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State whether the following are true or false.
a. In the AASHTO classification Table 4.1, the soils that are more suitable for roadwork are located on the left than right.
b. In AASHTO classification system, the better performing fine grained soils are the ones with lower group indices.
c. In AASHTO classification system, sands are classified as grains with 0.075-4.75 mm diameter.
d. The USCS symbol for clayey gravel is CG.
e. A soil with USCS symbol SM is sandy silt.
(a)
Find whether the statement is true or false.
Answer to Problem 4.1P
The statement, “In the AASHTO classification Table 4.1, the soils that are more suitable for roadwork are located on left than right” is true.
Explanation of Solution
Refer Table 4.1, “Classification of highway Subgrade Materials” in the textbook.
- Consider the Granular materials are listed left side in the table and Silt-clay materials are listed right side in the Table.
- The soil groups are classified by AASHTO system as A-1, A-2, A-3, A-4, A-5, A-6 and A-7.
- The group classification of the soil A-1 and A-2 belongs to left side of the table and A-4 to A-7 belongs to right side of the table.
- The general subgrade rating of the soil A-1 and A-2 has ‘excellent to good’.
- The general subgrade rating of the soil A-4 to A-7 has ‘fair to poor’.
Generally the rating from excellent to good subgrade materials are suitable for roadwork. So the classification of the soil A-1 and A-2 is used for roadwork, but the soil group A-4 to A-7 is not used for road work due to its poor rating.
Thus, the soils belongs to left side than the right side of the table is fit for roadwork.
Therefore, the statement, “In the AASHTO classification Table 4.1, the soils that are more suitable for roadwork are located on left than right” is true.
(b)
Find whether the statement is true or false.
Answer to Problem 4.1P
The statement, “In the AASHTO classification system, the better performing fine grained soils are the ones with lower group indices” is true.
Explanation of Solution
Refer Table 4.1, “Classification of highway Subgrade Materials” in the textbook.
- The AASHTO system classified the soil group as A-1, A-2, A-3, A-4, A-5, A-6 and A-7.
- The group classification of the soil A-1 and A-2 belongs to granular materials and the soil A-4 to A-7 belongs to Silt-clay materials
- From the sieve analysis the gravel, sand and fine sand are grouping under soil A1 and A2 and silty soils and clayey soils are grouping under A-4, A-5, A-6 and A-7.
- The soil group A-1 and A-2 is rated as ‘excellent to good’.so it is considered as better performing fine grained soils.
Thus, the better performing fine grained soils are the ones with lower group indices (A-1 and A-2).
Therefore, The statement, “In the AASHTO classification system, the better performing fine grained soils are the ones with lower group indices” is true.
(c)
Find whether the statement is true or false.
Answer to Problem 4.1P
The statement, “In the AASHTO classification system, sands are classified as grains with 0.075-4.75 mm diameter” is false.
Explanation of Solution
As per AASHTO system, the grain size from 2 mm to 0.075 mm is classified as sand.
As per USCS system, the grain size from 4.75 to 0.075 mm is classified as sand.
The sand is classified by USCS system, but in the given statement mentioned as AASHTO system. So the statement is wrong.
Therefore, The statement, “In the AASHTO classification system, sands are classified as grains with 0.075-4.75 mm diameter” is false.
(d)
Find whether the statement is true or false.
Answer to Problem 4.1P
The statement, “The USCS symbol for clayey gravel is CG” is false.
Explanation of Solution
Refer to Figure 4.3, “Flowchart group names for gravelly and sandy soil”
The group symbol ‘GC’ represents the group name as ‘clayey gravel’ and ‘clayey gravel with sand’.
As per USCS system, the correct group symbol for clayey soil is GC. Hence the given statement is wrong.
Therefore, The statement, “The USCS symbol for clayey gravel is CG” is false.
(e)
Find whether the statement is true or false.
Answer to Problem 4.1P
The statement, “A soil with USCS symbol SM is sandy silt” is false.
Explanation of Solution
Refer to Figure 4.3, “Flowchart group names for gravelly and sandy soil”
The group symbol ‘SM’ is represents the group name as ‘silty sand’ and ‘silty sand with gravel’.
As per USCS system, the correct group name for the symbol SM is silty sand and silty sand with gravel, but in the given statement it is mentioned as sandy silt. Hence, the given statement is wrong.
Therefore, the statement, “A soil with USCS symbol SM is sandy silt” is false.
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Chapter 4 Solutions
Fundamentals of Geotechnical Engineering (MindTap Course List)
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