Classification of Soil

P a g e | 5‐1 Chapter 5 Classification of Soil 1. Soil classification systems provide a common language to express concisely (a) strength characteristics of soils. (b) permeability characteristics of soils. (c) compressibility characteristics of soils. (d) general characteristics of soils. 2. The soil classification systems are mainly based on (a) grain-size distribution and plasticity of soils. (b) grain-size distribution and strength characteristics of soils. (c) plasticity of soils and strength characteristics of soils. (d) permeability, compressibility and strength characteristics of soil. 3. Which of the following soil classification systems does not consider the plasticity of soils? (a) Unified classification system (b) Textural classification system (c) AASHTO classification system (d) All of the above 4. The texture of soil refers to its (a) colour. (b) shape and size. (c) strength. (d) surface appearance. 5. If the particle size distribution of a soil shows 30% sand, 40% silt and 30% clay-size particles, its textural classification is (a) clay loam. (b) loam. (c) silty clay loam. (d) silty clay. 6. American Association of State Highway Officials (AASHTO) classification system was developed in (a) 1829. (b) 1929. (c) 1949. (d) 1969. 7. According to the American Association of State Highway Officials (AASHTO) classification system, soil is classified into (a) 3 (b) 5 (c) 7 (d) 9 major groups. P a g e | 5‐2 8. According to the AASHTO soil classification system, granular materials have (a) 35% or less passing through 75 μm sieve. (b) 50% or less passing through 75 μm sieve. (c) more than 35% passing through 75 μm sieve. (d) more than 50% passing through 75 μm sieve. 9. According to the AASHTO soil classification, the general subgrade rating for soils of group A-4, A-5, A-6 and A-7 is (a) fair to excellent. (b) fair to poor. (c) excellent to good. (d) excellent to poor. 10. According to the AASHTO soil classification, the term silty is applied when the fine fractions of soil have a plasticity index of (a) 10. (b) 10 or less. (c) 11. (d) 11 or more. 11. Group index (GI) is defined in terms of (a) percent passing 75 μm. (b) liquid limit. (c) plasticity index. (d) all of the above. 12. If the calculated value of GI is negative, it is taken as (a) 0. (b) 0.5. (c) 1.0. (d) none of the above. 13. If the calculated value of GI is 3.5, it is taken as (a) 3. (b) 3.5. (c) 4.0. (d) none of the above. 14. The group index of soils belonging to group A-3 is always (a) 0. (b) 0.5. (c) 1.0. (d) none of the above. 15. In general, the quality of performance of a soil as a subgrade material (a) is directly proportional to the group index. (b) is inversely proportional to the group index. (c) is inversely proportional to square of the group index. (d) does not depend on the group index. P a g e | 5‐3 16. The original form of Unified Soil Classification System was proposed by (a) Terzaghi in 1925. (b) Taylor in 1948. (c) Casagrande in 1948. (d) none of the above. 17. According to the Unified Soil Classification System (USCS), the fine-grained soils have (a) 50% passing through 75μm sieve. (b) 50% or more passing through 75μm sieve. (c) less than 50% passing through 75μm sieve. (d) none of the above. 18. The symbol for silt is (a) C. (b) M. (c) S. (d) none of the above. 19. The symbol O is used for (a) organic silts and clays. (b) organic soils. (c) peat. (d) none of the above. 20. Dual symbols are required for (a) sands with 5 to 12% fines. (b) gravels with 5 to 12% fines. (c) both (a) and (b). (d) none of the above. 21. The group symbol for silty sand is (a) SS. (b) SM. (c) MS. (d) none of the above. 22. The group symbol SC stands for (a) silty clay. (b) clayey silt. (c) sandy clay. (d) clayey sand. 23. For soils of group MH, (a) LL < 50 (b) LL ≤ 50 (c) LL > 50 (d) LL ≥ 50 P a g e | 5‐4 24. For soils of group GW, (a) Cu ≥ 4 and 1 ≤ Cc ≤ 3 (b) Cu ≥ 6 and 1 ≤ Cc ≤ 3 (c) Cu < 4 and 1 > Cc > 3 (d) Cu < 6 and 1 > Cc > 3 P a g e | 5‐5 Answers, Hints and Discussion 1. (d) 2. (a) 3. (b) 4. (d) 5. (a) Discussion: See Fig. 5.1. 6. (b) 7. (c) 8. (a) Discussion: (c) is correct for silt-clay materials. 9. (b) Discussion: (c) is correct for granular materials. 10. (b) Discussion: (d) is correct for the term clayey. 11. (d) 12. (a) 13. (c) 14. (a) 15. (b) 16. (c) 17. (b) Discussion: (c) is correct for coarse-grained soils. 18. (b) Discussion: (a) is correct for clay, and (c) for sand. 19. (a) Discussion: The symbol for peat, muck, and other highly organic soils is Pt. 20. (c) 21. (b) 22. (d) 23. (d) 24. (a) Discussion: (b), (c) and (d) are correct for SW, GP and SP, respectively.