6 max NP 10 max 10 max 11 min 11 min 10 max 10 max 11 min 11 minaUsual types of significant constituent materials Stone fragments, Fine gravel and
15、 sand sand Silty or clayey gravel and sand Silty soils Clayey soils General rating as subgrade Excellent to Good Fair to Poor aPlasticity index of A-7-5 subgroup is equal to or less than LL 30. Plasticity index of A-7-6 subgroup is greater than LL 30. (See Figure 2.) TS-1bM 145-2AASHTO 2015 by the A
16、merican Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-1b M 145-3 AASHTO 3.2. Classification ProcedureWith required test data available, proceed from left to right in Table 1 or Table 2, and the correct group will be fou
17、nd by process of elimination. The first group from the left into which the test data will fit is the correct classification. All limiting test values are shown as whole numbers. If fractional numbers appear on test reports, convert to the nearest whole number for purposes of classification. Group in
18、dex values should always be shown in parentheses after group symbol as: A-2-6(3), A-4(5), A-6(12), A-7-5(17), etc. 4. DEFINITIONS OF GRAVEL, SAND, AND SILT-CLAY 4.1. The terms “gravel,” “coarse sand,” and “silt-clay,” as determinable from the minimum test data required in this classification arrange
19、ment and as used in subsequent word descriptions, are defined as follows: 4.1.1. gravelmaterial passing sieve with 75-mm (3-in.) square openings and retained on the 2.00-mm (No. 10) sieve. 4.1.2. coarse sandmaterial passing the 2.00-mm (No. 10) sieve and retained on the 0.425-mm (No. 40) sieve. 4.1.
20、3. fine sandmaterial passing the 0.425-mm (No. 40) sieve and retained on the 75-m (No. 200) sieve. 4.1.4. silt-clay (combined silt and clay)material passing the 75-m (No. 200) sieve. 4.1.5. Boulders and cobbles (retained on 75-mm (3-in.) sieve) should be excluded from the portion of the sample to wh
21、ich the classification is applied, but the percentage of such material, if any, in the sample should be recorded. 4.1.6. The term “silty” is applied to fine material having plasticity index of 10 or less, and the term “clayey” is applied to fine material having plasticity index of 11 or greater. 5.
22、DESCRIPTION OF CLASSIFICATION GROUPS 5.1. Granular MaterialsContaining 35 percent or less passing the 75-m (No. 200) sieve (Note 2). 5.1.1. Group A-1The typical material of this group is a well-graded mixture of stone fragments or gravel, coarse sand, fine sand, and a nonplastic or feebly plastic so
23、il binder. However, this group also includes stone fragments, gravel, coarse sand, volcanic cinders, etc., without soil binder. 5.1.1.1. Subgroup A-1-a includes those materials consisting predominantly of stone fragments or gravel, either with or without a well-graded binder of fine material. 5.1.1.
24、2. Subgroup A-1-b includes those materials consisting predominantly of coarse sand, either with or without a well-graded soil binder. 5.1.2. Group A-3The typical material of this group is fine beach sand or fine desert blow sand without silty or clay fines or with a very small amount of nonplastic s
25、ilt. The group includes also stream-deposited mixtures of poorly graded fine sand and limited amounts of coarse sand and gravel. 5.1.3. Group A-2This group includes a wide variety of “granular” materials that are borderline between the materials falling in Groups A-1 and A-3 and the silt-clay materi
26、als of Groups A-4, A-5, A-6, and A-7. It includes all materials containing 35 percent or less passing the 75-m 2015 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-1b M 145-4 AASHTO (No. 200) sieve that ca
27、nnot be classified as A-1 or A-3 due to fines content or plasticity or both, in excess of the limitations for those groups. 5.1.3.1. Subgroups A-2-4 and A-2-5 include various granular materials containing 35 percent or less passing the 75-m (No. 200) sieve and with a minus 0.425-mm (No. 40) portion
28、having the characteristics of the A-4 and A-5 groups. These groups include such materials as gravel and coarse sand with silt contents or plasticity indexes in excess of the limitations of Group A-1, and fine sand with nonplastic silt content in excess of the limitations of Group A-3. 5.1.3.2. Subgr
29、oups A-2-6 and A-2-7 include materials similar to those described under Subgroups A-2-4 and A-2-5 except that the fine portion contains plastic clay having the characteristics of the A-6 or A-7 group. Note 2Classification of materials in the various groups applies only to the fraction passing the 75
30、-mm (3-in.) sieve. Therefore, any specifications regarding the use of A-1, A-2, or A-3 materials in construction should state whether boulders retained on the 75-mm (3-in.) sieve are permitted. 5.2. Silt-Clay MaterialsContaining more than 35 percent passing the 75-m (No. 200) sieve. 5.2.1. Group A-4
31、The typical material of this group is a nonplastic or moderately plastic silty soil usually having 75 percent or more passing the 75-m (No. 200) sieve. The group includes also mixtures of fine silty soil and up to 64 percent of sand and gravel retained on 75-m (No. 200) sieve. 5.2.2. Group A-5The ty
32、pical material of this group is similar to that described under Group A-4, except that it is usually of diatomaceous or micaceous character and may be highly elastic as indicated by the high liquid limit. 5.2.3. Group A-6The typical material of this group is a plastic clay soil usually having 75 per
33、cent or more passing the 75-m (No. 200) sieve. The group also includes mixtures of fine clayey soil and up to 64 percent of sand and gravel retained on the 75-m (No. 200) sieve. Materials of this group usually have high-volume change between wet and dry states. 5.2.4. Group A-7The typical material o
34、f this group is similar to that described under Group A-6, except that it has the high liquid limits characteristic of the A-5 group and may be elastic as well as subject to high-volume change. 5.2.4.1. Subgroup A-7-5 includes those materials with moderate plasticity indexes in relation to liquid li
35、mit and which may be highly elastic as well as subject to considerable volume change. 5.2.4.2. Subgroup A-7-6 includes those materials with high plasticity indexes in relation to liquid limit and which are subject to extremely high-volume change. Note 3Highly organic soils (peat or muck) may be clas
36、sified in an A-8 group. Classification of these materials is based on visual inspection, and is not dependent on percentage passing the 75-m (No. 200) sieve, liquid limit, or plasticity index. The material is composed primarily of partially decayed organic matter, and generally has a fibrous texture
37、, dark brown or black color, and an odor of decay. These organic materials are unsuitable for use in embankments and subgrades. They are highly compressible and have low strength. 2015 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a vio
38、lation of applicable law.TS-1b M 145-5 AASHTO 6. GROUP INDEX 6.1. The group index is calculated from the following formula: Group index = (F 35) 0.2 + 0.005 (LL 40) + 0.01 (F 15) (PI 10) where: F = percentage passing the 75-m (No. 200) sieve, expressed as a whole number. This percentage is based onl
39、y on the material passing the 75-mm (3-in.) sieve. LL = liquid limit, and PI = plasticity index. 6.1.1. When the calculated group index is negative, the group index shall be reported as zero. 6.1.2. The group index should be reported to the nearest whole number. 6.2. Figure 1 may be used in estimati
40、ng the group index, by determining the partial group index due to liquid limit and that due to plasticity index, then obtaining the total of the two partial group indexes. 6.3. When calculating the group index of A-2-6 and A-2-7 subgroups, only the PI portion of the formula (or of Figure 1) shall be
41、 used. 6.4. The following are examples of calculations of the group index: 6.4.1. Assume that an A-6 material has 55 percent passing the 75-m (No. 200) sieve, liquid limit of 40, and plasticity index of 25. Then, Group index = (55 35) 0.2 + 0.005 (40 40) + 0.01 (55 15) (25 10) = 4.0 + 6.0 = 10 6.4.2
42、. Assume that an A-7 material has 80 percent passing the 75-m (No. 200) sieve, liquid limit of 90, and plasticity index of 50. Then, Group index = (80 35) 0.2 + 0.005 (90 40) + 0.01 (80 15) (50 10) = 20.3 + 26.0 = 46.3 6.4.3. Assume that an A-4 material has 60 percent passing the 75-m (No. 200) siev
43、e, liquid limit of 25, and plasticity index of 1. Then, Group index = (60 35) 0.2 + 0.005 (25 40) + 0.01 (60 15) (1 10) = 25 (0.2 0.075) + 0.01 (45) (9) = 3.1 4.1 = 1.0 Report as zero. 6.4.4. Assume that an A-2-7 material has 30 percent passing the 75-m (No. 200) sieve, liquid limit of 50, and plast
44、icity index of 30. Then, Group index = 0.01 (30 15) (30 10) = 3.0 or 3 (Note that only the PI portion of the formula was used.) 2015 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-1b M 145-6 AASHTO Figure
45、 1Group Index Chart Group Index (GI) = (F 35) 0.2 + 0.005 (LL 40) + 0.01 (F 15) (PI 10)where F = Percent Passing 75-m sieve, LL = Liquid Limit, and PI =Plasticity Index.When working with A-2-6 and A-2-7 Subgroups, the Partial Group Index(PGI) is determined from thePI only.When the combined Partial G
46、roup Indices are negative, the Group Indexshould be reported as zero.Example:82 Percent Passing 75-m SieveLL = 38PI = 21Then:PGI = 8.9 for LLPGI = 7.4 for PIGI = 16PercentPassing75-m(No.200)SievePartialGroup IndexA-2-6 andA-2-75040302010050403020153560708090100504030201060708014010018050403020106070
47、801214161802468PlasticityIndexLiquid Limit 2015 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-1b M 145-7 AASHTO Note: A-2 Soils contain less than 35 percent finer than the 75-m (No. 200) sieve. Figure 2L
48、iquid Limit and Plasticity Index Ranges for Silt-Clay Materials 7. BASIS FOR GROUP INDEX FORMULA 7.1. The empirical group index formula devised for approximately within-group evaluation of the “clayey granular materials” and the “silt-clay materials” is based on the following assumptions: 7.1.1. Mat
49、erials falling within Groups A-1-a, A-1-b, A-2-4, A-2-5, and A-3 are satisfactory as subgrade when properly drained and compacted under moderate thickness pavement (base and/or surface course) of a type suitable for the traffic to be carried, or can be made satisfactory by additions of small amounts of natural or artificial binders. 7.1.2. Materials falling within the
